Patent Application
20220281119
The present invention relates to sensing technology.
In a manufacture line in a factory or the like, an industrial robot is installed for improving the productivity of a product to be manufactured. Examples of the industrial robot include a cooperative robot capable of cooperating with an operator. Japanese Patent Laid-Open No. 2020-104249 discloses an industrial robot including a torque sensor for detecting contact with the operator or an object.
The torque sensor includes a displacement detection device such as an encoder device, and obtains a torque value by using displacement information detected by the displacement detection device. In recent years, driving devices such as robots have come to be required of precise operation, and therefore torque sensors, that is, displacement detection devices have come to be required of high detection precision.
According to a first aspect of the present invention, a robot system includes a robot including, in a joint thereof, a reduction gear and at least one encoder, and a processing portion configured to obtain a torque value by using phase information based on a detection signal of the encoder. The encoder includes a scale including a pattern portion, and a head disposed to oppose the scale and configured to read the pattern portion of the scale and output the detection signal. The processing portion is configured to obtain, on a basis of the phase information, a first displacement amount of the scale in a first direction and a second displacement amount of the scale in a second direction. The first direction is a relative direction with respect to the head. The second direction is a relative direction with respect to the head and intersecting with the first direction. The processing portion is configured to obtain the torque value on a basis of the first displacement amount and the second displacement amount.
According to a second aspect of the present invention, a robot system includes a robot including, in a joint thereof, a reduction gear and at least one encoder, a processing portion configured to obtain a torque value by using phase information based on a detection signal of the encoder, and a storage portion configured to store a correction value associated with trajectory data of the robot. The encoder includes a scale including a pattern portion, and a head disposed to oppose the scale and configured to read the pattern portion of the scale and output the detection signal. The processing portion is configured to obtain, on a basis of the phase information obtained while the robot is operating in accordance with the trajectory data, a first displacement amount of the scale in a first direction that is a relative direction with respect to the head, and obtain the torque value on a basis of displacement information obtained by correcting the first displacement amount by using the correction value corresponding to the trajectory data.
Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.
Embodiments of the present invention will be described in detail below with reference to drawings.
The robot control device 300 serves as an example of a control portion, and controls the robot 200. A teaching pendant 400 serving as an example of a teaching device can be connected to the robot control device 300. The teaching pendant 400 is a device for performing teaching on the robot 200, and outputs teaching data to the robot control device 300. The robot control device 300 generates trajectory data on the basis of the teaching data, and operates the robot 200 in accordance with the trajectory data.
The robot 200 includes a robot arm 201, and a robot hand 202 serving as an example of an end effector. The robot arm 201 is, for example, a vertically articulated robot arm. A fixed end 201A that is a proximal end of the robot arm 201 is fixed to a stand 150. The robot hand 202 is attached to a free end 201B that is a distal end of the robot arm 201. The robot arm 201 includes a plurality of links 210, 211, 212, and 213, and the links 210 to 213 are rotatably interconnected by joints J1, J2, and J3. The joints J1 to J3 of the robot arm 201 are each provided with a driving device 230. As the driving device 230 of each of the joints J1 to J3, a driving device of an appropriate output matching a required torque is used.
In the robot arm 201, the joint J1 will be described as an example, and description of the other joints J2 and J3 will be omitted because these have a similar configuration to the joint J1 although the size and performance thereof may be different.
The torque sensor 500 is disposed on the flex spline 153 that is on the output side of the reduction gear 143. That is, the torque sensor 500 is disposed between the link 210 and the flex spline 153 of the reduction gear 143, that is, between the link 210 serving as an example of a first link and the link 211 serving as an example of a second link. Further, the torque sensor 500 measures a torque about the rotation axis C0 acting between the link 210 and the link 211, and outputs an electric signal corresponding to a torque value serving as a measurement value to the robot control device 300. The electric signal is a digital signal. The robot control device 300 controls the robot 200 on the basis of the torque value.
The robot control device 300 integrally controls the whole robot system. That is, the robot control device 300 controls the operation of the robot 200. Control of the operation of the robot 200 includes position control and force control. In position control, the robot control device 300 generates an operation command on the basis of the position of the tip of the hand of the robot 200, and outputs the generated operation command to the drive control device 260. In the force control, the robot control device 300 generates an operation command on the basis of the torque value that is a measurement value received from the torque sensor 500, and outputs the generated operation command to the drive control device 260. The drive control device 260 performs power supply control of the motor 141 in accordance with the operation command, and thus drives the motor 141. In force control, the robot control device 300 operates the robot 200 on the basis of the torque value output from the torque sensor 500. Therefore, the performance of the force control of the robot 200 depends on the precision, that is, the resolution of the torque sensor 500.
The support portions 501 and 502 are each a member having a flat plate shape, and has, for example, an annular shape centered on the rotation axis C0 as illustrated in
The elastic portion 503 includes a plurality of leaf springs 504 arranged radially at intervals around the rotation axis C0. When a torque acts between the links 210 and 211 illustrated in
The sensor body 590 includes at least one encoder used for measuring relative displacement between the support portions 501 and 502, that is, a torque acting between the support portions 501 and 502. The at least one encoder is preferably a plurality of encoders. The plurality of encoders are preferably four encoders 510. That is, in the first embodiment, the sensor body 590 includes four encoders 510. The four encoders 510 all have the same configuration. The four encoders 510 are arranged at positions with 90-degree symmetry about the rotation axis C0 at equal intervals. To be noted, although the number of the encoders 510 included in the sensor body 590 is preferably 4, the configuration is not limited to this. The number of encoders 510 included in the sensor body 590 may be, 1, 2, 3, 5, or more. The encoders 510 are each an incremental encoder. Although an incremental encoder will be described as an example in the present embodiment, the encoder may be of an absolute type. In addition, the encoders 510 are each preferably an optical encoder, an electrostatic capacitance encoder, or a magnetic encoder. Among these, an optical encoder is more preferable because higher detection resolution can be realized. Therefore, in the first embodiment, the encoders 510 are each an optical encoder.
The encoders 510 each may be a linear encoder or a rotary encoder. The relative displacement between the support portions 501 and 502 in the rotation direction about the rotation axis C0 is minute and can be regarded as displacement in a translational direction at the position of each encoder 510. Therefore, in the first embodiment, the encoders 510 are each a linear encoder. The encoders 510 are each capable of detecting relative displacement between the support portions 501 and 502 in the rotation direction about the rotation axis C0, that is, in the tangential direction.
The encoders 510 each include a scale 2, and a sensor head 7 serving as an example of a head disposed to oppose the scale 2. The sensor head 7 is a sensor unit. The scale 2 is fixed to and thus supported by one of the support portions 501 and 502. In the first embodiment, the scale 2 is fixed to and supported by the support portion 501. The sensor head 7 is fixed to and thus supported by the other of the support portions 501 and 502. In the first embodiment, the sensor head 7 is fixed to and thus supported by the support portion 502. To be noted, the scale 2 may be supported by the support portion 502, and the sensor head 7 may be supported by the support portion 501. By using the encoders 510, the relative displacement between the support portions 501 and 502 can be measured as a relative amount with respect to a certain standard position.
The computer 650 includes a central processing unit: CPU 651 that is a processor serving as an example of a processing portion. In addition, the computer 650 includes a read-only memory: ROM 652 storing a program 620 for causing the CPU 651 to perform arithmetic processing for obtaining a torque value τ, and a random access memory: RAM 653 used for temporarily storing data and so forth. In addition, the computer 650 includes I/O 654 that is an interface to the signal processing circuits 50 and external devices connected thereto such as the robot control device 300 and an unillustrated external storage. The CPU 651, the ROM 652, the RAM 653, and the I/O 654 are mutually communicably interconnected via a bus 660.
The torque value τ is torque information, that is, torque data, and may be a standardized value. The CPU 651 obtains phase information from each signal processing circuit 50, obtains the torque value τ by performing arithmetic processing in accordance with the program 620, and outputs the obtained torque value τ to the robot control device 300.
In the present embodiment, a storage device 670 includes the ROM 652 and the RAM 653 and serves as an example of a storage portion. To be noted, the configuration of the storage device 670 is not limited to this. In addition, the storage device 670 may be an internal storage, an external storage, or a combination of an internal storage and an external storage.
In addition, although the ROM 652 is a non-transitory recording medium that is readable for the computer 650 and the ROM 652 stores the program 620 in the present embodiment, the configuration is not limited to this. The program 620 may be recorded in any recording medium as long as the recording medium is a non-transitory recording medium that is readable for the computer 650. In addition, as the recording medium for supplying the program 620 to the computer 650, for example, flexible disks, optical disks, magneto-photo disks, magnetic tapes, and nonvolatile memories can be used.
The arithmetic processing unit 600 obtains relative displacement information between the support portions 501 and 502 on the basis of a detection signal that is an encoder signal from the sensor head 7 of each of the encoders 510. Then, the arithmetic processing unit 600 converts the obtained displacement information into the torque value τ, and outputs the torque value τ to the robot control device 300.
The torque sensor 500 includes a plurality of, for example, four encoder devices 550 as an example of a plurality of displacement detection devices. The encoder devices 550 each include the encoder 510, the signal processing circuit 50, and a partial function of the computer 650 illustrated in
The encoder 510 is an optical encoder of a light interference type, and is an incremental linear encoder. In addition, although the encoder 510 is of a reflection type in the first embodiment, the encoder 510 may be of a transmission type. The CPU 651 performs processing such as interpolation of a detection signal S obtained from the sensor head 7, writing and reading of information into and from the storage device 670, and output of a position signal.
The sensor head 7 is disposed at a position opposing the scale 2 in the Z direction. The scale 2 has a pattern portion 80. The sensor head 7 reads the pattern portion 80 of the scale 2 and outputs the detection signal S to the signal processing circuit 50. The sensor head 7 includes a light source 1 constituted by a light emitting diode: LED serving as an example of a light emitting unit, and two light receiving units 31 and 32. The light receiving units 31 and 32 are arranged at a distance from the light source 1 in the Y direction. In the first embodiment, the light source 1 is disposed between the two light receiving units 31 and 32. To be noted, although it is preferable to use the same units for the light receiving units 31 and 32 because the same parts can be used and the costs can be reduced, different types of light receiving units suitable for respective modulation periods of tracks that the light receiving units respectively read may be used.
The light receiving unit 31 includes a light receiving element array 91, and the light receiving unit 32 includes a light receiving element array 92. The light source 1 and the light receiving units 31 and 32 are mounted on a printed wiring board 4, and are sealed by transparent resin 5 that transmits light. Transparent glass 6 that transmits light is disposed on the surface of the resin 5. According to this configuration, the light source 1 and the light receiving units 31 and 32 are protected by the resin 5 and the glass 6.
The signal processing circuit 50 is constituted by, for example, a semiconductor element constituted by an integrated circuit chip: IC chip. The signal processing circuit 50 is mounted on, for example, the surface of the printed wiring board 4. To be noted, the position of the signal processing circuit 50 is not limited to this, and the signal processing circuit 50 may be disposed at a position different from a position on the printed wiring board 4. In
As illustrated in
The light beams received by the light receiving element arrays 91 and 92 are converted into electric signals. The electric signals are respectively transmitted to the circuit portions 511 and 512 of the signal processing circuit 50 as respective detection signals S1 and S2.
Incidentally, in the first embodiment, the support portion 501 of the sensor body 590 illustrated in
If the deformation force of the flex spline 153 is not acting on the support portion 501 of the torque sensor 500, the support portion 501 keeps the annular shape as illustrated in
When the torque sensor 500 is applied to a joint of the robot 200, the deformation force of the flex spline 153 acts on the support portion 501 of the torque sensor 500. As a result of this, the support portion 501 is also elliptically deformed similarly to the flex spline 153 as illustrated in
For example, it is assumed that the elliptical shape of the support portion 501 rotates clockwise about the rotation axis C0 as illustrated in
As described above, in the displacement of the scale 2 of each of the encoders 5101 to 5104, an error derived from the elliptical deformation of the support portion 501 is superimposed on the torque actually applied to the joint of the robot arm 201. Since the torque sensor 500 includes the four encoders 5101 to 5104, the error can be reduced to a certain extent by averaging the values detected by these. However, since the amount of displacement derived from the elliptical deformation varies among the encoders 5101 to 5104, the error cannot be eliminated by just the averaging processing.
Therefore, in the first embodiment, the displacement in the Y direction is also measured in the encoders 5101 to 5104, and a measured value of the displacement in the X direction is corrected on the basis of a measured value of the displacement in the Y direction to calculate an accurate torque value.
The pattern of the scale track 81 of the pattern portion 80 is read by the light receiving element array 91. The pattern of the scale track 82 of the pattern portion 80 is read by the light receiving element array 92. The scale track 81 includes a pattern row 801 as at least one first pattern row. The scale track 82 includes a plurality of pattern rows 802 as at least one second pattern row.
The pattern row 801 includes a plurality of pattern elements 810 serving as a plurality of first pattern elements periodically arranged in the X direction. The plurality of pattern elements 810 are arranged at intervals in the X direction at a predetermined pitch P1 serving as a modulation period. The plurality of pattern elements 810 each have a shape symmetrical with respect to an axis L1 serving as a first axis extending in the Y direction.
The pattern rows 802 each include a plurality of pattern elements 820 serving as a plurality of second pattern elements periodically arranged in the X direction. The plurality of pattern elements 820 are arranged at intervals in the X direction at a predetermined pitch P2 serving as a modulation period. The plurality of pattern elements 820 each have a shape asymmetrical with respect to an axis L2 serving as a second axis extending in the Y direction. In the present embodiment, the pitch P1 of the plurality of pattern elements 810 is equal to the pitch P2 of the plurality of pattern elements 820. That is, the interval between two adjacent axes L1 is equal to the interval between two adjacent axes L2.
Here, the pattern element 820 is asymmetrical with respect to every virtual axis extending in the Y direction at every position in the X direction. That is, there is no axis with respect to which the pattern element 820 is in line symmetry. In contrast, the pattern element 810 has one axis with respect to which the pattern element 810 is in line symmetry among virtual axes extending in the Y direction, and that axis is the axis L1.
In the first embodiment, the plurality of pattern rows 802 are continuously arranged in the Y direction. The length of each of the pattern rows 802 in the Y direction will be denoted by Y2. A plurality of pattern elements 820 of one row continuous in the Y direction constitute a pattern element group 825. In the pattern element group 825, the plurality of pattern elements 820 of the same shape are arranged in the Y direction at a period of the length Y2. In the first embodiment, a plurality of pattern element groups 825 are arranged at equal intervals at the pitch P2 in the X direction.
In each pattern row 802, the plurality of pattern elements 820 arranged at intervals in the X direction each include a rectangular portion 821 serving as a first portion and a rectangular portion 822 serving as a second portion disposed at a position displaced from the portion 821 in the X direction. The amount of displacement of the portion 822 in the X direction with respect to the portion 821 is preferably ⅙ of the pitch P2 between two adjacent pattern elements 820 among the plurality of pattern elements 820. In addition, the length of the portion 821 in the Y direction is preferably equal to the length of the portion 822 in the Y direction, that is, the length of each of the portions 821 and 822 in the Y direction is preferably Y2/2.
Although the pitch P1 and the pitch P2 may be different, the pitch P1 and the pitch P2 are preferably equal. The pitch P1 used for measuring the torque is preferably as small as possible. By setting the pitch P1 to be small, high resolution can be achieved for the torque sensor 500. In the description below, a case where the pitches P1 and P2 are 100 μm and the length Y2 is 50 μm will be described.
The pattern on the scale 2 is projected as an image doubled in size on the light receiving element array 91. Therefore, the detection range on the scale 2 is a range of 800 μm in the X direction and 400 μm in the Y direction. On the light receiving element array 92, due to the relationship between the width Y_pd and the length Y2, the detection range on the scale 2 is 8 pattern rows 802. To be noted, in the case where the value of Y_pd/Y2 is not an integer, the phase in the X direction varies depending on the detection position in the Y direction. Therefore, the value of Y_pd/Y2 is preferably an integer such that the position in the Y direction does not affect the detection phase in the X direction. The respective detection signals of the light receiving element arrays 91 and 92 are respectively output to the circuit portions 511 and 512 illustrated in
In the stage following the light receiving element array 91, four I-V conversion amplifiers 34, 35, 36, and 37 serving as first stage amplifiers are provided. The I-V conversion amplifiers 34, 35, 36, and 37 generate four-phase sine wave outputs S1(A+), S1(B+), S1(A−), and S1(B−) from the detection signal that is a current signal read from each light receiving element 90 of the light receiving element array 91. Regarding the relative phase of the four-phase sine waves, when S1(A+) is set as the standard with respect to the detection pitch, the phase of S1(B+) is about +90°, S1(A−) is about +180°, and the phase of S1(B−) is about +270°.
In a stage following the I-V conversion amplifiers 34, 35, 36, and 37, an A-phase differential amplifier 39 and a B-phase differential amplifier 40 are provided. The A-phase differential amplifier 39 and the B-phase differential amplifier 40 perform calculation of the following formulae (1) and (2) by using the four-phase sine wave outputs S1(A+), S1(B+), S1(A−), and S1(B−). As a result of this, the A-phase differential amplifier 39 and the B-phase differential amplifier 40 generate two-phase sine wave signals S1(A) and S1(B) from which direct current components have been removed.
S1(A)=S1(A+)−S1(A−) (1)
S1(B)=S1(B+)−S1(B−) (2)
In a stage following the A-phase differential amplifier 39 and the B-phase differential amplifier 40, the computer 650 illustrated in
As described above, the circuit portion 511 illustrated in
Here, the pattern of the pattern row 801 of
In addition, the pattern of the pattern rows 802 is a pattern detected as displacement in the X direction by the sensor head 7 when the sensor head 7 and the scale 2 are relatively displaced from each other in the X direction. Further, the pattern of the pattern rows 802 is a pattern detected as displacement in the X direction by the sensor head 7 when the sensor head 7 and the scale 2 are relatively displaced from each other in the Y direction.
In the first embodiment, the computer 650 obtains the torque value τ from which the error derived from the elliptical deformation of the support portion 501 has been removed by using the sine wave signals S1(A), S1(B), S2(A), and S2(B) that are phase information based on the detection signals S1 and S2 from the sensor head 7. Among the phase information, the sine wave signals S1(A) and S1(B) serve as first information, and the sine wave signals S2(A) and S2(B) serve as second information.
A control method for the robot 200 according to the first embodiment, and a torque detection method for the torque sensor 500 will be described in detail.
First, the control method for the robot 200 will be described with reference to the flowchart illustrated in
In step S102, the robot control device 300 obtains the torque value τ from the torque sensor 500 during control of the robot 200.
Next, in step S103, the robot control device 300 determines whether or not the torque value τ is larger than a threshold value TH. That is, whether or not the robot 200 has touched an operator or an object around the robot 200. If the robot 200 touches something, the torque value τ exceeds the threshold value TH.
In the case where the torque value τ is equal to or smaller than the threshold value TH, that is, in the case where the result of step S103 is NO, the robot control device 300 returns to the processing of step S101, and controls the robot 200.
In the case where the torque value τ is greater than the threshold value TH, that is, in the case where the result of step S103 is YES, in step S104, the robot control device 300 stops the operation of the robot 200. In addition, in step S105, the robot control device 300 performs alert processing. In the present embodiment, since the robot system 100 includes three torque sensors 500, the robot control device 300 transitions to the processing of steps S104 and S105 if any one of the three torque values exceeds the threshold value TH.
Examples of a method for stopping the operation of the robot 200 include quick stop, slow stop, moving in a reversed direction, and switching to impedance control. In addition, as the alert processing, for example, the robot control device 300 causes the robot 200 to output an error signal or an alert, displays the torque value τ on a terminal such as the teaching pendant 400, or obtain a log and store the log in a storage portion in the robot control device 300.
To be noted, the order of the processing of step S104 and the processing of step S105 may be reversed, or the processing of step S104 and the processing of step S105 may be performed simultaneously. In addition, one of the processing of step S104 and the processing of step S105 may be omitted.
The torque value τ obtained by the robot control device 300 in step S102 is detected as follows.
In step S201, the displacement calculation portion 680 detects, from the pattern row 801, phase Φ11 indicating the amount of displacement in the X direction. That is, the displacement calculation portion 680 obtains, as the phase Φ11, a first displacement amount of the scale 2 in the X direction relative to the sensor head 7 by using the sine wave signals S1(A) and S1(B) obtained from the circuit portion 511. The phase Φ11 is obtained in accordance with the following formula (3).
Φ11=A TAN 2 [S1(A), S1(B)] (3)
A TAN 2[Y, N is an arc tangent calculation function that determines the orthant and performs conversion into 0 to 2π phase. The phase Φ11 and the position of the scale 2 have a relationship illustrated in a graph of
To be noted, before performing the calculation of the formula (3), gain ratio and offset errors derived from offset, gain variation, and the like of each amplifier and included in the sine wave signals S1(A) and S1(B) may be corrected by using correction values obtained in advance. For example, for each of the sine wave signals S1(A) and S1(B), the gain ratio, that is, the amplitude ratio may be calculated by (maximum value−minimum value)/2 to calculate a correction value for equalizing the signal amplitude. Similarly, the offset error amount may be calculated by (maximum value+minimum value)/2 to calculate a correction value to correct the offset error. These correction values may be stored in the storage device 670.
Incidentally, the phase Φ11 includes an error Φ10′ in the X direction derived from relative displacement of the scale 2 in the X direction with respect to the sensor head 7 caused by the elliptical deformation of the support portion 501. To be noted, even if the scale 2 is relatively displaced in the Y direction with respect to the sensor head 7 due to the elliptical deformation of the support portion 501, the phase Φ11 is not affected.
That is, when a phase that is supposed to be obtained if the support portion 501 is not elliptically deformed and that does not include the error Φ10′ derived from the elliptical deformation is denoted by Φ10, the phase Φ11 satisfies the following formula (4).
Φ11=Φ10+Φ10′ (4)
For example, the phase Φ10 is zero in a state in which no torque is applied to the torque sensor 500, but the phase Φ11 that is actually detected includes the error Φ10′ due to the elliptical deformation of the support portion 501.
Next, in step S202, the displacement calculation portion 680 detects, from the pattern rows 802, phase Φ12 that is a displacement amount in the X direction. That is, the displacement calculation portion 680 obtains, as the phase Φ12, a displacement amount of the scale 2 in the X direction relative to the sensor head 7 by using the sine wave signals S2(A) and S2(B) obtained from the circuit portion 512. The phase Φ12 is obtained in accordance with the following formula (5).
Φ12=A TAN 2 [S2(A), S2(B)] (5)
The phase Φ12 includes the error Φ10′ in the X direction derived from relative displacement of the scale 2 in the X direction with respect to the sensor head 7 caused by the elliptical deformation of the support portion 501.
Further, the phase Φ12 includes an error in the Y direction derived from relative displacement of the scale 2 in the Y direction with respect to the sensor head 7 caused by the elliptical deformation of the support portion 501 as an error Φ10″ in the X direction. That is, the phase Φ12 satisfies the following formula (6).
Φ12=Φ10+Φ10′+Φ10″ (6)
How the error Φ10″ is superimposed on the phase Φ12 will be described below. For the sake of simpler description, description will be given assuming that the scale 2 is only relatively displaced in the Y direction with respect to the sensor head 7 and is not relatively displaced in the X direction.
The detection range of the scale track 82 will be denoted by R2. Only reflection light from the detection range R2 is received by the light receiving element array 92, and reflection light from a region outside of the detection range R2 is not received by the light receiving element array 92. In the scale track 82, the light emitted from the light source 1 is diagonally incident thereon, and in the light receiving element array 92, the reflection light from the scale track 82 is diagonally received. Therefore, the amount of light of the reflection light is not distributed evenly in the detection range R2. Among the reflection light from the detection range R2, reflection light of a large light amount greatly affects the light receiving sensitivity of the light receiving element array 92. Therefore, the reflection light from a portion where the light amount is large in the detection range R2 is dominant in the detection signal S2 output from the light receiving element array 92. Then, when the detection range R2 moves from the state illustrated in
In the first embodiment, the pattern element groups 825 each have a periodical shape as a result of the plurality of pattern elements 820 of the same shape being continuous in the Y direction. Therefore, when the detection range R2 moves in the Y direction by an amount equal to or greater than the length Y2, the phase Φ12 also changes periodically.
In the first embodiment, as illustrated in
In step S203, the displacement calculation portion 680 obtains a displacement amount ΔY serving as a second displacement amount of the scale 2 in the Y direction relative to the sensor head 7. Specifically, first, the displacement calculation portion 680 obtains a difference ΔΦ by subtracting the phase Φ11 from the phase Φ12. The difference ΔΦ is expressed by the following formula (7).
ΔΦ=Φ12−Φ11 (=Φ10″) (7)
That is, the difference ΔΦ corresponds to the error Φ10″. This means that the displacement calculation portion 680 calculates the error Φ10″ by obtaining the difference ΔΦ. The difference ΔΦ, that is, the error Φ10″ is a value that periodically changes in accordance with the displacement amount ΔY of the scale 2 in the Y direction relative to the sensor head 7.
The pattern element 820 is a pattern in which the portion 821 and the portion 822 are asymmetrically displaced from each other by ⅙ of the pitch P2. Therefore, the difference between the maximum value and the minimum value of the difference ΔΦ periodically changes in the range of (⅙)×2π [rad] in accordance with relative displacement of the scale 2 in the Y direction with respect to the sensor head 7. The displacement calculation portion 680 counts the number of cycles of the change of the difference ΔΦ that have occurred, and obtains the displacement amount ΔY from the count value at that time and the value of the difference ΔΦ.
In this manner, the displacement calculation portion 680 obtains the phase Φ11 from the sine wave signals S1(A) and S1(B), and obtains the displacement amount ΔY from the phase Φ11 and the sine wave signals S2(A) and S2(B).
Next, the displacement calculation portion 680 obtains the elliptical shape, that is, the ellipticity of the support portion 501 from the displacement amount ΔX in the X direction and the displacement amount ΔY obtained by converting the phase Φ11. Here, the positivity and negativity of the amount of error in the X direction derived from the deformation of the support portion 501 into an elliptical shape is reversed depending on the rotation direction of the wave generator 151 that is an input shaft of the reduction gear 143. Therefore, the displacement calculation portion 680 obtains the information of the rotation direction of the input shaft of the reduction gear 143 in advance from the robot control device 300. Specifically, when the input shaft of the reduction gear 143 rotates clockwise as illustrated in
The displacement calculation portion 680 obtains, on the basis of the ellipticity of the support portion 501 obtained in consideration of the information of the rotation direction of the input shaft of the reduction gear 143, the amount and direction of the error component in the X direction generated as a result of the support portion 501 being deformed in the Y direction.
The displacement calculation portion 680 obtains the difference between the ellipticity of the support portion 501 and the distance from the rotation axis C0 serving as the rotation center of the support portion 501 that is not receiving the deformation force illustrated in
Next, in step S204, the displacement calculation portion 680 obtains the phase Φ10 from the following formula (8) as displacement information in the X direction corresponding to the torque value τ. The phase Φ10 that is displacement information corresponds to the relative displacement amount of the support portion 501 with respect to the support portion 502 derived from the elastic deformation of the elastic portion 503 in which the error derived from the elastic deformation of the support portion 501 is canceled.
Φ10=Φ11−Φ10′ (8)
Then, in step S205, the torque calculation portion 681 calculates the torque value τ on the basis of four phases Φ10 respectively obtained for the four encoders 510. For example, the torque calculation portion 681 averages the four phases Φ10, and calculates the torque value τ by, for example, multiplying the average value by a predetermined coefficient such as a sensitivity coefficient proportional to an elastic modulus of the elastic portion 503. To be noted, the method for calculating the torque value τ is not limited to this, and the torque value τ may be alternatively obtained by converting each phase Φ10 into a provisional torque value and averaging the four provisional torque values. The displacement calculation portion 680 outputs the calculated torque value τ to the robot control device 300.
As described above, according to the first embodiment, the torque value τ can be obtained with high precision even in the case where the deformation force derived from the elliptical deformation of the reduction gear 431 is applied to the torque sensor 500 included in the joint of the robot 200. That is, the detection precision of the torque value τ is improved. Since the detection precision of the torque value τ is improved, the operation precision of the robot 200 can be improved. For example, by using the torque value τ for determining whether to stop the operation of the robot 200, the operation of the robot 200 can be quickly stopped when the robot 200 touches the operator or an object. In addition, in the case of performing force control of the robot 200 by using the torque value τ, the operation of the robot 200 can be controlled with high precision.
In addition, the order of processing of step S201 and processing of step S202 is not limited to the order described above, and the processing of step S201 may be executed after the processing of step S202, or these may be executed simultaneously if possible.
A modification example will be described.
A second embodiment will be described.
In the second embodiment, the encoder 510A illustrated in
The encoder 510A may be a linear encoder or a rotary encoder, but is a linear encoder also in the second embodiment similarly to the first embodiment. In addition, the encoder 510A is an optical encoder of a light interference type, and is an incremental encoder. In addition, although the encoder 510A is of a reflection type in the second embodiment, the encoder 510A may be of a transmission type.
The encoder 510A includes a scale 2A, and a sensor head 7A disposed at a position to oppose the scale 2A in the Z direction. The scale 2A includes a pattern portion 80A.
The sensor head 7A reads the pattern portion 80A of the scale 2A and outputs the detection signal S to the signal processing circuit 50A. The sensor head 7A includes a light source 1 constituted by an LED serving as an example of a light emitting unit, and one light receiving unit 3. The light receiving unit 3 has substantially the same configuration as the light receiving unit 31 described in the first embodiment. That is, in the second embodiment, the size of the sensor head 7A is reduced by omitting the light receiving unit 32.
The light receiving unit 3 is disposed at a distance from the light source 1 in the Y direction. The light receiving unit 3 includes the light receiving element array 9. The light source 1 and the light receiving unit 3 are mounted on the printed wiring board 4, and sealed by the transparent resin 5 that transmits light. The transparent glass 6 that transmits light is disposed on the surface of the resin 5. According to this configuration, the light source 1 and the light receiving unit 3 are protected by the resin 5 and the glass 6.
The signal processing circuit 50A is constituted by, for example, a semiconductor element constituted by an IC chip. The signal processing circuit 50A is mounted on, for example, the surface of the printed wiring board 4. To be noted, the position of the signal processing circuit 50A is not limited to this, and the signal processing circuit 50A may be disposed at a position different from a position on the printed wiring board 4. In
The pattern of the pattern portion 80A is read by the light receiving element array 9. The pattern portion 80A includes a plurality of pattern rows 801A as at least one first pattern row. In addition, the pattern portion 80A includes a plurality of pattern rows 802A as at least one second pattern row.
The pattern rows 801A each include a plurality of pattern elements 810A serving as a plurality of first pattern elements periodically arranged in the X direction. The plurality of pattern elements 810A are arranged at intervals in the X direction at a predetermined pitch P4 serving as a modulation period. The plurality of pattern elements 810A each have a shape symmetrical with respect to an axis L4 serving as a first axis extending in the Y direction.
The pattern rows 802A each include a plurality of pattern elements 820A serving as a plurality of second pattern elements periodically arranged in the X direction. The plurality of pattern elements 820A are arranged at intervals in the X direction at a predetermined pitch P5 serving as a modulation period. The plurality of pattern elements 820A each have a shape asymmetrical with respect to an axis L5 serving as a second axis extending in the Y direction. In the present embodiment, the pitch P4 of the plurality of pattern elements 810A is different from the pitch P5 of the plurality of pattern elements 820A. For example, the pitch P4 is 100 μm, and the pitch P5 is 200 μm. To be noted, a pattern row different from the pattern rows 801A and 802A may be included in the pattern portion 80A.
In the second embodiment, the plurality of pattern rows 801A and the plurality of pattern rows 802A are alternately arranged in the Y direction. The length of one pair of the pattern row 801A and the pattern row 802A in the Y direction will be denoted by Y4. The pattern portion 80A is configured such that the same shape is repeated at a period of the length Y4 in the Y direction.
In the second embodiment, the detection resolution can be switched by switching the switch circuit 41. By switching the switch circuit 41, the light receiving element array 9 can separately output the detection signal S1 based on the pattern rows 801A and the detection signal S2 based on the pattern rows 802A. That is, in the second embodiment, the circuit portion 51 can selectively obtain the detection signal S1 or the detection signal S2 from the light receiving element array 9 by switching the switch circuit 41. The circuit portion 51 generates the two-phase sine wave signals S1(A) and S1(B) obtained by removing direct current components from the detection signal S1 obtained from the light receiving element array 9. In addition, the circuit portion 51 generates the two-phase sine wave signals S2(A) and S2(B) obtained by removing direct current components from the detection signal S2 obtained from the light receiving element array 9. To be noted, in the case where a pattern row different from the pattern rows 801A and 802A is included in the pattern portion 80A, the switch circuit 41 may be configured to be switchable among three or more detection resolutions.
Here, the pattern of the pattern rows 801A is a pattern detected as displacement in the X direction by the sensor head 7A when the sensor head 7A and the scale 2A are relatively displaced from each other in the X direction. To be noted, the pattern of the pattern rows 801A is a pattern not detected as displacement in the X direction by the sensor head 7A when the sensor head 7A and the scale 2A are relatively displaced from each other in the Y direction.
In addition, the pattern of the pattern rows 802A is a pattern detected as displacement in the X direction by the sensor head 7A when the sensor head 7A and the scale 2A are relatively displaced from each other in the Y direction.
In the second embodiment, the displacement calculation portion 680 obtains the phase Φ10 for obtaining the torque value τ by the torque calculation portion 681 by using the sine wave signals S1(A), S1(B), S2(A), and S2(B) that are phase information based on the detection signals S1 and S2 from the sensor head 7A. Among the phase information, the sine wave signals S1(A) and S1(B) serve as first information, and the sine wave signals S2(A) and S2(B) serve as second information.
Hereinafter, since the control method for the robot 200 illustrated in
In step S201, the switch circuit 41 is switched to the state illustrated in
In step S202, the switch circuit 41 is switched to the state illustrated in
As described above, by switching the detection resolution by the switch circuit 41, the detection signal S1 based on the periodical pattern of the pitch P4 and the detection signal S2 based on the periodical pattern of the pitch P5 can be selectively output to the circuit portion 51 by using the one light receiving element array 9.
As described above, according to the second embodiment, the torque value τ can be obtained with high precision even in the case where the deformation force derived from the elliptical deformation of the reduction gear 431 is applied to the torque sensor similarly to the first embodiment. That is, the detection precision of the torque value τ is improved. Since the detection precision of the torque value τ is improved, the operation precision of the robot 200 can be improved. In addition, the size of the encoder 510A can be reduced, and thus the size of the torque sensor and the size of the robot can be also reduced.
To be noted, the order of processing of step S201 and step S202 is not limited to the order described above, and the processing of step S201 may be executed after the processing of step S202. In addition, the pattern elements 820A are each preferably asymmetrical with respect to the axis L5, and may have, for example, a wavy shape like the pattern elements 820 illustrated in
A third embodiment will be described.
In the third embodiment, the encoder 510B illustrated in
The encoder 510B may be a linear encoder or a rotary encoder, but is a linear encoder also in the third embodiment similarly to the first embodiment. In addition, the encoder 510B is an optical encoder of a light interference type, and is an incremental encoder. In addition, although the encoder 510B is of a reflection type in the third embodiment, the encoder 510B may be of a transmission type.
The encoder 510B includes a scale 2B, and a sensor head 7B disposed at a position to oppose the scale 2B in the Z direction. The scale 2B includes a pattern portion 80B.
The sensor head 7B reads the pattern portion 80B of the scale 2B and outputs the detection signal S2 to the signal processing circuit 50B. The sensor head 7B includes a light source 1 constituted by an LED serving as an example of a light emitting unit, and one light receiving unit 3. The light receiving unit 3 has substantially the same configuration as the light receiving unit 32 described in the first embodiment. That is, in the third embodiment, the size of the sensor head 7B is reduced by omitting the light receiving unit 31.
The light receiving unit 3 is disposed at a distance from the light source 1 in the Y direction. The light receiving unit 3 includes the light receiving element array 9. The light source 1 and the light receiving unit 3 are mounted on the printed wiring board 4, and sealed by the transparent resin 5 that transmits light. The transparent glass 6 that transmits light is disposed on the surface of the resin 5. According to this configuration, the light source 1 and the light receiving unit 3 are protected by the resin 5 and the glass 6.
The signal processing circuit 50B is constituted by, for example, a semiconductor element constituted by an IC chip. The signal processing circuit 50B is mounted on, for example, the surface of the printed wiring board 4. To be noted, the position of the signal processing circuit 50B is not limited to this, and the signal processing circuit 50B may be disposed at a position different from a position on the printed wiring board 4. In
The pattern of the pattern portion 80B is configured in a similar manner to the scale track 82 described in the first embodiment, and the scale track 81 described in the first embodiment is omitted. The pattern of the pattern portion 80B is read by the light receiving element array 9. The pattern portion 80B includes a plurality of pattern rows 802 as at least one pattern row. That is, the pattern portion 80B includes the plurality of pattern rows 802 configured in a similar manner to the first embodiment, and does not include the pattern row 801 described in the first embodiment.
The pattern rows 802 each include a plurality of pattern elements 820 periodically arranged in the X direction. The plurality of pattern elements 820 are arranged at intervals in the X direction at the predetermined pitch P2 serving as a modulation period. The plurality of pattern elements 820 each have a shape asymmetrical with respect to the axis L2 extending in the Y direction.
The plurality of pattern rows 802 are continuously arranged in the Y direction. The length of each of the pattern rows 802 in the Y direction will be denoted by Y2. A plurality of pattern elements 820 of one row continuous in the Y direction constitute a pattern element group 825. In the pattern element group 825, the plurality of pattern elements 820 of the same shape are arranged in the Y direction at a period of the length Y2. In the third embodiment, a plurality of pattern element groups 825 are arranged at equal intervals at the pitch P2 in the X direction.
In each pattern row 802, the plurality of pattern elements 820 arranged at intervals in the X direction each include a rectangular portion 821 serving as a first portion and a rectangular portion 822 serving as a second portion disposed at a position displaced from the portion 821 in the X direction. The amount of displacement of the portion 822 in the X direction with respect to the portion 821 is preferably ⅙ of the pitch P2 between two adjacent pattern elements 820 among the plurality of pattern elements 820. In addition, the length of the portion 821 in the Y direction is preferably equal to the length of the portion 822 in the Y direction, that is, the length of each of the portions 821 and 822 in the Y direction is preferably Y2/2. To be noted, the pattern elements 820 are each preferably asymmetrical with respect to the axis L2, and may have, for example, a wavy shape like the pattern elements 820 of the modification example illustrated in
The pattern of the pattern rows 802 is a pattern detected as displacement in the X direction by the sensor head 7B when the sensor head 7B and the scale 2B are relatively displaced from each other in the X direction. Further, the pattern of the pattern rows 802 is a pattern detected as displacement in the X direction by the sensor head 7B when the sensor head 7B and the scale 2B are relatively displaced from each other in the Y direction.
In the third embodiment, the displacement calculation portion 680 obtains the phase D10 for obtaining the torque value τ by the torque calculation portion 681 by using the sine wave signals S2(A) and S2(B) that are phase information based on the detection signal S2 from the sensor head 7B.
Hereinafter, since the control method for the robot 200 illustrated in
The torque detection method of the torque sensor in the third embodiment is different from the first embodiment. The robot 200 is an industrial robot. The robot 200 is used for successively manufacturing the same product, and repeats the same operation for this. Therefore, in the third embodiment, a correction value is measured and stored in the storage device 670 in advance. This storage operation is performed in a test run mode. Then, during an actual operation of the robot 200, that is, in the operation mode, the detection result of the encoder device 550B included in the torque sensor is corrected by using the correction value. Selection of the operation mode serving as a first mode and the test run mode serving as a second mode is performed by, for example, an operator operating the teaching pendant 400 illustrated in
Here, the correction value will be described in detail. Operating the robot 200 with no load means rotating the wave generator 151 of the reduction gear 143 of each of the joints J1 to J3 in a state in which the robot 200 does not collide with a person or an object. In other words, the phrase means that the robot 200 does not touch a person or an object and no collision of objects during assembly of a product occurs, and thus no torque is generated thereby. Generally, when operating a robot, a load is generated due to the gravity of the earth and the operation of the robot even when the robot does not collide with a person or an object. Therefore, even if collision with a person or an object does not occur, the torque sensor included in each joint of the robot detects a torque depending on the orientation and operation of the robot. Therefore, a correction value needs to be obtained by obtaining the trajectory data in accordance with the orientation and operation of the robot. The trajectory data to be obtained is a profile of the rotation angle of the rotation of the wave generator 151. That is, the CPU 651 obtains the correction value in accordance with the rotation angle of the wave generator 151 as trajectory data. In addition, this correction value corresponds to the phase Φ10′+Φ10″ expressed by the formula (6) in the case of operating the robot 200 with no load. That is, by operating the robot 200 with no load, a profile corresponding to the error of the phase Φ12 is obtained as the correction value. By calculating the correction value in accordance with the orientation and operation of the robot in this manner, for example, the contact force of the robot contacting a person or an object can be accurately detected when the robot system of the present embodiment is applied to a human-cooperative robot.
The control method for the robot 200 in a manufacture process is the same as that described in the first embodiment with reference to the flowchart illustrated in
In step S201B, the displacement calculation portion 680 loads the correction value from the table data 671B.
Next, in step S202B, the displacement calculation portion 680 detects, from the pattern rows 802, the phase Φ12 that is a displacement amount in the X direction. That is, the displacement calculation portion 680 obtains, as the phase Φ12, the displacement amount of the scale 2B in the X direction relative to the sensor head 7B by using the sine wave signals S2(A) and S2(B) from the circuit portion 51. The phase Φ12 is obtained by the formula (5) of the first embodiment described above. The phase Φ12 satisfies the formula (6) of the first embodiment described above. The correction value loaded in step S201B corresponds to the error Φ10′+Φ10″ in the formula (6).
Therefore, in step S203B, the displacement calculation portion 680 obtains the phase Φ10 by correcting the phase Φ12 by using the correction value, that is, by subtracting the correction value from the phase Φ12.
The processing of step S204B is substantially the same as the processing of step S205 described in the first embodiment. That is, in step S204B, the torque calculation portion 681 obtains the torque value τ on the basis of the four phases Φ10 respectively obtained for the four encoders 510B.
As described above, according to the third embodiment, the torque value τ can be obtained with high precision. That is, the detection precision of the torque value τ is improved. Since the torque value τ can be obtained with high precision, the operation precision of the robot 200 can be improved. In addition, the size of the encoder 510B can be reduced, and thus the size of the torque sensor 500 and the size of the robot 200 can be also reduced.
To be noted, the present invention is not limited to the embodiments described above, and can be modified in many ways within the technical concept of the present invention. In addition, the effects described in the embodiments are merely enumeration of the most preferable effects that can be obtained by the present invention, and the effects of the present invention are not limited to those described in the embodiments.
Although the case where the robot arm 201 is a vertically articulated robot arm has been described in the embodiments described above, the configuration is not limited to this. For example, various robot arms can be the robot arm 201, such as horizontally articulated robot arms, parallel link robot arms, and orthogonal robots.
In addition, although a case where the torque sensor is disposed on the output side of the reduction gear has been described in the embodiments described above, the configuration is not limited to this, and the torque sensor may be disposed on the input side of the reduction gear. It suffices as long as the torque sensor is disposed at a position where the elliptical deformation force of the reduction gear is transmitted to the torque sensor in the joint or the driving device.
In addition, although a case where the encoder is an incremental encoder has been described in the embodiments described above, the configuration is not limited to this, and the encoder may be an absolute encoder.
In addition, although a case where the torque sensor includes four encoders have been described in the embodiments described above, the configuration is not limited to this. For example, a case where the torque sensor includes only one encoder is also possible. In this case, the calculation for averaging the phase Φ10 is not needed when calculating the torque value τ. Of course, it is preferable that the torque sensor includes four encoders, and the error of the detected phase can be reduced by averaging four phases Φ10 detected by the four encoders.
In addition, although a case where the reduction gear is a strain wave reduction gear and the flex spline of the strain wave reduction gear has a cup shape has been described in the embodiments described above, the configuration is not limited to this. The flex spline may have a shape different from the cup shape, for example, a top hat shape.
In addition, although a case where the one CPU 651 realizes the functions of the plurality of displacement calculation portions 680 and the torque calculation portion 681 has been described, the configuration is not limited to this, and these functions may be realized by a plurality of CPUs.
As described above, the detection precision can be improved according to the present invention.
Embodiment(s) of the present invention can also be realized by a computer of a system or apparatus that reads out and executes computer executable instructions (e.g., one or more programs) recorded on a storage medium (which may also be referred to more fully as a ‘non-transitory computer-readable storage medium’) to perform the functions of one or more of the above-described embodiment(s) and/or that includes one or more circuits (e.g., application specific integrated circuit (ASIC)) for performing the functions of one or more of the above-described embodiment(s), and by a method performed by the computer of the system or apparatus by, for example, reading out and executing the computer executable instructions from the storage medium to perform the functions of one or more of the above-described embodiment(s) and/or controlling the one or more circuits to perform the functions of one or more of the above-described embodiment(s). The computer may comprise one or more processors (e.g., central processing unit (CPU), micro processing unit (MPU)) and may include a network of separate computers or separate processors to read out and execute the computer executable instructions. The computer executable instructions may be provided to the computer, for example, from a network or the storage medium. The storage medium may include, for example, one or more of a hard disk, a random-access memory (RAM), a read only memory (ROM), a storage of distributed computing systems, an optical disk (such as a compact disc (CD), digital versatile disc (DVD), or Blu-ray Disc (BD)™), a flash memory device, a memory card, and the like.
While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.
This application claims the benefit of Japanese Patent Application No. 2021-32211, filed Mar. 2, 2021, which is hereby incorporated by reference herein in its entirety.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2021-032211 | Mar 2021 | JP | national |
