This application is a National Stage Application, under 35 U.S.C. § 371, of International Application No. PCT/JP2018/016576 filed Apr. 24, 2018, which claims priority to Japanese Patent Application No. 2017 092029 filed May 3, 2017. The above-identified applications are incorporated by reference herein in their entireties.
The present invention relates to a robot system for accurately sensing contact between an arm of a robot or an instrument attached to the arm and another object.
Conventionally, a variety of robots have been used in factories and the like. Even now, robots are being actively developed for the purpose of improving positioning accuracy, safety, and the like. Also, articulated robots for performing more complex movement, and the like have come into practical use and are widespread.
In articulated robots that perform complex movement as described above, a technique for detecting that an arm portion or the like has been brought into contact with a structural object, a workpiece, an operator or the like to reduce accidents that may be caused by the contact is important. Conventionally, a variety of techniques for detecting contact between a robot and another object have been proposed.
For example, Patent Document 1 has proposed a technique for detecting a collision of an arm of a horizontally articulated robot by comparing and monitoring signals output from two encoders provided on the arm, the encoders being configured to detect relative rotation angles.
Also, Patent Document 2 has proposed a technique for determining whether or not a collision has occurred, by providing encoders (angle detecting means) on input and output sides of a deceleration device mounted on a joint of a robot arm, and calculating an error in the joint based on an angular difference between an input-side rotation angle and an output-side rotation angle.
Patent Document 1: Japanese Patent Application No. JP 2003-39376A
Patent Document 2: Japanese Patent Application No. JP 2015-3357A
However, in the techniques described in Patent Documents 1 and 2, due to the influence of, for example, shaft center misalignment or variations in bolting torque caused when the encoders are attached, angles detected by the encoders may vary slightly from the actual values. Accordingly, the accuracy in sensing contact made by the robot arm may be reduced by the variation. The impaired accuracy may not cause a problem if a contact object to be sensed is a structural object or the like, but will cause a safety issue if the object is a person.
Furthermore, there are also methods in which, in order to detect contact made by a robot arm, a contact sensing sensor is attached to a surface of the robot arm. However, in the case of an articulated robot arm, it is not clear which portion of the robot arm will make contact, and thus a large number of sensors need to be attached, leading to the problem of increased manufacturing cost.
The present invention has been proposed to solve the problems as described above, and it is an object thereof to provide a robot system that can improve reliability, economic efficiency, and the like in sensing contact with another object including a person, and can reduce damage that may be caused by accidental contact.
In order to achieve the aforementioned objects, the robot system according to the present invention at least includes a robot main body and a robot control unit, the robot main body including a motor; a deceleration device connected to a motor shaft of the motor; an arm connected to an output shaft of the deceleration device; a motor shaft-side angular sensor capable of detecting an angle of rotation of the motor shaft of the motor; and an output shaft-side angular sensor capable of detecting an angle of rotation of the output shaft of the deceleration device, the robot control unit being configured to detect a contact state between the arm or an instrument attached to the arm and another object.
The robot control unit includes: an angular sensor misalignment correction value storage unit in which an angular sensor misalignment correction value is stored, the angular sensor misalignment correction value being calculated based on an amount of misalignment when the motor shaft-side angular sensor and the output shaft-side angular sensor are attached; a motor shaft-side angle calculation unit configured to calculate a motor shaft-side angle based on the angle of rotation on the motor shaft side; an output shaft-side angle calculation unit configured to calculate an output shaft-side angle based on the angle of rotation on the output shaft side; a torsional deformation amount calculation unit configured to calculate an angular difference between the motor shaft-side angle and the output shaft-side angle, and correct the calculated angular difference using the angular sensor misalignment correction value to obtain a torsional deformation amount; a spring constant storage unit in which a spring constant of a region from the motor to the arm is stored; a contact determination threshold storage unit in which an allowable contact torque of the arm is stored; and a contact determination unit configured to calculate contact torque of the arm based on the torsional deformation amount and the spring constant stored in the spring constant storage unit, and detect the contact state when the calculated contact torque is larger than the allowable contact torque stored in the contact determination threshold storage unit.
The robot control unit may further include a motor control instruction unit configured to stop the motor when the contact state is sensed by the contact determination unit.
Furthermore, the robot control unit may further include a contact response gain storage unit in which a gain of the arm that responds to the contact torque is stored; and a motor control instruction unit configured to drive the motor at the speed obtained by multiplying a difference between the contact torque and the allowable contact torque by the gain, when the contact state is sensed by the contact determination unit.
According to the robot system of the present invention, it is possible to improve reliability and economic efficiency in sensing contact with another object. Furthermore, the contact sensing accuracy can be improved compared to that of conventional robot systems, thus realizing a reduction in damage that may be caused by accidental contact.
An index to the reference numerals used in the description follows:
1 . . . motor shaft-side angular sensor (encoder);
2 . . . output shaft-side angular sensor (encoder);
3 . . . motor shaft-side angle calculation unit;
4 . . . output shaft-side angle calculation unit;
5 . . . torsional deformation amount calculation unit;
6 . . . contact determination unit;
7 . . . motor control instruction unit;
8 . . . motor;
9 . . . angular sensor misalignment correction value storage unit;
10 . . . spring constant storage unit;
11 . . . contact determination threshold storage unit;
12 . . . contact response gain storage unit;
15 . . . arm;
16 . . . output shaft of a deceleration device 18;
17 . . . motor shaft of the motor 8;
18 . . . deceleration device;
20 . . . robot system;
21 . . . robot control unit;
22 . . . robot main body.
Typically, a servomotor or the like is used as the motor 8. Also, on one end side of the motor 8, one end of a motor shaft 17 is connected to an input shaft of the deceleration device 18, and on the other end of the motor 8, the motor shaft-side angular sensor 1 for the motor shaft is attached.
In the present embodiment, an encoder is used as the motor shaft-side angular sensor 1 for the motor shaft, and the encoder is configured to detect the rotation direction and the rotation angle of the motor shaft 17 of the motor 8, and output a measurement signal to the robot control unit 21. Note that the motor shaft-side angular sensor 1 is fixed to the motor shaft 17, but due to the inevitable influence of a processing accuracy limit or attachment accuracy for example, the shaft center of the motor shaft-side angular sensor 1 may be misaligned with the shaft center of the motor shaft 17.
The deceleration device 18 is constituted by a plurality of gear wheels (not shown), an output shaft 16, and the like. The arm 15 is coupled to this output shaft 16, and the output shaft-side angular sensor 2 for the output shaft is attached to an end of the output shaft 16. Note that, for example, a strain wave gearing, which is predominantly subject to elastic torsional deformation, is used as the deceleration device 18. However, the present invention is not limited to the above embodiment, and may also employ another type of deceleration device that has elastic torsional deformation between the output shaft and the input shaft.
In the present embodiment, the output shaft-side angular sensor 2 for the output shaft is also an encoder. The output shaft-side angular sensor 2 detects the rotation direction and the rotation angle of the output shaft 16, and outputs a measurement signal to the robot control unit 21. Note that the output shaft-side angular sensor 2 is fixed to the output shaft 16, but due to an inevitable influence of a processing accuracy limit or attachment accuracy for example, the shaft center of the output shaft-side angular sensor 2 may be misaligned with the shaft center of the output shaft 16.
The arm 15 has a predetermined length, and is provided with, at the leading end thereof, a tool, a workpiece holding means, or the like, which is not shown.
The motor shaft-side angle calculation unit 3 obtains a motor shaft-side rotation angle θm based on a signal received from the motor shaft-side angular sensor 1, and calculates a motor shaft-side angle θ1 by converting the motor shaft-side rotation angle θm into an output-side angle using the deceleration ratio N of the deceleration device 18. In other words, the motor shaft-side angle calculation unit 3 calculates θ1=θm÷N. The output shaft-side angle calculation unit 4 calculates an output shaft-side angle θ2 based on a signal received from the output shaft-side angular sensor 2.
The torsional deformation amount calculation unit 5 obtains an angular difference Δθd based on the motor shaft-side angle θ1, which is the result of calculation by the motor shaft-side angle calculation unit 3, and the output shaft-side angle θ2, which is the result of calculation by the output shaft-side angle calculation unit 4. That is, Δθd=θ1·θ2 is given. Furthermore, the torsional deformation amount calculation unit 5 corrects this angular difference using an angular sensor misalignment correction value θg[θ2] stored in the angular sensor misalignment correction value storage unit 9, and obtains a torsional deformation amount Δθ. That is, calculation of Δθ=Δθd·θg[θ2] is made. Here, the angular sensor misalignment correction value θg is stored, as an array with the output shaft-side angle θ2 serving as an argument, in the angular sensor misalignment correction value storage unit 9.
Here, illustration of angular sensor misalignment is given with reference to
Referring to
A flowchart of the contact torque calculation method is shown in
The motor control instruction unit 7 transmits an instruction to the motor 8 according to the state of determination of contact between the arm or an instrument attached to the arm and another object, the determination being made by the contact determination unit 6. Typically, an electric current instruction to instruct the motor 8 to generate rotation torque is transmitted from the motor control instruction unit 7 of the robot control unit 21 to the motor 8 of the robot main body 22.
A flow of angular sensor misalignment correction value measurement will be described with reference to
The present invention is applicable to a robot system that accurately senses contact between an arm of a robot or an instrument attached to the arm and another object.
1 Motor shaft-side angular sensor
2 Output shaft-side angular sensor
8 Motor
15 Arm
16 Output shaft
17 Motor shaft
18 Deceleration device
20 Robot system
21 Robot control unit
22 Robot main body
Y-axis Angular difference
X-axis Output shaft-side angle
1 Motor shaft-side angular sensor
2 Output shaft-side angular sensor
3 Motor shaft-side angle calculation unit
4 Output shaft-side angle calculation unit
5 Torsional deformation amount calculation unit
6 Contact determination unit
7 Motor control instruction unit
8 Motor
9 Angular sensor misalignment correction value storage unit
10 Spring constant storage unit
11 Contact determination threshold storage unit
12 Contact response gain storage unit
Start Contact Torque Calculation
S1 Read spring constant K
S2 Read angular sensor misalignment correction value θg
S3 Detect motor shaft-side angle θ1 and output shaft-side angle θ2
S4 Calculate angular difference
Δθd=θ1·θ2
S5 Perform correction using the angular sensor misalignment correction value
Δθ=Δθd·θg[θ2]
S6 Calculate contact torque
T=Δθ×K
End Contact Torque Calculation
Start Contact Determination
S7 Read spring constant K
S8 Read contact determination threshold Tc
S9 Read angular sensor misalignment correction value θg
S10 Detect motor shaft-side angle θ1 and output shaft-side angle θ2
S11 Calculate angular difference
Δθd=θ1·θ2
S12 Perform correction using the angular sensor misalignment correction value
Δθ=Δθd·θg[θ22]
S13 Calculate contact torque
T=Δθ×K
S14 Contact determination
T:Tc
Stop Motor
Start Contact Response
S15 Read spring constant K
S16 Shift to contact response mode
S17 Read contact response gain Gv
S18 Reads contact determination threshold Tc
S19 Read angular sensor misalignment correction value θg
S20 Detect motor shaft-side angle θ1 and output shaft-side angle θ2
S21 Calculate angular difference
Δθd=θ1·θ2
S22 Perform correction using the angular sensor misalignment correction value
Δθ=Δθd·θg[θ2]
S23 Calculate contact torque
T=Δθ×K
S24 Contact determination
T:Tc
S25 Calculate contact response speed
Vm=(T·Tc)×Gv
Drive Motor (Contact Response Operation)
Start Angular Sensor Misalignment Correction Value Measurement
S26 Rotate measurement shaft motor
S27 Detect motor shaft-side angle θ1 and output shaft-side angle θ2
S28 Calculate angular difference
Δθd=θ1·θ2
S29 Write angular sensor misalignment correction value
θg=Δθd
End Measurement
Number | Date | Country | Kind |
---|---|---|---|
JP2017-092029 | May 2017 | JP | national |
Filing Document | Filing Date | Country | Kind |
---|---|---|---|
PCT/JP2018/016576 | 4/24/2018 | WO | 00 |
Publishing Document | Publishing Date | Country | Kind |
---|---|---|---|
WO2018/203492 | 11/8/2018 | WO | A |
Number | Name | Date | Kind |
---|---|---|---|
20140379128 | Ishikawa | Dec 2014 | A1 |
20150177084 | Inoue | Jun 2015 | A1 |
Number | Date | Country |
---|---|---|
7-337055 | Dec 1995 | JP |
9-222910 | Aug 1997 | JP |
2003-39376 | Feb 2003 | JP |
2010-228028 | Oct 2010 | JP |
2010269412 | Dec 2010 | JP |
2013198955 | Oct 2013 | JP |
2015-3357 | Jan 2015 | JP |
2015-145045 | Aug 2015 | JP |
2016-221615 | Dec 2016 | JP |
Entry |
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International Search Report for International Application No. PCT/JP2018/016576 dated Jul. 31, 2018. |
Number | Date | Country | |
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20200078942 A1 | Mar 2020 | US |