TORQUE SENSOR

FIELD

The present disclosure relates to a torque sensor.

BACKGROUND

With recent shrinkage in workforce, it is expected to effectively use collaborative robots that work in the same spaces as humans. The collaborative robots that work in the same spaces as the humans, not only working capacity but also safety in operation is required. For example, for the safe operation of the collaborative robots, some of the collaborative robots include torque sensors calibrated in advance for the purpose of accurate detection of an external force due to external contact, interference, or the like.

CITATION LIST
Patent Literature

Patent Literature 1: JP 2009-103507 A

SUMMARY
Technical Problem

However, the torque sensors are an expensive product, causing a problem of burden of cost when the torque sensor is mounted on the collaborative robots. For example, in a torque sensor manufacturing process, use of a strain gauge is one of the factors that make the torque sensor expensive.

Therefore, the present disclosure proposes a torque sensor that achieves cost reduction while securing torque resolution as a sensor.

Solution to Problem

To solve the above problem, A torque sensor that provides a service that requires an identity verification process according to an embodiment of the present disclosure includes: a sensor unit that detects, from an output unit that is a rotational body of an actuator, a rotational position in an annular first area positioned at a first distance from a rotation center, and a rotational position in an annular second area positioned at a second distance longer than the first distance from the rotation center;a resilient body that is provided between the first area and the second area; and a detection unit that detects a torque applied to the output unit based on a result of the detection by the sensor unit.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram illustrating an overview of a torque sensor according to the present disclosure.

FIG. 2 is a cross-sectional view of an actuator according to an embodiment of the present disclosure.

FIG. 3 is a perspective view, axially exploded, of respective units of a device according to an embodiment of the present disclosure.

FIG. 4 is a perspective view, axially exploded, of the respective units of the device according to the embodiment of the present disclosure.

FIG. 5 is a three-view drawing of a detailed appearance configuration of a flexure element according to an embodiment of the present disclosure.

FIG. 6 is a perspective view partially illustrating a cross-section taken along line VI-VI of FIG. 5.

FIG. 7 is a perspective view partially illustrating a cross-section taken along line VII-VII of FIG. 5.

FIG. 8 is a diagram illustrating an exemplary configuration of a cutout portion according to a modification.

FIG. 9 is a diagram illustrating an exemplary configuration of a cutout portion according to a modification.

FIG. 10 is a diagram illustrating an example of insertion of a cushioning material according to a modification.

FIG. 11 is a diagram illustrating an example of a method of coupling an output unit according to a modification.

DESCRIPTION OF EMBODIMENTS

The embodiments of the present disclosure will be described in detail below with reference to the drawings. Note that in the following embodiments, the same portions are denoted by the same reference numerals and symbols, and a repetitive description thereof will be omitted. Furthermore, in the present description and the drawings, a plurality of component elements having substantially the same functional configurations will be distinguished by giving the same reference numerals or symbols followed by the different numerals or symbols in some cases.

Furthermore, the present disclosure will be described in the order of items shown below.

1. Overview of technology according to present disclosure
2. Exemplary device configuration
3. Modifications
4. Conclusion

1. Overview of Technology According to Present Disclosure

An overview of a technology according to the present disclosure will be described. The present disclosure relates to a torque sensor that is mounted to an actuator.

The torque sensor according to an embodiment of the present disclosure is a so-called phase difference torque sensor. The torque sensor of the present disclosure includes a sensor unit, a resilient body, and a detection unit. The sensor unit detects, from an output unit that is a rotational body of the actuator, a rotational position in an annular first area positioned at a first distance from a rotation center, and a rotational position in an annular second area positioned at a second distance longer than the first distance from the rotation center. The resilient body is provided between the first area and the second area. The detection unit detects a torque applied to the output unit on the basis of a result of the detection by the sensor unit. An overview of the torque sensor of the present disclosure will be specifically described below with reference to FIG. 1. FIG. 1 is a schematic diagram illustrating the overview of the torque sensor according to the present disclosure.

The torque sensor 200 according to an embodiment of the present disclosure (hereinafter, referred to as “torque sensor 200” as appropriate) is connected to the output unit 20 that is the rotational body of the actuator. For example, the torque sensor 200 rotates in a circumferential direction (directions indicated by an arrow dr) around a rotation axis passing through the rotation center C in synchronization with the output unit 20 by the power of a motor of the actuator.

As illustrated in FIG. 1, the torque sensor 200 includes a flexure element 210, a sensor unit 222, and a detection unit 223. The appearance of the flexure element 210 has a perfect circular shape in plan view. The flexure element 210 includes a first output unit 211 that corresponds to an output side of the motor, a second output unit 212 that corresponds to an output side of the actuator, and a resilient portion 213 that transmits the power of the motor from the first output unit 211 to the second output unit 212.

The resilient portion 213 functions as a resilient body. The resilient portion 213 is provided at least between the annular first area A₁ positioned at the first distance d₁ (the output side of the motor) from the rotation center C of the actuator and the annular second area A₂ positioned at the second distance d₂ (> d₁) (the output side of the actuator) from the rotation center C.

Furthermore, the sensor unit 222 detects the rotational position P₁ in the first area A₁ and the rotational position P₂ in the second area A₂, from the output unit 20 (flexure element 210). The detection unit 223 detects the torque applied to the output unit 20, on the basis of a result of the detection by the sensor unit 222. Specifically, the detection unit 223 performs calibration in advance and records an initial phase difference θ₁₂ corresponding to a difference in position generated between the rotational position P₁ and the rotational position P₂. Then, the detection unit 223 is configured to compare a difference in position generated between the rotational position P₁ and the rotational position P₂, detected when an external force applied to the output unit 20, with the initial phase difference θ₁₂, detecting the torque.

In this way, the torque sensor 200 of the present disclosure achieves cost reduction while securing the torque resolution as a sensor without using a strain gauge.

2. Exemplary Device Configuration

An exemplary device configuration according to an embodiment of the present disclosure will be described. FIG. 2 is a cross-sectional view of the actuator according to the embodiment of the present disclosure. FIG. 2 illustrates a cross-section of the actuator 1 to which the torque sensor 200 according to the embodiment of the present disclosure is mounted, taken along a vertical plane, of planes including the rotation axis of the actuator 1. Furthermore, FIGS. 3 and 4 are each a perspective view, axially exploded, of respective units of the device according to an embodiment of the present disclosure.

As illustrated in FIG. 2, the actuator 1 includes a motor unit 10 and the output unit 20. The motor unit 10 includes a geared motor fixing unit 11 that fixes a geared motor that is a power source driving a rotation shaft, and a geared motor output unit 12 that outputs power generated by the geared motor.

As illustrated in FIGS. 3 or 4, the torque sensor 200 is connected to the output unit 20. The torque sensor 200 includes the flexure element 210 and a functional unit 220.

The flexure element 210 has a disk shape having a predetermined thickness, and includes the first output unit 211, the second output unit 212, and the resilient portion 213.

The first output unit 211 is connected to the geared motor output unit 12 of the actuator 1. The second output unit 212 corresponds to the output side of the actuator 1. For example, in a case where the actuator 1 is installed at an elbow joint portion of a collaborative robot, the second output unit 212 is connected to a member constituting a forearm.

The resilient portion 213 transmits power of the actuator 1, from the first output unit 211 to the second output unit 212. FIG. 5 is a three-view drawing of a detailed appearance configuration of the flexure element according to an embodiment of the present disclosure. FIG. 5 illustrates a front surface 210FP, a right side surface 210SP, and a back surface 210BP of the flexure element 210 in order from the left. FIG. 6 is a perspective view partially illustrating a cross-section taken along line VI-VI of FIG. 5. FIG. 7 is a perspective view partially illustrating a cross-section taken along line VII-VII of FIG. 5.

For example, as illustrated in FIGS. 5 to 7, the resilient portion 213 includes a curved cutout portion SLα that extends in a circumferential direction (directions indicated by the arrow dr) about the rotation center C. The cutout portion SLα is formed inside the resilient portion 213 by performing laser processing spirally in a clockwise direction from the center portion of a metal disk constituting the flexure element 210, toward an outer peripheral portion thereof. Therefore, the resilient portion 213 flexibly responds to the power of the actuator 1 and the external force to the output unit 20. The flexure element 210 transmits the power of the actuator 1 from the first output unit 211 to the second output unit 212 while distorting the resilient portion 213.

In the flexure element 210, the first output unit 211 and the second output unit 212 are connected by the resilient portion 213 having the cutout portion SLα, forming a spring having increased entire length. Accordingly, the flexure element 210 can have wide flexibility. When the resilient portion 213 having the cutout portion SLα is regarded as the spring, a spring constant thereof is expressed by, for example, the following Formula (1). In Formula (1), “E” represents a modulus of direct elasticity, “b” represents a width of the spring, “t” represents a thickness of the spring, and “L” represents the entire length of the spring.

$[Mathematical Formula 1]$

As illustrated in FIGS. 3 to 5 or FIG. 7, the functional unit 220 of the torque sensor 200 includes an encoder disk 221, the sensor unit 222, and the detection unit 223. The encoder disk 221 includes a first encoder disk 221a that is provided at a position corresponding to the output side of the motor unit 10 of the actuator 1, and a second encoder disk 221b that is provided at a position corresponding to the output side of the actuator 1.

Each of the first encoder disk 221a and the second encoder disk 221b is installed on the back surface 210BP (surface on a side of the motor unit 10) of the flexure element 210 in the flexure element 210 (output unit 20).

The first encoder disk 221a has an inner diameter that coincides with the first distance d₁ from the rotation center C of the actuator 1. Therefore, when the first encoder disk 221a is installed so that the center of the first encoder disk 221a is coaxial with the rotation center C, the first encoder disk 221a is arranged at a position (the first area A₁) corresponding to the output side of the motor unit 10. The first encoder disk 221a is provided with a position detection pattern that can be read by a first sensor 222a. The position detection pattern provided on the first encoder disk 221a functions as a first position detection pattern that is provided in the first area A₁.

Furthermore, the second encoder disk 221b has an inner diameter that coincides with the second distance d₂ from the rotation center C of the actuator 1. Therefore, when the second encoder disk 221b is installed so that the center of the second encoder disk 221b is coaxial with the rotation center C, the second encoder disk 221b is arranged at a position (the second area A₂) corresponding to the output side of the actuator 1. The second encoder disk 221b is provided with a position detection pattern that can be read by a second sensor 222b. The position detection pattern provided on the second encoder disk 221b functions as a second position detection pattern that is provided in the second area A₂. Note that the present invention is not limited to the example of the torque sensor 200 provided with the encoder disk 221, but may use the torque sensor 200 directly provided with a position detection pattern that is configured to detect the rotational position in the first area A₁ and the rotational position in the second area A₂, on the back surface 210BP (the surface on the side of the motor unit 10) of the flexure element 210.

The sensor unit 222 is an encoder integrated circuit (IC) for position detection. The sensor unit 222 includes the first sensor 222a that is installed on the output side of the motor unit 10 (an inner peripheral side of the output unit 20) and the second sensor 222b that is installed on the output side of the actuator 1 (an outer peripheral side of the output unit 20).

The first sensor 222a reads the first encoder disk 221a (the position detection pattern) to detect the rotational position (e.g., the rotational position P₁) in the annular first area A₁ positioned at the first distance d₁ (the output side of the motor) from the rotation center C of the actuator 1. The second sensor 222b reads the second encoder disk 221b (the position detection pattern) to detect the rotational position (e.g., the rotational position P₂) in the annular second area A₂ positioned at the second distance d₂ (the output side of the motor) from the rotation center C of the actuator 1. The first sensor 222a and the second sensor 222b can be achieved by using a magnetic sensor such as an anisotropic magnetoresistance sensor, an optical sensor such as an optical displacement sensor, an induction current sensor such as an eddy current displacement sensor, or the like.

The detection unit 223 is a torque detection IC that is installed on an encoder board together with an encoder IC and the like corresponding to the sensor unit 222. The detection unit 223 detects the torque applied to the output unit 20, on the basis of a result of the detection by the sensor unit 222. The torque detected by the detection unit 223 is calculated according to the following Formula (2).

$\begin{matrix} Torque = ((θ_{2} - θ_{1}) + θ_{offset}) \times Gain (CW, CCW) & (2) \end{matrix}$

In Formula (2) described above, “θ_offset” represents a difference between sensor values detected by the sensor unit 222 at no load (when only gravitational acceleration acts). Furthermore, in Formula (2) described above, “θ₁” represents a sensor value detected by the first sensor 222a installed on the output side of the motor unit 10 (the inner peripheral side of the output unit 20). Furthermore, in Formula (2) described above, “θ₂” represents a sensor value detected by the second sensor 222b installed on the output side of the actuator 1 (the outer peripheral side of the output unit 20). In addition, in the following Formula (2), “Gain CW” represents sensitivity of the flexure element 210 in a clock wise (CW) direction. In addition, in the following Formula (2), “Gain CCW” represents sensitivity of the flexure element 210 in a counter clock wise (CCW) direction. “θ_offset,” “Gain CW,” and “Gain CCW” are measured in advance by performing calibration in advance.

The flexure element 210 transmits power of the actuator 1, from the first output unit 211 to the second output unit 212 while distorting the resilient portion 213. Therefore, the phase difference (shift in rotational position) occurs between the first output unit 211 and the second output unit 212. In addition, even when the output unit 20 is subjected to the external force during operation of the actuator 1, the resilient portion 213 of the flexure element 210 is distorted, causing the phase difference (shift in rotational position) between the first output unit 211 and the second output unit 212. The detection unit 223 measures the phase difference at no load while the actuator 1 is not subjected to any external force, enabling detection of the torque when the actuator 1 receives the external force. Specifically, as shown in Formula (2) described above, the torque can be calculated on the basis of “θ_offset” corresponding to the phase difference at no load while the actuator 1 is not subjected to any external force, and “θ₂ - θ₁” corresponding to a difference between the output side of the actuator 1 (the outer peripheral side of the output unit 20) and the output side of the motor unit 10 (the inner peripheral side of the output unit 20) when the actuator 1 is subjected to the external force. Note that the detection of the position by the sensor unit 222 and the detection of the torque by the detection unit 223 may be processed by the same IC.

3. Modifications
31. Variation (1) of Resilient Portion

Another exemplary configuration of the resilient portion 213 will be described. FIG. 8 is a diagram illustrating an exemplary configuration of a cutout portion according to a modification.

In the above embodiment, the description has been given of the example in which the cutout portion SLα is provided in the resilient portion 213 by processing the metal disk constituting the flexure element 210 spirally in one stroke in the clockwise direction by laser cutting, from the center to the outer peripheral portion. This example is not particularly limited, and the resilient portion 213 may include a plurality of cutout portions having different extending directions on the basis of the rotation center C, at positions where the cutout portions do not overlap each other. For example, as illustrated in FIG. 8, the resilient portion 213 may include a cutout portion SLR and a cutout portion SLL, at positions where the cutout portions do not overlap each other. The cutout portion SLR is formed inside the resilient portion 213 by performing laser processing on the metal disk constituting the flexure element 210, spirally in a clockwise direction from a processing start point SPR to a processing end point EPR, from the center portion toward the outer peripheral portion of the disk. Furthermore, the cutout portion SLL is formed inside the resilient portion 213 by performing laser processing on the metal disk constituting the flexure element 210, spirally in a clockwise direction from a processing start point SPL to a processing end point EPL, from the center portion toward the outer peripheral portion of the disk.

Note that the present invention is not limited to the example in which the cutout portion SLR in the clockwise direction and the cutout portion SLL in the counterclockwise direction are processed into one disk to form the flexure element 210. For example, the flexure element 210 may be configured by axially superimposing a disk having the cutout portion SLR in the clockwise direction and a disk having the cutout portion SLL in the counterclockwise direction.

32. Variation (2) of Resilient Portion

Furthermore, the resilient portion 213 may have a shape that is different from that of the cutout portion SL described in the above embodiment and those of the example illustrated in FIG. 8. FIG. 9 is a diagram illustrating an exemplary configuration of a cutout portion according to a modification. As illustrated in FIG. 9, the resilient portion 213 may include a plurality of cutout portions SLβ that is formed by processing part of a member constituting the flexure element 210.

32. Variation (3) of Resilient Portion

Furthermore, the resilient portion 213 is not limited to the example in which the resilient portion 213 is formed by processing the flexure element 210, and for example, may adopt a flat spiral spring at a position of the resilient portion 213 of the flexure element 210. This configuration may provide a further cost reduction effect upon mass production of the torque sensor 200.

3 -2. Cushioning Material

In the embodiments and the modifications described above, a cushioning material BM may be inserted into the cutout portion SL. FIG. 10 is a diagram illustrating an example of insertion of the cushioning material according to a modification. As illustrated in FIG. 10, the cushioning material BM is inserted over the entire circumference of the cutout portion SL of the resilient portion 13. For the cushioning material, silicone rubber, elastomer, or the like can be employed. Accordingly, a damper effect can be expected.

3 -3. Method of Coupling Output Side of Actuator

FIG. 11 is a diagram illustrating an example of a method of coupling the output unit according to a modification. As illustrated in FIG. 11, in the embodiments and modifications described above, the output side of the actuator 1 may be coupled to another member by using an Oldham coupling 30. This configuration makes it possible to accommodate a shift in the axial center that may be caused by the resilient portion 213 of the flexure element 210.

3-4. Detection of Torque by Image Processing

In the embodiments and the modifications described above, the torque sensor 200 may acquire an image obtained by capturing intervals between the cutout portions SL in the resilient portion 213 of the flexure element 210 to detect the torque from the acquired image. At this time, instead of the encoder disk 221 and the sensor unit 222, the torque sensor 200 preferably includes an imaging unit that is configured to image the intervals between the cutout portions SL provided in the resilient portion 213, and an image recognition unit that recognizes the image acquired by the imaging unit. The image recognition unit can be configured to use, for example, a trained model in which an image of the cutout portions SL is input and an estimation value of the torque applied to the actuator 1 (output unit 20) is output. The trained model can be generated by using any learning algorithm used for machine learning such as convolutional neural network (CNN).

4. Conclusion

The torque sensor 200 according to an embodiment of the present disclosure includes the sensor unit 222, the flexure element 210 that is the resilient body, and the detection unit 223. The sensor unit 222 detects, from the output unit 20 that is the rotational body of the actuator 1, the rotational position (e.g., the rotational position P₁) in the annular first area A₁ positioned at the first distance d₁ from the rotation center C, and the rotational position (e.g., the rotational position P₂) in the annular second area A₂ positioned at the second distance d₂ longer than the first distance d₁ from the rotation center C. The flexure element 210 that is the resilient body is provided between the first area A₁ and the second area A₂. The detection unit 223 detects the torque applied to the output unit 20, on the basis of a result of the detection by the sensor unit 222.

Accordingly, the torque sensor 200 achieves cost reduction while securing the torque resolution of the sensor without using the strain gauge.

Furthermore, the sensor unit 222 of the torque sensor 200 includes the first sensor 222a that detects the rotational position (e.g., the rotational position P₁) in the first area A₁ and the second sensor 222b that detects the rotational position (e.g., the rotational position P₂) in the second area A₂. This configuration makes it possible to accurately detect the rotational position in the first area A₁ and the rotational position in the second area A₂.

Furthermore, the torque sensor 200 further includes the first encoder disk 221a that functions as the first position detection pattern provided in the first area A₁, and the second encoder disk 221b that functions as the second position detection pattern provided in the second area A₂. The first sensor 222a detects the first encoder disk 221a functioning as the first position detection pattern to detect the rotational position (e.g., the rotational position P₁) in the first area A₁. The second sensor 222b detects the second encoder disk 221b functioning as the second position detection pattern to detect the rotational position (e.g., the rotational position P₂) in the second area A₂. This configuration makes it possible to detect the rotational position in the first area A₁ and the rotational position in the second area A₂, with a simple configuration.

Furthermore, the detection unit 223 of the torque sensor 200 detects the torque, on the basis of the phase difference between the rotational position P1 in the first area A1 and the rotational position P2 in the second area A2. This configuration makes it possible to secure the torque resolution.

Furthermore, the flexure element 210 of the torque sensor 200 that is the resilient body is formed by processing part of the member constituting the flexure element 210. This configuration makes it possible to reduce manufacturing cost of the flexure element 210 as much as possible.

Furthermore, the flexure element 210 of the torque sensor 200 that is the resilient body includes the curved cutout portion SL that extends in the circumferential direction (e.g., the directions indicated by the arrow dr) on the basis of the rotation center C of the actuator 1. This configuration makes it possible to cause the flexure element 210 to function as the resilient body.

Furthermore, the flexure element 210 of the torque sensor 200 that is the resilient body includes the cutout portion SLR and the cutout portion SLL that have different extending directions on the basis of the rotation center C, at positions where the cutout portions do not overlap each other. This configuration makes it possible to reduce a difference in torque gain between the clockwise direction (CW direction) and the counterclockwise direction (CCW direction).

Furthermore, the flexure element 210 of the torque sensor 200 that is the resilient body includes the cushioning material BM inserted into the cutout portion SL. Accordingly, a damper effect can be expected.

Furthermore, the flexure element 210 of the torque sensor 200 that is the resilient body may include a non-contact type flat spiral spring. This configuration may provide a further cost reduction effect upon mass production of the torque sensor 200, as compared with the laser processing for forming the cutout portion SL.

Furthermore, the torque sensor 200 may be configured so that the output side of the actuator 1 is coupled to another member by using the Oldham coupling 30. This configuration makes it possible to accommodate a shift in the axial center that may be caused by the resilient portion 213 of the flexure element 210.

The embodiments and modifications of the present disclosure have been described above, but the technical scope of the present disclosure is not limited to the embodiments and modifications described above, and various modifications and alterations can be made without departing from the spirit and scope of the present disclosure. Moreover, the component elements of different embodiments and modifications may be suitably combined with each other.

Furthermore, the effects descried herein are merely illustrative or exemplified effects, and are not limitative. In other words, with or in the place of the above effects, the technology of the present disclosure may achieve other effects that are clear to those skilled in the art from the description of this specification.

It is should be noted that the technology of the present disclosure naturally comes under the technical scope of the present disclosure, and the present technology may also be configured as below.

A torque sensor comprising:

a sensor unit that detects, from an output unit that is a rotational body of an actuator, a rotational position in an annular first area positioned at a first distance from a rotation center, and a rotational position in an annular second area positioned at a second distance longer than the first distance from the rotation center;
a resilient body that is provided between the first area and the second area; and
a detection unit that detects a torque applied to the output unit based on a result of the detection by the sensor unit.

The torque sensor according to (1), wherein

the sensor unit includes
a first sensor that detects the rotational position in the first area, and a second sensor that detects the rotational position in the second area.

The torque sensor according to (2), further comprising:

a first position detection pattern that is provided in the first area; and
a second position detection pattern that is provided in the second area;
wherein the first sensor
detects the first position detection pattern to detect the rotational position in the first area, and
the second sensor
detects the second position detection pattern to detect the rotational position in the second area.

The torque sensor according to (1), wherein

the detection unit
detects the torque, based on a phase difference between the rotational position in the first area and the rotational position in the second area.

The torque sensor according to claim 1, wherein

the resilient body
is formed by processing part of a member constituting the resilient body.

The torque sensor according to (5), wherein

the resilient body
includes a curved cutout portion that extends in a circumferential direction based on the rotation center.

The torque sensor according to (6), wherein

the resilient body
includes a plurality of the cutout portions that has different extending directions based on the rotation center, at positions where the cutout potions do not overlap each other.

The torque sensor according to (6), wherein

the resilient body
includes a cushioning material that is inserted into the cutout portion.

The torque sensor according to (1), wherein

the resilient body
includes a non-contact type flat spiral spring.

The torque sensor according to (1), wherein

the actuator has an output side that is coupled to another member by using an Oldham coupling.

Reference Signs List

1

ACTUATOR

10

MOTOR UNIT

20

OUTPUT UNIT

30

COUPLING

200

TORQUE SENSOR

210

FLEXURE ELEMENT

211

FIRST OUTPUT UNIT

212

SECOND OUTPUT UNIT

213

RESILIENT PORTION

220

FUNCTIONAL UNIT

221

ENCODER DISK

221
a

FIRST ENCODER DISK

221
b

SECOND ENCODER DISK

222

SENSOR UNIT

222
a

FIRST SENSOR

222
b

SECOND SENSOR

223

DETECTION UNIT

TORQUE SENSOR

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Abstract

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