Current limiting device, robotic system, and current limiting method

Abstract

The current limiting device (21) has a current limiting section (23) that limits the current supplied to the driving section (14) to a range of a limit value. The limit value is set to vary in accordance with the speed of the driving section (14).

Description

TECHNICAL FIELD

[0001] The present disclosure relates to a current limiting device, a robot system, and a current limiting method, and particularly relates to a current limiting device, a robot system, and a current limiting method that limit a current supplied to a motor. BACKGROUND

[0002] Conventionally, a robot in which an upper limit value of a current supplied to a motor is set is known. For example, a robot is disclosed in Japanese Patent Application Publication No. 2008-73790.

[0003] Japanese Patent Application Publication No. 2008-73790 discloses a robot that includes a robot body to which a plurality of links are connected via joints, a motor provided to the joint of the robot body, and a reduction unit that reduces the rotation of the motor. The robot is provided with a current measurement unit that measures a current supplied to the motor. Moreover, when the robot body is at rest, an upper limit value of the current supplied to the motor is set based on a current value measured by the current measurement unit. Specifically, when the robot is at rest, a constant upper limit value of the current is set in accordance with a torque of the motor required to maintain a prescribed posture. Thus, the driving torque imparted to the joint can be appropriately limited in accordance with the posture of the robot.

[0004] Patent Document 1: Japanese Patent Application Publication No. 2008-73790

[0005] In the existing robot provided with the reduction unit that reduces the rotation of the motor as described in Japanese Patent Application Publication No. 2008-73790, as the rotational speed of the reduction unit becomes larger, the loss torque of the reduction unit becomes larger. In addition, generally, the motor is configured such that as the rotational speed of the motor becomes larger, the torque generated by the motor becomes smaller. Therefore, as described in Japanese Patent Application Publication No. 2008-73790, in the case where a constant upper limit value of the current supplied to the motor is set, since the loss torque of the reduction unit becomes larger as the rotational speed of the motor becomes larger and the torque generated by the motor (driving unit) decreases, the desired torque cannot be output from the reduction unit. SUMMARY

[0006] The present disclosure was achieved to solve the above-described problems, and an object of the present disclosure is to provide a current limiting device and a current limiting method in which, in a structure in which an upper limit value of a current supplied to a driving unit is set, even in the case where the speed of the driving unit becomes large, a desired force or torque can be output from a driving force transmission unit.

[0007] To achieve the above object, a current limiting device according to a first aspect of the present disclosure limits current supplied to a driving section that generates a force or a torque by flowing the current and that transmits a driving force via a driving force transmission section, the current limiting device including a current limiting section that limits the current supplied to the driving section within a range of a limit value, the limit value being set to vary in accordance with a speed of the driving section.

[0008] In the current limiting device according to the first aspect of the present disclosure, as described above, the limit value of the current supplied to the driving section is set to vary in accordance with the speed of the driving section. Thereby, the limit value can be varied in accordance with a loss of the driving force transmission section that varies in correspondence with the speed of the driving section, and a reduction of the force or the torque generated by the driving section. As a result, in a structure in which an upper limit value of the current supplied to the driving section is set, even if the speed of the driving section becomes large, a desired force or torque can be output from the driving force transmission section.

[0009] A robot system according to a second aspect of the present disclosure includes a robot, and a robot control section that controls the robot, the robot including a joint, a motor provided to the joint, and a reduction section that reduces rotation of the motor, the robot control section including a current limiting section that limits current supplied to the motor within a range of a limit value, the limit value being set to vary in accordance with a speed of the motor.

[0010] In the robot system according to the second aspect of the present disclosure, as described above, the limit value of the current supplied to the motor is set to vary in accordance with the speed of the motor. Thereby, the limit value can be varied in accordance with a loss of the driving force transmission section that varies in correspondence with the speed of the motor, and a reduction of the force or the torque generated by the motor. As a result, a robot system in which an upper limit value of the current supplied to the motor is set, even if the speed of the motor becomes large, a desired force or torque can be output from the driving force transmission section can be provided.

[0011] A current limiting method according to a third aspect of the present disclosure limits current supplied to a driving section that generates a force or a torque by flowing the current and that transmits a driving force via a driving force transmission section, the current limiting method including: a step of acquiring a speed of the driving section; a step of setting a limit value of the current supplied to the driving section on the basis of the acquired speed of the driving section; and a step of supplying the current to the driving section within a range of the set limit value.

[0012] In the current limiting method of the third aspect of the present disclosure, as described above, there is provided a step of setting a limit value of current to be supplied to the driving section based on the speed of the driving section. Thereby, the limit value can be changed in accordance with the loss of the driving force transmission section that varies in correspondence with the speed of the driving section, and the reduction of the force or torque generated by the driving section. As a result, it is possible to provide a current limiting method in which, in a structure in which an upper limit value of current to be supplied to the driving section is set, even if the speed of the driving section becomes large, a desired force or torque can be output from the driving force transmission section.

[0013] According to the present disclosure, as described above, in a structure in which an upper limit value of current to be supplied to the driving section is set, even if the speed of the driving section becomes large, a desired force or torque can be output from the driving force transmission section. BRIEF DESCRIPTION OF DRAWINGS

[0014] Figure 1 is a diagram showing a structure of a robot system based on one embodiment of the present disclosure.

[0015] Figure 2 is a block diagram of a robot control section based on one embodiment of the present disclosure.

[0016] Figure 3 is a control block diagram of a robot control section based on one embodiment of the present disclosure.

[0017] Figure 4 is a diagram showing a relationship between a rotational speed of a motor and a loss torque of a deceleration section.

[0018] Figure 5 is a diagram showing a relationship between a rotational speed of a motor and a torque generated from the motor.

[0019] Figure 6 is a diagram showing a limit value that is constant regardless of a rotational speed of a motor.

[0020] Figure 7 is a diagram showing a limit value at a positive efficiency and a limit value at a negative efficiency when a rotational speed of a motor is constant.

[0021] Figure 8 is a diagram showing a limit value at a positive efficiency and a limit value at a negative efficiency that vary in accordance with a rotational speed of a motor.

[0022] Figure 9 is a diagram showing a limit value at a positive efficiency and a limit value at a negative efficiency in a case where a motor rotates in a positive direction.

[0023] Figure 10 is a diagram showing a limit value at a positive efficiency and a limit value at a negative efficiency in a case where a motor rotates in a negative direction.

[0024] Figure 11 is a flowchart for explaining a current limiting method based on one embodiment of the present disclosure.

[0025] Figure 12 is a diagram showing a structure of a robot for medical use based on a modified example.

[0026] Figure 13 is a block diagram (1) showing a structure of a robot control section based on a modified example.

[0027] Figure 14 is a block diagram (2) showing a structure of a robot control section based on a modified example. DETAILED DESCRIPTION

[0028] Hereinafter, one embodiment of the present disclosure embodying the present disclosure will be explained based on the drawings.

[0029] REFERENCE Figures 1-11 The structure of the robot system 100 based on the present embodiment will be explained.

[0030] As shown in Figure 1 , the robot system 100 is provided with a robot 10 and a robot control section 20 that controls the robot 10. The robot 10 is, for example, a 6-axis robot. In addition, the robot 10 is, for example, a robot for industry.

[0031] As shown in Figure 1 , the robot 10 includes an arm section 11. The arm section 11 has joints 12. The joints 12 are provided in plurality. For example, the joints 12 (joints 12a to 12f) are provided in six. In addition, the arm section 11 is installed to a base 13. The joint 12a is configured to be able to turn around an axis L1 extending in the vertical direction. The joint 12b is configured to be able to turn around an axis L2 extending in the horizontal direction. The joint 12c is configured to be able to turn around an axis L3 extending in parallel with respect to the axis L2.

[0032] The joint 12d is configured to be able to turn around an axis L4 orthogonal to the axis L3. The joint 12e is configured to be able to turn around an axis L5 orthogonal to the axis L4. The joint 12f is configured to be able to turn around an axis L6 orthogonal to the axis L5.

[0033] As shown in Figure 2As shown, motors 14a to 14f are provided respectively to the plurality of joints 12a to 12f. Further, reduction units 15a to 15f that transmit the respective driving forces of the motors 14a to 14f are provided respectively to the motors 14a to 14f. The motors 14a to 14f generate force or torque (in the present embodiment, torque) by flowing of electric current, and transmit the driving force via the reduction units 15a to 15f. Further, the reduction units 15a to 15f transmit by reducing the rotation of the motors 14a to 14f. Thereby, the joints 12a to 12f rotate. Hereinafter, the motors 14a to 14f are sometimes collectively referred to as motors 14. Further, the reduction units 15a to 15f are sometimes collectively referred to as reduction units 15. Furthermore, the motors 14 (14a to 14f) are one example of driving units. Further, the reduction units 15 (15a to 15f) are one example of driving force transmission units.

[0034] Encoders 16a to 16f are provided respectively to the motors 14a to 14f. The encoders 16a to 16f detect the angular positions of output shafts 17a to 17f of the respective motors 14a to 14f. The detected angular positions of the output shafts 17a to 17f are transmitted to a position / speed control unit 22 described later. Hereinafter, the encoders 16a to 16f are sometimes collectively referred to as encoders 16. Further, the output shafts 17a to 17f are sometimes collectively referred to as output shafts 17.

[0035] Further, a current limiter 21 that limits the electric current that is supplied to the motors 14 that transmit the driving force via the reduction units 15 is provided to the robot control unit 20. The current limiter 21 includes the position / speed control unit 22 and a current limiter unit 23 that limits the electric current supplied to the motors 14 within a range of a limit value.

[0036] The position / speed control unit 22 is electrically connected to the motors 14a to 14f respectively, causes the electric current to flow to the motors 14a to 14f respectively, and controls the torque that is output from the motors 14a to 14f respectively. Further, the position / speed control unit 22 includes a position control unit 22a (refer to Figure 3 ) and a speed control unit 22b (refer to Figure 3 ). Further, a storage unit 24 is connected to the position / speed control unit 22. A program for driving each of the motors 14a to 14f is stored in the storage unit 24.

[0037] Further, the current limiter unit 23 includes current limiter units 23a to 23f that are provided respectively to the plurality of motors 14a to 14f. Further, amplifiers 25a to 25f are provided between each of the current limiter units 23a to 23f and the motors 14a to 14f. Hereinafter, the amplifiers 25a to 25f are sometimes collectively referred to as amplifiers 25.

[0038] Next, the operation of the robot control unit 20 will be described with reference to the flowchart of FIG. 4.Figure 3 The torque control of the motor 14 will be described.

[0039] The position / speed control section 22 acquires a position command value (time history command position) of the joint 12 from the storage section 24 (upper command device). Further, the position control section 22a calculates a deviation of the acquired position command value from an angular position (actual angular position) obtained from the encoder 16 of the joint 12. Further, the position control section 22a multiplies the calculated deviation by a position gain. In addition, the position control section 22a differentiates the position command value, and calculates a speed, that is, a speed command value, as a target of the joint 12.

[0040] Next, the speed control section 22b adds the deviation multiplied by the above-mentioned position gain to the generated speed command value, and subtracts an actual angular speed obtained by differentiating the actual angular position from the added value, and calculates a speed deviation. Further, the speed control section 22b multiplies the calculated speed deviation by a speed gain. Thus, the speed control section 22b generates a target current value corresponding to a target torque output from the motor 14.

[0041] Further, the speed control section 22b transmits the generated target current value to the current limiter section 23. In a case where the transmitted target current value is within a range of a limit value of the current, the current limiter section 23 transmits the target current value to the amplifier 25 as it is. On the other hand, in a case where the transmitted target current value is outside the range of the limit value of the current, the current limiter section 23 transmits the target current value limited to a value within the range of the limit value of the current to the amplifier 25.

[0042] Here, in the present embodiment, the limit value of the current to be supplied to the motor 14 is set to vary according to the speed of the motor 14 (refer to Figure 8 ). One of reasons for setting the limit value of the current is to make the torque output from the motor 14 be equal to or less than the allowable torque of the drive system (for example, to suppress the torque of damaging the deceleration section 15, and the like).

[0043] On the other hand, as shown in Figure 4 , as the rotational speed (horizontal axis) of the deceleration section 15 increases, the loss torque (vertical axis) of the deceleration section 15 rises. Specifically, the deceleration section 15 includes Coulomb friction and viscous friction. The Coulomb friction is proportional to the force applied to the deceleration section 15. In addition, the viscous friction is friction caused by the viscosity of the grease, oil included in the deceleration section 15, and increases as the rotational speed of the deceleration section 15 increases.

[0044] In addition, as shown in Figure 5As shown, the torque (vertical axis) generated by the motor 14 decreases as the rotational speed (horizontal axis) of the motor 14 increases. This is because as the rotational speed (rotational velocity) of the motor 14 increases, the back electromotive force generated by the motor 14 increases, and the current is less likely to flow to the motor 14.

[0045] Here, as Figure 6 shown, in a case where the limit value of the current is constant regardless of the rotational speed of the motor 14, in a region where the rotational speed of the motor 14 is relatively large, the torque generated by the motor 14 decreases as the loss torque of the reduction portion 15 increases, and thus a desired torque cannot be generated from the reduction portion 15.

[0046] Therefore, in the present embodiment, as Figure 8 shown, the absolute value of the limit value is set to increase (in the case of positive efficiency described later) or decrease (in the case of negative efficiency described later) as the speed (rotational speed) of the motor 14 increases. In addition, the absolute value of the limit value is set to gradually increase or gradually decrease as the rotational speed of the motor 14 increases. Furthermore, in a case where the loss torque of the reduction portion 15 is caused only by friction, the absolute value of the limit value gradually increases or gradually decreases as the rotational speed of the motor 14 increases. However, depending on the control of the motor 14, there is also a case where the motor 14 is caused to change in such a manner that the absolute value of the limit value decreases according to the rotational speed and increases after a certain rotational speed.

[0047] In addition, as Figure 4 shown, the increase rate of the loss torque of the reduction portion 15 increases as the rotational speed of the reduction portion 15 increases. In addition, as Figure 5 shown, the decrease rate of the torque generated by the motor 14 increases as the rotational speed of the reduction portion 15 increases. Therefore, in the present embodiment, the change rate of the limit value is set to increase as the speed (rotational speed) of the motor 14 increases. Furthermore, Figure 8 the change rate of the limit value is one example, and there is also a case where the change rate of the limit value does not increase as the speed (rotational speed) of the motor 14 increases. That is, the change rate of the limit value is set in such a manner as to change in accordance with the change in the loss torque of the reduction portion 15.

[0048] In addition, a case where the direction of the driving direction (rotational direction) of the motor 14 is the same as the direction of the force or torque (in the present embodiment, torque) output from the motor 14 is referred to as positive efficiency. In other words, in the case of positive efficiency, in the motor 14 and the reduction portion 15, the torque is transmitted from the motor 14 side to the reduction portion 15 side. Positive efficiency corresponds to, for example, a case where the rotation of the joint 12 is accelerated by the motor 14. At the time of positive efficiency, the loss torque of the reduction portion 15 contributes negatively to the torque generated by the motor 14.

[0049] Furthermore, the situation where the driving direction (rotation direction) of motor 14 is opposite to the direction of the force or torque (in this embodiment, torque) output from motor 14 is called negative efficiency. In other words, in the case of negative efficiency, torque is transmitted from the output side of reduction gear 15 to the motor 14 side. Negative efficiency is, for example, equivalent to a large deceleration of motor 14. In the case of negative efficiency, the loss torque of reduction gear 15 contributes positively to the torque generated by motor 14. Thus, the contribution of the loss torque of reduction gear 15 to the torque generated by motor 14 is different in the cases of positive efficiency and negative efficiency.

[0050] Therefore, in this embodiment, as Figure 8 As shown, the current limiting values ​​include a positive efficiency limiting value when the driving direction (rotation direction) of the motor 14 is the same as the direction of the force or torque (in this embodiment, torque) output from the motor 14, and a negative efficiency limiting value when the driving direction (rotation direction) of the motor 14 is opposite to the direction of the force or torque (in this embodiment, torque) output from the motor 14, having a different value than the positive efficiency limiting value. Furthermore, the positive efficiency limiting value and the negative efficiency limiting value are set to vary according to the speed (rotational speed) of the motor 14. Additionally, the absolute value of the positive efficiency limiting value is larger than the absolute value of the negative efficiency limiting value.

[0051] like Figure 7 As shown, when the limit value for the efficiency of the motor 14 remains constant regardless of its speed, as the speed of the motor 14 increases, the loss torque of the reduction section 15, which contributes negatively, increases, and the torque on the output side of the reduction section 15 decreases. Furthermore, when the limit value for the efficiency of the motor 14 remains constant regardless of its speed, as the speed of the motor 14 increases, the loss torque of the reduction section 15, which contributes positively, increases, resulting in a larger torque being applied to the reduction section 15. Therefore, there are potential issues such as damage to the reduction section 15, loosening of bolts in the reduction section 15, or increased stress on the arm during deceleration.

[0052] Therefore, in this embodiment, as Figure 8 As shown, the absolute value of the limit value for positive efficiency is set to increase as the speed of motor 14 increases, and the absolute value of the limit value for negative efficiency is set to decrease as the speed of motor 14 increases.

[0053] Furthermore, as described above, the rate of increase in the loss torque of the reduction section 15 increases with the increase in the rotational speed of the reduction section 15 (see reference). Figure 4 Furthermore, the rate of decrease in torque generated by motor 14 increases as the rotational speed of motor 14 increases (see reference). Figure 5). Therefore, in the present embodiment, the increase rate of the limit value at the time of positive efficiency and the decrease rate of the limit value at the time of negative efficiency are set to increase as the rotational speed of the motor 14 becomes larger.

[0054] In detail, as shown in Figure 9 , when the current flows in the positive direction in the motor 14 (the current command value is positive), and the rotation of the motor 14 is in the positive direction (positive efficiency), the limit value at the time of positive efficiency is a positive value, and increases as the rotational speed of the motor 14 becomes larger. In addition, when the current flows in the positive direction in the motor 14 (the current command value is positive), and the rotation of the motor 14 is in the negative direction (negative efficiency), the limit value at the time of negative efficiency is a positive value, and decreases as the rotational speed of the motor 14 becomes larger.

[0055] In addition, as shown in Figure 10 , when the current flows in the negative direction in the motor 14 (the current command value is negative), and the rotation of the motor 14 is in the negative direction (positive efficiency), the limit value at the time of positive efficiency is a negative value, and decreases (the absolute value increases) as the rotational speed of the motor 14 becomes larger. In addition, when the current flows in the negative direction in the motor 14 (the current command value is negative), and the rotation of the motor 14 is in the positive direction (negative efficiency), the limit value at the time of negative efficiency is a negative value, and increases (the absolute value decreases) as the rotational speed of the motor 14 becomes larger.

[0056] In addition, in the present embodiment, the limit value is set so as to suppress damage to the reduction portion 15 due to the force or torque (in the present embodiment, the torque) generated by the motor 14, and maintain the force or torque (in the present embodiment, the torque) on the output side of the reduction portion 15 to a constant value. Specifically, the limit value at the time of positive efficiency is set so that the torque on the output side of the reduction portion 15 remains constant even if the rotational speed of the motor 14 increases. That is, the limit value at the time of positive efficiency is set so as to be able to compensate for the reduction amount of the torque generated by the motor 14 and the loss torque of the reduction portion 15 (and, suppress damage to the reduction portion 15). In addition, the limit value at the time of negative efficiency is set so as to suppress damage to the reduction portion 15 due to an increase in the loss torque of the reduction portion 15 even if the rotational speed of the motor 14 increases. The limit value at the time of positive efficiency and the limit value at the time of negative efficiency are obtained based on the results of actually driving the motor 14, measuring the loss torque of the reduction portion 15 and the reduction in the torque of the motor 14.

[0057] Next, with reference to Figure 11 , a current limiting method for limiting the current supplied to the motor 14 that transmits driving force via the reduction portion 15 will be described.

[0058] In step S1, the current limiting device 21 acquires the speed (rotational speed) of the motor 14. Specifically, the speed is acquired by differentiating the time history command position from the upper command device. Further, the rotational speed of the motor 14 can be acquired based on the angle position of the output shaft 17 of the motor 14 acquired from the encoder 16.

[0059] In step S2, the current limiting section 23 sets the limit value of the current to be supplied to the motor 14 based on the acquired speed (rotational speed) of the motor 14.

[0060] In step S3, the current limiting section 23 supplies the current to the motor 14 within the range of the set limit value. The above-described operations of steps S1 to S3 are repeated in the operation of the motor 14.

[0061] [Effects of the Present Embodiment]

[0062] In the present embodiment, the following effects can be obtained.

[0063] In the present embodiment, as described above, the limit value of the current to be supplied to the motor 14 is set to vary depending on the rotational speed of the motor 14. Thereby, the limit value can be varied in accordance with the loss of the reduction section 15 and the reduction of the torque generated by the motor 14, which vary in correspondence with the rotational speed (speed) of the motor 14. As a result, in the structure in which the upper limit value of the current to be supplied to the motor 14 is set, even in the case where the rotational speed of the motor 14 becomes large, the desired torque can be output from the reduction section 15.

[0064] Further, in the present embodiment, as described above, the absolute value of the limit value is set to become larger or smaller as the rotational speed of the motor 14 becomes larger. Here, there are a case where the loss of the reduction section 15 contributes positively to the torque generated by the motor 14 (a case of negative efficiency) and a case where the loss contributes negatively to the torque (a case of positive efficiency). Therefore, in the case where the loss of the reduction section 15 contributes negatively to the torque generated by the motor 14, by making the limit value of the positive efficiency larger as the rotational speed of the motor 14 becomes larger, the current to be supplied to the motor 14 can be adjusted so as to compensate for the reduction of the torque generated by the motor 14 and the loss of the reduction section 15. Further, in the case where the loss of the reduction section 15 contributes positively to the torque generated by the motor 14, by making the limit value of the negative efficiency smaller as the rotational speed of the motor 14 becomes larger, the current to be supplied to the motor 14 can be adjusted so as to remove the portion where the loss of the reduction section 15 becomes positive. As a result, in both the case where the loss of the reduction section 15 contributes positively and the case where the loss contributes negatively, the current to be supplied to the motor 14 can be appropriately adjusted.

[0065] Further, in the present embodiment, as described above, the rate of change of the limit value is set to increase as the rotational speed of the motor 14 increases. Thus, the rate of change of the loss of the speed reduction portion 15 and the rate of change of the reduction of the torque generated by the motor 14 increase as the rotational speed of the motor 14 increases, and therefore by setting the rate of change of the limit value to increase as the rotational speed of the motor 14 increases, it is possible to more appropriately adjust the current supplied to the motor 14. As a result, it is possible to appropriately adjust the torque of the motor 14.

[0066] Further, in the present embodiment, as described above, the limit value of the current includes the limit value at the time of positive efficiency when the driving direction (rotational direction) of the motor 14 is the same as the direction of the force or torque (in the present embodiment, torque) output from the motor 14, and the limit value at the time of negative efficiency when the driving direction (rotational direction) of the motor 14 is opposite to the direction of the force or torque (in the present embodiment, torque) output from the motor 14, and the limit value at the time of positive efficiency and the limit value at the time of negative efficiency are set to change in accordance with the rotational speed of the motor 14. Here, in the case of positive efficiency, the loss of the speed reduction portion 15 contributes negatively to the force generated by the motor 14, and in the case of negative efficiency, the loss of the speed reduction portion 15 contributes positively to the force generated by the motor 14. Therefore, as described above, the limit value includes the limit value at the time of positive efficiency and the limit value at the time of negative efficiency having a different value from the limit value at the time of positive efficiency, and thus in either case of positive efficiency and negative efficiency, it is possible to appropriately adjust the current supplied to the motor 14.

[0067] Further, in the present embodiment, as described above, the absolute value of the limit value at the time of positive efficiency is set to increase as the rotational speed of the motor 14 increases, and the absolute value of the limit value at the time of negative efficiency is set to decrease as the rotational speed of the motor 14 increases. Thus, in the case of positive efficiency, the loss of the speed reduction portion 15 contributes negatively to the torque generated by the motor 14, and therefore by setting the absolute value of the limit value at the time of positive efficiency to increase as the rotational speed of the motor 14 increases, it is possible to appropriately adjust the current supplied to the motor 14 so as to compensate for the reduction of the torque generated by the motor 14 and the loss caused by the speed reduction portion 15. Further, in the case of negative efficiency, the loss of the speed reduction portion 15 contributes positively to the torque generated by the motor 14, and therefore by setting the absolute value of the limit value at the time of negative efficiency to decrease as the rotational speed of the motor 14 increases, it is possible to suppress damage to the speed reduction portion 15 caused by applying excessive torque to the speed reduction portion 15.

[0068] Further, in the present embodiment, as described above, the increase rate of the limit value at the time of positive efficiency and the decrease rate of the limit value at the time of negative efficiency are set to increase as the rotational speed of the motor 14 increases. Thus, since the increase rate of the loss of the reduction portion 15 and the decrease rate of the reduction of the torque generated by the motor 14 increase as the rotational speed of the motor 14 increases, by setting the increase rate of the limit value at the time of positive efficiency and the decrease rate of the limit value at the time of negative efficiency to increase as the rotational speed of the motor 14 increases, it is possible to more appropriately adjust the current supplied to the motor 14.

[0069] Further, in the present embodiment, as described above, the limit value is set to change in accordance with the rotational speed of the motor 14. Thus, it is possible to change the limit value in accordance with the loss torque of the reduction portion 15 which changes in correspondence with the rotational speed of the motor 14, and the reduction of the torque generated by the motor 14. As a result, in the case where the rotational speed of the motor 14 increases, it is possible to adjust the current supplied to the motor 14 in consideration of the loss of the reduction portion 15 and the reduction of the torque generated by the motor 14, and thus it is possible to output the desired torque from the reduction portion 15 even in the case where the rotational speed of the motor 14 increases.

[0070] Further, in the present embodiment, as described above, the limit value is set so as to suppress damage to the reduction portion 15 due to the torque generated by the motor 14, and maintain the torque on the output side of the reduction portion 15 at a constant value. Thus, it is possible to suppress damage to the reduction portion 15, and it is possible to output the desired torque from the reduction portion 15.

[0071] Further, in the present embodiment, as described above, the motor 14 is provided to the joint 12 of the robot 10. Thus, in the motor 14 provided to the joint 12 of the robot 10, it is possible to output the desired torque from the reduction portion 15 even in the case where the rotational speed of the motor 14 increases.

[0072] [Modified Example]

[0073] Further, the present embodiment disclosed this time is to be considered in all respects as illustrative and not restrictive. The scope of the disclosure is not limited by the explanation of the embodiments described above, but is indicated by the claims, and includes all modifications (modified examples) equivalent in meaning and within the scope thereof.

[0074] For example, in the above-described embodiment, an example in which the present disclosure is applied to the robot 10 for industrial use is shown, but the present disclosure is not limited thereto. For example, as Figure 12As shown, the present disclosure can also be applied to a robot 30 for medical use. The robot 30 is provided with a positioner 31 (a multi-joint robot), an arm base 32, and a plurality of arms 33. A medical instrument 34 is attached to the front end of each of the plurality of arms 33. The current limiting device of the present disclosure, for example, limits the current flowing to the motor of the positioner 31 (the multi-joint robot), the joint of the arm 33. Thereby, in the robot 30 for medical use, even in the case where the speed (rotational speed) of the motor 14 becomes large, the desired torque can be output from the deceleration unit 15.

[0075] In particular, in the robot 30 for medical use, for reasons such as the space for arranging the robot 30 for medical use being limited, the number of joints being large, and the driving voltage being required to be low in order to reduce the impact at the time of collision, a low-output motor 14 is sometimes used with a high deceleration ratio. In this case, since the influence of the friction of the driving system becomes large, it is particularly effective to change the limit value of the current in accordance with the rotational speed of the motor 14 as in the present disclosure.

[0076] In addition, in the above-described embodiment, an example in which the motor 14 is applied as the "driving unit" of the present disclosure is shown, but the present disclosure is not limited thereto. For example, a proportional solenoid, a linear motor, a voice coil, a spherical actuator, or the like can be applied as the "driving unit" of the present disclosure. In addition, an electromagnetic powder clutch / brake, a hysteresis clutch / brake can be applied as the "driving unit" of the present disclosure.

[0077] In addition, in the above-described embodiment, an example in which the deceleration unit 15 is applied as the "driving force transmission unit" of the present disclosure is shown, but the present disclosure is not limited thereto. For example, in the case where the motor is a linear motor of linear motion, the driving force transmission unit transmits the force of the linear motion of the linear motor. In addition, the limit value is set to change in accordance with the speed of the linear motion of the linear motor.

[0078] In addition, in the above-described embodiment, an example in which the absolute value of the limit value at the time of positive efficiency is set to gradually increase as the rotation of the motor 14 becomes large, and the absolute value of the limit value at the time of negative efficiency is set to gradually decrease as the rotation of the motor 14 becomes large is shown, but the present disclosure is not limited thereto. For example, it can be set such that the absolute value of the limit value at the time of positive efficiency increases in stages as the rotation of the motor 14 becomes large, and the absolute value of the limit value at the time of negative efficiency decreases in stages as the rotation of the motor 14 becomes large.

[0079] In addition, in the above-described embodiment, an example in which the rate of change of the limit value is set to increase as the speed of the motor becomes large is shown, but the present disclosure is not limited thereto. For example, in the case where the rate of change of the torque reduction of the motor 14 accompanying the increase in the rotational speed of the motor 14 is small (in the case close to linear), or the like, the rate of change of the limit value can also be constant.

[0080] In addition, in the above-described embodiment, an example in which the limit value at the time of positive efficiency and the limit value at the time of negative efficiency are provided is shown, but the present disclosure is not limited thereto. For example, in a case where the difference between the limit value at the time of positive efficiency and the limit value at the time of negative efficiency is small, or the like, a common limit value can be provided in the positive efficiency and the negative efficiency.

[0081] In addition, in the above-described embodiment, an example in which the absolute value of the limit value at the time of negative efficiency is set to decrease as the rotation speed of the motor 14 increases is shown, but the present disclosure is not limited thereto. For example, depending on the control of the motor 14, in a high-speed region of the rotation speed of the motor 14, the absolute value of the limit value at the time of negative efficiency can be set to decrease as the rotation speed of the motor 14 increases.

[0082] In addition, in the above-described embodiment, an example in which the position / speed control section 22 is provided commonly with respect to the motors 14a to 14f (one position / speed control section 22) is shown, but the present disclosure is not limited thereto. For example, as shown in FIG. 6, position / speed control sections 122a to 122f can be provided individually with respect to the motors 14a to 14f. Figure 13

[0083] In addition, in the above-described embodiment, an example in which the position / speed control section 22 and the current limit sections 23a to 23f are provided individually is shown, but the present disclosure is not limited thereto. For example, as shown in FIG. 7, one control section 26 including the position / speed control section and the current limit section can be provided. Figure 14

[0084] In addition, in the above-described embodiment, an example in which the current limit section 23 is provided on the upstream side of the amplifier 25 is shown, but the present disclosure is not limited thereto. In the present disclosure, the current limit section 23 can be provided at some point of a line connecting the position / speed control section 22 and the motor 14 (the output side of the amplifier 25, a line from which the encoder 16 is fed back, or the like).

[0085] Explanation of Reference Numerals

[0086] 10 robot; 12, 12a to 12f joint; 14, 14a to 14f motor (drive section); 15, 15a to 15f speed reducer (drive force transmission section); 20 robot control section; 21 current limit device; 23, 23a to 23f current limit section; 30 robot (robot for medical use); 100 robot system.​​

Claims

1. A current limiting device that limits current supplied to a driving section that generates force or torque by flowing current and that transmits driving force via a driving force transmission section, wherein the current limiting device has a current limiting section that limits current supplied to the driving section within a range of a limit value, the limit value includes a limit value at the time of positive efficiency when a driving direction of the driving section is the same as a direction of force or torque output from the driving section, and a limit value at the time of negative efficiency when the driving direction of the driving section is opposite to the direction of force or torque output from the driving section, the limit value at the time of positive efficiency is set to increase as a speed of the driving section increases, and the limit value at the time of negative efficiency is set to decrease as the speed of the driving section increases.

2. The current limiting device according to claim 1, wherein an increase rate of the limit value at the time of positive efficiency and a decrease rate of the limit value at the time of negative efficiency are set to increase as the speed of the driving section increases.

3. The current limiting device according to claim 1 or 2, wherein the driving section includes a motor, the driving force transmission section includes a speed reduction section that reduces rotation of the motor to transmit, and the limit value is set to change in accordance with a rotational speed of the motor.

4. The current limiting device according to claim 1 or 2, wherein the limit value is set so as to suppress damage to the driving force transmission section due to force or torque generated by the driving section, and maintain force or torque on an output side of the driving force transmission section at a constant value.

5. The current limiting device according to claim 1 or 2, wherein the driving section includes a motor provided to a joint of a robot.

6. The current limiting device according to claim 5, wherein the robot includes a robot for medical use.

7. A robot system, wherein the robot system has: a robot; and a robot control section that controls the robot, the robot includes: a joint; a motor provided to the joint; and a speed reduction section that reduces rotation of the motor, the robot control section includes a current limiting section that limits current supplied to the motor within a range of a limit value, the limit value includes a limit value at the time of positive efficiency when a driving direction of the motor is the same as a direction of force or torque output from the motor, and a limit value at the time of negative efficiency when the driving direction of the motor is opposite to the direction of force or torque output from the motor, the limit value at the time of positive efficiency is set to increase as a speed of the motor increases, and the limit value at the time of negative efficiency is set to decrease as the speed of the motor increases.

8. A current limiting method that limits current supplied to a driving section that generates force or torque by flowing current and that transmits driving force via a driving force transmission section, wherein ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ The current limiting method includes: a step of acquiring a speed of the drive unit; a step of setting a limit value of current supplied to the drive unit based on the acquired speed of the drive unit; and a step of supplying current to the drive unit within the set limit value, the limit value includes a limit value at the time of positive efficiency when the driving direction of the drive unit is the same as the direction of force or torque output from the drive unit, and a limit value at the time of negative efficiency when the driving direction of the drive unit is opposite to the direction of force or torque output from the drive unit, the limit value at the time of negative efficiency having a value different from the limit value at the time of positive efficiency, the absolute value of the limit value at the time of positive efficiency is set to increase as the speed of the drive unit increases, the absolute value of the limit value at the time of negative efficiency is set to decrease as the speed of the drive unit increases.

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