JP2009196030A - Output torque limit circuit of industrial robot - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a torque limit circuit of an industrial robot, which properly limits an output torque at the end of the tool of the industrial robot by securing the assuredness of a torque signal detected by a force sensor. <P>SOLUTION: In the industrial robot formed of multiple spindles, when the torque signal detected by the force sensor attached to each shaft drive part and an instruction torque for the drive part detect the mismatch level over an allowable value set beforehand, a drive circuit is cut out. It is verified whether the torque signal detected by the force sensor is correct, and the output can be limited. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an output torque limiting circuit in an industrial robot in which each joint axis is driven by a servo motor.

  Conventionally, regarding an output torque limiting technique using a force sensor in an industrial robot in which each joint axis is driven by a servo motor, as disclosed in Non-Patent Document 1, the force sensor is used for industrial use. By arranging it between the wrist end of the robot and the work tool, the output torque during assembly work is limited. However, in this case, when the output torque exceeds the allowable torque or when the command torque and the torque signal detected by the force sensor do not match, the power of the servo motor is not shut off to ensure safety. There was no suggestion of this.

  Further, Patent Document 1 comprehensively describes a method for arranging a force sensor on each joint axis, including the prior art, but its use is similar to that of Non-Patent Document 1 described above during assembly work. The output torque was limited. However, this also does not ensure safety by shutting off the servomotor power when the output torque exceeds the allowable torque or when the command torque does not match the torque signal detected by the force sensor. There was no suggestion of this.

  On the other hand, in the patent document 2 of the applicants, there is a technique for duplicating a signal by doublely attaching a force sensor to the output part of the speed reducer, thereby ensuring the certainty of the torque signal detected by the force sensor. It is disclosed. However, this does not ensure the certainty of the torque signal from the force sensor by comparing the torque signal detected by the force sensor and the command torque signal, as in the present invention described later. Further, the torque in the XYZ directions is not limited by combining with the torque in the XYZ directions, nor is it suggested.

JP 2004-20368 A JP 2007-301691 A “Robot Engineering Handbook”, Robotics Society of Japan, 1990, p. 394

  In view of the above-described problems, the present invention can appropriately limit the output torque at the tool tip of an industrial robot by ensuring the certainty of the torque signal detected by the force sensor. An object of the present invention is to provide a torque limiting circuit for an industrial robot.

  In addition, the output torque limit solution ensures that the output torque does not exceed the allowable value by verifying that the torque signal detected by the force sensor is correct by comparing it with the command torque. The purpose is to provide.

  In order to achieve the above-mentioned object, in the invention according to claim 1, in an industrial robot composed of multiple axes, a torque signal detected by a force sensor attached to each axis driving unit and a command torque of the driving unit. And an output torque limiting circuit that shuts off the drive circuit when a discrepancy greater than a preset allowable value is detected.

  The invention according to claim 2 is configured such that, in the invention according to claim 1, a torque synthesized signal obtained by synthesizing the servo motor drive current is used as the command torque signal of the output torque limiting circuit.

  Further, in the invention according to claim 3, in the invention according to claim 1, the torque command signal of the servo motor driver that drives the servo motor is used as the command torque signal of the output torque limiting circuit.

  According to a fourth aspect of the invention, in the first aspect of the invention, as an instruction torque signal of the output torque limiting circuit, the operation of the industrial robot is performed in the internal model calculation unit provided in the robot control unit that controls the industrial robot. A command calculation torque signal obtained by calculation using the trajectory as an input is used.

  In the invention which concerns on Claim 5, a torque signal is synthesize | combined to each direction of XYZ from the torque signal detected by the force sensor attached to each axis drive part of the industrial robot comprised by multiple axes, and each of these XYZ An output torque limiting circuit that shuts off the drive circuit when any of the torque signals in the direction exceeds the specified output torque value, or when the combined torque signal in the XYZ directions exceeds the specified output torque value .

  In the invention according to claim 6, in the invention according to claim 5, after the torque necessary for maintaining the attitude of the industrial robot is subtracted from the torque signal detected by the force sensor, the torque signal in each direction of XYZ is obtained. A configuration using a synthesized signal is used.

  In the invention according to claim 7, in the invention according to claim 5 or 6, in addition to the output torque limit circuit, the output limit circuit according to any one of claims 1 to 4 is provided, so that the operation reliability of the force sensor signal processing circuit is improved. It was set as the structure which ensures property.

  In the invention according to claim 8, the signal transmission circuit of the position detector serially transfers the torque signal detected by the force sensor together with the position detection signal detected by the position detector.

  The invention according to claim 9 is the output torque limit according to any one of claims 1 to 7, wherein the torque signal detected by the force sensor is input from the signal transmission circuit in the invention according to claim 8. A circuit was used.

  As described above, in the invention according to claim 1, it is determined whether the torque signal detected by the force sensor is correct by comparing the torque signal detected by the force sensor with the command torque of the drive unit. It has been verified that the output torque can be limited.

  In the invention according to claim 2, the torque signal detected by the force sensor is detected by the force sensor by using the torque synthesized signal obtained by synthesizing the servo motor drive current that becomes the servo motor command torque as the command torque. It was verified whether or not the torque signal received was correct, and the output torque could be limited.

  In the invention according to claim 3, whether the torque signal detected by the force sensor is correct by using the torque signal detected by the force sensor as a torque command signal of a servo motor driver that drives the servo motor. It was verified whether or not the output torque could be limited.

  Further, in the invention according to claim 4, the torque signal detected by the force sensor is obtained by calculation using the operation trajectory of the industrial robot as an input in the internal model calculation unit provided in the robot control unit for controlling the industrial robot. By using the command calculation torque signal thus obtained, it is verified whether or not the torque signal detected by the force sensor is correct, and the output torque can be limited.

  Moreover, in the invention which concerns on Claim 5, a torque signal is synthesize | combined in each direction of XYZ from the torque signal detected by the force sensor attached to each axis drive part of the industrial robot comprised by multiple axes, These XYZ When any of the torque signals in each direction exceeds the output torque specified value, or when the torque signal obtained by combining the torque signals in the XYZ directions exceeds the output torque specified value, the drive circuit is shut off to output This has the effect of making it possible to limit the torque.

  In the invention according to claim 6, the torque required for maintaining the attitude of the industrial robot is subtracted from the torque signal detected by the force sensor attached to each axis drive unit of the multi-axis industrial robot. After that, torque signals are synthesized in the XYZ directions, and when any of the torque signals in the XYZ directions exceeds the output torque prescribed value, or the torque signal obtained by synthesizing the torque signals in the XYZ directions is the output torque prescribed value. When the value exceeds the value, the output circuit can be more accurately limited by cutting off the drive circuit.

  In the invention according to claim 7, when the torque value in the XYZ directions synthesized from the torque signal detected by the force sensor exceeds the output torque specified value, the drive circuit is shut off and at the same time the torque detected by the force sensor By confirming whether the signal is correct or not by comparing it with the command torque signal, there is an effect that it is possible to limit the output torque with higher reliability.

  In the invention which concerns on Claim 8, it is a signal transmission circuit of the position detector which serially transfers the torque signal detected by the force sensor together with the position detection signal detected by the position detector, thereby reducing wiring. As a result, it is possible to ensure the synchronism between the position detection signal detected by the position detector and the torque signal detected by the force sensor.

  In the invention according to claim 9, it is possible to limit the output torque more accurately and reliably while ensuring the synchronism between the position detection signal detected by the position detector and the torque signal detected by the force sensor. It became the effect of making it.

  The best mode for carrying out the present invention will be described with reference to the drawings. In each drawing, FIG. 1 is an output torque limiting circuit unit, FIG. 2 is a torque synthesis circuit unit that synthesizes a servo motor drive current, FIG. 3 is a torque command signal unit of a servo motor driver that drives the servo motor, and FIG. FIG. 5 is a model of a three-axis vertical articulated robot used for explaining an embodiment for synthesizing torque signals in XYZ directions from force sensor signals, and FIG. 6 is a force sensor signal. It is explanatory drawing of the signal transmission circuit part which carries out serial transmission.

  In the output torque limiting circuit section of FIG. 1, the comparison circuit 1 includes a force sensor detection torque signal and a command torque as a torque signal detected by the force sensor 10 attached to the drive section of each axis of the industrial robot. The signal is input, and it is compared whether or not it is within the preset allowable value range 2. As a result of this comparison, when the value is outside the range of the allowable value 2, it is determined that a mismatch has been detected, and a servo power cutoff signal is output. The comparison circuit 1 is prepared for the number of joint axes of the robot, the mismatch detection of each joint axis is connected by the OR circuit 3, and when a mismatch is detected in any one of the joint axes, a servo power cutoff signal is output. .

  Further, the force sensor detection torque signal as the torque signal detected by the force sensor 10 attached to the drive unit of each drive shaft of the industrial robot is input to the XYZ direction torque synthesis circuit 4 of FIG. Combined with torque in each direction. The torque in each direction of XYZ is input to the XYZ direction comparison circuit 5, and the XYZ direction comparison circuit 5 combines a preset torque regulation value 6 (for example, 150 Nm) with a value for each XYZ direction or a value obtained by combining the XYZ directions. As a result of the comparison, if the torque default value 6 is exceeded, a servo power cutoff signal is output.

  By the way, in a robot having a vertically articulated arm, posture holding torque is required to hold the posture against gravity acting on the mass of the arm itself and the mass of the load. The torque obtained by subtracting this posture holding torque is the torque output to the arm tip. Therefore, FIG. 1 further includes a subtracting circuit 7 for subtracting the attitude holding torque from the force sensor detection torque signal as the torque signal detected by the force sensor 10, and the output from the subtraction circuit 7 is the XYZ direction torque. Input to the synthesis circuit 4.

  In this way, the output torque in each of the XYZ directions is obtained from the force sensor detection torque signal as the torque signal detected by the force sensor 10 attached to the output unit of the industrial robot, and this output torque has a predetermined value. The torque signal detected by the force sensor 10 is compared with the command torque signal so as to verify whether the torque signal itself detected by the force sensor 10 is correct. The reliability of operation is guaranteed.

  In the torque synthesizing circuit section of FIG. 2, the current detection circuit 8 arranged on the servo motor power line detects the drive current of the servo motor 9. Then, the drive current of the servo motor 9 detected by the current detection circuit 8 is synthesized by the torque synthesis circuit 11 to generate a command torque signal. This command torque signal is used as the input of the command torque signal shown in FIG. Note that the method for detecting the drive current of the servo motor 9 and the method for synthesizing the drive current with torque are already known. For example, the technical document “Practice of AC Servo System Theory and Design” (General Electronic Publishing Company, 1990). Y., p. 74-81, p. 86-87).

  FIG. 3 shows a torque command section of a driver (servo motor driver 13 shown in FIG. 4 described later). This torque command is also described in the above-mentioned technical document “Practice of AC Servo System Theory and Design” and is well known. The torque command signal of this driver (servo motor driver 13) is used as the input of the command torque signal shown in FIG.

  FIG. 4 is an explanatory diagram of the internal model calculation unit 14 included in the robot control unit 12. The estimated command torque calculated by the internal model calculation unit 14 is output to the servo motor driver 13 and used as the input of the command torque signal shown in FIG. The details of the calculation process performed in the internal model calculation unit 14 will be described below with reference to FIG.

  FIG. 5 schematically illustrates a three-axis robot model (having three joint axes) having a vertical articulated structure. Note that the present invention can be applied to a 6-axis or 7-axis robot having more than 3 axes by sequentially expanding mathematical formulas, but here, in order to help understanding of the present invention, the operation of the present invention is performed. The following explanation will be given by taking a three-axis structure robot model that can be most effectively explained as an example.

  The joint axis of the robot shown in FIG. 5 is a first axis (axis around θ1) that rotates around an axis (Z axis) perpendicular to the ground contact surface of the robot, and the first axis that rotates around the X axis on the YZ plane. Two axes (axis around θ2), a third axis (axis around θ3) that rotates on the YZ plane at a position separated by an arm length L2, and a load WL is attached at a position separated by an arm length L3. Yes. With this three-axis configuration, the load WL can be moved to the XYZ spatial position.

  The arms of the second axis (axis around θ2) and the third axis (axis around θ3) have their own masses W2 and W3, respectively, as shown in FIG. Arranged as a position. Since the first axis rotates around an axis perpendicular to the ground surface, no posture holding torque due to gravity is required, but the second axis has a mass W3 of the third axis and a load mass WL in addition to its own mass W2. Therefore, the output torque of the second shaft is a torque obtained by subtracting these attitude holding torques. Further, since the third shaft requires posture holding torque for holding its own mass W3 and load mass WL, the output torque of the third shaft is a torque obtained by subtracting these posture holding torques.

  Here, the angular positions of the joint axes are θ1, θ2, and θ3 in radians. Further, θ2 and θ3 are expressed as angles that are lines parallel to the ground plane. Further, in order to express the expression shortly, Cos θ1 is simply expressed as C1 and Sin θ3 as S3.

  First, the position (XL, YL, ZL) of the load WL in FIG. 5 is expressed by the following equations (1) to (3), respectively.

  Further, if the torque signals detected by the force sensor 10 attached to the drive unit of each joint axis are expressed as T1, T2, T3, the XYZ combined torque (T1X, T1Y, T1Z) of the first axis is respectively Expressions (4) to (6) are obtained.

  Further, the XYZ combined torque (T2X, T2Y, T2Z) of the second axis is expressed by the following equations (7) to (9), respectively.

  Further, the XYZ combined torque (T3X, T3Y, T3Z) of the third axis is expressed by the following equations (10) to (12), respectively.

  Further, torques (TX, TY, TZ) obtained by combining the XYZ combined torques of the first axis to the third axis are expressed by the following equations (13) to (15), respectively.

  From these formulas (13) to (15), in FIG. 1 described above, the XYZ direction comparison circuit 5 compares whether or not the torque prescribed value 6 is exceeded in any of XYZ directions. The direction comparison circuit 5 outputs a servo power cutoff signal. Alternatively, the torque TA obtained by combining the torques in the XYZ directions may be calculated by the following equation (16), and the XYZ direction comparison circuit 5 may determine whether or not the torque TA exceeds the specified torque value 6.

  Further, the mass center of gravity position (X2L, Y2L, Z2L) of the second axis and the mass center of gravity position (X3L, Y3L, Z3L) of the third axis are respectively the same as the above-described equations (1) to (3). The following equations (17) to (22) are obtained.

  Further, the attitude holding torque T2H of the second axis is a sum of torques for holding the mass W2 of the second axis, the mass W3 of the third axis, and the mass of the load WL, and is expressed by the following equation (23).

  Further, the attitude holding torque T3H of the third axis is the sum of the torques holding the third axis mass W3 and the load mass WL, and is given by the following equation (24).

  The operation of the subtraction circuit 7 shown in FIG. 1 is as follows. That is, by substituting T2 ′ = T2−T2H in place of T2 in Expressions (7) to (9) and T3 ′ = T3−T3H in place of T3 in Expressions (10) to (12), respectively, An output torque in the XYZ directions obtained by subtracting the posture holding torque from the torque signal detected by the force sensor 10 can be obtained.

  Further, when the accelerations obtained by second-order differentiation of the angles of the joint axes of the first axis to the third axis are set as α1, α2, and α3, respectively, the command calculation torques T1E, T2E, and T3E of each joint axis are: The following equations (25) to (27) are obtained, respectively.

  Calculations of the equations (25) to (27) are performed in the internal model calculation unit 14 of the robot control unit 12 shown in FIG. 4, and the obtained command calculation torques T1E, T2E, T3E are used as the command torque signals shown in FIG. Use. Compared to the case where a command torque signal obtained by synthesizing the motor drive current or the torque command of the servo motor 13 is used, the calculation method based on the internal model in the internal model calculation unit 14 increases the calculation amount but the drive unit. It is possible to exclude errors caused by the existing viscous resistance.

  By the way, as in the arithmetic expression described above, when calculating the torque component in the XYZ directions from the torque signal detected by the force sensor 10, the calculation is performed based on the position of each joint axis. Therefore, the simultaneity between the torque signal detected by the force sensor 10 and the position detection signal is important for ensuring the calculation accuracy. Therefore, as shown in FIG. 6, the torque signal from the force sensor 10 is detected by the force sensor circuit 16, the position detection signal from the position detector 15 is detected by the position detection circuit 17, and these signals are also combined. Serial transmission is performed by the transmission circuit 18. As a result, the number of wires can be reduced, and the simultaneity of the torque signal and the position detection signal can be ensured.

  The embodiment of the present invention has been described above. In the above-described embodiment, the three-axis robot having the vertical articulated structure has been described in order to more specifically describe the contents of the present invention. However, a general six-axis robot or a seven-axis configuration having redundant axes is used. Needless to say, this robot can be applied in the same way as described above. The present invention is not limited to a vertical articulated structure, and can be applied to a linear motion type shaft configuration or a horizontal articulated structure robot with a simpler arithmetic expression.

  In an output torque limiting circuit for an industrial robot having a multi-axis configuration, when the output torque exceeds an allowable value, the power is cut off and the output torque can be limited. As the use of the present invention, for example, when an operator and an industrial robot work together, if the output torque of the robot is 150 Nm or less, there is no need to partition the worker and the robot with a safety fence. It is possible to work in an environment where the worker and the robot coexist, thereby reducing the work space.

It is explanatory drawing of the output torque limiting circuit which is an example of embodiment of this invention. It is explanatory drawing of the control part which synthesize | combines the drive current of the servomotor 9 which is an example of embodiment of this invention, and produces a command torque signal. It is explanatory drawing of the control part which makes the torque command of the servomotor driver 13 which is an example of embodiment of this invention a command torque signal. It is explanatory drawing of the internal model calculating part 14 which the robot control part 12 which is an example of embodiment of this invention comprises. It is explanatory drawing of the robot model of the vertical articulated structure which is an example of embodiment of this invention. It is explanatory drawing of the serial transmission part of the signal from the force sensor 10 which is an example of embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Comparison circuit 2 Permissible value 3 OR circuit 4 XYZ direction torque synthesis circuit 5 XYZ direction comparison circuit 6 Torque regulation value 7 Subtraction circuit 8 Current detection circuit 9 Servo motor 10 Force sensor 11 Torque synthesis circuit 12 Robot controller 13 Servo motor driver 14 Internal model calculation unit 15 Position detector (encoder)
16 Force sensor circuit 17 Position detection circuit 18 Signal transmission circuit

Claims (9)

  In an industrial robot composed of multiple axes, a drive circuit is detected when a mismatch between the torque signal detected by the force sensor attached to each axis drive unit and the command torque of the drive unit exceeds a preset allowable value. An output torque limiting circuit for an industrial robot characterized in that the motor is cut off.   2. The output torque limiting circuit for an industrial robot according to claim 1, wherein the command torque is a torque synthesis signal obtained by synthesizing a servo motor drive current.   2. The output torque limiting circuit for an industrial robot according to claim 1, wherein the command torque according to claim 1 is a torque command signal of a servo motor driver that drives a servo motor.   The command torque according to claim 1 is a command calculation torque obtained by calculation using an operation trajectory of the industrial robot as an input in an internal model calculation unit provided in a robot control unit that controls the industrial robot. The output torque limiting circuit for an industrial robot according to claim 1.   A torque signal is synthesized in each direction of XYZ from torque signals detected by a force sensor attached to each axis drive unit of an industrial robot composed of multiple axes, and any of the torque signals in each direction of XYZ is An output torque limiting circuit for an industrial robot, which cuts off a drive circuit when an output torque specified value is exceeded or when a torque signal obtained by combining torque signals in XYZ directions exceeds an output torque specified value.   6. The industrial use according to claim 5, wherein after the torque necessary for maintaining the posture of the industrial robot is subtracted from the torque signal detected by the force sensor, torque signals in the XYZ directions are combined with the torque signal. Robot output torque limit circuit.   An output torque limiting circuit for an industrial robot, comprising the output torque limiting circuit according to any one of claims 1 to 4 in addition to the output torque limiting circuit according to claim 5 or 6.   A signal transmission circuit for a position detector, wherein a torque signal detected by a force sensor is serially transferred together with a position detection signal detected by a position detector.   The output torque limiting circuit for an industrial robot according to any one of claims 1 to 7, wherein a torque signal detected by the force sensor is input from the signal transmission circuit according to claim 8.

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