JP2002337078A - Method/device for controlling robot - Google Patents

Abstract

PROBLEM TO BE SOLVED: To aim at positioning of a robot more accurately at a higher speed regardless of an attitude of the robot, in the case of controlling the industrial robot having a low rigidity factor, by suppressing generation of vibration in an arm tip end caused by the low rigidity factor thereof, and by particularly suppressing vibration at stopping time. SOLUTION: In this constitution, a preset moving time and a maximum speed are calculated beforehand from a moving distance and maximum acceleration (S1), sampling time is counted in a time calculation part (S3), from this count value, the lapse of time is calculated (S4), and from this lapse of time, a target acceleration generation part calculates target acceleration (S5), a position detection part detects the present position (S6), by this position an approximate expression is selected (S7), a target speed generation part calculates a target speed (S8), this target speed is converted into an actual target speed (S9), a speed detection part detects the present speed (S10), a control arithmetic part calculates (S11) and outputs (S12) a control amount so as to follow up to the actual target speed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for controlling a robot having a low rigidity portion such as an industrial robot, and more particularly to a method for controlling a robot requiring high-speed and high-precision positioning control.

[0002]

2. Description of the Related Art When controlling an industrial robot or the like having a low rigidity factor, vibration of an arm tip caused by the low rigidity factor becomes a problem. Particularly in positioning control for transferring parts, assembling and other operations, a large acceleration is applied to increase the speed. At the point where the acceleration greatly changes, vibration occurs, resulting in residual vibration, which causes a robot control error, and also requires waiting for the vibration to converge, resulting in problems such as high speed.

Conventionally, in order to suppress such vibration during positioning of the robot, conventionally, vibration generated at the tip of the robot arm is detected by an acceleration sensor or the like attached to the tip of the robot arm, and the acceleration is fed back as a disturbance torque so as to reduce the acceleration. Vibration is controlled by controlling. However, this control method detects vibration generated at the end of the robot arm and suppresses the vibration by feeding it back.Therefore, it is possible to prevent the generation of vibration even though it has the effect of suppressing the generated vibration to a smaller extent. Did not.

On the other hand, the prior arts disclosed in Japanese Patent Application Laid-Open Nos. H6-114761, H6-1114762, and H6-170769 disclose the length of the acceleration period and the length of the deceleration period. A technology has been shown in which the vibration generated at the start of acceleration or deceleration is canceled by the vibration generated at the end of acceleration or deceleration. In other words, the motor current waveform has two peaks in both the positive and negative directions due to the acceleration and deceleration of the robot arm, and this time difference, that is, the torque peak time difference, shows the vibration corresponding to the natural frequency of the robot arm, that is, the natural vibration period. By controlling the timing of acceleration / deceleration so as to act in the direction of suppression, residual vibration when the robot arm is stopped is suppressed.

[0005]

As described above, in the general prior art for suppressing the vibration of the robot, the vibration generated at the tip of the robot arm is detected and the feedback is performed to suppress the vibration. However, although the effect of suppressing the generated vibration was smaller, the generation of the vibration could not be prevented.

Further, Japanese Patent Application Laid-Open Nos. H6-114761 and H6-111
No. 4762, and Japanese Patent Application Laid-Open No. H6-170769, control for controlling the timing of acceleration and deceleration so that the torque peak time difference acts in the direction of suppressing vibration corresponding to the natural frequency of the robot arm, that is, the natural vibration cycle According to the method, the acceleration of the tip of the robot arm changes according to the motor current, that is, the torque at the time of acceleration and deceleration, but at the time of stop, it vibrates due to the inertial force and elastic force of the robot arm. By adjusting the time difference between the positive and negative torque peaks to the natural frequency, the residual vibration is suppressed by canceling the vibration generated by the torque peak.

[0007] However, this control method also has the effect of suppressing the generated vibration to a lesser extent because the vibrations are canceled out together, but it is difficult to prevent the generation of the vibration. Since the natural frequency of the robot changes depending on its posture, it is necessary to find the natural frequency for each operation. Furthermore, at the time of assembly that requires a complicated movement, the posture of the robot also changes, so that the natural frequency also changes.

The present invention has been made in view of these problems. When controlling an industrial robot or the like having a low rigidity factor, it suppresses the occurrence of vibration at the tip of the arm due to the low rigidity factor. It is a first object of the present invention to suppress vibration at the time of stop and accurately and quickly position the robot regardless of the posture of the robot. It is a second object to calculate the target speed of the low resonance control more easily.
A third object is to provide a target acceleration of the low resonance control more accurately.

It is a fourth object of the present invention to easily calculate a target speed of the low resonance control from a basic expression which is a function of time. A fifth object is to make it possible to calculate the target speed of the low resonance control in response to a change in the control target or an arbitrary moving distance. A sixth object is to more easily calculate the target speed of the low resonance control. It is a seventh object of the present invention to enable calculation of a target speed and a target acceleration of the low resonance control in accordance with a change in a control target and an arbitrary moving distance. Also,
An eighth object of the present invention is to provide a robot control device that can easily calculate the target speed of the low resonance control and can give the target acceleration more accurately. In addition, a robot controller that can easily calculate a target speed of low resonance control from a basic expression that is a function of time and that can provide a target acceleration more accurately is provided. Aim.

[0010]

According to a first aspect of the present invention, there is provided a method for controlling a robot having one or more axes and a low rigidity portion.
The robot arm is operated using low resonance control that suppresses residual vibration by minimizing the rate of change of acceleration. According to the second aspect of the present invention, in the first aspect of the present invention, an approximate expression having a target speed of the low resonance control given as a function of time as a function of the position is stored, and the detected position is stored as the detected position. The target speed of the low resonance control is calculated from the approximate formula, and the actual speed is controlled to follow the target speed.

According to the third aspect of the present invention, there is provided the second aspect.
In the robot control method described above, the basic equation of the target acceleration of the low resonance control given as a function of time is stored, and the target acceleration of the low resonance control is calculated from the time and the stored basic equation. It is configured to feed forward the target acceleration. According to a fourth aspect of the present invention, in the first aspect of the invention, a basic expression of a target speed of the low resonance control given as a function of time is stored, and a table of time corresponding to the distance is provided. , The time is calculated from the distance, and the target speed is calculated from the basic formula of the stored target speed and the searched time.

According to the invention described in claim 5, according to claim 4,
In the invention described above, the time corresponding to the distance of the table is a normalized time. According to a sixth aspect of the present invention, in the first aspect of the present invention, a table of a target speed of the low resonance control corresponding to the distance is stored, and the target speed of the low resonance control is calculated from the distance by searching the table. Configuration. According to the seventh aspect of the present invention, in the second, third, fourth or sixth aspect, the target speed or the target acceleration of the low resonance control calculated by the basic expression, the approximate expression or the table is a normalized value. The maximum speed is calculated from the moving distance and the maximum acceleration, and the actual target speed or the target acceleration is calculated from the normalized value and the maximum acceleration or the maximum speed.

According to the invention of claim 8, in the control device for a robot having one or more axes and having a low rigidity portion, an approximate expression or a distance, wherein a target speed of the low resonance control is a function of a position. Target speed storage means for storing a table of target speed corresponding to, target acceleration storage means for storing a basic expression of the target acceleration of the low resonance control, detection means for detecting the position, counting means for counting time, A target speed calculation unit that calculates a target speed from the position detected by the detection unit and an approximate expression or a table; and a target acceleration calculation unit that calculates a target acceleration from the time counted by the counting unit and a basic expression. Equipped.

According to a ninth aspect of the present invention, in the control device for a robot having one or more axes and a low rigidity portion, a basic formula of a target speed and a basic formula of a target acceleration of low resonance control are stored. Basic expression storing means, position detecting means, counting means for counting time, time storing means for storing a table of time corresponding to the distance, and a target obtained from the time obtained from the table and the basic expression. A speed calculating means for calculating a speed and an acceleration calculating means for calculating a target acceleration from the counted time and the basic formula are provided.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows the configuration of the industrial robot system. Here, a horizontal articulated robot is taken as an example, but the present invention is not limited to this. The robot may be a vertical type, an orthogonal type, or other types, and the number of axes is not specified.

In FIG. 1, a robot 1 holds a part by a robot hand 12 attached to and detached from a tip of a robot arm 11. Here, a three-finger robot hand is taken as an example, but the invention is not limited to this. Robot arm 11
Is rotationally driven and vertically driven by a motor 13 built in the gantry. Each axis is controlled by the control unit 2 including the memory 21 and the CPU 22, and the tip of the robot arm is position-controlled via the drive unit 3, so that the robot arm can take an arbitrary position. Low resonance control is used for position control of the robot arm tip by the control unit 2.

The low resonance control is control for minimizing the rate of change in acceleration that excites resonance. That is, the minimization problem is solved using the square integral of the differential value of the acceleration as an evaluation function.
The solution is a quintic. Each equation is shown below, and the trajectory is shown in FIG.

[0018]

(Equation 1)

The target position may be given by a relative position, an absolute position, or a target moving distance. When given by a relative position or an absolute position, the current position is detected and the moving distance is calculated.
A target speed and a target acceleration at the current position are calculated based on the moving distance and the set moving time, and speed control is performed.

FIG. 3 shows a control block diagram. Control target 3
Reference numeral 4 denotes a robot arm, and a control operation unit 33 calculates a control amount of each axis drive motor for moving the distal end of the robot arm to a target position. Position detection unit 3 for each sampling
6. The speed detector 35 detects the current position and current speed of the tip of the moving robot arm. Note that the speed may be calculated from the current position. A target speed is calculated by the target speed generator 31 from the detected current position, and a target acceleration is calculated by the target acceleration generator 32 from the time calculated by the time calculator 37. The control calculation unit 33 gives the target acceleration as feedforward, performs control calculation to eliminate the difference between the target speed and the current speed, and calculates a control amount. The target moves to the target position by being speed-controlled to the target speed calculated from the position.

The low-resonance control basic equations shown in the above equations (1) to (4) are functions of time, and the position to be detected is a position. Therefore, it is necessary to calculate a target speed and a target acceleration corresponding to the position. is there. Therefore, a function of the position for calculating the target speed was obtained. Since the position is a quintic equation and is difficult to solve, an approximate equation was determined. The approximation formula is a polynomial approximation for position.
The position, velocity, and acceleration were normalized (divided by the maximum value) and used as data. By performing normalization, an approximate expression is obtained from data that does not include variables, and it is possible to cope with a change in the control target and an arbitrary moving distance. The approximate expression is shown below.

[0022]

(Equation 2)

From the above (8), (9) and (10), Vnom
Is a function of Xnom. If the approximation is made as it is, the approximation becomes higher order, and the operation speed and accuracy are problematic. Therefore, the approximation part is divided by the position, and the approximate expression of each part is derived. Speed, not just position
It may be divided by acceleration.

The approximation order and the number of divisions are not particularly specified, but the approximation order is low, and the smaller the number of divisions, the better. The approximation order and the number of divisions are in a trade-off relationship. This time, the approximation order was specified in the allowable range, and the division was performed so that the degree of approximation was within the allowable range. Further, the target acceleration is calculated from the basic equation using a time obtained by counting the sampling time, not the detected position fed back from the viewpoint of feedforward.

In FIG. 3, the derived approximate expression is stored in the target speed generator 31. As a result, the detected position is fed back, an approximate expression is selected from the position, and the target speed is calculated. The target acceleration generating section 32 stores a basic formula, and the time calculating section 37 calculates the target acceleration from the time calculated by counting the sampling time.

FIG. 4 shows a control flow. As shown in the figure, a set moving time and a maximum speed are calculated from a maximum acceleration determined in advance by a moving distance and a performance of the robot (S1).
If the speed is not 0 (No in S2), the time calculation unit 37 counts the sampling time (S3), and calculates the elapsed time from the count value (S4). Further, the target acceleration generator 32 calculates a target acceleration from the elapsed time (S5). Subsequently, the position detection unit 36 detects the current position (S6), and selects an approximate expression based on the position (S6).
7), the target speed generator 31 calculates the target speed (S
8) The target speed is converted into an actual target speed as described later (S9). Further, the speed detection unit 35 detects the current speed (S10), and the control calculation unit 33 calculates a control amount so as to follow the actual target speed (S11) and outputs it (S1).
2).

In the above description, an approximate expression as a function of the position is obtained in order to obtain the target speed from the detected position. However, the relationship between the position and the time may be tabulated, and the corresponding time may be retrieved from the detected position from the table. A configuration block diagram in this case is shown in FIG. 5, and a control flow is shown in FIG. Prior to the control of the control flow, a table of time corresponding to the detected position is created, and this time is a normalized time divided by the set movement time.

As shown in FIG. 5, in this embodiment, a position-time table 38 is provided in addition to the configuration shown in FIG. 3, and a time table corresponding to this position is stored in the position-time table 38. Remember. Then, as shown in FIG. 6, the target speed generator 31 searches the detected position for a normalized time corresponding to this position (S21), and uses the basic formula stored in the target speed generator 31 to obtain A target speed is calculated from the normalized time (S22), converted to an actual target speed (S23), and output.

Alternatively, a table of the target speed corresponding to the detected position may be created, and the target speed corresponding to the detected position may be searched. FIG. 7 shows a flow of calculating the target speed in this case.
Shown in In such a configuration, the position-target speed table is stored in the target speed generator 31, and as shown in FIG. 7, the target speed generator 31 searches the detected position for the target speed corresponding to this position. (S31), it is converted to the actual target speed (S32) and output.

As described above, the target speed and the target acceleration obtained by the basic expression, the approximate expression, or the table are normalized values. For this reason, the actual acceleration is multiplied by the maximum acceleration determined by the moving distance and the device performance in advance. Further, the maximum speed is calculated from the set moving time previously obtained from the maximum acceleration and the moving distance, and the target speed obtained by the basic formula, the approximate expression or the table is multiplied by the maximum speed and converted into the actual target speed (S9). , S23, S32). The actual target acceleration is fed forward, the speed is detected again, and control is performed so as to follow the actual target speed.

In the block diagram of FIG. 1, a memory 21 constituting the control unit 2 stores an approximate expression using a target speed as a function of a position.
Alternatively, a table of the target speed corresponding to the distance and a basic formula of the target acceleration are stored. As an example of position detection (not shown), an encoder value attached to
Is read into the CPU 22 to calculate the position of the tip of the robot arm, and is converted into a distance. The CPU 22 calculates the target speed from the distance and the approximate expression or table stored in the memory. The CPU 22 counts the number of times of sampling, calculates the time from the sampling interval (time) and the number of times, and calculates the target acceleration from this time and the basic expression of the target acceleration stored in the memory. As an example of speed detection (not shown), a differential value of the detected position is used. The target acceleration calculated by the CPU 22 is fed forward, and the speed is fed back to perform a control calculation so as to follow the calculated target speed, thereby calculating a control amount. Drive unit 3
Drives each axis motor from the control amount.

In the configuration diagram shown in FIG. 1, a memory 21 constituting the control unit 2 stores a basic expression of a target speed, a basic expression of a target acceleration, and a table of time corresponding to a distance. As an example of position detection (not shown), an encoder value attached to the motor is read into the CPU 22 constituting the control unit 2, the position of the tip end of the robot arm is calculated, and converted into a distance. The CPU 22 calculates the time from the distance and the table, and calculates the target speed from the basic formula of the time and the target speed stored in the memory. The CPU 22 counts the number of times of sampling, calculates the time from the sampling interval (time) and the number of times, and calculates the target acceleration from this time and the basic expression of the target acceleration stored in the memory. As an example of speed detection (not shown), a differential value of the detected position is used. The target acceleration calculated by the CPU 22 is fed forward, and the control amount is calculated by controlling the control so as to follow the calculated target speed by feeding back the speed. The drive unit 3 drives each axis motor from the control amount.

[0033]

As described above, according to the present invention,
According to the first aspect of the present invention, since the robot arm operates by the low resonance control that suppresses the residual vibration by minimizing the rate of change of the acceleration, the robot having the low rigidity portion is controlled by the low resonance control that suppresses the residual vibration. Irrespective of the posture of the robot, the vibration of the tip of the robot arm, especially at the time of stoppage, which is caused by the low rigidity factor is suppressed, so that it is not necessary to wait for the vibration to be established. It can be positioned at the target position.

According to the second aspect of the present invention, in the first aspect,
In the described invention, an approximate expression that uses the target speed of low resonance control given as a function of time as a function of position is stored, and the target speed of low resonance control is calculated from the detected position and the stored approximate expression, Since the actual speed is controlled so as to follow the target speed, the target speed can be easily calculated without creating a correlation table, the memory for movement control may be small, and an accurate target can be calculated for each control calculation. You can get speed.

According to the third aspect of the present invention, there is provided the second aspect.
In the robot control method described above, a basic expression of a target acceleration of the low resonance control given as a function of time is stored, and a target acceleration of the low resonance control is calculated from the time and the stored basic expression, and the calculated target is calculated. Since the acceleration is feed-forwarded, it is possible to provide an accurate target acceleration based on time that is not affected by a tracking error.

According to the fourth aspect of the present invention, the first aspect is provided.
In the described invention, the basic formula of the target speed of the low resonance control given as a function of time is stored, and a table of time corresponding to the distance is provided, and the table is searched to calculate the time from the distance, Since the target speed is calculated from the stored basic formula of the target speed and the searched time,
The target speed corresponding to the moving distance can be easily obtained from the basic expression without considering the accuracy of the approximate expression (the effect of the approximation error), and an accurate target speed can be obtained for each control calculation.
According to the fifth aspect of the present invention, since the time corresponding to the distance of the table is the normalized time in the fourth aspect of the invention, the time data obtained by searching the table for an arbitrary moving distance is obtained. Can be used without processing to easily determine the target speed.

According to the sixth aspect of the present invention, there is provided the first aspect.
In the described invention, a table of the target speed of the low resonance control corresponding to the distance is stored, and the table is searched to calculate the target speed of the low resonance control from the distance. ) Does not need to be considered, and no computing power is required. In the invention according to claim 7,
In the invention of claims 2, 3, 4, and 6, the target speed or target acceleration of the low resonance control calculated by the basic expression, the approximate expression or the table is a normalized value, and the set moving time is calculated from the moving distance and the maximum acceleration. And the maximum speed are calculated, and the actual target speed or target acceleration is calculated from the normalized value and the maximum acceleration or the maximum speed. The corresponding target speed and target acceleration can be obtained.

Further, in the invention according to claim 8, an approximate expression in which the target speed of the low resonance control is a function of the position or a table of the target speed corresponding to the distance is stored, and the basic expression of the target acceleration of the low resonance control is stored. Is stored, the current position is detected,
The elapsed time is counted, the target speed is calculated from the detected position and the approximate expression or table, and the target acceleration is calculated from the counted time and the basic expression. It is possible to give an accurate target acceleration based on time that is not affected by errors.

According to the ninth aspect of the present invention, the basic formula of the target speed and the basic formula of the target acceleration of the low resonance control are stored, the current position is detected, the elapsed time is counted, and the time corresponding to the distance is calculated. The table is stored, the target speed is calculated from the time obtained from the table and the basic formula, and the target acceleration is calculated from the counted time and the basic formula. Therefore, the accuracy of the approximation formula (effect of approximation error) The target speed corresponding to the moving distance can be easily obtained from the basic formula without considering the equation, and an accurate target speed can be obtained for each control operation.The target acceleration can be calculated from the basic formula, and the tracking error can be calculated. It is possible to give an accurate target acceleration based on time which is not affected by the above.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an industrial robot system showing one embodiment of the present invention.

FIG. 2 is an explanatory diagram of a robot control method according to an embodiment of the present invention.

FIG. 3 is a configuration block diagram of a robot control device according to an embodiment of the present invention.

FIG. 4 is a control flowchart of a robot control method according to an embodiment of the present invention.

FIG. 5 is a block diagram showing a configuration of a robot control device according to another embodiment of the present invention.

FIG. 6 is a main part control flow chart of a robot control method showing another embodiment of the present invention.

FIG. 7 is a main part control flow chart of a robot control method showing another embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Robot 2 Control part 3 Drive part 11 Robot arm 12 Robot hand 22 CPU 31 Target speed generation part 32 Target acceleration generation part 33 Control calculation part 35 Speed detection part 36 Position detection part 37 Time calculation part 38 Position-time table

 ──────────────────────────────────────────────────続 き Continued on the front page F-term (reference)

Claims (9)

[Claims] 1. A method for controlling a robot having one or more axes and having a low rigidity portion, wherein the robot arm is operated using low resonance control that suppresses residual vibration by minimizing the rate of change of acceleration. A method for controlling a robot, comprising: 2. The robot control method according to claim 1, wherein an approximate expression in which a target speed of the low resonance control given as a function of time is a function of the position is stored, and the detected position and the stored approximate expression are stored. From the target speed of the low resonance control,
A control method for a robot, wherein the control is performed so that an actual speed follows a target speed. 3. The robot control method according to claim 2, wherein a basic expression of a target acceleration of the low resonance control given as a function of time is stored, and the target acceleration of the low resonance control is obtained from the time and the stored basic expression. A robot control method comprising: calculating a target acceleration; and feeding forward the calculated target acceleration. 4. The robot control method according to claim 1, wherein a basic expression of a target speed of the low resonance control given as a function of time is stored, a table of time corresponding to the distance is provided, and the table is searched. And calculating a time from the distance, and calculating the target speed from the stored basic formula of the target speed and the searched time. 5. The robot control method according to claim 4, wherein the time corresponding to the distance of the table is a normalized time. 6. The robot control method according to claim 1, wherein a table of a target speed of the low resonance control corresponding to the distance is stored, and the table is searched to calculate a target speed of the low resonance control from the distance. A method for controlling a robot, comprising: 7. The robot control method according to claim 2, wherein the target speed and the target acceleration of the low resonance control calculated by a basic expression, an approximate expression or a table are normalized values. A method of controlling a robot, comprising: calculating a target moving time and a maximum speed from a distance and a maximum acceleration; and calculating an actual target speed and a target acceleration from the normalized value and the maximum acceleration or the maximum speed. 8. A controller for a robot having one or more axes and a low rigidity portion, wherein an approximate expression using a target speed of low resonance control as a function of position, or a table of target speeds corresponding to a distance is provided. Target speed storage means for storing; target acceleration storage means for storing a basic expression of a target acceleration for low resonance control; detection means for detecting a position; counting means for counting time; and a position detected by the detection means. A robot comprising: a target speed calculating means for calculating a target speed from a formula and an approximate expression or a table; and a target acceleration calculating means for calculating a target acceleration from the time counted by the counting means and a basic formula. Control device. 9. A robot control device having one or more axes and a low-rigidity portion, comprising: a basic expression storage means for storing a basic expression of a target speed and a basic expression of a target acceleration of low resonance control; Detection means for detecting the time, counting means for counting time, time storage means for storing a table of time corresponding to the distance, speed calculation means for calculating a target speed from the time obtained from the table and the basic formula, A control device for a robot, comprising: acceleration calculation means for calculating a target acceleration from the counted time and a basic expression.