JPH06309040A - Controller for robot arm - Google Patents

Abstract

PURPOSE:To decrease the positional deviation of the current position of an arm tip from a target position as much as possible at the time of compliance control over an articulated robot and to reduce the vibration of the robot arm generated when the compliance control is switched to position control. CONSTITUTION:An arm tip force arithmetic part 8 which calculates an arm tip force F for moving the arm tip part toward the target position consists of a decision means 8a which decides whether or not the positional deviation DELTAx is larger than a specific value (a), a 1st arithmetic means 8b which calculates the arm tip force F in proportion to the positional deviation DELTAx when the decision result is YES, and a 2nd arithmetic means 8c which calculates an arm tip force F larger than the arm tip force F proportional to the positional deviation DELTAx when the decision result is NO.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control device for moving a hand portion of a robot arm in a state of low rigidity with respect to a target position, and more particularly to a measure for reducing the amount of displacement of the current position of the hand portion from the target position. .

[0002]

2. Description of the Related Art Conventionally, when performing work using a robot arm, it is known to switch a plurality of operation controls in the middle according to a work operation. For example,
When assembling an assembly part at a predetermined location, position control is performed to move the hand part of the robot arm that grips the part to the predetermined assembly location quickly and accurately, and when the assembly part is assembled at the predetermined location. The compliance control for flexibly moving the hand portion with respect to the external force from the restraint surface applied to the hand portion is switched. When performing such compliance control, a method using force feedback that reduces the hand force based on a predetermined rigidity characteristic coefficient so as to be in inverse proportion to the magnitude of the external force from the restraint surface is disclosed in, for example, Japanese Patent Laid-Open No. 1-142812. It is known from the publication. Further, a device in which the rigidity characteristic coefficient can be arbitrarily rewritten is known, for example, from Japanese Utility Model Laid-Open No. 4-104315.

On the other hand, it is also known that the above force feedback is not used, but instead, the hand force is changed based on the amount of displacement of the current position with respect to the target position of the hand portion. This device is provided with a hand force calculation means for calculating a hand force based on the above-mentioned position shift amount, and in the hand force calculation means, F = k · Δx (k: rigidity characteristic coefficient, Δx: position shift amount ) Calculates the hand force (F). Then, the hand portion is moved toward the target position with a small hand force (F) proportional to the position shift amount (Δx).

[0004]

However, in the above-mentioned conventional compliance control that does not use force feedback, the hand force (F) also decreases proportionally as the position shift amount (Δx) decreases as shown in FIG. Therefore, if the positional deviation amount (Δx) is smaller than a certain value, the hand force (F) becomes smaller than the resistance force such as the frictional force generated at the movable portion of the robot arm during its operation. Sometimes. Then, in the case of compliance control that does not perform force feedback, the robot arm does not bend due to the resistance force and cannot actually operate even in the absence of external force. A deviation equal to the deviation amount will be left. Such a deviation becomes larger when the rigidity characteristic coefficient (k) is set to be smaller in order to increase the flexibility of the robot arm.

When the assembly work is finished and the compliance control is returned to the position control, the deviation becomes a large disturbance. That is, the robot arm is driven with a large control force in an attempt to eliminate the deviation at the moment when the position control is switched to, and this causes a situation in which the robot arm vibrates greatly. That is, the presence of such a deviation causes the control system to be unstable and causes unexpected interference between the robot arm and the outside world.

The present invention has been made in view of the above circumstances, and an object thereof is to minimize the positional deviation amount of the current position with respect to the target position of the hand portion of the robot arm during the compliance control, thereby ensuring the compliance control. The purpose of this is to reduce the vibration of the robot that occurs when switching from position control to position control.

[0007]

In order to achieve the above object, according to the invention of claim 1, even when the displacement amount of the current position with respect to the target position of the hand portion of the robot arm is small, the hand force as large as possible is exerted. By being able to obtain it, the hand portion can be moved toward the target position against the resistance of the robot arm itself.

Specifically, in the present invention, FIG. 2 and FIG.
As shown in, the hand part (1a) is moved to the target position (xd) based on the amount of displacement (Δx) of the current position (x) with respect to the target position (xd) of the hand part (1a) in the robot arm (1). Comprising a compliance control means (A) provided with a hand force calculation means (8) for calculating a hand force (F) for moving toward the robot, and the hand portion (1a) of the robot arm (1) is calculated as described above. Hand power (F)
It is premised on the control device of the robot arm that is moved toward the target position (xd) in the state.

Then, as shown in FIG. 1, the hand force calculating means (8) controls the position shift amount (Δx) by a predetermined value (a).
When the positional deviation amount (Δx) is equal to or larger than a predetermined value (a), the positional deviation amount (Δx) is determined by the judging means (8a) for judging the magnitude of the positional deviation amount and the output of the judging means (8a). First computing means (8b) for proportionally computing the hand force (F)
When the positional deviation amount (Δx) is less than the predetermined value (a) and the output of the determination means (8a) is reached, the fingertip having a larger hand force (F) proportional to the positional deviation amount (Δx). The second calculation means (8c) for calculating the force (F).

According to a second aspect of the present invention, in the first aspect of the invention, the second computing means (8c) is provided with a positional deviation amount (Δ
x) is a predetermined value (a), the first calculation means (8b)
The hand force (F) is calculated so as not to exceed the reference value (k · a) calculated by.

According to a third aspect of the present invention, in the second aspect of the present invention, the second computing means (8c) changes the rate of change of the hand force (F) with respect to the positional deviation amount (Δx) by the positional deviation amount (Δx).
x) is large on the side close to 0 and small on the side close to the predetermined value (a), and is continuously changed according to the positional deviation amount (Δx).

[0012] In the invention of claim 4, the above-mentioned claim 1 or 2
In the invention, the second calculating means (8c) increases the rate of change of the hand force (F) with respect to the positional deviation amount (Δx) to a predetermined value (a) when the positional deviation amount (Δx) is close to 0. The configuration is such that it is changed stepwise according to the amount of positional deviation (Δx) so that it becomes smaller on the near side.

According to a fifth aspect of the present invention, in the above first to fourth aspects of the invention, as shown in FIG. 2, the hand portion (1a) of the robot arm (1) is in a highly rigid state at a target position (x).
Position control means (B) for controlling to move toward d) is provided. Further, the compliance control means (A) is capable of switching between the compliance control of the robot arm (1) and the position control means (B) of the position control of the robot arm (1).

[0014]

With the above construction, in the invention of claim 1, the position shift amount (Δx) of the current position (x) with respect to the target position (xd) of the hand part (1a) in the robot arm (1).
Based on the above, the hand force (F) for moving the hand portion (1a) toward the target position (xd) is calculated by the hand force calculating means (8). At this time, the displacement amount (Δ) is determined by the determination means (8a) of the hand force calculation means (8).
The magnitude of x) with respect to the predetermined value (a) is determined. When the positional deviation amount (Δx) is equal to or greater than the predetermined value (a), the first
The hand force (F) is calculated by the calculating means (8b) in proportion to the positional deviation amount (Δx). On the other hand, the displacement amount (Δ
When x) is less than the predetermined value (a), the positional deviation amount (Δ
x, which is larger than the hand force (F) proportional to (F)
Is calculated by the second calculating means (8c). Therefore, when the displacement amount (Δx) is large, the hand force (F) is reduced as in the conventional case, so that the hand portion (1
It is possible to move a) flexibly with respect to the outside world. On the other hand, when the positional deviation amount (Δx) is small, the hand portion (1a) is moved to the target position (x
It is driven so as to move toward d), which makes it possible to reduce the amount of positional deviation (Δx) against the resistance of the robot arm (1) itself.

According to the second aspect of the invention, the positional deviation amount (Δx)
Is less than the predetermined value (a), the positional deviation amount (Δx)
Is a predetermined value (a), the second value is set so as not to exceed the reference value (k · a) calculated by the first calculating means (8b).
The hand force (F) is calculated by the calculating means (8c), and as a result, the hand portion (1) has a larger hand force (F) than before.
Since the low rigidity state of the hand portion (1a) is ensured despite the movement of (a), it is possible to prevent the compliance control from being impaired.

According to the third aspect of the invention, the positional deviation amount (Δx)
When the hand force (F) is calculated by the second calculation means (8c) on the basis of the above, first, the displacement amount (Δx) is calculated with a large change rate on the side close to 0, which is sufficiently small. The hand force (F) is calculated. On the other hand, on the side close to the predetermined value (a), the hand force (F) is calculated with a small change rate with respect to the positional deviation amount (Δx). As a result, even when the displacement amount (Δx) is smaller than the predetermined value (a), the hand force (F) does not become so small as to be proportional thereto, and a relatively large hand force (F) is calculated. The rate of change (F) is calculated based on the rate of change that changes smoothly by continuously changing the rate of change in accordance with the amount of displacement (Δx).

According to the fourth aspect of the invention, the positional deviation amount (Δx)
When the hand force (F) is calculated by the second calculation means (8c) based on the above, a sufficiently small hand force (F) is calculated with a large change rate on the side where the positional deviation amount (Δx) is close to 0. On the other hand, on the side close to the predetermined value (a), a relatively large hand force (F) is calculated with a small change rate. Then, the rate of change is changed stepwise according to the amount of positional deviation (Δx), so that the hand force (F) can be changed at the same rate at the same step.
Is calculated.

According to the fifth aspect of the present invention, during compliance control, the robot arm (1) is controlled by the compliance control means (A) so that the hand portion (1a) moves toward the target position (xd) with a low rigidity. To be done. On the other hand, at the time of position control, the position control means (B) controls the hand part (1a) to move toward the target position (xd) in a highly rigid state. When the compliance control is switched to the position control, the hand part (1
Since the position shift amount (Δx) of the current position (x) with respect to the target position (xd) in (a) is small, the robot arm (1 It is possible to reduce the vibration generated in ().

[0019]

Embodiments of the present invention will be described below with reference to the drawings.

(Embodiment 1) FIG. 2 shows a multi-joint robot (1) as a robot arm according to the first embodiment of the present invention. (1a) from the current position (x) to the target position (x
It is designed to move toward d). Further, the control device for controlling the operation of the articulated robot (1) includes:
For example, a compliance control means (A) for flexibly moving the hand portion (1a) with respect to an external restraint surface (3) that restrains the movement of the hand portion (1a) when assembling the assembly part at a predetermined location, Between the part supply position where the parts are supplied and a predetermined assembly position where the parts are assembled, the hand part (1
Position control means (B) for fast and precise movement of a) are provided. Then, the compliance control of the articulated robot (1) by the compliance control means (A) and the position control by the position control means (B) can be switched as needed.

At the time of the compliance control, the hand force (F) for moving the hand part (1a) of the articulated robot (1) toward the target position (xd) is the rigidity characteristic (Ka) in each of the three axis directions, It is calculated based on (Kb) and (Kc) and converted into the rotational torque (τ) of each joint (2), but here, in order to simplify the description, based on one stiffness characteristic (K). The hand force (F) is calculated.

FIG. 3 shows the configuration of the compliance control means (A). The compliance control means (A) is an encoder (5) for detecting the current angle (q) of the joint (2) in the articulated robot (1). ) And the output of the encoder (5), the target angle (qd) is subtracted from the current angle (q) detected by the encoder (5) to obtain the amount of angular deviation of the joint (2) with respect to the target angle (qd). The subtraction unit (6) for calculating (Δq) and the output of the subtraction unit (6), and the angular deviation amount (Δq) calculated by the subtraction unit (6) is used as the target position (xd) of the hand portion (1a). Angle to convert the current position (x) to the position shift amount (Δx)
The output of the position / conversion unit (7) and the angle / position conversion unit (7) is received, and the hand portion (1a) is targeted based on the positional deviation amount (Δx) converted by the angle / position conversion unit (7). A hand force calculation unit (8) as a hand force calculation unit that calculates a hand force (F) to be moved toward a position (xd), and an output of the hand force calculation unit (8), and a hand force calculation unit (8). A force / torque converter (9) for converting the hand force (F) calculated by 8) into a joint torque (τ) necessary for rotationally driving the joint (2).
It has and. Further, the stepping motor (10) of each joint (2) is driven based on the joint torque (τ) from the force / torque converting unit (9), while the output shaft of the stepping motor (10) has the above An encoder (5) is arranged in series so as to detect its rotation angle.

The calculation operation in the hand force calculation unit (8) will be described with reference to the flow chart shown in FIG. First, the positional deviation amount (Δx) converted by the angle / position conversion unit (7) is input in step S1, and step S
Move to 2. This step S2 constitutes the judging means (8a) in the present invention, in which the absolute value (| Δx |) of the positional deviation amount (Δx) is equal to or greater than the predetermined value (a) (|
It is determined whether or not Δx | ≧ a> 0). The judgment is YE
If S, the process proceeds to step S3. The step S3 is
It constitutes the first calculating means (8b) in the present invention, and here, the hand force (F) is calculated by F = k · Δx (k: rigidity characteristic coefficient). Then, in step S4, the hand force (F) is output and the process ends. On the other hand, if the determination is NO, the process proceeds to step S5.

The step S5 constitutes the second calculating means (8c) in the present invention, and here, the hand force (F) is calculated by F = k · a · sin (Δx · π / 2a). . Then, the process proceeds to step S4, the hand force (F) is output, and the process ends.

The relationship between the hand force (F) and the position shift amount (Δx) in the above calculation is proportional as in the conventional case when | Δx | ≧ a as shown in the characteristic curve of FIG. On the other hand, when | Δx | <a, unlike the conventional case, the hand force (F) in the proportional relationship is larger. Specifically, for example, in the range of 0 <Δx <a, the rate of change of the hand force (F) with respect to the positional deviation amount (Δx) is large on the side where the positional deviation amount (Δx) is close to 0, and the predetermined value ( It is configured to be small on the side close to a) and to be continuously reduced according to the amount of positional deviation (Δx). Also,
When the positional deviation amount (Δx) is the predetermined value (a), the hand force (F) calculated by the first calculating means (8b) is used as a reference value (k · a), and the reference value (k · a) ) Is not exceeded (F ≦ k · a), the hand force (F) is calculated. still,
In the above description, when the displacement amount (Δx) and the hand force (F) are minus, the minus means that the directions are opposite.

Therefore, according to the first embodiment, first, the angular deviation amount (Δq) of the joint (2) is calculated from the current angle (q) and the target angle (qd) of the joint (2). Next, the angular displacement amount (Δq) is converted into the positional displacement amount (Δx) of the current position (x) with respect to the target position (xd) of the hand portion (1a), and this positional displacement amount (Δx) is calculated. It is output to (8). The hand force calculation unit (8) calculates the hand portion (1) based on the positional deviation amount (Δx).
A hand force (F) for moving a) toward the target position (xd) is calculated.

At this time, first, the hand force calculating section (8)
The determining means (8a) determines whether or not the absolute value (| Δx |) of the positional deviation amount (Δx) is equal to or larger than the predetermined value (a). When | Δx | ≧ a, the hand force (F) is calculated by the first calculating means (8b) in proportion to the absolute value (| Δx |). As a result, when the absolute value (| Δx |) of the positional deviation amount (Δx) is large, the hand force (F) is reduced in proportion to the absolute value (| Δx |), so that the fingertip is the same as the conventional one. The part (1a) moves flexibly with respect to the restraining surface (4) in the external environment.

On the other hand, when | Δx | <a, the second calculating means (8c) calculates a hand force (F) larger than the hand force (F) proportional to the absolute value (| Δx |). As a result, when the absolute value (| Δx |) is small, the target position (x) is larger than the conventional hand force (F) that is calculated so as to be proportional to the absolute value (| Δx |).
Since the hand portion (1a) is moved toward (d), the positional deviation amount (Δx) can be surely reduced regardless of the frictional force at the joint (2) of the multi-joint robot (1). In addition, since the hand force (F) is calculated so as not to exceed the reference value (k · a), the absolute value (|
Compliance control is not impaired when Δx |) is small.

The hand part (1a) of the articulated robot (1) is in a low rigidity state by the compliance control means (A) during compliance control, and is in a high rigidity state by the position control means (B) during position control. Each is controlled to move toward the target position (xd). Then, when the compliance control is switched to the position control, the position deviation amount (Δx) of the current position (x) with respect to the target position (xd) of the hand portion (1a) becomes small. The vibration that occurs in the articulated robot (1) can be made small by rapidly eliminating Δx).

In each of the first embodiment, the characteristic curve between the positional deviation amount (Δx) and the hand force (F) in the range of | Δx | <a has a sine waveform. Other smooth curves may be taken.

(Embodiment 2) The flowchart of FIG. 6 shows the processing operation in the hand force calculation unit (8) as the hand force calculation means according to the second embodiment. In this process,
The steps S'1 to S'4 in the figure are the same as the steps S1 to 4 (see FIG. 4) of the first embodiment, and only the other steps S'5 to S'9 are different from the first embodiment. That is, in step S5 ′, which is moved to when the determination as to whether or not the absolute value (| Δx |) of the positional deviation amount (Δx) is equal to or larger than the predetermined value (a) in step S′2, is step S5 ′, The absolute value (| Δx |) of the quantity (Δx) is greater than or equal to the predetermined value (b) (|
It is determined whether or not Δx | ≧ b, 0 <b <a). When the determination is YES, the process proceeds to step S'6, while NO
If so, the process proceeds to step S'7. Then, in step S′7, the hand force (F) is calculated by F = k1 · Δx (k1: stiffness characteristic coefficient, k1> k).

On the other hand, in step S'6, it is determined whether or not the amount of positional deviation (Δx) is plus (Δx ≧ 0). When the determination is YES, the process proceeds to step S'8, while when the determination is NO, the process proceeds to step S'9. In step S′8, F = k2 · Δx + c (k2: stiffness characteristic coefficient, k2 <k,
The hand force (F) is calculated by 0 <c ≦ k · a). On the other hand, in step S′9, the hand force (F) is calculated by F = k2 · Δx−c, and the hand force (F) is output in step S′4, and the process ends. Here, the steps S'7 to S'9 constitute the second calculating means (8c) in the present invention.

As shown in FIG. 7, the relationship between the position shift amount (Δx) and the hand force (F) by the hand force calculating means (8) is proportional to each other when | Δx | ≧ a, as shown in FIG.
When | Δx | <a, the hand force (F) is larger than the proportional value. Specifically, 0 <Δ
In the range of x <a, the amount of displacement of the hand force (F) (Δ
The rate of change with respect to x) is large on the side where the positional deviation amount (Δx) is close to 0 and small on the side close to the predetermined value (a), and before and after the positional deviation amount (Δx) reaches the predetermined value (b). It is configured to gradually decrease in. In particular,
When the displacement amount (Δx) matches the predetermined value (b),
The hand force (F) has a maximum difference from the conventional hand force (F).

The second embodiment can also achieve the same effects as the first embodiment.

In each of the above-described Embodiments 2, the characteristic curve between the displacement amount (Δx) and the hand force (F) in the range of 0 ≦ Δx <a is composed of two line segments. It may be composed of three or more line segments.

In each of the first and second embodiments described above, the compliance control using only the rigidity characteristic as a parameter is shown, but the mass characteristic or the damping characteristic may be added as a parameter.

Further, although the articulated robot (1) is described in each of the first and second embodiments, other types of robots may be used.

[0038]

As described above, according to the invention of claim 1, when the compliance control is performed so that the hand of the robot arm moves toward the target position with low rigidity, the target position of the hand is detected. The magnitude of the positional deviation of the current position with respect to the predetermined value is judged by the judging means, and when the positional deviation is equal to or more than the predetermined value, the first calculating means calculates a small hand force as in the conventional case, while the predetermined value is calculated. When it is less than the above, the second calculating means calculates the hand force larger than the conventional one, so that the hand force can be made larger than the conventional one even when the positional displacement amount is smaller than the predetermined value.
As a result, the hand portion can be moved toward the target position without yielding to a resistance force such as a frictional force in the movable portion of the robot arm, and the positional deviation amount can be reliably reduced.

According to the second aspect of the present invention, when the position displacement amount of the hand portion is less than the predetermined value, the reference value calculated by the first calculating means when the position displacement amount is the predetermined value is not exceeded. As described above, since the hand force is calculated by the second calculating means, it is possible to secure the low rigidity of the hand portion when the hand force is increased and the position shift amount is reduced, and the compliance control is impaired. Can be avoided.

According to the third aspect of the invention, when the displacement amount is less than the predetermined value, the rate of change of the hand force with respect to the displacement amount is large when the displacement amount is close to 0 and small when the displacement amount is close to the predetermined value. The hand force can be calculated based on the rate of change that changes smoothly by adopting a configuration in which the position change amount is continuously changed according to the position shift amount.
The effect of the invention can be specifically obtained.

According to the fourth aspect of the invention, when the displacement amount is less than the predetermined value, the rate of change of the hand force with respect to the displacement amount is large on the side where the displacement amount is close to 0 and small on the side close to the prescribed value. With such a configuration that the amount of positional deviation is changed stepwise as described above, the hand force can be calculated at the same rate of change at the same stage, and the effect of the invention of claim 2 can be obtained concretely. be able to.

According to the fifth aspect of the present invention, when the compliance control by the compliance control means is switched to the position control by the position control means, the target position of the hand portion can be made small, so that the position displacement amount of the hand portion is reduced. It is possible to reduce the vibration generated in the robot arm when it is rapidly eliminated by the position control.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of the present invention.

FIG. 2 is a conceptual diagram showing an articulated robot and its control device according to the first embodiment of the present invention.

FIG. 3 is a block diagram showing compliance control means.

FIG. 4 is a flowchart showing a processing operation of a hand force calculation unit.

FIG. 5 is a characteristic curve diagram showing a relationship between a hand force calculated by a hand force calculation unit and a positional deviation amount.

FIG. 6 is a flowchart showing a processing operation of a hand force calculation unit according to the second embodiment of the present invention.

FIG. 7 is a view corresponding to FIG. 5 of the second embodiment.

FIG. 8 is a view corresponding to FIG. 5 of a conventional example.

[Explanation of symbols]

 1 Articulated robot (robot arm) 1a Hand part 8 Hand force calculation unit (hand force calculation means) 8a Judgment means 8b First calculation means 8c Second calculation means A Compliance control means B Position control means xd Target position x Current position Δx Positional deviation a Predetermined value F Hand force

Claims (5)

[Claims] 1. The hand portion (1a) of the robot arm (1) is moved to the target position (xd) based on the amount (Δx) of displacement of the current position (x) from the target position (xd) of the hand portion (1a). Comprising a compliance control means (A) provided with a hand force calculation means (8) for calculating a hand force (F) for moving toward the robot, the hand portion (1a) of the robot arm (1) is calculated as described above. In the controller of the robot arm that is moved toward the target position (xd) in the state of the applied hand force (F), the hand force calculation means (8) includes the position shift amount (Δx).
Determination means (8a) for determining the magnitude of the predetermined value (a) of
And the output of the determination means (8a), the positional deviation amount (Δ
When x) is greater than or equal to a predetermined value (a), the first computing means (8b) that computes the hand force (F) in proportion to the displacement amount (Δx), and the output of the determining means (8a) Position deviation amount (Δ
and a second calculation means (8c) for calculating a hand force (F) larger than the hand force (F) proportional to the positional deviation amount (Δx) when x) is less than the predetermined value (a). A robot arm control device characterized by the above. 2. The robot arm control device according to claim 1, wherein the second computing means (8c) controls the first computing means (8b) when the positional deviation amount (Δx) is a predetermined value (a). A control device for a robot arm, which is configured to calculate a hand force (F) so as not to exceed a calculated reference value (k · a). 3. The robot arm control device according to claim 2, wherein the second computing means (8c) changes the rate of change of the hand force (F) with respect to the positional deviation amount (Δx) when the positional deviation amount (Δx) is 0. A controller for a robot arm, which is configured to continuously change in accordance with the positional deviation amount (Δx) such that it is large on the side close to the predetermined value and small on the side close to the predetermined value (a). 4. The robot arm control device according to claim 2, wherein the second computing means (8c) changes the rate of change of the hand force (F) with respect to the positional deviation amount (Δx) when the positional deviation amount (Δx) is 0. A controller for a robot arm characterized in that it is configured to change stepwise in accordance with the amount of positional deviation (Δx) such that it is large on the side closer to (a) and smaller on the side closer to a predetermined value (a). 5. The robot arm control device according to claim 1, 2, 3 or 4, wherein the hand portion (1a) of the robot arm (1) is moved toward the target position (xd) in a highly rigid state. The position control means (B) for controlling the robot arm (1) is provided so that the compliance control means (A) can switch between the compliance control of the robot arm (1) and the position control means (B) of the robot arm (1). A controller for a robot arm characterized by being provided.