JPH0782371B2 - Robot assembly control method - Google Patents

Abstract

PURPOSE:To perform various assembling operation speedily and smoothly by shifting force and moment in detection center successively according to three operation for position error correction, attitude error correction, and assembly. CONSTITUTION:The arm part of a robot 8 is provided with a force sensor 15 which detects force and moment, a gripping device 3, and an insertion component 1, and the contacting force between the insertion component 1 and a component 2 to be inserted is detected by the sensor 15 to drive the robot 8 by a controller 14 based on the detection result. In this case, the force and moment are shifted in detection center to the size where the griping device 3 is not present beyond the tip of the assembly component 1 when an error in position is corrected, to the tip of the assembly component 1 when an error in attitude is corrected, or to the side where the gripping device 3 is present beyond the tip of the assembly component 1 during assembly. Consequently, various assembling operations are performed speedily and smoothly.

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an assembly work control method by a robot, which is configured to perform an assembly work, particularly a fitting work, by performing feedback control by a force sensor.

[Conventional technology]

In the fitting work of mechanical parts, fitting by free fall shown in FIG. 7 is widely used. In the figure, the inserted component 2 has a sufficient funnel-shaped guiding surface with respect to the inserting component 1. The funnel-shaped guide surface has a maximum diameter near its entrance, and the hole diameter gradually decreases as the depth increases. For this reason, it is easy to correct the position / orientation error, and it is particularly difficult for the initial scuffing to occur. Therefore, it is widely used for precise fitting work. However, there are drawbacks such as an increase in processing load and an increase in guide portions.

Therefore, a mechanism has been developed that uses a mechanical elastic structure to correct the position / orientation error by making the inserted component follow the inserted component. Hereinafter, as an example of the mechanical elastic structure, US Pat.
4,155,169 and the drawings. Normal RCC
The mechanism will be described. Figure 8 shows the outline of the RCC mechanism. In the figure, the insertion part 1 is gripped by the gripping device 3. The gripping device 3 includes the trapezoidal link member 4 and the pedestal 5,
A trapezoidal link with the tip O of the insertion part 1 as the center of rotation is configured. Further, the pedestal 5 constitutes a parallel link by the parallel link member 7 and the outer frame 6. As described above, the trapezoidal link and the parallel link which are provided in series to meet the pedestal 5 are provided at the tip of the wrist of the robot through the outer frame 6. The operation of the RCC mechanism will be described below with reference to FIGS. FIG. 9 shows a state immediately after the insertion component 1 contacts the insertion target component 2. Although the contact reaction force is generated by the contact, the force in the insertion direction (Z-axis direction) is canceled by the action reaction, and only the translational force F in the X-axis and Y-axis directions acts on the rotation center O of the trapezoidal link. When the translational force acts on O, the parallel link member 7 tilts in the direction in which the translational force decreases, and as a result, the insertion part 1 makes a translational movement,
The position error is corrected. When the position error is corrected, the insert part 1 is in a state of looking through the entrance of the insert part 2,
In addition to the force in the Z-axis direction, the forces in the X-axis and Y-axis directions are counterbalanced by the action reaction. This state is shown in FIG. First
In FIG. 10, when the axial direction of the insertion part 1 and the axial direction of the inserted part 2 do not match, the rotation center O of the trapezoidal link
A moment M centering around is generated. The moment M
As a result, the trapezoidal link member 4 is tilted in the direction in which the moment becomes smaller as shown in FIG. 10, the axis of the insert part 1 and the axis of the insert part 2 move so as to coincide, and the attitude error is corrected. As described above, the RCC mechanism has an elastic structure consisting of parallel links and trapezoidal links, which translates and rotates in the direction of the contact reaction force acting between the inserted part and the inserted part, resulting in position error and posture. Correct the error and perform the fitting work.

[Problems to be solved by the invention]

However, in the above-mentioned conventional technique, when the dimension of the insert component 1 changes greatly as shown in FIG. 11, the rotation center O of the trapezoidal link and the tip of the insert component 1 greatly separate. This distance is δZ. In this case, when the translational force F acts on the tip of the insertion part 1, the translational force F and the moment of F × δZ act on the rotation center O of the trapezoidal link, so that the insertion part 1 rotates about O along with the translational motion. Also, the position error is not corrected. Further, when a moment M acts on the tip of the insertion part 1, a translational force of M / δZ acts on the rotation center O of the trapezoidal link together with the moment M, so that the insertion part 1 performs a translational motion as well as a rotational motion about O,
No posture error correction is performed. Further, when the axial direction of the inserted component is not vertical, the component force of gravity is confused with the contact reaction force, which prevents smooth fitting work.

In this way, the RCC mechanism lacked versatility.

An object of the present invention is to provide an assembly work control method capable of performing general-purpose fitting work.

[Means for solving problems]

In order to achieve the above-mentioned object, the present invention is a robot assembly work in which a force sensor is attached between the arm tip of a robot and a gripping device, and an assembly part gripped by the gripping device is assembled into a part to be assembled under the control of the robot. In the control method,
A first control step of drivingly controlling an actuator of the robot to lower an assembly part gripped by the gripping device to a part to be assembled, and descending the assembly part in the first control step, When the tip of the part comes into contact with the part to be assembled, the virtual first point F, which is separated from the tip of the assembly part by a predetermined distance from the reaction force Fs detected by the force sensor, is located on the opposite side of the gripping device. And calculates a virtual reaction force F _eF , and drives the actuator of the robot in a direction to reduce the reaction force based on the calculated virtual reaction force F _eF centered on the first F point. Controlling the first F of the assembly
A second control step of adjusting the position of the tip of the assembly part around the point to match the assembled part; and a case where the tip position of the assembly part is adjusted to match the assembled part in the second control step,
From the reaction force Fs detected by the force sensor, a virtual second reaction force F _ec is calculated centering on a virtual second C point set near the tip of the assembly part, and the calculated second The actuator of the robot is driven and controlled in a direction to reduce the reaction force based on a virtual reaction force F _eC centering on the C point 2 and the posture of the assembly parts is centered on the second C point. The force sensor detects when the tip position and the posture of the assembly component are corrected in accordance with the assembly target component in the third control process and the second and third control processes. An imaginary third point B, which is distant from the tip of the assembly part to the gripping device side by a predetermined distance from the reaction force Fs
The reaction force F _eB of the _robot is calculated, and the actuator of the robot is drive-controlled in a direction to decrease the reaction force based on the virtual reaction force F _eB centered on the calculated third point B, And a fourth control step of rotating the assembly part around the third point B to assemble the assembly part into the assembly target part.

[Action]

The present invention relates to a method of controlling assembly work by a robot,
The center of motion of the assembly is moved by sequentially moving the center of force / moment detection according to the three operations of position error correction, posture error correction, and assembly, and translational motion is used to correct the position error. When correcting the attitude error, mainly the rotational movement is centered around the tip of the assembly part, and during assembly the rotational movement is centered around the detection center located on the gripping device side from the tip of the assembly part. It is possible to have versatility and adapt to various assembling work so that quick and smooth assembling work can be realized.

〔Example〕

 Examples of the present invention will be described below.

FIG. 1 shows an outline of a general-purpose assembly device for carrying out the present invention. The robot 8 has a U.S. Pat. No. 4,094,
The force sensors shown in the specification and drawings of 192, or equivalent thereto, can detect translational forces F _X , F _Y , F _{Z in the} directions of three orthogonal axes and moments M _X , M _Y , M _Z around the respective axes. A force sensor is provided, and the main body portion provided with the gripping device 3 and the insertion part 1 at the tip thereof, and a control device that takes in a feedback signal from the force sensor 15 and outputs a drive signal of the robot 8. When the fitting operation is performed in the above assembling apparatus, a contact reaction force is generated by the contact between the insert component 1 and the insert target component 2. This contact reaction force is detected by the force sensor 15 and is the force of the sensor coordinate system (the center of the sensor 15 is the origin). Is output as. Contact reaction force Among three consecutive fitting operations, position error correction operation (the front of the insertion part 1 is the force / moment detection center F as shown in FIG. 4) and posture error correction operation (No. 5
As shown in the figure, the tip of the insertion part 1 is used as the force / moment detection center C. ) And the insertion work (as shown in FIG. 6, the rear side of the insertion part 1 is the force / moment detection center B). Using the equation (1), the force / moment at points F, C, and B shown in FIG. And is output from the coordinate conversion unit 9 that is sequentially converted to.

Contact reaction force Are incorporated into the controller 14. Contact reaction force Is the force / moment at points B, C, and F shown in FIG. Will be converted to either. In FIG. 2, point S represents the position of the origin of the sensor coordinate system, and the coordinate axes are represented by Xs, Ys, and Zs.
Also, point C is the origin [C: (P _XC , P _YC , P _ZC )] of the insert part tip coordinate system located at the tip of the insert part 1, and point B is the sensor coordinate system rather than the insert part tip coordinate system origin C. Inserted component rear coordinate system origin [B: (P _XB , P _YB ,
P _ZB )], point F is the insertion part forward coordinate system origin [F: (P _XF , P _YF , P _ZF )] that is opposite to the insertion part rearward coordinate system with respect to the insertion part tip coordinate system origin C, X _B , Y _B , Z _B , X _C , Y _C ,
Z _C , X _F , Y _F , and Z _F represent each coordinate axis. Here, the origin position of each coordinate system of the inserted part represented by the sensor coordinate system is represented by (P _X , P _Y , P _Z ) and the posture change is represented by (n, o, a). At this time, the transformation matrix from the sensor coordinate system to each coordinate system of the inserted part Is a translational component p and a rotation component (n, o, a), Can be expressed as The transformation matrix Insertion parts force / moment of each coordinate system Is Can be expressed as In this way, the force / moment expressed in each coordinate system of the inserted part Is equivalent to when the detection center of force / moment is virtually moved to points F, C, and B. further Is the force / moment at the addition point 10 Subtracted from Becomes

In the main control unit 11 using Of the force / moment detection center Either of them, or calculate the reciprocal, and at the addition point 12 the target of the force / moment detection center Or the reciprocal is added, and the coordinate conversion unit
At 13, the angles Θ of the joints of the robot 8 To drive the robot 8. Therefore, in this case, the center of detection of force / moment and the robot actually respond and the center of motion in which the robot operates matches.

By doing so, when the position error of the assembly part is corrected, the point F on the opposite side of the gripping device from the tip of the assembly part is virtually set as the center of force / moment detection. It is easy to control.

Similarly, when correcting the attitude error of the assembly parts,
Since the virtual center of detection of the moment is set to the point C and the point B is set during the assembly of the assembled parts, that is, when the assembled parts are inserted into the non-assembled parts, the assembly control of the assembled parts is facilitated.

The assembling apparatus having the above configuration operates in the same manner as the RCC mechanism when an external force is applied to the insertion component 1. For this operation, select the backward coordinate system of the insertion part in Fig. 3 and
The case where the detection center of the moment is located at the point B will be described as an example. In FIG. 3A, when a translational force F ₁ that passes through the force / moment detection center B is applied to the insertion part 1, Since the translational force component of is equal to F _1, and the moment component is calculated as, In the case of, the insertion part 1 makes a translational motion in the direction of the translational force F ₁ and reaches the position indicated by the broken line. From point B in FIG. When the translational force F ₂ is applied to the points separated by The translational force component of is equal to F _2, and the moment component is Is calculated as In the case of, the insertion part 1 has a moment in addition to the translational movement in the direction of the translational force F _2. It makes a rotational movement in the direction of and reaches the position of the broken line.

When a moment M ₁ is applied around point B in FIG. The translational force component of is calculated as the moment component is equal to M ₁ . In the case of, the insert part 1 makes a rotational motion around the point B in the direction of the moment M ₁ and reaches the position of the broken line.

The case where the backward coordinate system of the insert part is selected has been described above. However, when the forward coordinate system of the insert part is selected, the rotation center only moves to the point F, and when the tip end coordinate system of the insert part is selected, the rotation center only moves to the point C. The translational movement is the same as described above. In this way, the assembly device operates in the same way as the RCC mechanism.

When the fitting work is performed in the assembling apparatus, the fitting work is disassembled into three continuous works, position error correction, posture error correction, and insertion work. Will be described. The position error correction will be described with reference to FIG. Since the insertion component 1 has a positional error with respect to the insertion target component 2, the insertion component 1 is in contact with the insertion target component 2 at a part of its end surface. The contact causes a contact reaction force F _A as a resultant force of the distribution force. Since the contact reaction force F _A is not on the central axis of the insert part 1,
When the center of force / moment detection is on the central axis,
The translational force component of the force / moment detected at the force / moment detection center is equal to F, and the moment component can be expressed as the outer product of the position error and F _A. Therefore, it makes a rotational movement and a translational movement around the detection center of force / moment. Here, in the fitting work, the force in the vertical direction toward the figure is Therefore, the insertion component 1 does not perform a translational motion in the vertical direction. Moreover, the translational motion in the horizontal direction toward the figure is unknown. However, depending on the moment, it rotates about the center of force / moment detection. Therefore, the insertion component 1 always performs a rotational movement around the center of force / moment detection by the contact reaction force. When the center of the force / moment is located at the point B, the insertion part 1 rotates clockwise around the point B toward the same figure, so that the tip of the insertion part 1 moves away from the inlet of the insertion target part 2. . Power·
When the detection center of the moment is located at the point C, the insertion part 1 rotates clockwise around the point C toward the same figure, so that the tip of the insertion part 1 almost moves from the inlet of the insertion target part 2. do not do. When the force / moment detection center is located at the point F, the insertion part 1 makes a clockwise rotational movement around the point F toward the same figure, so that the tip of the insertion part 1 is at the entrance of the insertion target part 2. Move to get closer. As described above, it is most desirable to position the force / moment detection center at the point F for position error correction.

The error correction of the posture will be described with reference to FIG. The position error is corrected, the insertion part 1 looks into the entrance of the insertion part 2, and eventually the outer diameter of the insertion part 1 and the inner diameter of the insertion part 2 are different, so that they come into contact at two contact points 40, 41. And contact reaction forces F _A1 and F _A2 are generated. At the force / moment detection center, the translational force is the resultant force of F _A1 and F _A2 , and the moment component is F _A1 and the cross product of the position vector between the force / moment detection center and the contact point 40, and F _A2 and the force It is detected as the sum of the outer products of the position vectors between the detection center of the moment and the contact point 41. At this time, the translational force generated between the insertion part 1 and the insertion part 2 is And does not perform translational movement. However, since the moment is not a moment to be balanced, a rotational motion is performed counterclockwise around the detection center of force / moment. When the detection center is located at point B or F,
Since the rotary motion is performed around the point B or the point F, the tip of the insert part 1 moves away from the entrance of the insert part 2. When the detection center is located at the point C, since the rotational movement is about the point C, the tip of the insertion part 1 does not move away from the inlet of the insertion target part 2 but only performs the rotation motion. As a result, the contact points 40, 41 move to the vicinity of the diameter of the tip of the insertion part 1 and no moment is generated. This is a state in which the central axis of the insert part 1 and the central axis of the part to be inserted are aligned with each other, and there is no posture error. In this way, the attitude error is corrected. Therefore, it is desirable to position the force / moment detection center at point C when correcting the attitude error. The inserting operation will be described with reference to FIG. Usually, it is called a prying when it cannot be inserted smoothly and stops halfway. Prying is caused by frictional force or plastic deformation due to the contact between the insert part 1 and the insert part 2, and is generated at the two contact points 42, 43. One of the contact points 42, 43 is located at the tip of the insertion part 1 and the other is located at the entrance of the insertion part.
The straight line connecting the points intersects with the center lines of the insert part 1 and the insert part 2. Among the contact reaction forces generated at the contact points 42 and 43, the translational forces have the same magnitude and opposite directions, so that they are offset and only the moment is detected. When the detection center is located at the point F or the point C, the insertion part 1 has a side that is strongly pressed against the side wall of the part to be inserted 2 and a side that is to be separated from the side wall because the insertion part 1 is rotated around the point F or the point C. Occurs and the prying progresses further. When the detection center is located at the point B, the insertion part 1 moves so as to separate from the side wall of the insertion target part 2 at the contact points 42 and 43 due to the rotational movement around the point B, and escapes from the prying. In this way, the insertion is performed without twisting. Therefore, at the time of insertion, it is most desirable to locate the detection center on the midpoint of the straight line connecting the contact points 42, 43 or at the point B closest to the midpoint.

The position of the center of force / moment detection and the work characteristics during fitting / work have been described above, but this was confirmed by experiments. The results are shown in Table 1 below. In the figure, the leftmost column shows where the force / moment detection center is located, and the uppermost column shows each work during the fitting work.

Also, in the table, ○, ×, and △ indicate workability, indicating that they are good, impossible, and possible, but it takes time. As a result, it was confirmed that the relationship between the force / moment detection center and the workability described in FIGS. 4, 5 and 6 was correct. The desired force / moment detection center is the F point for position error correction, the C point for posture error correction, and the B point for insertion.
It was confirmed that it was a point.

Based on the above results, during fitting work, the center of force / moment detection should be set to point F in front of the tip of insert part 1 when correcting position errors, and tip C point of insert part 1 when correcting position errors. In addition, during insertion, when the insertion component 1 is positioned at the point B behind the tip of the insertion component 1, quick and smooth fitting work can be performed.

Further, when the force / moment detection center is always positioned between the tip of the insertion part 1 and the insertion part 2 during insertion, a better fitting operation can be performed.

The case has been described above where the coordinate system of the force / moment detection center and the robot's motion center are changed on software to perform the fitting work. A method will be described in which the same fitting work can be performed even if the detection gain of is changed for each operation.

When F _f is calculated with the detection center fixed inside the controller 14, the gain adjustment matrix Newly established But And process. Normal Is an identity matrix, but when correcting the position error, C
_{When 15} and C ₂₄ are positive numbers, it is equivalent to virtually generating translational forces F _X and F _Y using the moment generated by the contact, and translational motion is added to the position error correction. Become. When correcting and inserting the posture error, C ₄₄ and C ₅₅ of the diagonal components are set to a number greater than 1, and the other diagonal components are
1, and the other components increase the gain of rotational motion with respect to the detected moment. By changing the gain of the contact reaction force detected in this way according to the work content, the same operation as the state in which the detection center is moved is equivalently performed.

Also, as the detection center is fixed inside the control device 14, Or the response gain adjustment matrix Newly established, However And process. Normal Translational components K _{1 to} K ₃ and rotational components K _{4 to} K ₆ are all 1,
When correcting the position error, among translation components, K _{1 to} K in the X and Y axis directions
_By setting ₂ to be greater than 1 and the rotational components K _{4 to} K ₆ to be or near, it is possible to make translational motion larger than rotational motion. Also, during correction of posture error, during insertion, K _{1 to} K ₂ in the translational components in the X and Y axis directions should be smaller than 1, and K _{4 to} K ₅ around the X and Y axes in the rotational components should be larger than 1. Causes the rotational movement to be larger than the translational movement. The position of the detection center calculated from the contact reaction force detected in this way,
By changing the gain of either the speed or the acceleration or the reciprocal number according to the work content, the same operation as the state in which the detection center is moved is equivalently performed.

In the above-mentioned first to third embodiments, the target value of force / moment is compensated in the direction of gravity so that the fitting work independent of the axial direction of the inserted component can be performed.

〔The invention's effect〕

As described above, according to the present invention, the following effects (1), (2) and (3) can be obtained.

(1) It is versatile because it does not require hardware changes for dimensional changes of inserted parts.

(2) By changing the position of the detection center, it is possible to fit even if there is a large initial position / orientation error in the fitting work. It also improves speed.

(3) Unlike the RCC mechanism, the effect of gravity can be compensated for, so fitting work that is completely unrelated to the posture and direction of the axis of the inserted part can be performed.

[Brief description of drawings]

FIG. 1 is a schematic view of an embodiment of the present invention, FIG. 2 is a sketch drawing, FIGS. 3, 4, 5, and 6 are operation explanatory views, and FIG. 7 is a cross section showing a simple fitting operation. FIG. 8 is a schematic view showing a conventional RCC mechanism, and FIGS. 9, 10, and 11 are operation explanatory views when a fitting operation is performed by the mechanism shown in FIG. 1 ... Inserted part, 2 ... Inserted part, 3 ... Gripping device, 8 ... Robot, 9,13 ... Coordinate conversion part, 10, 12 ... Addition point, 11 ... Main control part, 14 ... Control device, 15 ... Force sensor .

Continuation of front page (51) Int.Cl. ⁶ Identification code Office reference number FI Technical display location G05B 13/02 C 7531-3H

Claims (1)

[Claims] 1. A method for controlling an assembly work by a robot, wherein a force sensor is attached between an arm of a robot and a gripping device, and an assembly part gripped by the gripping device is assembled into an assembly target part under the control of the robot. A first control step of drivingly controlling an actuator to lower an assembly component gripped by the gripping device to a component to be assembled, and lowering the assembly component in the first control step, the tip of the assembly component When the object comes into contact with the part to be assembled, a virtual first F point distant from the tip of the assembly part by a predetermined distance from the tip end of the assembly part to the opposite side of the gripping device from the reaction force Fs detected by the force sensor. The reaction force F _eF, and the calculated first F
Based on a virtual reaction force F _eF centering on a point, the actuator of the robot is drive-controlled in a direction to reduce the reaction force, and the assembly part is rotated about the first F point of the assembly part. A second control step of adjusting the position of the tip to the assembled part, and a reaction force detected by the force sensor when the tip position of the assembled part is adjusted to the assembled part in the second control step. Fs
From the virtual second C set near the tip of the assembly
A virtual second reaction force F _eC is calculated around the point, and the virtual reaction force F _eC centered around the calculated second C point is used to decrease the reaction force. A third control step of drivingly controlling the actuator of the robot to adjust the posture of the assembly part to the assembled part around the second point C, and the second and third control steps. When the tip position and posture of the component are corrected according to the assembly target component, a virtual third point B away from the tip of the assembly component by a predetermined distance from the reaction force Fs detected by the force sensor. A virtual third reaction force F _eB is calculated centering on the center, and based on the _calculated virtual reaction force F _eB centered on the third B point, the reaction force is reduced in the direction described above. The robot actuator is driven and controlled, and the assembly parts are rotated around the third point B to assemble the assembly parts. And a fourth control step of assembling into vertical parts.