JP2002331428A - Screw fastening method and device by force control robot - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a screw fastening method and a device by a force control robot capable of surely and efficiently fastening a screw regardless of an installing state of the screw to a work part, capable of miniaturizing the device constitution, and capable of automatic fastening work in a narrow place by the robot. SOLUTION: A nut runner 16 having on an output shaft a socket 18 for holding a male screw 20 is arranged on a robot body 10 via a force sensor 14 so that the male screw 20 and a female screw 26 installed in a work 24b are fastened by positioning operation by force control of the robot body 10 executed by a robot control part 12 on the basis of an output result of the force sensor 14, and rotation control of the nut runner 16 executed by a nut runner control part 22 on the basis of a command from the robot control part 12.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for tightening a screw by a force control robot which tightens at least two works by a male screw and a female screw using a robot having a force sensor.

[0002]

2. Description of the Related Art It is well known that when joining one work and another work having the same structure to each other, a male screw and a female screw are screwed together and integrated. An automatic screw tightening device is used. The screw on one work side is fixed to the work by welding or the like,
The workpieces are not necessarily mounted at the same position and at the same angle, and some variations occur when mounting.

In a conventional screw automatic tightening device, when the axial lines of a male screw and a female screw are made to coincide with each other to smoothly insert a bolt, the axial movement of a socket holding the bolt is moved by a spring. Absorption, floating of the socket, and detection by various compliance devices and a plurality of sensors are used to prevent the screw from climbing or entering obliquely. For instance,
As shown in Japanese Patent No. 88875, a configuration in which a socket of a nut runner is automatically aligned with a copper ball and a compression spring is a preferable example.

[0004]

However, in such a configuration, there is a problem that the device itself becomes large and it is difficult to perform an automatic screw tightening operation in a narrow space.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problem, and has a reduced size of the apparatus, which makes it possible to easily and reliably perform an automatic tightening operation in a small space. It is an object of the present invention to provide a method and an apparatus for tightening a screw by a force control robot which can increase the efficiency of the attaching work.

[0006]

According to the present invention, there is provided a method for tightening a screw by a force control robot having a force sensor, the method comprising the steps of: Displacing the robot to match the axis of the female screw; and, after the axes match, tightening the screw by performing force control by the output of the force sensor only in the screw tightening axial direction. (Invention of claim 1).

In the above-described method of tightening a screw by a force control robot, the tightening state of the screw is recognized from the output result of the force sensor, and the number of rotations of the screw is changed according to the tightening state of the screw. It is preferable to carry out the tightening (invention of claim 2).

[0008] With this configuration, since the robot is also used for force control, a torque control device required for screw tightening is not required. Further, by automatically aligning the axes of the male screw and the female screw, the screw can be securely tightened. Further, by controlling the screw rotation speed in accordance with the screw tightening state, the screw can be securely tightened and the efficiency of the tightening operation is improved.

Further, the present invention provides a robot having a force sensor, fastening means having a socket for holding a screw on an output shaft, and controlling the posture of the robot by the force control based on an output result of the force sensor. Robot control means for
And a tightening control unit that controls a screw tightening rotation speed of the tightening unit based on an output result of the force sensor (the invention according to claim 3).

In this case, the robot control means includes a calculation means for calculating a movement amount of the screw, a detection means for detecting a movement amount of the robot, and a difference between the movement amount of the screw and the movement amount of the robot. And determining means for determining whether the difference is within a predetermined range, and force control switching means for performing force control only in the screw tightening axis direction, according to the determination result of the determining means. It is preferable to have (the invention of claim 4).

That is, with the above-described configuration, it is possible to easily confirm the alignment of the screw axes and to perform uniaxial control only in the screw tightening axis direction with a simple hardware configuration and a simple control method. Is reduced in size, enabling automatic screw tightening work in a small space,
The effect of improving the reliability of the apparatus accompanying the reduction in the number of parts and the manufacturing cost can be obtained.

Further, the robot control means includes a storage means for storing a plurality of screw tightening rotational speeds of the tightening means, and a rotational speed for determining an optimum screw tightening rotational speed from an output result of the force sensor. Determining means for selecting an optimum screw tightening rotation speed from the storage device based on a result of the determination by the rotation speed determination device; and a screw selected by the rotation speed selection device. The fastening means may be rotated at the fastening rotation speed (the invention according to claim 5).

With this configuration, the screw rotation speed can be easily controlled by a simple hardware configuration and control method, so that the device configuration can be reduced in size and automatic control in a small space is possible. The screw tightening operation can be performed, and the effect of improving the reliability of the apparatus accompanying the reduction in the number of parts and the manufacturing cost can be obtained.

Further, by performing the tightening at the optimum rotational speed according to the state of the tightening, the screw can be securely tightened, and the efficiency of the tightening operation can be further improved.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION A preferred embodiment of a method for tightening a screw by a force control robot according to the present invention will be described in detail with reference to the accompanying drawings. .

FIG. 1 shows a robot body 10 according to the present embodiment. The robot body 10 is electrically connected to a robot control unit 12 and is controlled by the robot control unit 12. The robot body 10 includes a first arm 1
0a, a second arm 10b, a third arm 10c, and a first encoder 10 for detecting a displacement amount of the first arm 10a.
d, a second encoder 10e for detecting the amount of displacement of the second arm 10b, and a third encoder 10f for detecting the amount of displacement of the third arm 10c. A nut runner 16 is attached to the distal end of the third arm 10 c of the robot body 10 via a force sensor 14, and the nut runner 16 includes a socket 18. The socket 18 is a male screw 20 for tightening and integrating two works.
Hold the head. In addition, in FIG.
Denotes a female screw to which the male screw 20 is screwed, and reference numeral 2
Reference numerals 4a and 24b denote works integrated by the male screw 20 and the female screw 26.

Therefore, the outputs of the force sensor 14 and the encoders 10d, 10e, and 10f for detecting the displacements of the arms 10a, 10b, and 10c of the robot body 10.
Is input to the robot control unit 12. The robot controller 12 controls the first arm 10a and the second arm 10 of the robot body 10 based on the output results of the force sensor 14 and the encoders 10d, 10e, and 10f.
b and the third arm 10c, and outputs a command signal to the nut runner control unit 22. The nut runner control unit 22 rotates the socket 18 of the nut runner 16 at a predetermined rotation speed based on the command signal.

FIG. 2 is a schematic longitudinal sectional view of the nut runner 16. The nut runner 16 includes a motor 27, and a rotation drive shaft (not shown) of the motor 27 is connected to a shaft 32 via a gear train 30. A gear 34 is fixed to the shaft 32, and the gear 34 meshes with the gear 36.
A shaft 40 having a spline groove is fitted into the center of the gear 36, and a piston 42 is fixed to one end of the shaft 40. The piston 42 and the shaft 40 are housed in the cylinder 38 in an airtight manner.

In fact, one end of the cylinder 38 has a port 4
3 is formed, and a return spring 44 is disposed inside the cylinder 38. One end of the return spring 44 is seated on the piston 42, and the other end is seated on a step 45 formed on the cylinder 38. The socket 18 is fixed to the other end of the shaft 40.
In this case, the socket 18 may be an air chuck type socket. Reference numerals 33, 3
7, 41 are a gear 34, a gear 36 and a shaft 40, respectively.
1 shows a bearing that rotatably supports.

In the above configuration, the gear train 30, the gears 34 and 36 rotate under the rotation of the motor 27, and the socket 18 rotates with the rotation of the shaft 40 having the spline grooves, while the piston 42 rotates. Is port 43
When the pressure fluid is introduced into the shaft 40 to move the shaft 40 together with the socket 18, while the port 43 is opened to the atmosphere, the piston 42 returns to the position shown in FIG.

FIG. 3 is a block diagram showing a hardware configuration of the robot control unit 12. As shown in FIG. The robot control unit 1
2 has a CPU 60. The CPU 60 has a ROM
64, RAM 66, nonvolatile memory 68, operation panel 72,
The input device 70, the output device 74, and the external communication device 78 are connected via the bus 62.

The ROM 64 stores a system program, and the RAM 66 temporarily stores various data processed by the CPU 60. In the nonvolatile memory 68,
Various parameters to be saved even when the power is turned off are stored. The operation panel 72 includes a display device and input keys (not shown). The input device 70 includes the force sensor 14
And a first provided on each joint axis of the robot body 10.
To the third encoders 10d, 10e, and 10f. The axis servo circuit 76 for controlling the positions of the first to third arms 10a, 10b, and 10c of the robot body 10 is connected to the output device 74. The external communication device 78 is connected to the nut runner control unit 22.

Next, a screw tightening procedure according to the present embodiment will be described with reference to FIGS.

FIGS. 4 and 5 are flowcharts showing the procedure of screw tightening of the robot. In FIG. 7A, F
x, Fy, and Fz indicate detection axes in the vector direction of the force sensor 14, and Tx, Ty, and Tz indicate detection axes in the moment direction of the force sensor. Of these, the vector in the tightening axis direction of the screw is the Fz. FIG. 8 is a graph showing a change in force with time for a vector Fz in the direction of the screw tightening axis during the output of the force sensor.

In FIG. 4, when the process starts, the robot controller 12 is energized, and in step S1,
The male screw 20 inserted into the distal end receiving portion of the socket 18 is moved from the original position to the approach point by the robot body 10. Here, the original position is a reference point of a screw tightening operation in which the distal end of the robot main body 10 waits while the male screw 20 is held in the socket 18, and the approach point is a value which is previously taught to the robot controller 12. Work 24
a is a schematic position from the original position. FIG. 7A shows the positional relationship between the male screw 20 and the female screw 26 at the time when the process of step S1 is completed. At this time, the force sensor 1
No. 4 has not yet issued an output signal (see T0 in FIG. 8).

FIG. 8 does not show a change in the amount of force in the vector direction and moment direction other than Fz, but the amount of force in the vector Fz in the screw tightening axis direction is L1.
(See FIG. 8) until the vector direction F
x, Fy, Fz, the moment directions Tx, Ty, Tz
Is performed in all directions. When the process of step S1 is completed by the leading end of the robot body 10 reaching the approach point, the robot control unit 12 starts the force sensor 14 and the process of force control (step S2).

Here, the force control (step S15) will be described in detail with reference to FIG. In step S15a, the CPU 60 of the robot control unit 12
The external acting force in the vector direction and the external acting force in the moment direction are acquired from the force sensor 14 via the zero. Next, in step S15b, the CPU 60 determines whether the external acting forces in the two directions have become equal to the set target values. When it is determined that they are equal to the target set values, it is determined that the current position and orientation of the robot body 10 is at the target position and orientation, and the force control ends.

If it is determined that the target set value is not equal to the external acting force, the flow shifts to step S15c to perform force control. In step S15c, a position where the forces are balanced is calculated. The position where the forces are balanced is a position where the set target value is equal to the value of the external acting force (the value of the force sensor 14), and means a movement target position of the robot body 10. Here, the target speed and the target position of each axis are calculated from the target value, the external acting force (the value of the force sensor 14), each axis value and the speed of the robot body 10, and the like. Step S15d
The CPU 60 outputs the target speed and the target position calculated in step S15c to each axis servo circuit 76 via the output device 74. Step S15
In step e, the robot body 10 determines in step S15
Move to the target position at the target speed based on the instruction content in d.

Returning to the description of FIG. In step S3, the robot body 10 is further moved to determine whether the male screw 20 and the female screw 26 have sufficiently contacted. Force sensor 14
Is greater than the contact determination value L0 (see FIG. 8), it is determined that the male screw 20 and the female screw 26 have contacted, and the process proceeds to step S4. On the other hand, if the output does not exceed the contact determination value L0. Determines that the male screw 20 and the female screw 26 are not in contact with each other or the contact amount is insufficient, and repeats step S15 (force control) until the contact exceeds the contact determination value L0. The contact determination value L0 is stored in advance in the ROM 64 of the robot control unit 12 as an optimum value in consideration of the characteristics of the screw, or the optimum value is calculated by the CPU 60 of the robot control unit 12 each time. 68 and the like.

Further, the operator can arbitrarily change the value from the operation panel 72. FIG. 7B shows a positional relationship between the male screw 20 and the female screw 26 when it is determined in step S3 that the male screw 20 and the female screw 26 have sufficiently contacted each other.

When the male screw 20 and the female screw 26 reach the positional relationship shown in FIG. 7B, the process proceeds to step S4, and the nut runner 16 is rotated at a medium speed. The medium speed rotation means that even when the axes of the male screw 20 and the female screw 26 do not coincide with each other, the male screw 20 is not rotated.
And a rotational speed that does not damage the connecting portion of the female screw 26 and the female screw 26.

The CPU 60 of the robot controller 12 transmits the number of rotations, rotation start / end commands, and the like to the nut runner controller 22 connected via the external communication device 78.
The nut runner control unit 22 rotates the nut runner 16 according to the command received from the robot control unit 12. This rotation speed (medium speed rotation) is stored in advance in the ROM 64 of the robot controller 12 as an optimum value in consideration of the characteristics of the screw, or the CPU 60 of the robot controller 12.
The optimum value is calculated in each case by the nonvolatile memory 6
8 or the like.

Further, a plurality of values of the number of revolutions are stored in the ROM 64 or the non-volatile memory 68.
If U60 selects the optimum rotation value, it is possible to further improve the tightening accuracy and increase the work efficiency.
If the operator can change the value arbitrarily from the operation panel 72, it is clear that the degree of freedom of the control itself is further increased.

Next, in step S5, the male screw 20
It is determined whether or not the axis of the female screw 26 matches. That is, a difference between the amount of movement of the screw in the axial direction calculated by the rotation speed of the nut runner 16 and the screw lead pitch and the amount of movement of the robot body 10 in the tightening axis direction is calculated, and the difference is within an allowable range. In some cases, it is determined that the axes of the male screw 20 and the female screw 26 match.

For example, the pitch per rotation of the screw in this embodiment is P [mm], and the rotation speed of the nut runner 16 is R0 [r. p. m], the screw movement amount per second is R0 * P / 60 [mm], which is the command value of the screw movement amount when the axes are aligned. The pitch per one rotation of the screw is stored in a storage means such as the ROM 64 or the non-volatile memory 68 of the robot control unit 12,
Referenced by U60.

On the other hand, the amount of movement of the robot body 10 in the direction of the screw tightening axis per unit time is determined by the CPU 60 by the output of the first to third encoders 10d, 10e, and 10f provided on each joint axis of the robot body 10. The result can be confirmed by acquiring the result via the input device 70. If the CPU 60 determines in step S5 that the amount of movement of the screw in the axial center direction matches the amount of movement of the robot body 10 in the direction of the screw tightening axis, the process proceeds to step S5.
Proceed to 6. If it is determined that the movement amounts do not match,
It is determined that the axes do not match, and step S15
(Force control) is repeated.

In step S6, the force control is uniaxial control only in the direction of the tightening axis, and the force control of the other axes is stopped. This control is performed by the CPU 60 of the robot controller 12 by the input device 7.
In other words, only the output result in the axial direction to be controlled is made valid with respect to the output result of the force sensor 14 obtained through 0, and the force control is performed only in that direction.

In step S6, the force applied in the direction of the tightening shaft (see L1 in FIG. 8) is determined by the male screw 2 when the nut runner 16 is rotated at a high speed in step S7 described later.
This is a pressing force applied in the direction of the tightening axis so that the robot body 10 can follow the movement of 0 without delay. The positional relationship between the male screw 20 and the female screw 26 at this time is shown in FIG. 7C, and the output value of the force sensor 14 at this time is shown as L1 in FIG. L1 is a value detected by the force sensor 14 on the pressing force applied in the tightening axis direction in step S6.

When reaching L1 in FIG. 8, the nut runner 16 is rotated at high speed in step S7. Here, the high-speed rotation is performed to increase the efficiency of the screw tightening operation. The CPU 60 of the robot control unit 12 transmits a rotation speed, a rotation start / end command, and the like to the nut runner control unit 22 connected via the external communication device 78. The nut runner control unit 22 rotates the nut runner 16 according to the command received from the robot control unit 12. This rotation speed (high-speed rotation) is stored in advance in the ROM 64 of the robot control unit 12 as an optimum value in consideration of the characteristics of the screw or the like, or the optimum value is calculated by the CPU 60 of the robot control unit 12 each time. And stored in a storage means such as the sex memory 68.

Further, a plurality of rotation speed values are stored in the ROM 64 or the non-volatile memory 68, and a CPU
If the 60 selects the optimum rotation value, further tightening accuracy and work efficiency can be improved. further,
Obviously, if the operator can freely change the value from the operation panel 72, the degree of freedom of the control itself is further increased.

In step S8 shown in FIG. 5, it is determined whether the screw tightening torque during the high-speed rotation has reached the snag torque L2 (see FIG. 8). The snug torque L2 indicates a change point at which the torque increases immediately before the tightening of the screw ends, and is stored in advance in the ROM 64 of the robot control unit 12 as an optimum value in consideration of the characteristics of the screw, or
The optimum value is calculated each time by the CPU 60 of the robot controller 12 and stored in the nonvolatile memory 68.

Further, the operator can arbitrarily change the value from the operation panel 72. When the current screw tightening torque, that is, the value of the screw tightening axial vector Fz of the force sensor 14 reaches the snag torque L2, it is necessary to reduce the screw tightening rotation speed in order to secure the screw tightening torque. . When the output value of the force sensor 14 has reached the snag torque L2, the process proceeds to step S9. If the output value of the force sensor 14 does not reach the snag torque L2, step S15 (force control) is repeated until the output value of the force sensor 14 reaches the snag torque L2.

The output value of the force sensor 14 is the snag torque L
If the number has reached 2, the process proceeds to step S9, and the rotation speed of the nut runner 16 is reduced to low speed. Robot controller 12
CPU 60 transmits the number of rotations, rotation start / end commands, and the like to the nut runner control unit 2 connected via the external communication device 78.
2 is transmitted. The nut runner control unit 22 rotates the nut runner 16 according to the command received from the robot control unit 12. This rotation speed (low-speed rotation) is determined in advance as an optimum value in consideration of the characteristics of the screw and the like, and the robot controller 1
The optimum value is calculated each time by the CPU 60 of the robot controller 12 or stored in the storage means such as the nonvolatile memory 68.

Further, a plurality of values of the number of revolutions are stored in the ROM 64 or the non-volatile memory 68.
If U60 adopts the method of selecting the optimum rotation value, it is possible to further improve the tightening accuracy and increase the work efficiency. If the operator can change the value arbitrarily from the operation panel 72, it is clear that the degree of freedom of the control itself is further increased. FIG. 7D shows the positional relationship between the male screw 20 and the female screw 26 at this time.

In step S10, it is determined whether the screw tightening torque has reached the specified tightening torque L3 (see FIG. 8). The tightening specified torque L3 is stored in advance in the ROM 64 of the robot control unit 12 as an optimal value in consideration of the characteristics of the screw, or the CPU 60 of the robot control unit 12.
The optimum value is calculated in each case by the nonvolatile memory 6
8 or the like. Further, the operator can arbitrarily change the value from the operation panel 72.

The current screw tightening torque, that is, the value of the screw tightening axial vector Fz of the force sensor is the tightening specified torque L
When the number has reached 3, the process proceeds to step S11. If the output value of the force sensor does not reach the specified tightening torque L3, step S15 (force control) is repeated until the output value of the force sensor reaches the specified tightening torque L3.

FIG. 7E shows the positional relationship between the male screw 20 and the female screw 26 when it is determined in step S10 that the specified tightening torque has been reached, that is, when the screw tightening is completed.

When it is determined that the specified tightening torque has been reached, the rotation of the nut runner 16 is stopped (step S1).
1) In step S12, the force control is stopped. Next, the socket 18 is removed from the male screw 20 (step S1).
3), the robot returns to the original position (step S14), and ends a series of screw tightening operations.

In the present embodiment, the male screw 20 and the female screw 2
6 is performed by force control using a force sensor, and the determination of the alignment of the male screw 20 and the female screw 26 is calculated based on the rotation speed of the nut runner 16 and the lead pitch of the screw. The difference is calculated by calculating the difference between the amount of movement of the screw in the axial center direction and the amount of movement of the robot in the direction of the tightening axis (step S5).

On the other hand, if it is possible to use the force sensor 14 having sufficiently high detection accuracy of the axis, the processing and determination of the coincidence of the axes of the male screw 20 and the female screw 26 can be made only by the output of the force sensor 14. And the determination processing based on the movement amount can be omitted.

[0051]

As described above, according to the present invention, in the operation of tightening the male screw and the female screw, the position and posture control function of the male screw with respect to the female screw, and the torque required when the male screw and the female screw are tightened. By performing all the control functions with the robot's force control, the torque control device required for screw tightening is not required, the device configuration is downsized, the automatic screw tightening work in a small space becomes possible, and the number of parts is reduced. And the effect of improving the reliability of the device accompanying the reduction of the manufacturing cost.

Further, by automatically aligning the axes of the male screw and the female screw, the screw can be securely tightened. Further, the screw tightening speed is changed according to the tightening state of the screw and the screw is tightened, so that the efficiency of the screw tightening operation is improved.

[Brief description of the drawings]

FIG. 1 is an overall view of a screw tightening device by a force control robot according to an embodiment.

FIG. 2 is a schematic longitudinal sectional view of a nut runner.

FIG. 3 is a block diagram illustrating a hardware configuration of a robot control unit.

FIG. 4 is a flowchart showing a screw tightening procedure.

FIG. 5 is a flowchart showing a screw tightening procedure.

FIG. 6 is a flowchart illustrating an outline of force control.

FIG. 7 is a positional relationship diagram of a male screw and a female screw corresponding to a screw tightening process.

FIG. 8 is a graph showing a change in output of a force sensor (in the direction of a screw tightening axis).

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 10 ... Robot main body 12 ... Robot control part 14 ... Force sensor 16 ... Nut runner 18 ... Socket 20 ... Male screw 22 ... Nut runner control part 24a, 24b ...
Work 26 Female screw 60 CPU 62 Bus 64 ROM 66 RAM 68 Non-volatile memory 70 Input device 72 Operation panel 74 Output device 76 Each axis servo circuit 78 External communication device

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Sumio Noguchi 1-10-1 Shinsayama, Sayama City, Saitama Prefecture Honda Engineering Co., Ltd. (72) Inventor Masaru Maruo 1-10-1 Shinsayama, Sayama City, Saitama Prefecture Hondae Engineering Co., Ltd. F term (reference) 3C007 AS06 BS10 KS34 KS35 KX06 LV12 NS24

Claims (5)

[Claims] 1. A method of tightening a screw by a force control robot having a force sensor, the method comprising: displacing the robot to match the axes of a male screw and a female screw based on an output result of the force sensor; Tightening the screw by performing force control based on the output of the force sensor only in the screw tightening axial direction after the axes match, and tightening the screw by the force control robot. Method. 2. A method for tightening a screw by a force control robot according to claim 1, wherein a tightening state of the screw is recognized from an output result of the force sensor.
A screw tightening method by a force control robot, wherein the screw tightening speed is changed according to the screw tightening state to perform screw tightening. 3. A robot having a force sensor, a tightening means having a socket for holding a screw on an output shaft, and a robot control means for controlling the posture of the robot by the force control based on an output result of the force sensor. And a tightening control means for controlling a screw tightening rotation speed of the tightening means in accordance with an output result of the force sensor. 4. The screw tightening device according to claim 3, wherein the robot control means includes: a calculating means for calculating a moving amount of the screw; a detecting means for detecting a moving amount of the robot; Determining means for calculating a difference between the movement amount of the screw and the movement amount of the robot, and determining whether or not the difference is within a predetermined range; And a force control switching means for controlling only the force of the screw. 5. The screw tightening device according to claim 3, wherein said robot control means stores a plurality of screw tightening rotation speeds of said tightening means, and said force sensor. A rotational speed determining means for determining an optimal screw tightening rotational speed from the output result of the rotational speed, and a rotational speed for selecting an optimal screw tightening rotational speed from the storage means based on the determination result of the rotational speed determining device. A screw tightening device by a force control robot, comprising: selecting means, and rotating the tightening means at the screw tightening rotational speed selected by the rotational speed selecting means.