JPH07214435A - Automatic screw tightening device - Google Patents

Abstract

PURPOSE:To realize sure screw tightening action regardless of the posture of the other member and the shift of screw holes, in the case of an automatic screw tightening device equipped with a screwing mechanism at the arm tip portion of a multijoint robot. CONSTITUTION:A force sensor 71 to detect force that is received at the time of a screwing mechanism 2 conducting screwing, is fitted to the base end portion of the screwing mechanism 2, and the output end of the force sensor 71 is coupled to a robot control circuit 15. The robot control circuit 15 sets, at the time of screwing, the target posture of the bit 23 of the screwing mechanism 2 on the same line with force vector, and conducts the feeback control of the posture of a robot arm.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic screw tightening device equipped with a screw tightening mechanism at the tip of an arm of an articulated robot to automatically tighten a screw on a mating workpiece such as a sheet metal member.

[0002]

2. Description of the Related Art Conventionally, in a production line that involves assembly work in which sheet metal members are fastened to the main body of the device with screws, or sheet metal members are fastened together with screws, an automatic screw tightening device is installed to automate the work. Has been planned. As such an automatic screw tightening device, there is known one in which a screw tightening mechanism is attached to the arm tip of an articulated robot.
(JP-A-60-180779 [B25B23 / 10], Jitsukaihei 2-78230 [B23P19 / 06], etc.). The screw tightening mechanism has a bit at the tip thereof which is driven to rotate by a motor, and the screw is tightened by engaging the tip of the bit with a screw of a mating member.

In a conventional automatic screw tightening device, an articulated robot operates in accordance with preset teaching data to automatically move the screw tightening mechanism to a work position.
Then, the bit is rotationally driven with the bit engaged with the head of the mating screw. At this time, the torque acting on the bit is detected by the torque sensor to control the screw tightening torque and the like.

[0004]

However, in the conventional automatic screw tightening device, after the bit is engaged with the screw, the attitude of the bit is kept constant, and the bit is pushed into the screw and the bit is rotated. Since only driving is performed, there are the following problems. For example, as shown in FIG. 4 (b), when the sheet metal member (21) is not perpendicular to the pushing direction X of the bit (23) but is slightly inclined, the reaction force F acting on the screw (22) is The screw 22 does not oppose on the same line as the pushing force direction X, and a moment based on the reaction force F acts on the screw 22. As a result, when the screw (22) is deviated from the pushing direction X and inclined, the screwing by the bit (23) is not normally performed, and the bit (23) is caught in the sheet metal member (21). Rotation may stop halfway.

Further, as shown in FIG. 5B, two sheet metal members (21a)
In the work of fastening (21b) to each other, screw holes (24a) (2
Similarly, when the center of 4b) is deviated, in the conventional automatic screw tightening device, when the screw (22) is inclined with respect to the pushing direction X, the screwing by the bit (23) is not normally performed,
There is a problem that the rotation of the bit (23) stops halfway.

An object of the present invention is to provide an automatic screw tightening device capable of reliable screw tightening regardless of the posture of the mating member and the deviation of the screw holes.

[0007]

In the automatic screw tightening device according to the present invention, a force sensor (71) is provided at the base end of the screw tightening mechanism (2) for detecting the force received by the screw tightening mechanism when tightening the screw. It is equipped with The output end of the force sensor (71) is connected to the robot control circuit (15), and the robot control circuit (15) has the same direction of action as the force detected by the force sensor (71) when tightening the screw. The target posture of the spindle of the screw tightening mechanism (2) is set on the line, and the posture of the robot arm is feedback-controlled.

[0008]

[Operation] The arm posture of the multi-joint robot (1) at the time of screw tightening is controlled by the robot control circuit (15), and the main shaft of the screw tightening mechanism (2) acts on the force detected by the force sensor (71). The direction is corrected so that it is collinear with the direction. Therefore, depending on the state of the mating member, for example, as shown in FIG.
Alternatively, as shown in FIG. 5 (b), even if the reaction force F acting on the screw (22) does not face each other on the same line as the pushing direction X temporarily, the direction of the main shaft of the screw tightening mechanism is the reaction force F. Corrected in the direction. Accordingly, the posture of the screw (22) is also corrected on the same line as the reaction force F as shown in FIG. 4 (c) or 5 (c). As a result, the screw (22) does not generate a large moment based on the reaction force F, and the normal screwing operation is realized.

[0009]

According to the automatic screw tightening device of the present invention, reliable screw tightening is possible regardless of the posture of the mating member and the deviation of the screw holes.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below with reference to the drawings. FIG. 1 shows the overall configuration of an automatic screw tightening device according to the present invention, in which a well-known 6-axis force sensor (71) is attached to the arm tip of a 6-DOF articulated robot (1).
A screw tightening mechanism (2) is attached. Screw tightening mechanism
(2) is configured, for example, by equipping the tip end of a driver mechanism "DLV-3148FJN" manufactured by Nippon Electric Seiki Co., Ltd. with a chuck mechanism manufactured by Nitto Seiko Co., Ltd., for example. The 6-axis force sensor (71) is the main shaft of the screw tightening mechanism (2), that is, the bit.
With the Z-axis as the axial direction of (23), a force vector F consisting of six components of three-axis force components of X-axis, Y-axis, and Z-axis and torque components around each axis is detected. The detection signal is fed back to the force sensor controller (7).

The control circuit (15) of the articulated robot (1) includes a system controller (3) and a robot arm controller.
It is composed of (4), servo controller (5), servo driver (6) and force sensor controller (7), and is supplied from an encoder (not shown) that detects the rotation angle of each joint of the articulated robot (1). The pulse is fed back to the robot arm controller (4) and the servo controller (5).

Teaching data for causing the robot arm to perform a predetermined operation are registered in the system controller (3), and based on the teaching data, the position command value Xd is sent to the robot arm controller (4). Is given.

The robot arm controller (4) executes kinematic conversion, calculation, etc. on the basis of the encoder pulse sent from the articulated robot (1) and the position command value Xd to calculate each joint. The rotation angle θ is calculated as a target trajectory command value, and the result is supplied to the servo controller (5). The servo controller (5) calculates the movement amount of each joint axis as a function of time based on the rotation angle, the encoder pulse, and the force feedback value from the force sensor controller (7), and the result is calculated by the servo driver ( Send to 6). In response to this, the servo driver (6) generates a drive current for each joint and supplies it to the multi-joint robot (1).

FIG. 2 is a block diagram of force control (impedance control) executed by the robot control circuit. Here, the command value Xd, the force vector F detected by the 6-axis force sensor (71), and the position and orientation X of the arm tip in the working coordinate system are given to the impedance model (8) described later. Accordingly, the acceleration obtained from the impedance model (8) is subjected to the non-linear compensation (9) to compensate the non-linear relationship between the acceleration and the torque due to friction or the like. At this time, the rotation angle θ of each joint and the load torque τ _f obtained by inversely transforming the reaction force vector F by the Jacobian matrix (12) are given to the non-linear compensation (9). The torque τ _a obtained through the non-linear compensation (9) is converted into the rotation angle θ of each joint through the robot manipulator dynamics (10). At this time, the load torque τ _f from the Jacobian matrix (12) is given to the robot manipulator dynamics (10). As a result, the rotation angle θ of each joint obtained from the robot manipulator dynamics (10) passes through the coordinate conversion determinant (11),
It is converted to the position and orientation X of the tip of the robot arm in the work coordinate system.

The control block of FIG. 2 is an articulated robot.
The force control method of (1) has a general configuration, but is characterized in that the impedance model (8) is configured as follows. That is, the force F and displacement ΔX (command value Xd and actual movement X
The difference (X−Xd)) and the relation (X−Xd)) dynamically control the articulated robot (1) so that the following equation 1 is satisfied.

[0016]

[Equation 1]

Here, M is a mass characteristic, D is a damping characteristic, and K is
Indicates rigidity characteristics, and the impedance characteristics are defined by a set of coefficients (M, D, K). In order to control the articulated robot (1) so as to satisfy the relationship of the mathematical expression 1, the control may be performed so that the movement amount X of the arm tip portion becomes a value expressed by the following mathematical expression 2.

[0018]

[Equation 2]

Therefore, the impedance model (8) of FIG.
By configuring as shown in FIG. 3, the target control can be realized. In FIG. 3, S represents a derivative, 1 / S represents an integral, Gp and Gv represent loop gains of position and velocity, respectively, and the first circuit section (13) is an acceleration responsive to the command value Xd. A second circuit portion (14) for controlling the operation and for performing the operation of the equation 2 is added.

The coefficient of (M, D, K) works hard against the reaction force F with respect to the force and moment in the screw tightening direction and is soft against the direction that determines the posture of the screw tightening mechanism. Each value is determined so that it operates. As a result, the acceleration command value is changed.

4 (a), (b) and (c) show the operation when the tapping screw (22) is screwed into the screw hole (24) of the sheet metal member (21). As described above, while the head of the tapping screw (22) is engaged with the bit (23), the bit (23) is rotated while being pushed in and screwed. On the other hand, when the sheet metal member (21) is inclined as shown in FIG. 4 (b), the tapping screw
The reaction force F that the (22) receives from the sheet metal member (21) does not face the pushing direction X of the bit (23) on the same line as shown in the figure. The posture of (23) is corrected. As a result, the pushing direction X of the bit (23) and the direction of the reaction force F oppose each other on the same line, and a normal screwing operation is realized.

Further, FIGS. 5A, 5B and 5C show two sheet metal members.
This shows the operation of fastening (21a) and (21b) to each other with the tapping screw (22), with the bit (23) engaged with the head of the tapping screw (22) as shown in FIG. 5 (a). (2
3) Push in and rotate to screw in. On the other hand, when the screw holes (24a) and (24b) of the two sheet metal members (21a) and (21b) are misaligned as shown in FIG.
Since the reaction force F received by (22) does not face the pushing force X of the bit (23) on the same line as shown in the figure, the posture of the bit (23) as shown in FIG. Will be fixed.
As a result, the pushing direction X of the bit (23) and the direction of the reaction force F oppose each other on the same line, and a normal screwing operation is realized.

The above description of the embodiments is for explaining the present invention, and should not be construed as limiting the invention described in the claims or limiting the scope. The configuration of each part of the present invention is not limited to the above-mentioned embodiment, and it goes without saying that various modifications can be made within the technical scope described in the claims.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of an automatic screw tightening device according to the present invention.

FIG. 2 is a control block diagram in the apparatus.

FIG. 3 is a block diagram showing an impedance model.

FIG. 4 is an explanatory diagram of a screwing operation with respect to one sheet metal member.

FIG. 5 is an explanatory diagram of a screwing operation with respect to two sheet metal members.

[Explanation of symbols]

 (1) Articulated robot (2) Screw tightening mechanism (23) Bit (71) 6-axis force sensor (8) Impedance model (15) Robot control circuit

Claims (1)

[Claims] 1. An automatic screw tightening device comprising a screw tightening mechanism (2) at a tip of an arm of an articulated robot (1), wherein a screw tightening mechanism is screwed at a base end of the screw tightening mechanism (2). A force sensor (71) that detects the force received at the time of is attached, the output end of the force sensor is connected to the robot control circuit (15), the robot control circuit (15), when tightening the screw,
An automatic screw tightening device characterized by setting a target posture of a spindle of a screw tightening mechanism (2) on the same line as a direction of a force detected by a force sensor (71) and performing feedback control of the posture of a robot arm.