JPH09138706A - Device for automatically calibrating original point of movable body - Google Patents

Abstract

PROBLEM TO BE SOLVED: To precisely calibrate an original point even if a low rigidity part having mechanical viscosity and a spring characteristic is given to a driving mechanism SOLUTION: For calibrating the original point of a robot where a movable body 4 is driven by the driving mechanism of a driving motor 6 and the like, the absolute position of the movable body 4 is detected by an encoder 12 and the position of the movable body 4 is controlled, the movable body 4 is made to collide with a stopper 10a, prescribe torque is added to the movable body 4 for prescribed time and the original point is calibrated based on the absolute position of the movable body 4 after torque is impressed. Even if the low rigidity part K exists in the driving mechanism by the impression of torque after the collision of the stopper 10a, the movable body 4 can be stopped in the prescribed position and the original point can precisely be calibrated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for automatically calibrating the origin of a movable body in a robot or machine tool.

[0002]

2. Description of the Related Art Conventionally, in a robot, a movable body such as a hand for fixing a work is moved by a drive mechanism such as a drive motor and a speed reducer, and the absolute position of the movable body is detected by an absolute position detector such as an encoder. And the movable body is controlled to a desired position. In such absolute position detection, it is important to improve the position accuracy with respect to the origin, but if there is a deviation in the detection position due to external factors or it is necessary to replace the drive motor or encoder, the origin It is necessary to calibrate. In the conventional method, the origin calibration is performed by the encoder output value when the movable body is moved to the mechanical stopper position.

[0003]

However, if the drive mechanism has high rigidity, the conventional method can perform the origin calibration with sufficient accuracy, but the drive mechanism has mechanical viscosity and spring characteristics. In a low-rigidity robot,
There is a problem that the origin calibration cannot be performed accurately because the position accuracy is poor.

The present invention has been made in view of the above problems, and an object thereof is to accurately calibrate the origin of a drive mechanism even if the drive mechanism has mechanical viscosity and spring characteristics.

[0005]

In order to achieve the above-mentioned object, in the invention described in claims 1 and 2, a constant torque is applied to the movable body for a predetermined time after the movable body collides with the blocking member. In addition, the origin is calibrated based on the absolute position of the movable body after the torque is applied.

Therefore, even when the drive mechanism has mechanical viscosity, spring characteristics, etc., the movable body is stopped at a fixed position by the above-mentioned torque application after the movable body collides with the blocking member. Therefore, the origin calibration can be performed accurately.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments in which the present invention is applied to a robot will be described below. In FIG. 1, a movable body 4 provided with a hand 2 for fixing a work is attached to a ball screw 8 rotated by a drive motor 6, and by driving the drive motor 6, the movable body 4 becomes a frame body. It is configured so as to move in the left-right direction in the figure within 10. When the movable body 4 comes into contact with the left end portion (hereinafter referred to as a stopper) 10a of the frame body 10, the movable body 4
Is prevented from moving.

Although not shown, a speed reducer is provided between the drive motor 6 and the ball screw 8. In the drive mechanism that drives the movable body 4 from the drive motor 6 via the speed reducer and the ball screw 8, mechanical viscosity,
It has a low rigidity and has a spring characteristic, and the low rigidity portion such as the spring characteristic is shown as K in the figure. An absolute position detection type encoder 12 is attached to the drive motor 6. The encoder 12 has a drive motor 6
A signal indicating the absolute position of the movable body 4 is output by the rotation of.

The control circuit 20 is constituted by including computer means, detects the absolute position of the movable body 4 by a signal from the encoder 12, and drives the drive circuit 22 to control the movable body 4 to a desired position. A control command signal (a signal that commands the rotation direction and the rotation speed of the drive motor 6) is output to. The drive circuit 22 receives the control command signal and current-drives the drive motor 6. The drive circuit 22 has a torque limiting mechanism that limits the torque of the drive motor 6 to a constant value.

In the above structure, first, the operation for setting the origin calibration position will be described. FIG. 2 shows the processing of the control circuit 20 in that case. When performing this setting operation,
First, the operator fixes the movable body 4 at the reference position P1 shown in FIG. The control circuit 20 stores the encoder output value (D1) at the reference position P1 (step 10).
0). After this, the operator fixes the movable body 4 at the reference position P2 at which the movable body 4 collides with the stopper 10a of the frame body 10. The control circuit 20 stores the encoder output value (D2) at the reference position P2 (step 101). Then, the moving amount of the movable body 4, that is, D2-D1 is stored as the origin calibration position (step 102). This origin calibration position (D
2-D1) is a target for updating the origin calibration position thereafter, and is non-volatilely stored in the control circuit 20.

Next, the origin calibration operation performed after the above origin calibration position is set will be described. Control device 20
Performs an automatic origin calibration process shown in FIG. 3 when an origin calibration command is output from an input device (not shown). First, a control command signal is output to the drive circuit 22 to move the movable body 4 in the left (+) direction in FIG. 1, that is, the stopper 10a direction (step 200). After that, the movable body 4 moves to the stopper 10.
It is determined whether or not it collided with a (step 201). As shown in FIG. 4, the torque of the drive motor 6 increases immediately after the movable body 4 hits the stopper 10a, and it can be determined that the movable body 4 collides with the stopper 10a at time t1. Since the torque of the drive motor 6 corresponds to the control command signal from the control circuit 20 to the drive circuit 22, the control circuit 20 determines from the control command signal whether or not the movable body 4 collides with the stopper 10a. .

When it is determined that the movable body 4 has collided with the stopper 10a, it is determined whether a predetermined time T (for example, 10 milliseconds) has elapsed (step 202). in this case,
As shown in FIG. 4, since the torque of the drive motor 6 is limited to a constant value by the operation of the drive circuit 22, a constant torque is applied to the movable body 4 for a predetermined time T. As a result, even if the drive mechanism that drives the movable body 4 from the drive motor 6 via the speed reducer has low rigidity having mechanical viscosity and spring characteristics, it can be processed in the same manner as high rigidity. The movable body 4 can be stopped at the position of the stopper 10a.

At time t2 after a lapse of a certain time T, the drive motor 6 is stopped (step 203), and the encoder output value (D3) at that time and the origin calibration position (D2-D1) previously set and stored are used. , Offset amount (D2
-D1-D3) is calculated (step 204). The offset amount in this case is the reference position P2 shown in FIG.
And the deviation from the operation end position of the movable body 4 after a constant torque is applied to the movable body 4 for a predetermined time T.

After the above origin calibration process is performed, the current position of the movable body 4 when the robot is actually driven is obtained as the encoder output value (D) + offset amount. This means that the calibration position has been updated to the operation end position described above, that is, the origin has been calibrated. When the drive motor 6, the encoder 12 or the like is replaced, or when another condition requiring the origin calibration process occurs, the origin calibration command is given to the control circuit 20 to perform the origin calibration again.

Although a robot having one movable body 4 has been described in the above embodiment, many robots of this type have a multi-axis structure, and an example of such a case is shown in FIG. The robot shown in FIG. 5 is a four-axis cylindrical coordinate type robot, and the drive mechanism as described above is provided for each axis. In the case of such a multi-axis configuration, when setting the above-mentioned reference positions P1 and P2, first fix each axis to a predetermined reference position using a jig or the like, and use each encoder output value at that time. P1 is obtained in the coordinate format, then each axis is fixed at a position where it collides with each stopper, and P2 is also obtained in the coordinate format. The origin position calibration for each axis is performed using these coordinates P1 and P2.

[Brief description of the drawings]

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

FIG. 2 is a flowchart showing a process of setting an origin calibration position.

FIG. 3 is a flowchart showing an automatic origin calibration process.

FIG. 4 is a diagram showing the torque of the drive motor and the origin configuration timing.

FIG. 5 is a perspective view when the present invention is applied to a cylindrical coordinate type robot having a four-axis configuration.

[Explanation of symbols]

2 ... Hand, 4 ... Movable body, 6 ... Drive motor, 8 ... Ball screw, 10 ... Frame body, 10a ... Stopper, 12 ... Encoder, 20 ... Control circuit, 22 ... Drive circuit.

Claims (2)

[Claims] 1. A drive mechanism (6) for moving a movable body (4).
8) and an absolute position detecting means (1) for detecting the absolute position of the movable body.
2), a blocking member (10a) that is on the moving path of the movable body and abuts on the movable body to block the movement of the movable body, and a fixed member after the movable body collides with the blocking member. Means for performing origin calibration based on the absolute position of the movable body after applying torque to the movable body for a predetermined time, and automatic origin calibration of the movable body. apparatus. 2. Means (100-102) for setting and storing an origin calibration position based on an absolute position of the movable body detected when the movable body is in contact with the blocking member, the origin calibration is performed. Means (200-204) for obtaining an offset amount from the set and stored origin calibration position and the absolute position of the movable body after the torque application (20)
4) The automatic origin calibration device for a movable body according to claim 1, further comprising: