JPH0521703B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to a method for setting the origin of machine coordinates in a feed device such as an NC machine tool.

2. Description of the Related Art In a feeding device having a pulse generator as a position detector, a method using a limit switch is known as a method for setting the origin of a machine coordinate system when starting up the machine or returning after a power outage.

This is a method in which a slider such as a table is moved back at low speed until it comes into contact with a limit switch for detecting the origin position, and the count data in the coordinate register is cleared by performing the logical product of the output of the limit switch and the Z phase of the pulse generator. be.

Since the above method is a manual method, it takes a long time to complete the origin setting.Recently, there are systems that automate the coordinate origin setting by using an absolute type potentiometer instead of a limit switch. Proposed.

FIG. 2 shows an example of a servo-type feed device that uses both a pulse generator and a potentiometer as a position detector, and the slider 1 is fed by a servo motor 2 and a ball screw 3. A tachogenerator 4, a pulse generator 5, and a potentiometer 6 are connected to the main shaft of the servo motor 2.
The output is sent to the servo control device 7 to form a speed feedback loop.

The pulse generator 5 has A-phase, B-phase, and Z-phase outputs, and the outputs are input to the NC control device 8, counted by a counter 9, and inputted to the CPU 10 as current position data of the slider 1. On the other hand, the potentiometer 6 outputs the absolute position of the slider 1 as a voltage change, and outputs the absolute position of the slider 1 as a voltage change.
After being digitized and quantized by the converter 11 with a resolution equal to the lead of the ball screw 3,
Input to CPU10. 14 is a memory for storing input data to the CPU 10, calculation data, etc.

The origin setting of the mechanical coordinate system of the above feeder is the third
The procedure is as shown in the figure.

When a predetermined operation command is input from the input device 12 to the CPU 10, the CPU 10 outputs the positional deviation as a speed command to the servo control device 7, feeds the slider 1, and keeps the slider 1 at a constant speed until it contacts the reference surface 13. to retreat.

Then, after confirming that the slider 1 has come into contact with the reference surface 13, the command from the input device 12 is cut off. At this time, the CPU 10 stores in the memory 14 the position data of the pulse generator 5 and the potentiometer 6 at the position where the slider 1 has stopped.

Furthermore, when the origin setting command and origin offset data are input to the CPU 10 from the input device 12, the PCU 1
0 is set by calculating the origin of the machine coordinates using the position data previously stored in the memory 14 and the origin offset data. The origin offset data referred to here is the amount of offset between the origin on the NC coordinates and the position where the slider 1 abuts the reference surface 13, and is a known value that is uniquely determined at the time of machine assembly.

Problems to be Solved by the Invention In the above method, when setting the origin, the user simply moves the slider 1.
Since the rear end surface is simply pressed against the reference surface 13 at a constant speed, there is no guarantee that the pressing force exerted by the slider 1 on the reference surface 13 is constant. Therefore, if the torque of the servo motor 2 varies, the amount of deflection of the styder 1 or the reference surface 13 will vary in units of microns, which will shift the origin of the mechanical coordinate system and reduce accuracy.

Means for Solving the Problems The present invention attempts to improve the accuracy of the origin position by ensuring that the torque of the servo motor does not exceed a predetermined value when setting the origin. Specifically, when the slider is given a predetermined feed and pressed against the reference surface, the current of the servo motor is limited so that the torque of the servo motor does not exceed a predetermined value.

Embodiment As shown in FIG. 1, the basic origin setting operation is the same as the conventional one, but when retracting the slider 1 and pressing it against the reference surface 13, the CPU 10 sends the servo control device 7 a predetermined command in step and step. At the same time, a current limit command is given to control the torque of the servo motor 2 so that it does not exceed a certain preset value.

In other words, when setting the origin, the slider 1 is fed at a constant speed that is slower than during normal operation, but at the same time, current is limited so that when the slider 1 contacts the reference surface 13, The pressing force exerted on the reference surface 13 is controlled so as not to exceed a certain value.

As a result, even if the origin setting operation is repeated,
The pressing force of the slider 1 against the reference surface 13 always falls within a certain range.

Effects of the Invention As described above, according to the present invention, by controlling the torque of the servo motor when pressing the slider against the reference surface so as not to exceed a predetermined value, no matter how many times the origin setting is performed, the reference surface or The amount of deflection of the slider can always be kept constant, and the error in the origin position can be reduced to improve positioning accuracy and reliability.

[Brief explanation of drawings]

FIG. 1 is a flowchart showing an embodiment of the method of the present invention, FIG. 2 is an explanatory diagram showing an example of a servo feeder, and FIG. 3 is a flowchart showing a conventional origin setting method. 1...Slider, 2...Servo motor, 5...
Pulse generator, 6...potentiometer,
7... Servo control device, 8... NC control device, 1
3...Reference surface.

Claims (1)

[Claims] 1. In addition to a pulse generator, an absolute type potentiometer is provided as a position detector for a slider fed by a servo motor, and a predetermined feed is given to the slider to move the slider to a reference plane. This method calculates and sets the origin of the machine coordinates based on the position data of the pulse generator and potentiometer when the slider is pressed against the slider, and the origin offset data stored in advance. 1. A method for setting a coordinate origin of an NC feeding device, the method comprising: controlling the current of a servo motor so that the torque of the servo motor does not exceed a predetermined value when the servo motor is pressed against the servo motor.