JPS58206365A - Positioning device in machine tool - Google Patents

Abstract

PURPOSE:To improve positioning speed and accuracy in an above-captioned device for controlling a machine tool by the difference between command and feedback pulses, by resetting an error counter to zero in the instant of contacting a tool with a workpiece to stop a table and repositioning the table on the basis of contents at a time just prior to the contact and the number of invalidated command pulse. CONSTITUTION:An error counter 60 is reset to zero through a reset circuit 70 by a detected output S1 of a tool-workpiece contact detector 52. As a result, a table 10 is stopped by a drive amplifier 26, and a content E at a time just prior to contact of a tool with a workpiece is latched at 68, and the number K of command pulse invalidated at the zero reset is counted by an over-output counter 74. Then, the contents E and K of the latch circuit 68 and the over-output counter 75 are read to be subtracted from the total number of output pulse, so as to precisely decide an actual contact position for use as repositioning data. With this constitution, although the table is moved at a high speed, it is stopped in the instant of contact of the tool with the workpiece, thereby obviating overrun of the table and achieving precise positioning operation.

Description

[Detailed Description of the Invention] The present invention is a positioning device for a machine tool, and in particular, is configured to control the relative movement of a tool and a workpiece based on the contents of an error counter that counts the difference between a command pulse and a feedback pulse. related to things.

Conventionally, as this type of device, there has been one shown in FIG. 1, for example. The machine tool positioning device shown in the figure positions the workpiece 46 at a processing position where it contacts a tool 50 by moving an XY table holding the workpiece 46 in the XY directions. To explain this figure in more detail, the XY table is the X-axis table 1.
0 and a Y-axis table 38. X-axis table 1
The ball screw 12, the nut 14,
It is moved and driven by a mechanical drive system consisting of gears 20 and 24 and an X-axis motor 22. The same goes for the Y-axis table 38, which is driven to move in the Y direction by the Y-axis motor 4°. X-axis motor 22 and Y-axis motor 40 are driven by drive amplifiers 26 and 44, respectively. The drive amplifier 26t'i on the X-axis side is controlled by the X-direction movement control circuit 28.
The drive amplifiers 44 on the X-axis side are each controlled by a Y-direction movement control circuit 42. Furthermore, each movement control circuit 2B
, 42 operate based on instructions from the NC device (numerical control device) 32. The command is given as the number of pulses generated per unit time, that is, command pulses. The NC device 32 also controls the operation of the main shaft 48 to which the tool 5o is attached. The control operation is carried out according to a program pre-programmed on the tape 34. Movement control circuits 28 and 42 trigger error counter 60 and D/A & converter 62, respectively. This error counter 6o is
The difference between the command pulse sent from 2 and the feedback pulse obtained by detecting the actual movement amount of the workpiece 46 is counted. The feedback pulse is given from a rotation angle detector 30, called an encoder, installed in the pattern drive system of the XY table. The housing is provided with a contact detection device 52 for detecting whether the workpiece 46 has come into contact with the tool 50 or not.

As a detailed example of this contact detection device 52 is shown in FIG. Apply E0. At this time, the tool 50 and the workpiece 4
A capacitor C is connected in parallel between 6 and 6. Here, when the workpiece 46 and the tool 50 come into contact with each other or come very close to each other, the potential v0 between them rapidly decreases, and this decrease in potential is detected by the voltage comparator 24 having a reference voltage v1, and its detection output is Sl turns on the lamp 25 and is sent to the NC#c device 3. This allows the N.C.
The device 32 issues a stop command by such means as zeroing the content of the command pulse, thereby positioning the workpiece 46 at a machining position where it contacts the tool 50.

The relative position of the workpiece 46 and the tool 50 is determined in the above manner, but what must be taken into consideration here is that the command pulses issued from the NC device 32 are updated at regular time intervals. This means that it will be carried out. Therefore, when the moving speed of the workpiece 46 is fast, even if the contact detection device 52 detects contact between the workpiece 46 and the tool 50 while the command pulse is being updated, the next Until the command pulses are updated, the workpiece 46 continues to move, causing what is called an overrun, and may even collide with the tool 50 in some cases. In order to prevent such a situation, in the conventional apparatus, when the workpiece 46 approaches the tool 50, the moving speed of the workpiece 46 has to be significantly reduced. However, this has caused a problem in that it takes a very long time to complete positioning.

This invention was made in view of the above-mentioned conventional problem, and its purpose is to prevent overrun by t'= even if the relative movement of the workpiece and tool is performed at a relatively high speed until just before they come into contact. To provide a positioning device for a machine tool which can prevent the occurrence of dropouts, thereby greatly increasing the speed of positioning, and performing positioning without any errors due to overruns.

In order to achieve the above object, the present invention includes a contact detection device that detects whether or not a tool and a workpiece come into contact with each other at a machining position, and a contact detection device that detects whether or not a tool and a workpiece come into contact with each other. A positioning device for a machine tool comprising a digital position control means configured to control the relative movement of a workpiece based on the contents of an error counter that counts the difference between a command pulse and a feedback pulse, the detection device as described above. The contents of the error counter are forcibly set to zero the moment contact is detected, and the latch circuit retains the contents immediately before the error counter is set to zero. The present invention is characterized in that an overoutput counter is provided for counting invalid command pulses, and the contents of the latch circuit and the overoutput counter can be used as data for positioning.

Hereinafter, preferred embodiments of the present invention will be celebrated based on the drawings.

FIG. 3 shows an embodiment of a machine tool according to the present invention.

Note that the basic configuration is the same as that of the conventional one described above, so a detailed explanation will be omitted.

In FIG. 3, the error counter 60 is connected to the contact detection device 52.
It is forcibly reset to zero by the detection output S1 from. The zero reset is reset circuit 7
This is done via 0. Further, a latch circuit 68 that holds the contents of the error counter 60 immediately before it is reset, and an overoutput counter 74 that counts the number of command pulses that become invalid when the error counter 60 is reset to zero are provided. ing. Part 11, error counter 60. A logic circuit including AND gates 64 and 72, an inverter 66, and the like is formed to control the over-output counter 74 and the like.

Now, in FIG. 3, the table 10 moves and the tool 5
0 and the workpiece 46 approach or come into contact with each other, the contact detection output S1 is generated, and the content E of the error counter 60 is first held in the latch circuit 68, and then the content of the error counter 60 is immediately forced to zero. will be reset. This causes drive amplifier 26 to immediately stop table 10 without waiting for the next update of the command pulse by NC device 32. After this, the command pulse sent from the NC device ff132 becomes invalid and is sent to the over-output counter 74. Therefore, even if the workpiece 46 approaches or contacts the tool 50 between command pulses given from the NC device 32, its movement can be immediately stopped at the point of approach or contact. As a result, even if the workpiece 46 is moved at a relatively high speed until it approaches or contacts the tool 50, the workpiece 46 is immediately stopped at the point of approach or contact without overrunning the tool 50. accurately positioned. On the other hand,
The NC device 32 accurately determines the actual contact position by reading the contents E and K of the latch circuit 68 and over-output counter 74, for example, by subtracting (E+K) from the total number of output pulses. can be determined.

Note that the relative movement between the workpiece 46 and the tool 5o may be performed at a constant speed as in the above-mentioned embodiment, but the effect cannot be sufficiently obtained even if the relative movement is performed in stages. be.

As described above, the machine tool positioning device according to the present invention can greatly improve the positioning speed with relatively simple additional means, while also reliably preventing overruns during positioning. high positioning accuracy can be obtained.

[Brief explanation of drawings]

FIG. 1 is a perspective view schematically showing a conventional positioning device for a machine tool, FIG. 2 is a circuit diagram showing a portion thereof, and FIG. 3 is a circuit showing an embodiment of the positioning device according to the present invention. The same members in each figure are given the same reference numerals, 10.38 is the X-axis and Y-axis table, 22.40 is the X-axis and Y-axis motor, 26.46IIi X-axis and Y-axis drive amplifier, 28
and 42 are X-direction and Y-direction movement control circuits, 32 is an NC device, 46 is a workpiece, 50 is a tool, 52 is a contact detection*tit s b Ou ah difference counter, 6
8 is a latch circuit, 70 is a reset box, and 74t'i overoutput counter. Agent: Patent Attorney Shin Kuzuno - (1 person) Mr. Kame, Commissioner of the Japan Patent Office 1.・Display of items Special sentry J Sho 57-0883
07 @ 2. Name of the machine tool positioning device 3, supplementary + E Detailed description of the invention, column 4C explanation in the song of the mountain in Figure 1,
.

Claims (1)

[Claims] (1) A contact detection device that detects whether the tool and workpiece have come to a machining position where they contact each other, and commands the relative movement of the tool and workpiece until this detection device detects contact. In a positioning device for a machine tool having a digital position control means configured to perform control based on the contents of an error counter that counts the difference between a pulse and a feedback pulse, the positioning device for a machine tool has a digital position control means configured to perform control based on the contents of an error counter that counts the difference between a pulse and a feedback pulse. In addition to forcibly setting the contents of the Htg4 difference counter to zero, there is also a latch circuit that holds the contents of the 1-difference counter just before it was set to zero, and a latch circuit that holds the contents of the above 1-difference counter and the left counter is invalid because it has been set to zero. 7. A machine tool characterized in that a withdrawal output counter is provided to count the command pulses resulting in , and the contents of the output latch circuit and the contents of the withdrawal output counter can be used as data for positioning. positioning device.