JPH0413724B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to position detection of a table, tool, etc. in a machine tool, and more particularly to a positioning control device that accurately detects position information of a position control object (table, tool, etc.) at the time of previous power cut-off when the power is turned on again. Conventional position detection in this type of machine tool uses an incremental type pulse encoder (incremental encoder) that is related to the movement of the position controlled object, and the contents of a reversible counter are determined by count pulses generated based on the output of the encoder. This is generally done by controlling the increase or decrease. FIG. 1 is an explanatory diagram of position detection using an incremental encoder, and shows the processing process of the output signal of the encoder using a time chart. In the figure, signals A and B are the A-phase and B-phase output waveforms of the incremental encoder, and a phase difference of π/2 is given between them. Therefore, by determining the phase leading or slowing relationship between the signals A and B, it is possible to detect movement of a controlled object such as a table or a tool in the forward or reverse direction. Signals C, D, E, F, and G represent processed signals for the above detection. First, by differentiating signal A, we can differentiate the short-width positive pulse at the rising edge of signal A and the rising edge shown in signal C. A differential pulse train is created by the negative pulse of the same width at the falling edge. This differential pulse train C consists of a positive pulse train D and a negative pulse train E.
The two-phase outputs A and B of the encoder are
AND is performed with the inverted value of the signal B in order to determine the phase relationship between the two signals. As a result, a count-up pulse F representing the amount of movement of the controlled object in the positive rotational direction is obtained using the positive pulse train D and the inverted value, and a countdown pulse G representing the amount of movement in the negative rotational direction is obtained using the negative pulse train E and the inverted value. By driving a reversible counter with these signals F and G, position information of the controlled object is detected. The above detection system is widely used today because of its advantages in terms of technical ease and economy, etc.
There is a drawback that when the power is once turned off and then turned on again and restarted according to the position information at the time of the previous power cut, an error occurs in the information. That is, in the time chart of FIG. 1, if the power is turned off at point A of signal A, there is a possibility that point I will shift due to mechanical changes and/or characteristics of the encoder when the power is turned on again. When this state occurs and the point low is detected when the power is turned on again, the count up pulse x becomes uncounted as is clear from the figure, causing an error of (-)1 pulse in the position information. On the other hand, if it is point RO when the power is turned off and it is YES when it is turned on again, (+)
It is clear that this results in an error of one pulse.
Further, the same can be said about points C and D for the countdown pulse y. Because of these drawbacks, systems using incremental encoders have had the trouble of always having to return to the origin when starting the machine. This kind of hassle can be solved by using absolute
This problem can be solved by using an encoder (scale for detecting absolute values), but absolute encoders not only increase the cost of the system but also have drawbacks such as being unsuitable for long-distance detection. Therefore, the present invention aims to improve the above-mentioned drawbacks of the conventional technology.The purpose of the present invention is to automatically correct the error in position information when the power is turned off and then turned on again by using an incremental encoder that has been widely used in the past. The object of the present invention is to provide a positioning control system capable of correcting. In order to achieve the above object, the present invention generally compares the two-phase output level state of the pulse encoder when the power is turned off and the two-phase output level state of the pulse encoder when the power is turned on again. In this case, the error is automatically corrected by determining the presence or absence of a count pulse within the time span between when the power is turned off and when it is turned on again, and increasing or decreasing the count pulse by 1. . Embodiments of the present invention will be described below with reference to the drawings. FIG. 2 is a block diagram showing an embodiment of the present invention, which includes a position detection means for electrically detecting the position of a machine to be controlled, such as a table or a tool, a microcomputer system for managing the position information, It has a detection circuit that supplies information on machine power-off to the computer system. The position detection means includes an incremental encoder 10, a waveform shaping circuit 12, a direction discrimination circuit 14, and a counter 16. As described above, the encoder 10 extracts mechanical position information as electrical signals A and B having a phase difference of π/2, and supplies the electrical signals A and B to the waveform shaping circuit 12. The circuit 12 removes high frequency components, shapes the waveforms, and converts the signals A and B to internal logic levels. The output of the waveform shaping circuit 12 is used in the direction discrimination circuit 14 to generate a count-up pulse F and a count-down pulse G according to the signal processing process described in connection with FIG.
This drives the counter 16. The microcomputer system has 20 CPUs,
It has a program memory 22, a data memory 23, first and second input ports 24, 26, and an output port 28, which are connected to the CPU via an internal bus,
The waveform shaping circuit 12 via the first input port 24
and a second input port 2
6 to the output of counter 16 and further via output port 28 to mechanical actuator 40.
It is now possible to provide processing information to Reference numeral 30 denotes a power-off detection circuit which not only provides power-off information to the CPU 20 but also drives the power backup circuit 32 to prevent data in the data memory 23 from volatilizing. In the above configuration, if power is supplied,
Since the position information of the controlled object is taken in from the counter 16 to the CPU 20 via the second input port 26, the current position can be known. When a power cutoff occurs in this state, the CPU 20 learns of the power cutoff from the power cutoff detection circuit 30, and the first input port 2
4 is opened to take in the level state of the two-phase outputs A and B of the encoder at the time of power cut-off, and at the same time, position information at the same time is introduced from the second port 26, and these are stored in the data memory 23. This data is held by the power backup circuit 32 during power cut-off. When the power is turned on again, the level states of the two-phase outputs A' and B' of the encoder 10 at the time of the power-on again are taken in through the first input port 24, and the two-phase outputs at the time of power-off are stored in the memory 23. The comparison with the level states of A and B is
This is performed by a comparison means provided in the CPU 20. Figure 3 shows the level state between the encoder's two-phase outputs A and B. If the power is cut off at point a, the level states of signals A and B at the time of power cut are "0" and "0". It is. Signal when power is turned on again
There is no problem if the level states of A' and B' match. However, when restarting, the two-phase output of point b
If A' and B' are given, the level states are different between a when the power is turned off and b when it is turned on again, and if count pulses F and G exist in the time width limited by these points a and b, then As mentioned above, errors occur. Therefore, if there is a level difference between the two-phase outputs A, B and A', B' when the power is turned off and then turned on again, the count pulse will be generated within the time width of the encoder output limited at both times. whether it exists or not
When a count pulse is detected by the discrimination means provided in the CPU 20, the CPU 20 corrects the count error with respect to the count pulse.
This is given by the correction means provided in the. The need to correct the count pulses due to the difference in level between when the power is turned off and when it is turned on again is as shown in the table shown in relation to FIG. 3.

[Table] In other words, if signals A and B at the time of shutoff are at levels 1 and 0, and A' and B' at the time of restart are 0 and 0, the count pulse in question will be double counted, so -1
A pulse correction is given, and if the signals A and B at the time of cut-off are 0 and 0, and they are 1 and 0 at the time of reinsertion, the count pulse in question has become a no-count, so a +1 pulse correction is given. Although the control device described above is limited to cases where the error is within 1/4 cycle, there is no problem with the usefulness of the present invention since the machine is generally braked when the power is cut off. In the above embodiment, the case where one count is counted for each period of the output pulse of the encoder has been described, but it can be applied to cases where counting is performed more than this, and it can also be applied to resolvers. It is. As explained above, according to the present invention, when the power is turned on again, errors in count pulses are automatically corrected based on the level state of the two-phase output of the encoder when the power was previously cut off and the level state when the power was turned on again. Therefore, although an incremental encoder is used, there is no need to perform a return to the origin, and therefore not only the operability is improved, but also an economically inexpensive control device can be provided.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram of position detection using an incremental encoder, Fig. 2 is an embodiment of the present invention,
FIG. 3 is an explanatory diagram of error correction. 10... Incremental encoder, 12
... Waveform shaping circuit, 14 ... Direction discrimination circuit, 16
...Counter, 20...CPU, 22, 23...
Memory, 24, 26, 28... Port, 30...
Power failure detection circuit, 32...Power backup circuit.

Claims (1)

[Claims] 1. In a positioning control device for a machine tool that has an incremental pulse encoder and detects position information of a position control target of the machine tool by controlling the contents of a counter to increase or decrease in accordance with count pulses based on the two-phase output of the encoder. ; storage means for storing the two-phase output level state of the encoder and position information of the position control target when the power is turned off; and the stored two-phase output level state and the output level state of the encoder when the power is turned on again. and a determining means for determining the presence or absence of a count pulse within the time width between when the power is cut off and when the power is turned on again, in the case of a discrepancy in the comparison by the comparison means; A positioning control device for a machine tool, comprising: a correction means for automatically correcting an error in position information when the power is turned on again compared to when the power is turned off by increasing or decreasing the contents of the counter by one count pulse. .