JP2004279188A - Absolute position detector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To make precisely detectable the absolute position, even when the accumulated number of revolutions of a motor exceeds the maximum count number of a multi-revolution counter. <P>SOLUTION: The remainder (M) of dividing the maximum count of the multi-revolution counter by the number of revolutions of the motor per one rotation of a mobile body is calculated. A correction count value is updated by adding/subtracting the remainder (M) to/from the initial value of the correction count value every time when the count number of the multi-revolution counter returns from the maximum number minus one to zero. When the count number of the multi-revolution counter returns from the maximum count number to zero, the correction count value is made as the initial value of the count number, and the absolute coordinates of the rotational position of the mobile body are calculated from the count number of a single-counter and the count number of the multi-counter after the correction. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an absolute position detecting device that detects a position of a moving body such as a table of a machine tool.
[0002]
[Prior art]
In a machine tool, methods for detecting the position of a moving body include an absolute position detection that detects an absolute position and an increment position detection that accumulates an increment from a reference point and detects a relative position. .
[0003]
In the case of a rotary table such as a rotary table of a machine tool, which can be rotated endlessly in forward and reverse directions, it is difficult to detect the position of the table depending on the increment method. Therefore, in recent years, an absolute position detection method has been adopted.
[0004]
In the absolute position detection method, a single counter that counts pulses during one rotation of the rotating shaft of the motor is provided as a counter that counts pulses output from a position detector provided in a motor that rotates the table, and a rotation of the motor. It is combined with a multi-rotation counter that accumulates and counts the number of shaft rotations.
[0005]
For example, the number of rotations of the motor for one rotation of the table is 360, the number of pulses counted by the single counter during one rotation of the rotation axis of the motor is 1000, and the number of pulses of the multi-rotation counter when the table stops is 1000. Assuming that the count number is 14000 and the count number of the single counter is 500,
14000 = 360 × 39 + 100
Therefore, the position of the table can be detected by multiplying (100 × 1000 + 500) by the rotation angle per count of the single counter.
[0006]
The multi-rotation counter has an upper limit rather than being able to count the number of rotations of the motor without limit, and the maximum number of rotations of the multi-rotation counter is a multiple of the number of rotations of the motor required for one rotation of the table (for example, in the above example, (14400 counts), the absolute position of the table can be obtained without any problem even if the multi-rotation counter counts 14399 and returns to 0.
[0007]
The number of rotations of the motor for one rotation of the table is mainly determined by the reduction ratio in design, but it is not always the case that the maximum count of the multi-rotation counter is divisible by the count of one rotation of the table.
[0008]
In such a case, for example, considering an example in which the number of rotations of the motor for one rotation of the table is 230 rotations (the maximum number of rotations of the multi-rotation counter is 14400), If the count of is 10,000,
10,000 = 230 × 43 + 110
Therefore, at this time, the remaining count number 110 corresponds to the position of the table. In other words, until the count of the multi-turn counter crosses the maximum count and returns to 0, the count of the remainder of the count of the multi-turn counter divided by 230 and the count of the single counter at that time are used. The absolute position of the table can be detected.
[0009]
[Problems to be solved by the invention]
However, after the table turns further and crosses over the maximum count number -1 of the multi-turn counter and returns to 0, the situation is different and the absolute position of the table cannot be determined.
[0010]
In the case of the above example, since the count number of the multi-rotation counter at the time when the table goes around the 62nd lap is 14260 counts, when the motor further rotates and counts 140 times, it reaches the maximum count number -1 of 14399. , And returns to 1, 2,... Again. However, when the count value of the multi-turn counter crosses zero, the count value of the multi-turn counter should be 140, which is the remainder after being divided by 230. The actual position will be shifted by 140 counts. Then, when the multi-revolution counter crosses 0 next, a shift of 140 counts is further added. For example, if the rotary table is continuously rotated in one direction, the current absolute position of the table and the NC device are not changed. The position that is recognized does not match at all.
[0011]
Therefore, an object of the present invention is to solve the above-mentioned problem of the related art, and to accurately detect an absolute position even if the cumulative number of rotations of a motor exceeds the maximum count of a multi-rotation counter. An object of the present invention is to provide an absolute position detecting device.
[0012]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides a pulse generator which is connected to a rotating shaft of a motor driving a moving body and outputs a pulse corresponding to a rotation angle of the rotating shaft, wherein the rotating shaft of the motor is First counter means for counting the number of output pulses of the pulse generator during rotation; and cumulatively counting the number of rotations of the rotating shaft of the motor based on the output pulses of the pulse generator to the maximum count number-1. A rotary absolute position detecting device having a second counting means for counting up to (M), wherein the maximum counting number of the second counting means is divided by a motor rotation number per rotation of the moving body (M). Is calculated, and each time the count number of the second counting means returns from the maximum count number −1 to 0, the remainder (M) is increased or decreased from the initial value of the correction count value, and the correction count value is updated. Means for making the count value for correction the initial value of the count number when the count number of the second count means returns to 0 from the maximum count number -1; and the first counter means Calculating means for calculating absolute coordinates of the rotational position of the moving body from the counted number of the moving object and the corrected count number of the second counting means.
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment of an absolute position detecting device according to the present invention will be described with reference to the accompanying drawings.
[0014]
FIG. 1 shows a rotary table to which an absolute position detecting device according to the present invention is applied. The rotary table 10 includes a table base 11 and a table 12. On the upper surface of the bed 13, guide rails 14a and 14b for guiding the linear movement of the table base 11 are laid.
[0015]
Reference numeral 15 indicates a servomotor that drives the rotation of the table 12. The servo motor 15 rotates the worm 16 and transmits a driving torque to the table 12 via a ring gear 17 meshing with the worm 16. The table 12 can be continuously rotated in both forward and reverse directions, and the direction of rotation can be changed in the middle.
[0016]
Next, FIG. 2 is a configuration block diagram of the absolute position detection device according to the present embodiment.
Reference numeral 18 is an absolute encoder used as a position detector. The absolute encoder 18 includes a pulse generator 19 and a counter circuit including a single counter 20 and a multi-turn counter 21.
[0017]
The pulse generator 19 is directly connected to the rotation axis of the servomotor 15, and generates a pulse every time the rotation axis rotates 1/1000 °, and generates a pulse every time the rotation axis rotates once. . The former pulse is introduced into the single counter 20 and counted. The latter pulse is introduced into the multi-turn counter 21 and counted. The multi-rotation counter 21 can count the pulses generated for each rotation of the rotation shaft and cumulatively count the rotation number of the rotation shaft from the maximum count number −1, for example, from 0 to 14399. ing.
[0018]
The single counter 20 and the multi-turn counter 21 are connected to an NC device 22, and the count data is introduced into a calculation device 23 of the NC device 22, and the calculation device 23 calculates the absolute coordinates of the table 12 according to a flowchart of FIG. I do. The NC device 22 has a backup memory 25 that retains data even when the power supply becomes 0ff, in addition to a storage device 24 that reads and writes data during normal processing. A display device 26 displays the calculated absolute coordinates and the like in real time.
[0019]
Next, the contents of the processing for calculating the absolute coordinates of the table 12 will be described with reference to the flowcharts of FIGS.
[0020]
First, FIG. 3 is a flowchart showing the contents of an initialization process to be performed together with the position adjustment for establishing the origin before the operation of the rotary table 10 is started.
[0021]
In the case of the rotary table 10 of this embodiment, the number of rotations of the servo motor 15 required to make one rotation of the table 12 is S, and the maximum value of the count of the multi-rotation counter 21 is Rmax. It is assumed that the maximum value Rmax of the count number is a value that is not divisible by the rotation speed S. In such a case, as described in the section of the prior art, each time the multi-rotation counter 21 repeats returning to 0 after counting the maximum value as it is, a deviation occurs in the count value, and the actual position of the table is changed. become unable to know. Therefore, a variable called Multioff is newly set as a count value for correction.
[0022]
First, in the first step S10, the maximum count number Rmax of the multi-rotation counter 21 is divided by the rotation number S, and the remainder M is obtained. The value of the remainder M is stored in the backup memory 25 so as not to be lost even when the power of the NC device 22 is turned off (step S11). Next, the initial value of Multioff is set to 0 (step S12). The Multioff data is also stored in the backup memory 25 (step S13).
[0023]
Next, FIG. 4 is a flowchart showing a flow of a process of calculating absolute coordinates of a rotating table in the rotary table 10 in which the positioning of the table 12 and the initialization process of FIG. 3 have been completed.
First, when the servo motor 15 is started (Step S20), Multioff and OldRct are read from the backup memory 25 (Step S21). The value of Multioff is initially an initial value 0. Here, OldRct is the count number of the multi-rotation counter 21 when the table 12 stopped last time. Thereafter, while the table 12 rotates, the single counter 20 counts the number of pulses proportional to the rotation angle of the rotation axis of the servo motor 15, outputs the count number signal to the NC device 22, and the arithmetic device 23 The count number of the counter 20 can be detected (step S22). Here, the current count number of the single counter 20 is Ct. Similarly, the multi-rotation counter 21 counts a pulse generated each time the number of rotations of the servo motor 15 makes one rotation, and outputs a count number signal to the NC device 22. Can be detected (step S23). Here, the current count number of the multi-turn counter 21 is Rct.
[0024]
Next, in step S24, Rct-OldRct is set in the register A. Then, no matter how fast the servomotor 15 rotates, the change in the count of the multi-rotation counter 21 in a short time does not exceed 1/4 of the maximum count Rmax. Rmax−Rmax / 4 is compared (step S25). If the absolute value of A is larger, it is determined that the count number of the multi-rotation counter 21 has crossed zero, and the process proceeds to steps S31 and S32 for updating the correction count value Multioff. At this time, the change in the count number, that is, the value of the register A is small, so that the process proceeds to step S26.
[0025]
In this step S26, since Multioff is 0, the count number Rct is set in the register B. Then, in step S27, the absolute coordinates of the table 12 are obtained by the following formula.
[0026]
Absolute coordinate = ｛(B * C + Ct) * θ + α｝ ÷ Remainder of 360 ... (1)
here,
C: count number of the single counter per rotation of the rotating shaft θ: moving amount of the single counter 20 per count [°]
α: Offset amount at position setting [°]
In the following step S28, the current count number Rct is set as the value of OldRct, and while the table 12 is not stopped, the process returns from the determination in step S29 to step S22, and the above processing is repeated to detect the absolute position of the table 12. Is done.
Here, FIG. 5 is a diagram schematically showing a change in the count number Rct by the multi-rotation counter 21 while the table 12 rotates. The horizontal axis indicates the cumulative number of rotations of the table 12, and the vertical axis indicates the count Rct. In FIG. 5, the solid line shows the case where the count number is corrected, and the two-dot chain line shows the case where the count number is not corrected. When the correction is not performed, the count value is cumulatively shifted by the remainder M every time the count number Rct of the multi-rotation counter 21 crosses zero.
[0027]
On the other hand, in the present embodiment, correction is performed as follows in order to prevent deviation of the count value.
The multi-turn counter 21 does not reach the maximum count number Rmax-1 and does not return to 0 until the table 12 turns to the n1 +1 time. Therefore, by repeating the above-described steps S22 to S29, the absolute coordinates of the table 12 are obtained. Can be obtained without any problem.
[0028]
However, if the count number Rct of the multi-rotation counter 21 reaches Rmax-1 while the table 12 is turning n1 times and the rotation is performed one more time, the count 12 returns to 0, and at this time, the value of Rmax-the previous count number OldRct is calculated. Since the absolute value of the difference is larger than Rmax−Rmax / 4, it can be determined that the count Rct crosses zero (yes in step S25). Then, the count value is corrected using the correction count value Multioff as follows.
[0029]
That is, it is determined whether the count Rct is increasing or not based on the sign of the register A (step S31). If the count is increasing, the multi-turn counter is set to the value of the correction count value Multioff which had been the initial value 0 until then. A remainder M obtained by dividing the maximum count Rmax of 21 by the number of revolutions S is set (step S32).
[0030]
Next, the value of the register B is set to a value obtained by adding the correction count value Multioff to the count number Rct of the multi-rotation counter 21 (step S26). Thus, the register B increases by M, 2M, 3M, and M each time it crosses 0. In this way, the count value reflecting the actual position of the table 12 is corrected immediately after crossing 0, so that the absolute coordinates of the table 12 are calculated without error by calculating the expression (1) in step S27. Can be calculated.
[0031]
Similarly, as shown in FIG. 5, when the table 12 is further rotated and reaches the n2 times and the count value of the multi-turn counter 21 crosses 0, M is further added to the correction count value Multioff. Then, the count is updated to 2M, and the count is corrected to start from 2M, so that there is no error in the count number.
[0032]
On the other hand, when the table 12 rotates in the reverse direction, the count Rct is in the direction of decreasing in step S31. In this case, when the count of the multi-rotation counter 21 crosses 0 while decreasing, the count is updated to the value obtained by subtracting M from the value of Multioff in step S33, so that no error occurs in the apparent count number. ing.
[0033]
When the table 12 is stopped, the data of the correction count values Multioff and OldRct are stored in the backup memory 25 in step S28, so that they are not lost even if the power is turned off. When activated, the data of Multioff and OldRct previously stored will be read. In this way, even if the maximum count Rmax of the multi-rotation counter 21 is not divisible by the number of revolutions S of the servo motor required to make one round of the table 12, no matter how many times the table 12 rotates, In addition, the ablute coordinates can be accurately calculated regardless of the direction of rotation.
[0034]
Also, even if the table 12 is slightly rotated manually or the like from the position where it was stopped last time while the power is turned off, the data of the previous OldRct is backed up, and the count value of the multi-rotation counter 21 crosses zero. Since the determination as to whether or not to perform the determination is made by comparing the change in the count number with Rmax-Rmax / 4, as in step 25, the absolute coordinates can be correctly calculated without being affected by the movement during power-off. .
[0035]
As described above, the present invention has been described with reference to the embodiment applied to the rotary table. However, the present invention is not limited to this, and the upper limit of the multi-rotation count is set so that the moving distance crosses zero. The same applies to large linear axes.
[0036]
【The invention's effect】
As is apparent from the above description, according to the present invention, even if the maximum count of the multi-rotation counter is not divisible by the number of rotations of the motor necessary for the rotating moving body to make one revolution, the table 12 is No matter how many rotations are made, the absolute coordinates can be calculated accurately.
[Brief description of the drawings]
FIG. 1 is a perspective view showing a rotary table to which an absolute position detecting device according to the present invention is applied.
FIG. 2 is a block diagram of an absolute position detecting device according to an embodiment of the present invention.
FIG. 3 is a flowchart showing initial setting processing that is also performed at the time of positioning performed to establish an origin.
FIG. 4 is a flowchart showing the flow of a process for calculating absolute coordinates according to an embodiment of the present invention.
FIG. 5 is a diagram schematically showing a change in a count Rct by a multi-rotation counter 21.
[Explanation of symbols]
Reference Signs List 10 rotary table 11 table base 12 table 13 bed 15 servo motor 16 worm 17 ring gear 18 absolute encoder 22 NC device

Claims (2)

A pulse generator that is connected to a rotation axis of a motor that drives a moving body and that outputs a pulse corresponding to the rotation angle of the rotation axis; and the number of output pulses of the pulse generator during one rotation of the rotation axis of the motor. A rotary type having first counter means for counting and second counting means for cumulatively counting the number of rotations of the rotating shaft of the motor to the maximum count number -1 based on output pulses of the pulse generator; An absolute position detection device,
A remainder (M) is calculated by dividing the maximum count number of the second counting means by the number of motor revolutions per rotation of the moving body, and the count number of the second counting means is increased from the maximum count number -1 to 0. Means for updating the correction count value by increasing or decreasing the remainder (M) from the initial value of the correction count value each time the process returns to
Correction means for setting the correction count value to an initial value of the count number when the count number of the second count means returns from the maximum count number -1 to 0;
Calculating means for calculating absolute coordinates of the rotational position of the moving body from the count number of the first counter means and the corrected count number of the second count means;
An absolute position detecting device comprising: The absolute position detecting device according to claim 1, further comprising a backup storage device that stores the correction count value and retains data even when power is turned off.

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