JPH0528841B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a positioning control device equipped with a Z-phase incremental encoder as a position measuring device. [Prior Art] Generally, in a positioning servo system that measures position using an incremental encoder, the position when the power is turned on is not known, so it is necessary to perform an origin search. At this time, if highly accurate positioning is required, an origin detection switch and a Z-phase encoder are used, and the origin of the servo system is searched by the signal from the origin detection switch and the Z-phase pulse of the encoder. FIG. 5 shows an example of a conventional connection circuit interposed between the encoder 1 and origin detection switch 2 and a controller (not shown) used for such an origin search. This circuit is a photocoupler PC used to electrically isolate the encoder and origin detection switch side from the controller side.
1 to PC4 and each photocoupler's light emitting element LED1
~ Consists of resistors R1 to R4 connected to LED4 and resistors R5 to R8 connected to light receiving elements LRD1 to LRD4 of each photocoupler, and light emitting elements LED1 to LED4 and light receiving element of each photocoupler.
A predetermined voltage (for example, +5V) is applied to LRD1 to LRD4 via resistors R1 to R8 connected to each element. The encoder 1 and origin detection switch 2 are connected to the light emitting element of each photocoupler in this connection circuit, while the controller is connected to the light receiving element of each photocoupler. The encoder described above outputs a plurality of encoded pulse signals called A-phase, B-phase and Z-phase, and each output is transmitted to the controller side via photocouplers PC1 to PC3 of the connection circuit shown in FIG. Here, the A phase and B phase of the encoder are used as pulses for position measurement, and the Z phase generates one pulse for each rotation of the encoder. In addition, the origin detection switch is installed so that the ON/OFF state changes near the origin of the servo system, and its output is output from the photocoupler PC.
4 to the controller side. When searching for the origin, the origin detection switch is usually turned ON (or OFF) as shown by the broken line a in Figure 7.
The position of the Z-phase pulse detected immediately after P ₀
is the origin. Origin detection switch is ON from the beginning
In this case, as shown by broken line b, by moving until it turns OFF and then returning to the ON state,
Detect Z-phase pulse. FIG. 6 is a flowchart showing a conventional origin search procedure. First, the state of the origin detection switch is checked at fixed time intervals (same as the normal servo cycle), and the target position Xd is increased or decreased depending on the state.
In other words, if the switch is ON, the target position
is increased by ΔX ₁ , and if the switch is OFF, the target position Xd is decreased by ΔX ₁ . Thereafter, it is checked whether or not a Z-phase pulse has been detected. If not, the target position Xd is decreased by _ΔX2 , and when a Z-phase pulse is detected, the position counter is reset and the origin search is completed. When detecting the last Z-phase pulse, the increment amount ΔX ₂ is made smaller than the first increment amount ΔX ₁ in order to reduce the origin error. If it is desired to suppress the error within the range of ±1 pulse, the increment amount ΔX ₂ per cycle is set to 1 pulse. [Problems to be Solved by the Invention] However, in such a conventional method, since the relationship between the state change of the origin detection switch and the Z-phase pulse is unknown, the final Z-phase pulse detection is performed at a very low speed. I have no choice but to. Therefore, as shown in Figure 7, the Z-phase pulse is detected after the origin detection switch is turned ON (the origin search is completed).
It took a long time. For example, if the number of Z-phase pulses generated per encoder rotation is 4000,
When increasing or decreasing the target position by checking the state of the home detection switch every 5 msec, assuming that the increment amount per time is 1 pulse, it will take up to 20 seconds from the time the home detection switch is turned on until the Z-phase pulse is detected. There was a problem that it took a long time to get there. The present invention has been made in view of such problems, and an object of the present invention is to shorten the time required for origin search in a positioning control device as described above. [Means for solving the problem] As shown in FIG.
Equipped with a Z-phase incremental encoder 1 that generates a phase pulse signal, and an origin detection switch 2 installed so that the state changes near the origin,
In a servo system positioning control device, when the state of the origin detection switch 2 changes, holding means 3 holds the state before the change until an edge of the Z-phase pulse signal output from the encoder 1 is detected, and the servo The system is moved at high speed from the position when the holding means 3 changes from the predetermined first state to the second state to a position near the origin determined by the interval between two adjacent edges of the Z-phase pulse signal. from this position near the origin, the holding means 3
It is characterized by comprising a control means 4 which outputs a signal for displacing at a low speed to the origin position detected by changing from the second state to the first state. [Operation] In the present invention, when the state of the origin detection switch changes, the holding means holds the state before the change. The state of this holding means changes when the edge of the Z-phase pulse signal is detected after the state of the origin detection switch changes. Here, the origin is detected by the position of the edge of the Z-phase pulse signal when the holding means changes from a predetermined second state to a first state (for example, from OFF to ON). On the other hand, since the interval between the edges of the Z-phase pulse signal corresponds to one rotation of the encoder, the edge of the Z-phase pulse signal is detected after the state of the origin detection switch changes, and the holding means From the first state to the second state (for example, from ON to
OFF), the distance from the edge position to the origin corresponds to the interval between the edges of the Z-phase pulse signal and is known. Therefore, the origin is a position that is a known distance away from the edge position when the holding means changes from the first state to the second state, but in reality there is an error, and it is a position near the origin. be. Therefore, the control means causes the servo system to displace at high speed from the position when the holding means changes from the first state to the second state to the position determined by the interval between the edges of the Z-phase pulse signal. By this,
Precisely detecting the origin by quickly detecting a position near the origin and changing the position at a low speed from the position near the origin to the origin position detected when the holding means changes from the second state to the first state. I can do it. [Embodiment] FIG. 2 shows an example of a connection circuit interposed between the encoder 1, origin detection switch 2, and control means 4 as an embodiment of the present invention shown in FIG. This connection circuit consists of photocouplers PC1 to PC4.
and the light emitting elements LED1 to LED4 of each photocoupler
and resistors R5 to R8 connected to the light receiving elements LRD1 to LRD4 of each photocoupler. Then, the light receiving elements LED1 to LED4 and the light receiving element LRD1 of each photocoupler
~LRD4, resistor R1 connected to each element
~A predetermined voltage (for example, +5V) is applied via R8, an encoder and an origin detection switch are connected to the light emitting element side of each photo coupler, and a controller is connected to the light receiving element side of each photo coupler. This is the same as the conventional example shown in the figure. However, in this circuit, the output side of the photocoupler PC3, which transmits the Z-phase output of the encoder 1,
In other words, the output terminal of the light receiving element LRD3 is NAND
connected to one of the two input terminals of gate Q1,
This gate output section is connected to the DQ flip-flop Q2.
is connected to the CK terminal of In addition, the output side of the photocoupler PC4 that transmits the output of the origin detection switch 2, that is, the output terminal of the light receiving element LRD4,
Connected to the D terminal of the DQ flip-flop Q2. PR terminal of DQ flip-flop Q2 and
A constant voltage Vcc is applied to the CLR terminal. Furthermore, since the state of the DQ flip-flop Q2 is undefined when the power is turned on, the initial state of the DQ flip-flop Q2 is determined by applying a pulse from the control means 4 to the other of the two input terminals of the NAND gate Q1. ing. The above NAND gate Q1 and DQ flip-flop Q
2 constitutes the holding means 3 shown in FIG. Therefore, when the Z-phase pulse from encoder 1 is applied to one of the input terminals of NAND gate Q1 via photocoupler PC3, NAND gate Q1
A pulse output from the DQ flip-flop Q2 is applied to the CK terminal of the DQ flip-flop Q2. On the other hand, a signal indicating the state of the origin detection switch 2 is applied to the D terminal of the DQ flip-flop Q2. Therefore, the Q terminal of DQ flip-flop Q2 has
The state of the origin detection switch (ORG1) held at the edge of the CK input, that is, the Z-phase pulse, is output. That is, as shown in FIG. 4, when the state of the origin detection switch 2 changes between one Z-phase pulse Z ₁ and the next Z-phase pulse Z ₂ , the state change is as follows.
When the next Z-phase pulse _Z2 is input, it appears as the Q output of the DQ flip-flop Q2. Furthermore, as shown in Figure 4, the position where the state of ORG1 changes is when moving in the + direction (indicated by a broken line)
and when moving in the - direction (shown by the solid line),
The encoder shifts by one rotation (interval between Z-phase pulses). The present invention utilizes this fact to speed up the origin search. FIG. 3 is a flowchart showing the origin search procedure by the control means 4. The control means 4 is composed of, for example, a microcomputer. First, to explain the outline of the procedure, the signal (ORG1) indicating the state of the origin detection switch is checked every fixed period (same as the normal servo period), and the target position is updated according to the state. And ORG1
The position when changes from OFF to ON (Fig. 4)
P ₀ ) is the origin. At this time, if the increment amount for each fixed period is increased, the origin search time will be shortened, but the error will become larger. On the other hand, if the increment amount is reduced in order to reduce the error, the origin search time becomes longer. Therefore, first search at high speed for the point where ORG1 changes from ON to OFF (P in Figure 4), then move at high speed to the vicinity of the point where ORG1 changes from OFF to ON (origin P ₀ ), and then Search precisely. To explain according to Figure 3, first, ORG1 is
If it is 0FF, move the target position Xd at high speed (increment amount ΔX ₁ )
Subtract with . When ORG1 turns ON or if it is ON from the beginning, the target position Xd is added at high speed (increment amount ΔX ₁ ) until ORG1 turns OFF. As a result, the current position is approximately the point P in FIG. 4, and the distance from this point to the origin P ₀ is one revolution of the encoder, as described above, and is known. however,
It contains errors because it moved at high speed to the current position. The amount of error is a maximum of one increment amount ΔX ₁ .
Therefore, the search time is shortened by moving from the current position to the vicinity of the origin P ₀ at high speed, and the final origin search is performed with approximately the amount of error remaining. Therefore, in the procedure shown in FIG. 3, the number of times N to move at high speed to the vicinity of the origin as described above is determined as follows. N=(A-ΔX ₁ )÷ΔX ₁ A is the amount of movement for one rotation of the encoder (number of pulses) Set this number of high-speed movements N to counter C (C
←N), the above high-speed movement, that is, the operation of subtracting the target position Xd at high speed (increment amount ΔX ₁ ) (Xd←Xd−
Each time ΔX ₁ ) is performed, the counter value C is decremented by 1, and when (C←C−1) and C=0, ORG1 is checked. As a result, if ORG1 is OFF, the target position Xd is subtracted at low speed (increment amount ΔX ₂ ),
When ORG1 turns ON, the position counter is reset and the origin search is completed. According to this search procedure, for example, if the number A of Z-phase pulses generated per encoder rotation is 4000,
When checking the state of the origin detection switch every 5 msec, if the first increment ΔX ₁ is 30 pulses and the last increment ΔX ₂ is 1 pulse, then N = (4000-30) ÷ 30 ≒ 132 (times) Low speed Number of movements = 4000 - 30 x 132 = 40 (times) Therefore, the time T from when ORG1 changes from ON to OFF until the origin search is completed is T = 0.005 x (132 + 40) = 0.86 (seconds). , much shorter than the conventional time (about 20 seconds). This is also clear from the comparison between FIG. 4 and FIG. 7. The embodiments of the present invention have been described above, but the constituent elements of the present invention, particularly the holding means interposed between the encoder and origin detection switch and the control means, are as follows:
Not limited to the circuit shown in FIG. 2, any circuit can be used as long as it has a similar function. [Effects of the Invention] As described above, the positioning control device of the present invention has the following effects:
When the state of the origin detection switch changes, the holding means holds the state before the change until the edge of the Z-phase pulse signal output from the encoder is detected, and the holding means holds a predetermined state for the servo system. The holding means moves at high speed from the position when the first state changes to the second state to a position near the origin determined by the interval between two adjacent edges of the Z-phase pulse signal, and from this position near the origin, the holding means 2
Since the device is equipped with a control means that outputs a displacement signal for displacing at a low speed to the origin position where the state changes from the state to the first state, when searching for the origin, the displacement is performed at high speed to a position near the origin in accordance with the change in the state of the holding means. This has the effect of greatly shortening the time required to search for the origin, and ultimately enabling accurate detection of the origin.

[Brief explanation of the drawing]

Fig. 1 is a configuration diagram of the present invention, Fig. 2 is a diagram showing a connection circuit of an embodiment, Fig. 3 is a flow chart showing the origin search procedure of the embodiment, and Fig. 4 is a diagram showing the position of the origin search according to the embodiment. Fig. 5 is a diagram showing the connection circuit of the conventional example, Fig. 6 is a flowchart showing the origin search procedure of the conventional example, and Fig. 7 is the relationship between the position and time of the origin search according to the conventional example. FIG. 1...Origin detection switch, 2...Encoder,
3... Holding means, 4... Control means, PC1 to PC4
...Photocoupler, R1 to R8...Resistor, Q1
...NAND gate, Q2...DQ flip-flop.

Claims (1)

[Claims] 1. Positioning of a servo system equipped with a Z-phase incremental encoder that generates a Z-phase pulse signal every rotation, and an origin detection switch installed so that the state changes near the origin. In the control device, when the state of the origin detection switch changes,
The state before the change is maintained until the edge of the Z-phase pulse signal output from the encoder is detected.
and a holding means for holding the servo system, from the position when the holding means changes from the predetermined first state to the second state, depending on the interval between two adjacent edges of the Z-phase pulse signal. Control for outputting a signal for displacing at high speed to a determined position near the origin and displacing at low speed from the position near the origin to an origin position detected when the holding means changes from the second state to the first state. A positioning control device comprising: means.