JPH0667240B2 - Speed controller for digital servo system with pulse encoder - Google Patents

Description

The present invention relates to a speed control device for a digital servo system having a pulse encoder, and more particularly to a digital control device having a pulse encoder for calculating and controlling the speed from output pulses of the pulse encoder. The present invention relates to a speed control device for a servo system.

[Conventional technology]

Conventionally, a speed control device for a servo motor is, for example, a numerical control device (CNC) that controls a machine tool by a computer.
It is used to control the movement of the tool of the device system (relative movement of the tool with respect to the work fixed to the table) and the movement of the hand of the industrial robot. Then, the conventional speed control device is configured to, for example, attach a tacho generator to a servo motor, measure the output voltage of the tacho generator, and detect and control the speed. This tachogenerator can generate an output voltage proportional to the rotation speed of the motor, and in particular, even if the motor is rotating at a very low speed, it can generate an output voltage proportional to the rotation speed. A conventional speed control device using a tacho generator can perform accurate and stable speed control even when the motor is rotating at a very low speed.

Conventionally, as a motor used for a CNC system, an industrial robot, or the like, for example, a brushless AC servomotor which is advantageous in terms of maintenance has been used. However, attaching a tacho-generator to such a brushless AC servomotor reduces the maintenance advantage and is also disadvantageous in terms of cost. In addition, in order to maintain the maintenance advantage of the brassless AC servo motor,
It is possible to install a brushless tachogenerator as a tachogenerator on the motor.
Using a tachogenerator would be more expensive.

By the way, a pulse encoder is attached to the servo motor used for the CNC system and industrial robots, etc., and the position and movement distance of the CNC system tool and robot hand controlled by the servo motor from the output pulse of this pulse encoder. Is calculated and controlled. As a speed control device for a conventional digital servo system having a pulse encoder, a speed control device that uses the output of a pulse encoder attached to a servomotor is generally used.

[Problems to be solved by the invention]

As described above, the conventional speed control device that uses the output pulse of the pulse encoder attached to the servo motor has an advantage that it is advantageous in terms of maintenance and is low in cost. However, since such a conventional speed control device only sequentially counts the output pulses from the pulse encoder for every constant speed control sampling period, as described in detail below, particularly when the servo motor is operated at a low speed. When rotating, that is, when the tools of the CNC system or the hands of the industrial robot are moving at a very low speed, accurate and stable speed control cannot be performed.

FIG. 6 is a diagram for explaining the problems of the conventional speed control device.

For example, as shown in FIG. 6 (a), even if the interval between the pulses detected by the pulse encoder attached to the servo motor is slightly longer than the speed control sampling period, the section II in FIG. The number of pulses counted at is zero. On the contrary, as shown in FIG. 6 (b), even if the pulse interval detected by the pulse encoder is slightly shorter than the speed control sampling period, the pulses counted in the section II in FIG. The number is 2. Further, even if the pulse interval output from the pulse encoder is constant, that is, the rotation speed of the servo motor is constant, as shown in FIG.
The number of pulses counted in I, III, IV, VI, VII, is zero, interval
The number of pulses counted in II, V, and VIII is 1. As described above, in the speed control device of the digital servo system having the conventional pulse encoder, the speed overestimation or the speed underestimation for a maximum of one pulse may be performed in each section in principle. Such one pulse error is counted in the speed control sampling cycle when the servo motor is rotating at high speed, that is, when the tool of the CNC system or the hand of the industrial robot is moving at high speed. Since the number of pulses is large, there is no problem. However, when the servo motor is rotating at a low speed, that is, when the tool of the CNC system or the hand of the industrial robot is moving at a very low speed, the number of pulses counted in the speed control sampling period is small (for example, The number of pulses is 0 or 1), and there is a problem that the speed control of the tools of the CNC system, the hand of the industrial robot, etc. is inaccurate and unstable due to the large influence of the error for one pulse described above.

FIG. 7 (a) is a diagram showing pulses counted when the servo motor starts rotating, and FIG. 7 (b) is a diagram showing signals processed by the conventional speed control device.

As shown in FIG. 7 (a), when the adjacent pulse intervals of the output pulses 71, 72, ..., 7n of the pulse encoder are gradually shortened with the time (continuous of the speed control sampling period T) as the horizontal axis. That is, when the servo motor starts to rotate, the signal processed by the conventional speed control device changes the actual rotation speed of the servo motor (such as the tool of the CNC system or the industry as shown in Fig. 7 (b)). The movement speed of the robot's hand, etc.) is significantly different from the
Control of tools such as C system and hands of industrial robots was inaccurate and unstable.

In view of the problems of the above-described conventional speed control device, the present invention expresses a pulse interval including each end of the speed control sampling period in units of small sections, and also at each end of the speed control sampling period and each end thereof. The end pulse distance between the pulse counted immediately before or the pulse counted immediately after is expressed in units of small intervals, and a predetermined function using the pulse interval and the edge pulse distance expressed in units of these small intervals By weighting the output pulses counted within the speed control sampling period by, the speed control is accurately and stably performed especially when the servo motor is rotating at a low speed.

[Means for solving problems]

FIG. 1 is a block diagram showing the configuration of a speed control device of a digital servo system having a pulse encoder according to the present invention.

According to the present invention, there is provided a speed control device of a digital servo system having a pulse encoder for calculating and controlling the rotation speed of the servo motor from the output pulse of the pulse encoder attached to the servo motor, wherein the speed control sampling cycle is Speed control sampling period dividing means 11 for dividing into a plurality of small intervals, output pulse counting means 12 for counting the output pulses of the pulse encoder within the speed control sampling period, and both ends of the speed control sampling period. Including the pulse interval including the small section as a unit, the end pulse distance between each end of the speed control sampling period and the pulse counted immediately before or after each end of the speed control sampling period Between pulses expressed in units of sections and in units of small sections Weighting processing execution means 13 for performing weighting processing on the output pulses counted in the speed control sampling period by the following function using the distance and the end pulse distance: Here, P (X) is the number of calculated pulses, X is the section of the speed control sampling period, n is the number of pulses counted in the section X, and a ₀ and an are pulse intervals including both ends of the section X. Small section, b ₀ represents the end pulse distance between the start end of the section X and the pulse counted immediately after the start end, and Cn represents the section The end pulse distance between the end of X and the pulse counted immediately before the end is displayed in the small section, and the output pulse within the speed control sampling period in which the weighting process is performed There is provided a speed controller for a digital servo system having a pulse encoder for controlling the speed of the digital servo system.

[Work]

According to the speed control device of the digital servo system having the pulse encoder of the present invention having the above-mentioned configuration,
The speed control sampling cycle dividing means 11 divides the speed control sampling cycle into a plurality of equal intervals, and the output pulse counting means 12 counts the output pulses of the pulse encoder within the speed control sampling cycle. Further, the weighting processing execution means 13 represents the pulse interval including each end of the speed control sampling period in units of small sections, and also the pulse counted immediately before or after each end of the speed control sampling period or immediately after each end. The end pulse distance from the counted pulses is expressed in units of small intervals, and the speed control is performed by a predetermined function using the pulse interval and the end pulse distance expressed in units of these small intervals. The output pulse counted within the sampling period is weighted. Then, the speed of the digital servo system is controlled by the output pulse within the speed control sampling period in which the weighting process is executed. This makes it possible to accurately stabilize the speed control of the digital servo system, especially when the servo motor is rotating at a low speed, that is, when the tool of the CNC system or the hand of the industrial robot is moving at a very low speed. You can do it.

〔Example〕

An embodiment of a speed control device for a digital servo system having a pulse encoder according to the present invention will be described below with reference to the drawings.

FIG. 2 is a block diagram schematically showing a CNC system using the speed control device of the present invention.

The CNC system 1 shown in FIG. 2 shows a machine tool that processes a workpiece 7 with a cutting tool 6. The microprocessor 2 gives a predetermined command to the X-axis control unit 3a and the Y-axis control unit 3b in order to move the cutting tool 6 in accordance with a command input from a paper tape or the like. The X-axis control unit 3a controls the rotation of the X-axis servo motor 4a, and the Y-axis control unit 3b controls the rotation of the Y-axis servo motor 4b. The X-axis servomotor 4a and the Y-axis servomotor 4b move the tip portion 6a of the tool to cut the workpiece 7 into a predetermined shape.

The X-axis servomotor 4a and the Y-axis servomotor 4b are provided with pulse encoders 5a and 5b, respectively, and output pulses of these pulse encoders 5a and 5b are supplied to the microprocessor 2. With the output pulses sent from these pulse encoders 5a and 5b, the position and movement distance of the tip end portion 6a of the tool moved by the X-axis servo motor 4a and the Y-axis servo motor 4b are calculated and controlled. ing. Furthermore, the CNC system 1 using this speed control device uses the output pulses of these pulse encoders 5a and 5b,
The rotational speeds of the X-axis servomotor 4a and the Y-axis servomotor 4b are detected to calculate the moving speed of the tip portion 6a of the tool.

FIG. 2 shows how the cutting tool 6 forms a circular recess inside the work 7. However, the speed control device of the present embodiment is configured so that the tip 6a of the tool for cutting the work 7 is Accurate and stable speed control can be performed when the movement is mainly in the X-axis direction and hardly in the Y-axis direction.
That is, the speed control device of the present embodiment can accurately and stably perform speed control of the digital servo system when the tool of the CNC system, the hand of the industrial robot or the like is moving at a very low speed. Is.

FIG. 3 is a flowchart showing a process in the speed control device of the present invention, and FIG. 4 is a diagram for explaining an example of a process in the speed control device of the present invention.

In the speed control device of the digital servo system having the pulse encoder of the present invention, when the speed control process is started, first, in step 31, the speed control sampling period T is divided into equal intervals by the current control sampling period t. Here, the speed control sampling cycle T is a sampling cycle for detecting the actual moving speed of the tip of the tool, for example, when the servomotor rotates in accordance with a command output from the microprocessor. Thus, the output pulses of the pulse encoder attached to the servo motor are counted. This speed control sampling period is, for example, 2 mse
c. It is about time. The current control sampling cycle t is a sampling cycle for changing the voltage applied to the servo motor according to the current command according to the speed command and detecting the current actually flowing through the servo motor by the applied voltage. , 0.25 msec., Which is a fixed interval shorter than the speed control sampling period T. Thus, for example, the speed control sampling period T is 2 mse
When the current control sampling period t is 0.25 msec. in c.
As shown in FIG. 4, the speed control sampling period T
Will be equally divided into eight small sections by the current control sampling period t.

Next, in step 32, the output pulses of the pulse encoder are counted within the speed control sampling period T. Reference numerals 41 to 44 in FIG. 4 indicate counted output pulses of the pulse encoder.

Further, proceeding to step 33, the pulse interval including each end of the speed control sampling period T is expressed with the current control sampling period t as a unit. For example, when the section II of the speed control sampling period in FIG. 4 is described, the pulse 42 and the pulse 4 including the start end II _S of the speed control sampling period are included.
Pulse interval a ₀ with 3 and pulse interval a between pulse 44 and pulse 45 including the end II _E of the speed control sampling period
n is represented by the current control sampling period t. Specifically, in the illustrated example, a ₀ = 4t, an = 4t.

In step 34, the end pulse distance between each end of the speed control sampling period T and the pulse counted immediately before or immediately after each end of the speed control sampling period T is set in units of the current control sampling period t. Express as. End pulse distance b _0, and the speed control sampling period between pulses 43 counted immediately after the first the four sections II of Figure is described, the starting end of the speed control sampling period II _S and its starting end II _S of represented by the terminating II _E and the end pulse distance cn current control sampling cycle t between the pulse 44 is counted immediately before the termination II _E. Specifically, in the illustrated example, b ₀ = 1.5t and cn = 2.5t.

Then, the process proceeds to step 35, and the output pulse counted in the speed control sampling period is weighted by a predetermined function using the pulse interval and the end pulse distance expressed in the current control sampling period t as a unit. To execute. This weighting process is performed not only on the output pulses counted within the speed control sampling period T, but also on the start end II _{S of the} speed control sampling period.
This is also to consider the pulse counted immediately before and the pulse counted immediately after the end II _E of the speed control sampling period. As the function used in this step 35, for example, the following function is preferable.

Here, P (X) is the number of calculated pulses, X is the section of the speed control sampling period, n is the number of pulses counted in the section X, and a ₀ and an are pulse intervals including both ends of the section X. A small section, b ₀ represents the end pulse distance between the start end of the section X and the pulse counted immediately after the start end, and cn represents the section. The end pulse distance between the end of X and the pulse counted immediately before the end is displayed in the small section. That is, the above function is not limited to the number n of pulses counted in the section X of the first term on the right side of the function, but also the number of pulses n for the number n of pulses counted in the speed control sampling period in the second and third terms. Is weighted.

For example, in the section II of FIG. 4 described above, n = 2,
a ₀ = 4t, an = 4t, b ₀ = 1.5t, cn = 2.5t, Therefore, the calculated pulse number P (II) in the section II in which the weighting process is performed is 2.

When the servo motor starts rotating, the above-mentioned function is calculated, for example, as a ₀ = ∞.

For example, in the section I of FIG. 4, n = 2, a ₀ = ∞, a
_{1 = 4t, b 0 = 1.5t} , a c ₂ = 2.5 t, Therefore, the calculated pulse number P (I) in the section I on which the weighting process is performed is 1.63. Here, if a ₀ = ∞ in the section I in which the servo motor starts rotating, this section I
The pulse calculated in step 1 will be underestimated, but in the section I where the servo motor starts to rotate, a ₀ is a ₀ =
The value is not limited to ∞, and may be set from the outside, for example, a ₀ = 5t.
In that case, a ₀ can be selected optimally for each system.

As described above, when the weighting process is performed on the output pulses counted in the speed control sampling period T in step 35, the process proceeds to step 36, and the speed control sampling period T in which the weighting process is performed is performed. The speed of the servo system, specifically, the rotation speed of the servo motor (moving speed of the tool of the CNC system or the hand of the industrial robot) is controlled by the output pulse counted by.
In this way, the speed control processing in the speed control sampling cycle T ends, but the speed control processing described above is repeatedly performed in each speed control sampling cycle T.

FIG. 5 is a diagram showing pulses counted when the servo motor starts to rotate and signals processed by the speed control device of the present invention.

This FIG. 5 (a) is the same as FIG. 7 (a) described above, and the output pulses 51, 52, ..., 5n of the pulse encoder are plotted with time (continuous of the speed control sampling period T) as the horizontal axis.
This shows the case where the adjacent pulse intervals of are gradually shortened, that is, the case where the servo motor starts rotating. At the start of rotation of the servo motor, the signal processed by the speed control device of the present embodiment is, for example, as shown in FIG. It is very similar to the moving speed of the hand of an industrial robot. As a result, at the start of rotation of the servo motor, for example, the movement speed of the tool of the CNC system or the hand of the industrial robot can be accurately and stably controlled. Here, the signal of FIG. 5 (b) is processed by a ₀ = 5t in the section where the servo motor starts rotating in the above-mentioned function.

In the above embodiments, the case where the servo motor is rotating in one direction and the case where the servo motor starts rotating have been described. However, in other cases, particularly, when the servo motor is rotating at a low speed. In addition, the signal processed by the speed control device of this embodiment is similar to the actual moving speed of the tool of the CNC system or the hand of the industrial robot. However, in each case, the weighting of the output pulses counted within the speed control sampling period needs to be done with some consideration for the function used.

For example, when the servo motor stops rotating (when the tool of the CNC system or the hand of the industrial robot stops), four sections where the number of pulses counted in the speed control sampling cycle is zero are continuous. Then CNC
It is necessary to set parameters from the outside so that it can be determined that the system tools, industrial robot hands, etc. have stopped. Also, for example, when the servo motor rotates not only in one direction but also in the opposite direction (when the tool of the CNC system or the hand of the industrial robot moves not only in one direction but also in the opposite direction), the servo motor Pulse encoder output pulses need to be signed so that the pulses counted when the motor is rotating in one direction are positive and the pulses counted when the servo motor is rotating in the opposite direction are negative. There is.

Further, in the speed control device of the digital servo system having the pulse encoder of the present invention, it is not limited to the current control sampling cycle that the speed control sampling cycle is equally divided into small sections. It may be used to evenly divide the speed control sampling period into subsections according to the clock period. Further, as the function for performing the weighting process on the output pulse counted within the speed control sampling period, various functions other than the above-mentioned function can be used. Further, the speed control device of the digital servo system having the pulse encoder of the present invention can be used for, for example, a CNC system such as an automatic guided vehicle or a digital servo system other than an industrial robot, but in particular, a CNC The system is most suitable for a digital servo system that moves a table of a precision machine tool (relative movement of a tool with respect to a work fixed to the table) that requires precise control.

〔The invention's effect〕

As described above in detail, the speed control device of the digital servo system having the pulse encoder according to the present invention is
A pulse interval including each end of the speed control sampling period is expressed in units of small sections, and an end between each end of the speed control sampling period and a pulse counted immediately before or immediately after each end of each speed control sampling period. Partial pulse distance is expressed in small sections, and weighting is applied to the output pulses counted in the speed control sampling cycle by a predetermined function using the pulse interval and end pulse distance expressed in small sections. By
In particular, speed control can be accurately and stably performed when the servo motor is rotating at a low speed.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a speed control device of a digital servo system having a pulse encoder according to the present invention, and FIG. 2 is a block diagram schematically showing a CNC system using the speed control device of the present invention. FIG. 3 is a flowchart showing a process in the speed control device of the present invention, FIG. 4 is a diagram for explaining an example of a process in the speed control device of the present invention, and FIG. 5 is a count when the servomotor starts rotating. Pulse and the signal processed by the speed control device of the present invention, FIG. 6 is a diagram for explaining the problems of the conventional speed control device, and FIG. 7 is a diagram when the servomotor starts to rotate. FIG. 5 is a diagram showing pulses counted in the signal and signals processed by a conventional speed control device. (Description of symbols) 1 ... CNC system, 2 ... microprocessor, 3a, 3b ... axis control unit, 4a, 4b ... axis servomotor, 5a, 5b ... pulse encoder, 6 ... cutting tool, 6a ...... Tip of tool, 7 ... Work, 11 ... Speed control sampling period dividing means, 12 ... Output pulse counting means, 13 ... Weighting processing executing means.

Claims (2)

[Claims] 1. A speed control device for a digital servo system having a pulse encoder for calculating and controlling the rotation speed of the servo motor from the output pulses of a pulse encoder attached to the servo motor, wherein the speed control sampling period is at regular intervals. A speed control sampling period dividing means for dividing into a plurality of small sections, an output pulse counting means for counting the output pulses of the pulse encoder within the speed control sampling period, and a pulse interval including each end of the speed control sampling period. Is expressed in units of the small section, and the end pulse distance between each end of the speed control sampling period and the pulse counted immediately before or after each end of the speed control sampling cycle is expressed in units of the small section. And the pulse interval expressed in units of the small section. And weighting processing means for executing a weighting process to the count output pulses at the rate control sampling period by the following function using the fine end pulse length, Here, P (X) is the number of calculated pulses, X is the section of the speed control sampling period, n is the number of pulses counted in the section X, and a ₀ and an are pulse intervals including both ends of the section X. Small section, b ₀ represents the end pulse distance between the start end of the section X and the pulse counted immediately after the start end, and Cn represents the section The end pulse distance between the end of X and the pulse counted immediately before the end is displayed in the small section, and the output pulse within the speed control sampling period in which the weighting process is performed A speed control device for a digital servo system, comprising a pulse encoder for controlling the speed of the digital servo system. 2. The apparatus according to claim 1, wherein the subintervals representing the pulse interval and the edge pulse distance are defined by a current-limited sampling period.