JPS58169207A - Numerical controller - Google Patents

Abstract

PURPOSE:To perform optimum numerical control by adding a position deviation reader to a digital servo system numerical controller, and comparing a command pulse with a feedback pulse on the basis of the read output of the reader and carrying out speed control so that working force is constant. CONSTITUTION:Pulses from a command generation part 1 are integrated by the command counter 20 of a comparator 11 and feedback pulses from a position detector 16 are also integrated by the counter 21 similarly. At the timing of a timing generation part 24, the current feedback counter value is subtracted from the current command counter value at a part 22 and their difference is supplied to an output latch 23. Its output is synchronized with a D/A converter 12 by the timing generation part 24 and amplified to drive a motor 14, holding load torque constant.

Description

[Detailed description of the invention]

The present invention relates to a numerical control device. Numerical side a] In applied machine tools, such as N and C lathes, the main shaft rotation speed and feed rate, which determine the cutting speed,
The speed is determined based on experience and calculations, and controls are applied to keep the speed constant during cutting. Especially in NC lathes, etc., when the cutting tool moves perpendicular to the spindle and the radius from the spindle center changes, the spindle rotation speed is changed so that the circumferential speed, that is, the relative speed of the tool and workpiece, remains constant. A constant circumferential speed control method is used to keep the circumferential speed constant. However, this method cannot cope with cases where the original cutting speed settings are not appropriate, or where there are large changes in machining conditions due to changes in the depth of cut due to variations in material dimensions, tool deformation, etc. It was necessary for the operator to observe the cutting conditions and change the spindle rotation speed and feed speed tube according to the situation. This has been dealt with by changing the set value itself on the t'iNC command tape, or by using an override function that multiplies the spindle rotation speed and feed rate by a factor while the machine is in operation. The cane was a problem when driving at night or when driving unmanned. On the other hand, as a trial, various cutting conditions such as cutting force, spindle torque, tool vibration, temperature, and running were measured by installing a gold detector tube, and the data was used to determine whether cutting force was constant, tool life was optimal, and machining There is an adaptive control device that automatically changes the number of revolutions per spindle, feed speed, depth of cut, etc. based on an evaluation function such as minimum cost, but it requires a complicated system for altitude control, so it is expensive and difficult to control. It was not practical in terms of reliability. FIG. 1 is a schematic configuration diagram of a conventional digital laser type numerical control device, and in the figure, 1 is a command pulse generation section;
Command input section 2 for reading key data, NC chip f4
A display section 3 displays the status of the NCC and NC, and a tape input section 5 reads the NCC commands.A command input section 22 displays a tape input section 5 for creating commands to actually operate the machine from the information on the tape.
, NO tape 4t - A control section 6 configured by a microcomputer that controls the control section 6, and an interpolation section 7 that generates command pulses for each axis corresponding to straight lines, circular arcs, etc. according to the commands created by the control section 6. compose The command/4' pulse from the command/gurus generation section 1 enters a servo section 10 provided for each axis. Although only the - axis is shown here, the comparator 11 detects the difference between the number of command pulses from the command pulse generator 1 and the number of feedback pulses from the position detector 16.1. The digital to analog converter 12 converts it into an analog/4G quantity, and the mechanical system 15 is increased by increasing 14 with an 7'13.
The drive 15 processes the workpiece with a cutting tool. Then, the machining state is detected by the position detector 16 and inputted to the comparator 11 as a feedback pulse. Here, since the content of the comparator 11 is a positional deviation, an abnormal situation occurs such as when a feedback loose wire is broken or the tool gets caught on something and cannot be moved, and the feedback loop or loop does not return. Therefore, the positional deviation becomes a very large value, and the servo causes the motor to output high output, but if the positional deviation exceeds the set range, it indicates that the servo system is abnormal. It was configured to make a judgment, issue an alarm, and stop the machine at the same time. In other words, the configuration shown in Fig. 1 has a limit in its ability to cope with changes in the depth of cut due to variations in material dimensions, changes in machining conditions due to tool deterioration, etc. If you can't move, do you have to do more? The torque of the motor would increase, which could lead to damage to the tool. The purpose of the present invention is to provide a numerical control device I that can perform optimal control without the aforementioned processing condition detector or advanced system, by utilizing the functions of conventional numerical control devices and adding only a few devices. It is on offer. In the present invention, the positional deviation in numerical control is read out, the load torque of the servo system is calculated from that wax, and the servo system is controlled in speed so that the machining force is constant. That is, in the present invention, since the command pulse output from the command pulse generation section issues a movement command at a constant speed, the contents of the comparator are designed in consideration of the fact that it is a steady speed deviation in the sense of control theory. . Where is the steady speed deviation? 1, generally #==Fc
/to+FR'Tc/(K@TP) -(11FC=
Command speed, K: Open loop gain of the system, FR: Feed rate when the motor is at the rated rotation speed, To: Motor shaft equivalent load torque, TP: Motor rated torque. Here, K, F, and TP are constants, so the steady speed deviation 8 is the command speed F. and load torque T. It is determined by the steady speed deviation 6 and the command speed F. If you know the load torque T. can be determined, the torque Tc is proportional to the cutting force, and the force Pi, P:R”
D @ also −+ (2) R: Cutting resistance, D: Depth of cut, F: Cutting speed, so cutting speed F,? By adjusting the cutting force, the load torque can be changed. The present invention utilizes these (1) and (2) to calculate the steady speed deviation and load torque. Hereinafter, one embodiment of the present invention will be explained according to Figures 1 to 5. Hardware configuration:
2; As shown in the figure, it is a trap.
A position deviation reading device 17 is added to the control device, and the position deviation reading device 17 continuously reads the comparison state of the comparator 11, and provides feedback to the control section 6#/c of the command pulse generation section 1. It is. The internal configuration of the comparator 11 shown in FIG. 2 is shown in FIG. The same applies to the feedback/source signal from the detector 16. The command counter I, which is an up/down counter, integrates this command)4 pulses, and the feedback pulse pulse is integrated by a similar feedback counter 21. and,
When the timing of the timing generator sequence is set, the value of the feedback counter is subtracted from the value of the command counter at that time using the subtractor η, and the difference is stored in the output latch device. This is necessary in order to keep the output to the digital-to-analog converter 12 constant during this conversion time, since the two counters change every moment, but a certain amount of time is required for digital-to-analog conversion. Furthermore, the timing generator array is connected for synchronization with the digital-to-analog converter. In such a comparator, it can be said that the position deviation value is at the output latch, so the position deviation successive device 1
7C. As shown in the same figure, a pass buffer 25 is connected to the output of the output latch B, and the pass buffer 25t-
The configuration can be easily achieved by adding the successive control section 26 to the comparator 11. As mentioned earlier (Equation 11 holds true in a steady feed state, positional deviation during acceleration and deceleration is not necessary, and if Equation (1) is processed using the positional deviation at this time, incorrect control will occur. By the way, in the command reference generation unit 1, automatic acceleration/deceleration is normally applied in order to avoid giving a shock to the mechanical system.This means that the vertical axis is the command speed f and the horizontal axis is the time ti and the time constant tTM of the mechanical system, the fourth
It will look like the figure. Since acceleration is applied in accordance with the time constant TM of the mechanical system, the speed is several times TM from the start.
At point A, the mechanical system is considered to have settled into a steady state. In addition, in the case of deceleration, the function type of the command speed changes at point B, so the function type can be changed using the software 6 air in the command base generation unit 1, or the function type can be changed using the ff-) control of the There are 28 things that need to be changed. Therefore, when using software, you can set the position deviation sampling end flag etc. at the same time when changing the function type.
In the case of using hardware, it is sufficient to interrupt the microcomputer with a dirt signal and similarly set the position deviation sampler end flag in the interrupt processing program. In this way, if the positional deviation from point A to point B is sun gridded, this will represent the steady speed deviation. Next, configure the software

[Shown in Figure 5. That is,
A start is made, and the process waits until reaching the steady speed deviation detection starting point A shown in FIG. 4 described above in step (9). When the point A is reached, the process proceeds to step 31, where the steady speed deviation - is taken in from the position deviation reading device 17 to the control section 60 microcomputer in the command pulse generation section 1. In step 32, the steady speed deviation taken in oscillates with short periodic fluctuations, so if the processing is performed simply using this value, there is a possibility that excessive control will occur. A digital Ronoyass filter is constructed by averaging the values, and high frequency components of the steady speed deviation are removed. In the process, the open loop fl' is determined by the mechanical system.
In, motor rated feed speed -, motor rated torque TP
and command speed F. Based on equation (1), load torque Tc? calculate. - Mechanical constants are written in the constant area of the memory in the control unit 6 so that they can be used with different machines. Also, the command speed is determined by the command on the NC tape and the state of the operating parts such as the override switch, and this is calculated and determined by the microcomputer in the control unit 6, so if you save this result in memory, you can speed up the command speed. F. is obtained. The optimum load torque is determined by complex factors such as the material of the workpiece, the shape and material of the tool, the cutting method, the cutting purpose (finishing is rough cutting, etc.), and how to consider the economical efficiency of cutting. The numerical values used for determining the maximum value C and minimum value of torque, the maximum value E and minimum value F of the fluctuation rate of load torque, etc. are input from the command input section, and the determination is made by an external circuit (not shown). Let's do it. First, the spindle override cancel flag is determined to determine whether the spindle rotation speed can be changed during the process.
If the change is not possible, go to step 39, and if the change is possible, the processes from the process part to section are performed. The override cancel flag is set by a switch in the command input section 2. The load torque calculated in the process 11 is compared with the maximum applied load torque value C, and if the calculated load torque is larger, the main shaft rotational speed is overridden by one step and decelerated by about 10% between processes. In step 37, the calculated load torque is compared with the minimum load torque value, and if the calculated load torque is smaller,
The spindle rotation speed is accelerated by one step and overridden between processes.
Accelerate by about 0%. To execute the override, it is sufficient to perform the same process as when the override switch of the command input section 2 is switched, so the microcomputer in the dividing section 6 increases or decreases the command speed i by 10% and performs the speed change process. That's fine. Next, in order to prevent load torque fluctuations, consider changing the feed rate, which has a faster response than the spindle rotation speed. Then, in step 39, the feed override cancel flag determines whether the feed speed can be changed, and the process sum ~
Process the shrine. The override cancellation flag is
Unlike the main shaft, there is no dedicated switch, but settings can be made from the command input section 6 by key operation. Furthermore, in the process, the difference between the load torque average value up to the previous time and the load torque calculated this time is calculated, and the load torque is differentiated with respect to time to calculate the load torque fluctuation rate. Then, in step 4, it is compared with the maximum load torque variation rate E, and if the calculated value is larger, then in step 42, the command speed tube is overridden by one stage of deceleration, and the speed is decelerated by about 10%. In step 43, it is compared with the load torque fluctuation rate minimum value F, and if the calculated value is smaller, in step 44, the command speed i-1 stage acceleration is overridden and the acceleration is approximately 10%. Acceleration/deceleration is the same as for the main axis, and all processing is performed when the override switch is switched. Step 45: Calculate the average load torque used in the process. This is calculated from the average load torque P up to the previous time, the load torque Q this time, and the number of samplings N up to the previous time, and the average load torque V = = (N@P+Q)/(N+1)
-Calculate from (3). Then, in step 46, which is stored in the memory of the control unit 6, it is determined whether the deceleration start point B, which is the end point of sampling the steady speed deviation, has been reached, and if the point B has not yet been reached, the above-mentioned Process 3
Repeat the process from 1 and when you reach points L and B, start the main speed control process I.
lf program? finish. By performing such control a, cutting can be performed with a constant load torque, that is, cutting force, and effects such as improved surface finish, optimization of tool life, and reduction in total cutting time can be obtained. Due to the external setting, the override of the spindle and feed speed is prohibited. Therefore, the depth of cut D'
Assuming that F is constant, the value divided by the cutting speed F represents the cutting resistance. As the tool wears out, the cutting resistance increases rapidly, so the state of tool wear can be determined by looking at the average load torque when canceling the override. Furthermore, since the data can be used as actual measurement data when determining the values of C, D, E, F, etc. used in each determination of speed control, it can be displayed externally on the display unit 3. In this embodiment, the spindle rotational speed is changed according to the value of the load torque, and the control is performed in which the feed p speed is changed according to the value of the variation rate of the load torque. There are also methods that change only the spindle rotation speed depending on the value of , methods that change only the feed speed by calculating only the load torque fluctuation rate, and methods that only change the feed speed depending on the value of the load torque. This can be achieved by making some changes, and it is possible to perform optimal control according to the characteristics of the mechanical system. According to the above embodiments, complicated and expensive sensors are added to respond to changes in various cutting conditions such as changes in the material of the workpiece, changes in the cutting bit due to replacement or wear, and changes in the depth of cut due to variations in dimensions before machining. Without further ado, sir? Since the load torque of the motor is calculated and the command speed is controlled so that the cutting force is constant, the speed setting value on the NC tape is automatically set to 1. In addition, since the cutting force is adjusted to the optimum value during cutting, rough values are not required, and the operator does not need to monitor the cutting condition. This eliminates the need for operators to monitor cutting conditions, and to reduce the need for tools when changing the material of the workpiece or replacing the tool. In this case, there is no need to change the speed setting value on the KNC tape 5, and the same NC tape can be used. In addition, with conventional numerical control devices, if the servo system becomes unable to move due to tool interference, etc., the position deviation will increase rapidly and before the alarm stops, the servo will increase the torque of the motor and cause damage to the tool. However, according to this embodiment, when the positional deviation increases rapidly, the cutting speed can be controlled to decrease, so abnormal situations such as tool breakage can be prevented. In the above embodiment, the NC lathe device was described as a machine tool that applied numerical control, but the application is not limited to this, but can be applied to any device that applies numerical control, for example, loget, printing, etc. It can be said to be ideal for equipment, etc. As is clear from the above description, according to the present invention, the set values for load machining conditions, etc. are automatically adjusted to optimal values, so it is only necessary to determine rough values.
It has the advantage of simplifying worker monitoring, and can be said to be the most suitable numerical control device.

[Brief explanation of drawings]

Fig. 1 is a schematic block diagram of a conventional digital numerical control device, Fig. 2 is a schematic block diagram showing an embodiment of the present invention corresponding to Fig. 1, and Fig. 3 further shows the main parts of Fig. 2. FIG. 104 is a block diagram specifically showing the acceleration/deceleration of the commanded speed and the speed of arm turn over time, and FIG. 5 is a flowchart explaining the operation of the apparatus shown in FIG. 2. 1... Command pulse generation section, 2... Command input section, 3.
... Display IL 4... NC tape, 5... Tape input section, 615... 1111J comb section, 7... Interpolation section,
10...Ser is part, 11...Comparator, 12...Digital to analog converter, 13...Ser is 7yg, 1
4... Ser is a motor, 15... Mechanical part, 16...
Position detector, 17... Position 1 difference reading device, B... Command/I pulse counter, 2]... Feedback pulse counter, 2o22... Subtractor, n... Deviation latch, U... - Timing generation section, δ...output part, addition...readout section J control part. Representative Patent Attorney Tori Akimoto Figure 1 Figure 3

Claims (1)

[Claims] A command/IP pulse creation unit that creates a command/gus for operating a load device based on input data;
This numerical control device is a numerical control device comprising a sensor section that compares the difference between the command pulse from the pulse generation section and the feedback pulse from the load device, and operates the load device based on the comparison result. A numerical control device characterized in that it is provided with a position deviation reading circuit which successively reads the p position deviation from the sago section and feeds back the value to the command noyars generation section.