RU2772478C1 - Active control system for error compensation and method for operation thereof - Google Patents

Abstract

FIELD: controlling.

SUBSTANCE: group of inventions relates to active control systems applied on metal working machines, and can be used on grinding machines. The active control system consists of a measuring apparatus connected with a drive and a dimensional comparing apparatus connected with a driver and a control unit connected with an actuator. The dimensional comparing apparatus and the driver are coupled via a setting converter. The driver is coupled with the temperature comparing apparatus via a temperature converter, the temperature comparing apparatus is connected with two temperature sensors. The main loop compares the current size of the processed part with the size of a sample part, changes the operating mode of the machine, and stops processing when the part reaches said size. The first additional loop corrects the setting level in the course of processing the part, based on the results of comparing the temperature thereof with the sample part, and compensates for the temperature deformation of the processed part, and the second loop corrects the setting level after the part is processed, measures the sample part, and compensates for the error from the setting level offset.

EFFECT: accuracy of processing the part is increased.

2 cl, 4 dwg

Description

The present invention relates to active control systems used on metalworking machine tools, and in particular on grinding machines, and to methods of operating such systems.

In the machining of workpieces, especially those with precise dimensions, active control is used to improve accuracy. The use of active control also creates the possibility of multi-machine maintenance and the use of lower-skilled workers. In a broad sense, active control is such control, as a result of which intervention is carried out in the processing process (manually or automatically).

Increasing the accuracy of processing with the use of active control is achieved by compensating for a number of errors caused, for example, by inaccurate settings of the technological system, wear and temperature deformation of the cutting tool, etc.

According to known data [Design of technological processes of machine-building industries: textbook / [V.A. Timiryazev [i dr.]. - St. Petersburg: Lan, 2014, p. 95], means of active control (ACS) of sizes according to their functions are divided into four groups:

1. Devices that control parts directly during processing.

2. Adjusters.

3. Blocking devices.

4. Devices that control parts before processing.

The most accurate of them are devices that control the dimensions of the part directly in the process of processing them (hereinafter we will talk about active control in the process of processing).

From the practice of using active control, the latter is most conveniently implemented in grinding operations due to the absence of chips, the presence of which makes it difficult to measure the dimensions of the part during processing.

There is a wide variety of systems that implement active control [Geiler Z.Sh. Self-adjusting active control systems. - 2nd ed. revised and additional M.: Mashinostroenie, 1978. - 224 p.], [Active size control / S.S. Volosov, M.L. Shleifer, V.Ya. Ryumkin and others; Ed. S.S. Volosov. - M.: Mashinostroenie, 1984. - 224 p.]. The traditional scheme of active control in external cylindrical grinding is given in [3, p. 96, fig. 4.1-a]. The measurement of the part is carried out by a measuring device, the data from which are sent to the comparing device, which also receives data on a given size from the setting device. When the specified size is reached, the signal of the lack of mismatch of these data is amplified by the amplifying device and the machine is turned off.

However, not all errors can be compensated for by applying active control. One of the uncompensated errors is the temperature deformation of the workpiece. The proportion of temperature errors can be approximately 40-60% of the total processing error.

As you know, during machining (especially when grinding), there is a significant release of heat from the cutting process, and the part heats up. As a result, due to the heating of the part, its geometric dimensions change. If the workpiece is measured hot, then this leads to measurement errors. If intervention in the machine setting is carried out on the basis of such measurement results, this will lead to an error in the size of the part. And since when using active control, the measurement of the part can occur directly in the process of processing, then this error arises.

To compensate for thermal deformations of the workpiece under active control, various schemes and devices are proposed. They can be based on the measurement:

- workpiece;

- temperature deformations of the workpiece;

- coolant temperature, etc.

They are based on a special additional circuit that corrects the SAO setting based on the results of these measurements.

SAC have become more widespread in which the setting is corrected by controlling the temperature of the workpiece.

Structural diagram of the CAC with compensation for temperature deformations of the workpiece to control its temperature is given in [Geiler Z.Sh. Self-adjusting active control systems - 2nd ed. revised and additional M.: Mashinostroenie, 1978. S. 128, fig. 40]. The measurement of the part is carried out by a measuring device, the data from which are received through the converter as a change in the input signal value (the size of the workpiece) of the main control circuit, which is continuously compared in the control unit with the set value corresponding to the finished size of the part. When the equality of the set value and the input signal is reached, the control unit gives a command to the actuator and the feed stops. With certain ratios of the set value and the input signal, the feed rate can be changed. In the compensation circuit, its converter takes into account the change in size from the temperature of the part, transmits data to the setpoint, which proportionally changes the set value.

Closest to the proposed one is one of the devices that implements the above scheme, which compares the temperature of the workpiece and the measuring device that controls the size of the workpiece, is given in [Geiler Z.Sh. Self-adjusting active control systems - 2nd ed. revised and additional M.: Mashinostroenie, 1978., S. 138, fig. 45].

Compressed air from the network through the filter and stabilizer unit and inlet nozzles enters the reading device, to the nozzle of the measuring device and to the counter-pressure nozzle of the compensating device.

The thermal resistance, which measures the temperature of the bracket, is built directly into the device carriage. The workpiece temperature is measured by a thermal resistance, which is in contact with the workpiece along its end near the processing zone. Thus, the average temperature of the product is measured, according to which a correction is introduced. The signal from the thermal resistance, which rotates with the part, is taken through a collector mounted on the headstock spindle of the machine product. Both thermal resistors are included in the electrical circuit that controls the position of the backpressure damper, the displacement of which controls the backpressure branch gap. Since the measuring branch and the counterpressure branch are identical in characteristics, the change in the gap of the counterpressure branch corresponds to the change in the gap of the measuring branch. It follows from this that if the command to complete the processing was given with the set gaps of both branches, then when changing one gap, the command is issued by the device with an equal change in the second gap. The electrical part of the thermal compensation system consists of a self-balancing bridge circuit, in which thermal resistances are included, and a servo amplifier with a reversible motor that shifts the back pressure damper. Thermal resistances form two arms of the bridge, the other two arms are formed by resistances and a rheochord.

The unbalance voltage is removed from the diagonal of the bridge, which is amplified by the voltage amplifier and fed to the servomotor. The latter shifts the slider of the reochord to the balance of the bridge. The slider of the rheochord is directly connected to the microscrew, so that when the slider is turned, due to the movement of the microscrew, the shutter rotates and thus the gap above the counterpressure nozzle changes.

Before starting work, any SAK is adjusted to a given size. During operation, the initial setting level, as a rule, changes in an undesirable direction under the influence of various factors. The reason for this is: wear of measuring tips, thermal and elastic deformations, vibrations of the technological system. A shift in the initial setting level can also be caused by a shift in the characteristics of electrical, mechanical and pneumatic devices and factors whose appearance and influence cannot be taken into account.

To check the level of adjustment, one has to stop the processing process, check the level of adjustment and, if necessary, perform a sub-adjustment of the ACS. This leads to loss of productivity and requires a certain skill of the worker.

To maintain the level of initial adjustment, it is proposed to introduce an additional contour and a reference part (standard), based on the measurement results of which a decision is made on the need for adjustment and, if necessary, a correction is made to its level.

The disadvantage of such an ACS is the occurrence of an additional error introduced by the system itself, namely, a shift in the ACS setting level by a given size, especially during prolonged operation. In addition, if there is an exemplary part in the SAC, such a scheme for compensating for the thermal deformation of the workpiece is not effective. The main disadvantage of the well-known SAC is the lack of consideration of the temperature difference between the exemplary and machined parts.

Obviously, the temperatures of the workpiece and the exemplary one outside the processing zone are different. The temperature of the sample part is equal to the ambient temperature, because it is not processed. The temperature of the part during processing differs significantly from the ambient temperature. For the reliability of the measurement results of the machined part after it is removed from the machine, the temperature of the latter should not differ from the ambient temperature.

In the case of using a reference part, to maintain the required size of the workpiece, the temperature difference between the workpiece and the reference part matters, and not the temperature of the measuring device. The main thing is that when measuring the workpiece and the exemplary one, the temperature of the measuring device does not change. And if the process of checking the adjustment against a reference part takes a short time, then the temperature of the measuring device cannot change significantly.

To eliminate these shortcomings, a SAC with two additional interdependent compensation circuits is proposed.

A system for active control of the size of a part during its processing on a grinding machine, comprising a measuring device connected to a drive and a comparing dimensional device connected to a master device and a control unit that is connected to an actuator, the system being equipped with two temperature sensors designed to measure the temperatures of the processed and exemplary part, a tuning transducer connected to the specified comparing dimensional device and a setting device, and a comparing temperature device connected to the indicated two temperature sensors and connected to the setting device through a temperature converter, while the active control system is made in the form of a main control loop that provides a comparison of the current the size of the workpiece with the size of the reference part, and two interdependent compensation control loops, one of which is the temperature difference loop, provides compensation for the deformation of the workpiece and includes the specified measuring device that compares the dimensional device, the setting device that compares the temperature device and the temperature converter, and the other - the adjustment level offset circuit, provides compensation for the error from the adjustment level offset relative to the allowable offset value of the active control system and includes the specified comparing dimensional device, setting device and tuning transducer.

A method for active control of the size of a part during its processing on a grinding machine using an active control system, wherein the measuring device is adjusted to a given size according to a reference part, the signal obtained during the measurement is stored in the setting device, the size of the workpiece is continuously measured by the measuring device during processing and transmission signals about the size of the part to the comparing device for comparison with the stored signal of the master device, and if they are equal, the comparing device sends a signal to the control unit, which stops processing the part by controlling the actuator, while during processing the temperature of the processed and reference parts is measured by means of thermal sensors , the signals from which are sent to the comparing temperature device and, when the permissible temperature difference is exceeded, the comparing temperature device sends a signal to the temperature converter, which makes a correction to the signal of a given size in the setting device, and after the end of processing, the measuring device is removed from the workpiece and the size of the reference part is measured, while

exceeding the allowable value of the adjustment offset, the comparing dimensional device generates a signal and transmits it to the adjustment converter, which makes a correction to the signal of the specified size of the part in the setting device.

In FIG. 1 shows a diagram of the device of the proposed SAK (on the example of circular external grinding).

In FIG. 2 shows a diagram of the device with the signals generated by the elements involved in the initial adjustment to the required size according to the exemplary part.

In FIG. 3 shows a diagram of a device with signals generated by the elements involved in the processing of a part using a circuit that compensates for the thermal deformation of the part.

In FIG. 4 shows a diagram of the device with the signals generated by the elements involved in making corrections to the tuning level after the end of the processing of the part.

In accordance with FIG. 1, the active control system consists of a measuring device 1 connected to a drive 2 and a comparing dimensional device 3 connected to a master device 4 and a control unit 5, which in turn is connected to an actuator 6, which compares a dimensional device 3 and a master device 4 in addition to the direct connections are also connected through the tuning converter 7, in addition, the setting device 4 is connected to the comparing temperature device 8 through the temperature converter 9, and the comparing temperature device 8 is connected to two temperature sensors 10.

The tuning level offset circuit includes a comparing dimensional device 3, a setting device 4 and a tuning transducer 7.

The temperature difference circuit includes a measuring device 1, a measuring device 3, a setting device 4, a temperature device 8, and a temperature converter 9.

The measuring device 1 can be a measuring clamp. Actuator 2 may be hydraulic, pneumatic, electromagnetic or otherwise.

The proposed SAC works as follows.

The workpiece 11 is installed on the machine. Before starting its processing, the measuring device 1 is adjusted to the required size according to the exemplary part 12, which for convenience of work can be located between the measuring tips of the device 1. The signal obtained during the measurement of the exemplary part 12 enters the setting device 4, bypassing the comparing device 3, where it is stored.

The grinding wheel 13 is brought to the workpiece 11 and the grinding process is started, while the size of the workpiece 11 is continuously changed. With the beginning of the processing process, the measuring device 1 is driven by the drive 2 to the workpiece 11 and continuously measures its size. The received data about the size of the part 11 comes from the measuring device 1 to the comparing dimensional device 3, where it is compared with the specified size from the setting device 4.

In the absence of disturbing influences, the control process proceeds as usual with control during processing.

When the specified size of the part 11 is reached, the signal of the absence of a mismatch between the size of the part 11 and the specified size stored in the master device 4 is fed to the control unit 5, and from it to the actuator 6, and the processing stops. The grinding wheel 13 and the measuring device 1 are retracted from the part 11 for the convenience and safety of its removal and installation of the next one.

In real conditions, the system is affected by disturbing influences, primarily heating of the part 11 from the cutting process.

During processing, the temperatures of the part 11 and the exemplary part 12 are measured by temperature sensors 10, the signals from which are sent to the comparing temperature device 8. When the permissible temperature difference is exceeded, the comparing temperature device 8 generates a mismatch signal and transmits it to the temperature converter 9, which corrects the signal a given size in the setting device 4. As a result, the signal for the end of processing transmitted to the control unit 5 will be given earlier or later relative to the initial setting without taking into account disturbing influences.

In this way, the temperature deformation of the part 11 is compensated.

After the processing of the part 11, the latter is removed, and the measuring device 1 is removed from the processing zone and measures the exemplary part 12. If the adjustment level offset does not exceed the allowable value, the next part 11 is processed. If the adjustment level shift exceeds the allowable value, the circuit starts to work adjustment level offset.

The signal from the measuring device 1, which measures the exemplary part 12, is compared with the signal from the setting device 4 (available after the initial setting) in the comparing dimensional device 3. If the allowable value of the setting offset is exceeded, the comparing dimensional device 3 generates a mismatch signal and transmits it to the tuning converter 7 , which makes a correction to the signal of a given size in the setting device 4.

This compensates for the offset of the SAK setting level.

Next, a new part 11 is installed and the operation of the system is repeated.

Thus, this SAK has two additional control loops, which are interdependent, since temperature and size of reference part 12 is used to operate two circuits.

These contours must work sequentially: the first - during the processing of the part, the second - after the end of the processing of the part and before the start of processing the next one.

The technical result is to increase the accuracy of processing each part, as well as to reduce the number of defective products.

Claims (2)

1. A system for active control of the size of a part during its processing on a grinding machine, containing a measuring device connected to a drive and a comparing dimensional device connected to a setting device and a control unit that is connected to an actuator, characterized in that it is equipped with two thermal sensors designed for measuring the temperatures of the workpiece and sample parts, a tuning transducer connected to the specified comparing dimensional device and a setting device, and a comparing temperature device connected to the indicated two temperature sensors and connected to the setting device through a temperature converter, while the active control system is made in the form of a main circuit control, which provides a comparison of the current size of the workpiece with the size of the reference part, and two interdependent compensation control loops, one of which is the temperature difference loop, provides for compensation for thermal deformation of the workpiece and includes the specified measuring device that compares the dimensional device, the setting device that compares the temperature device and the temperature converter, and the other - the adjustment level offset circuit, provides compensation for the error from the adjustment level offset relative to the allowable offset value of the active control system and includes the specified comparing dimensional device, setting device and tuning transducer. 2. The method of active control of the size of the part during its processing on a grinding machine using the active control system according to claim 1, characterized in that the measuring device is adjusted to a given size according to the exemplary part, storing the signal obtained during the measurement in the setting device, continuous measurement of the size of the workpiece by the measuring device during processing and transmission of signals about the size of the part to the comparing device for comparison with the stored signal of the master device, and if they are equal, the comparing device sends a signal to the control unit, which stops processing the part by controlling the actuator, while during processing, they measure the temperature of the processed and exemplary parts by means of temperature sensors, the signals from which are sent to the comparing temperature device, and when the permissible temperature difference is exceeded, the comparing temperature device sends a signal to the temperature th converter, which makes a correction to the signal of a given size in the setting device, and after the end of processing, the measuring device is removed from the workpiece and the size of the reference part is measured; which makes a correction to the signal of the specified size of the part in the setting device.

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