JP2008221361A - Temperature controller of machine tool - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enhance the responsiveness and accuracy of temperature control while eliminating the inverter control of a refrigerating machine to reduce the cost and size of the temperature controller of a machine tool. <P>SOLUTION: This temperature controller of a machine tool comprises: a cooling circuit 2 for circulating a heat medium liquid to the machine tool; the refrigerator 5 driven at a specified rotational speed; a condenser 6 for liquefying the refrigerant gas compressed by the refrigerator; an expansion valve 7 for restricting and expanding the liquefied refrigerant gas; a heat exchanger 8 for cooling the heat medium liquid by the restricted and expanded refrigerant gas; a bypass passage 4 for introducing the refrigerant gas immediately after leaving the refrigerator into the heat exchanger while bypassing the condenser; a bypass valve 9 installed in the bypass passage; reference temperature set means 10, 13, a temperature sensor 21 for detecting a return liquid temperature; and a temperature control means 10 for controlling, by feedback, the openings of the expansion valve and the bypass valve so that the temperature difference between the return liquid temperature and a reference temperature is constant. The temperature control means operably connects the opening of the expansion valve to the opening of the bypass valve at a value corresponding one-to-one for simultaneous control. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a temperature control device for a machine tool that controls the temperature of a heat medium liquid to be circulated in a machine tool and suppresses thermal deformation. More specifically, the present invention relates to a temperature control device for a machine tool that eliminates the need for inverter control of a refrigerator, enables cost reduction and size reduction of the temperature control device, and improves responsiveness and accuracy of temperature control.

  The machine tool body deforms due to environmental temperature, heat from the heat generating part, and the like. Since the deformation of the airframe affects the processing accuracy, conventionally, the temperature of each part of the airframe has been controlled to a constant temperature. Various methods of temperature control have been proposed, but a constant flow-controlled cooling oil that is normally temperature-controlled is always supplied to the heat generating part of the machine tool to cool the heat generating part. This cooling oil is cooled by the refrigerant through the heat exchanger.

  As a technique for improving the accuracy of temperature control of such a machine tool, a technique such as the following Patent Document 1 has already been proposed by the inventors of the present invention. Patent Document 1 describes a temperature control method for a machine tool in which a transient deviation and a steady deviation are reduced by feedforward control, and a bypass path for bypassing refrigerant gas immediately after leaving the refrigerator. And expanding the variable range of the cooling capacity in the low load region by opening the solenoid valve provided in the bypass.

  However, the technique of Patent Document 1 also has the following problems. First, in order to perform control by feedforward control, an interface circuit is required to send the rotation speed command information of the spindle of the machine tool to the temperature control device, and software is also required to send the rotation speed command information As a result, the system change on the machine tool side takes time to develop the system and increases the cost of the entire system. In addition, in order to perform feedforward control, it is necessary to create a control table that stores the relationship between the rotation speed of the spindle of the machine tool and the cooling capacity of the refrigerator as a database. The system development time and cost were increasing.

Therefore, the inventors of the present invention have proposed a technique as described in Patent Document 2 below. Patent Document 2 describes a temperature control method and apparatus for a machine tool that can improve response characteristics and accuracy of temperature control only by feedback control. That is, according to the temperature control method of Patent Document 2, even when the amount of heat generated by the heat source of the machine tool changes, the transient deviation between the set temperature and the coolant temperature can be reduced. The time until the temperature becomes stable (settling time) can be shortened.
Japanese Patent No. 2529905 JP 2007-038329 A

  Since the temperature control devices of Patent Document 1 and Patent Document 2 described above drive the refrigerator by inverter control to change and control the rotation speed, an inverter control drive device is required, and the cost of the temperature control device increases. However, there is a problem that the temperature control device is increased in size. In addition, as described above, the temperature control technique of Patent Document 1 has a problem in that the cost of the entire system increases because feedforward control is performed.

  Therefore, the present invention eliminates the need for inverter control of the refrigerator, enables cost reduction and downsizing of the temperature control device, and improves temperature control responsiveness and accuracy. An object is to provide an apparatus.

  In order to achieve the above object, a temperature control device for a machine tool according to the present invention includes a cooling circuit that circulates a heat medium liquid in a machine tool, and a refrigerator that is driven at a constant rotational speed to compress refrigerant gas. A condenser for radiating and liquefying the heat of the refrigerant gas compressed by the refrigerator; an expansion valve for constricting and expanding the liquefied refrigerant gas; and a low-pressure low-temperature gas-liquid that is constricted and expanded A heat exchanger for cooling the heat medium liquid with the refrigerant gas in a mixed state, and the refrigerant gas immediately after exiting the refrigerator is introduced into the heat exchanger by bypassing the condenser A bypass path, a bypass valve provided in the middle of the bypass path, a reference temperature setting means for setting a reference temperature, and a return liquid temperature that is a temperature of the heating medium liquid after cooling the spindle head is detected. A temperature sensor for performing As the temperature difference sensor and the return liquid temperature detected with said reference temperature becomes constant, and a temperature control means for feedback controlling the opening of the opening and the bypass valve of the expansion valve. The temperature control means simultaneously controls the opening degree of the expansion valve and the opening degree of the bypass valve in a one-to-one correspondence with each other so that the opening degree of the expansion valve is a maximum value in a control range. When the opening of the bypass valve becomes the minimum value of the control range, the opening of the bypass valve becomes the maximum value of the control range when the opening of the expansion valve becomes the minimum value of the control range. It is.

  In the temperature control device for a machine tool, it is preferable that the opening degree of the expansion valve and the opening degree of the bypass valve have a linear function relationship.

  In the temperature control device for a machine tool, it is preferable that the temperature control means controls the opening degree of the expansion valve and the opening degree of the bypass valve by PID control.

  In the temperature control device for a machine tool, it is preferable that the expansion valve and the bypass valve are capable of controlling the opening degree by a digital value.

  Since this invention is comprised as mentioned above, there exist the following effects.

  Since the opening degree of the expansion valve and the opening degree of the bypass valve are linked and controlled, the cooling capacity of the temperature control device can be changed and controlled continuously and accurately from the minimum value to the maximum value. Thus, smooth and highly accurate temperature control over a wide range is possible without performing inverter control of the refrigerator, and responsiveness of temperature control can be improved. In particular, the accuracy of temperature control in a region with a small heat load can be greatly improved. Further, the inverter control drive device is unnecessary, and the temperature control device can be reduced in cost and size.

  The expansion valve opening and bypass valve opening are linked and controlled by the relationship of the linear function, which simplifies the calculation contents of the temperature control means, reduces the cost of the temperature control device, and improves the responsiveness of the temperature control. Is possible.

  Since the temperature control means controls the opening degree of the expansion valve and the opening degree of the bypass valve by PID control, high-accuracy, high-speed response and high-stable control becomes possible.

  Since the opening degree of the expansion valve and the bypass valve can be controlled by digital values, the opening degree can be controlled with high accuracy.

  Embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing a configuration of a temperature control device 1 of the present invention. Here, a spindle head will be described as an example of a typical heat source of a machine tool. A spindle is rotatably supported on the spindle head, and a tool or a workpiece is attached to the spindle and is driven to rotate. Since the rotation speed of the spindle of the machine tool fluctuates from a stopped state to several thousand revolutions per minute, the spindle head supporting the spindle is cooled and temperature control is performed. A certain temperature difference is maintained. That is, the control target is to keep the temperature of the spindle head at a constant temperature difference with respect to the reference temperature. However, the constant temperature difference in this case includes the case where the temperatures are equal (temperature difference 0).

  The reference temperature is generally set to a room temperature or a temperature of a member (for example, a bed or a column) having a large time constant (a large heat capacity) in a component of the machine tool. The temperature of the reference part measured by the reference temperature sensor 13 is set as the reference temperature. The reference temperature may be selected from among the temperatures measured at a plurality of positions, or an average value of a plurality of measured values may be used as the reference temperature. Moreover, it is good also as a reference temperature by giving an appropriate calculation to a measured value.

  In FIG. 1, a cooling circuit 2 is provided to cool a spindle head of a machine tool, and cooling oil circulates in the cooling circuit 2 as a heat medium liquid. A cooling pump 22 provided in the cooling circuit 2 is driven by a drive motor 23 to circulate the cooling oil in the cooling circuit 2 at a constant flow rate. The cooling oil is cooled by the heat exchanger 8, and then flows into the spindle head to cool the spindle head. The cooling oil after cooling the spindle head returns to the cooling pump 22 through the cooling circuit 2. The temperature (return oil temperature) of the cooling oil after cooling the spindle head is detected by the temperature sensor 21, and feedback control is performed so that the return oil temperature becomes the set temperature. The set temperature is set to a value having a certain temperature difference from the reference temperature. The temperature difference may be 0. In this case, the set temperature is equal to the reference temperature. The temperature sensor 21 is not limited to the position shown in FIG. 1 and may be disposed at any position as long as the return oil temperature can be detected. For example, it may be arranged on the inflow side of the cooling pump 22.

  On the other hand, with respect to the refrigerant flowing into the heat exchanger 8, first, the refrigerant gas is compressed by the refrigerator 5 and sent to the condenser 6. In the condenser 6, the heat of the refrigerant gas that has been compressed and has risen in temperature is radiated and liquefied. The condenser 6 is cooled by air cooling by a cooling fan 61. The liquefied refrigerant gas is further squeezed and expanded when passing through the expansion valve 7 to enter a low-temperature and low-pressure gas-liquid mixed state. This low-temperature and low-pressure gas-liquid mixed refrigerant gas flows into the heat exchanger 8 to cool the cooling oil. The refrigerant gas takes the heat of the cooling oil in the heat exchanger 8 and vaporizes, and efficiently cools the cooling oil by the heat of vaporization. The refrigerant gas flowing out of the heat exchanger 8 returns to the refrigerator 5 and circulates in the circulation circuit 3.

  The refrigerator 5 is driven by a normal AC power source and is driven at a constant rotational speed. In the present invention, the inverter 5 is not used for driving the refrigerator 5, and the refrigerator 5 is driven at a constant rotational speed. Thereby, an inverter control drive device becomes unnecessary, the cost of the temperature control device 1 can be reduced, and the temperature control device 1 can be downsized.

  In the circulation circuit 3 in which the refrigerant gas from the refrigerator 5 circulates, a bypass path 4 is provided for allowing a part of the refrigerant gas that has been compressed to rise in temperature to flow into the heat exchanger 8 without being cooled. The bypass passage 4 is provided with a bypass valve 9 which is a flow rate adjusting valve. The bypass 4 is provided to reduce and adjust the cooling capacity for cooling the cooling oil. When the bypass valve 9 is in the open state, the high temperature gas is mixed with the low temperature refrigerant gas and flows into the heat exchanger 8, so that the cooling capacity is reduced. By changing and controlling the opening degree of the bypass valve 9, the cooling capacity can be changed and controlled. When the bypass valve 9 is fully closed, the high temperature gas is not mixed, and the cooling capacity of the refrigerator 5 is maximized.

  The temperature controller 10 controls the opening of the expansion valve 7 and the opening of the bypass valve 9 to control the temperature of the spindle head of the machine tool. In addition, a display unit 11 and an input unit 12 are connected to the temperature control unit 10. Various parameters relating to temperature control can be confirmed by the display unit 11, and these parameters can be input by the input unit 12. As for the temperature of the spindle head, the temperature of the cooling oil that has returned after cooling the spindle head (return oil temperature) is detected by the temperature sensor 21, and the detected value is used as the representative temperature value of the spindle head. Feedback control is performed so that the return oil temperature becomes the set temperature.

  Feedback control is performed with high accuracy, high speed response and high stability by PID control. That is, feedback control is performed by changing and controlling the opening degree of the expansion valve 7 and the opening degree of the bypass valve 9 by PID control. The opening of the expansion valve 7 and the opening of the bypass valve 9 are simultaneously controlled in conjunction so as to have a one-to-one relationship.

  FIG. 2 is a graph showing an interlocking relationship between the opening degree of the expansion valve 7 and the opening degree of the bypass valve 9. The opening degree of the expansion valve 7 is X, and the opening degree of the bypass valve 9 is Y. The horizontal axis in FIG. 2 represents the opening degree X, and the vertical axis represents the opening degree Y. Further, the minimum value of the control range of the opening degree X of the expansion valve 7 is x1, and the maximum value is x2. And let the minimum value of the control range of the opening degree Y of the bypass valve 9 be y1, and let the maximum value be y2. When the opening degree X of the expansion valve 7 is changed from the minimum value x1 to the maximum value x2, the opening degree Y of the bypass valve 9 is changed from the maximum value y2 to the minimum value y1 in conjunction therewith.

  That is, when the opening degree X of the expansion valve 7 is the minimum value x1, the opening degree Y of the bypass valve 9 is set to the maximum value y2, and when the opening degree X of the expansion valve 7 is the maximum value x2, the opening degree Y of the bypass valve 9 is set. Is the minimum value y1. The interlocking relationship between the opening degree X and the opening degree Y is represented by a straight line connecting the point A (x1, y2) and the point B (x2, y1). That is, the opening degree X and the opening degree Y have a linear function relationship. This linear equation is expressed by the following equation 1.

(y2−y1) (X−x1) + (x2−x1) (Y−y2) = 0 Equation 1
In addition, the expansion valve 7 and the bypass valve 9 move a valve body by driving a stepping motor, and adjust the opening degree of the valve. For this reason, the opening degree of each valve can be accurately adjusted by the opening degree command of a digital value.

FIG. 3 is a graph showing the adjustment range of the cooling capacity Q of the temperature control device 1. By controlling the opening X of the expansion valve 7 and the opening Y of the bypass valve 9 together, the cooling capacity Q of the temperature control device 1 can be smoothly controlled over a wide range. As shown in the figure, by changing the opening X of the expansion valve 7 from the minimum value x1 to the maximum value x2, the cooling capacity Q can be changed and controlled continuously and accurately from the minimum value 0 to the maximum value _Qmax. it can. At this time, the opening degree Y of the bypass valve 9 is controlled in conjunction with the opening degree X of the expansion valve 7 as shown in FIG.

In the temperature control device 1 of FIG. 1, a configuration in which a fixed throttle capillary (capillary tube) or the like is provided instead of the expansion valve 7 is also conceivable. In this case, the cooling capacity Q is adjusted only by the change control of the opening degree of the bypass valve 9, but a wide range of continuous change control as shown in FIG. 3 cannot be performed. In particular, when the minimum value of the cooling capacity Q cannot be set to 0 as shown in FIG. 3 and the cooling capacity is less than that, it is necessary to perform on / off control at the minimum value Q _min . For this reason, the accuracy of temperature control in a region with a small heat load is greatly deteriorated.

  As a result of experiments, it has been found that when a capillary with a fixed throttle is used, the amount of low-temperature refrigerant gas flowing into the heat exchanger 8 cannot be controlled in a wide range and lacks quick response. For this reason, the time (stable time) until the oil temperature is stabilized when the output of the spindle is changed becomes longer. In addition, temperature control in a region with a small heat load is on / off control, and high-precision temperature control is difficult. During the on / off control, a steady deviation between the return oil temperature and the set temperature also occurs.

In contrast, in the present invention, since the opening degree X of the expansion valve 7 and the opening degree Y of the bypass valve 9 are controlled in conjunction with each other, the cooling capacity Q of the temperature control device 1 is changed from the minimum value 0 to the maximum value Q _max. Can be controlled continuously and with high accuracy. Thereby, smooth and highly accurate temperature control over a wide range is possible without performing inverter control of the refrigerator 5, and the responsiveness of temperature control can be improved. In particular, the accuracy of temperature control in a region with a small heat load can be greatly improved. Further, the inverter control drive device is not necessary, and the temperature control device 1 can be reduced in cost and size.

  According to the present invention, smooth and highly accurate temperature control over a wide range is possible, and responsiveness of temperature control can be improved. In particular, the accuracy of temperature control in a region with a small heat load can be greatly improved. Further, the inverter control drive device is unnecessary, and the temperature control device can be reduced in cost and size.

It is a figure which shows the structure of the temperature control apparatus 1 of the machine tool of this invention. 4 is a graph showing an interlocking relationship between the opening degree of the expansion valve 7 and the opening degree of the bypass valve 9. 4 is a graph showing an adjustment range of a cooling capacity of the temperature control device 1.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Temperature control apparatus 2 Cooling circuit 3 Circulation circuit 4 Bypass path 5 Refrigerator 6 Condenser 7 Expansion valve 8 Heat exchanger 9 Bypass valve 10 Temperature control part 11 Display part 12 Input part 13 Reference temperature sensor 21 Temperature sensor 22 Cooling pump 23 Drive motor 61 Cooling fan

Claims (4)

A cooling circuit (2) for circulating the heat transfer fluid to the machine tool;
A refrigerator (5) driven at a constant rotational speed to compress the refrigerant gas;
A condenser (6) for radiating and liquefying the heat of the refrigerant gas compressed by the refrigerator (5);
An expansion valve (7) for constricting and expanding the liquefied refrigerant gas;
A heat exchanger (8) for cooling the heat medium liquid by the refrigerant gas in a gas-liquid mixed state of low pressure and low temperature that has been swelled and expanded;
A bypass path (4) for introducing the refrigerant gas immediately after leaving the refrigerator (5) into the heat exchanger (8), bypassing the condenser (6);
A bypass valve (9) provided in the middle of the bypass path (4);
Reference temperature setting means (10, 13) for setting the reference temperature;
A temperature sensor (21) for detecting a return liquid temperature which is the temperature of the heat medium liquid after cooling the spindle head;
The opening (X) of the expansion valve (7) and the opening of the bypass valve (9) so that the temperature difference between the return liquid temperature detected by the temperature sensor (21) and the reference temperature is constant. Temperature control means (10) for feedback control of (Y),
The temperature control means (10) controls the opening degree (X) of the expansion valve (7) and the opening degree (Y) of the bypass valve (9) simultaneously in conjunction with a value corresponding to one-to-one. When the opening (X) of the expansion valve (7) reaches the maximum value (x2) of the control range, the opening (Y) of the bypass valve (9) becomes the minimum value (y1) of the control range, and the expansion When the opening (X) of the valve (7) becomes the minimum value (x1) of the control range, the opening (Y) of the bypass valve (9) becomes the maximum value (y2) of the control range. A temperature control device for a machine tool. A temperature control device for a machine tool according to claim 1,
A temperature control device for a machine tool, wherein the opening (X) of the expansion valve (7) and the opening (Y) of the bypass valve (9) have a linear function relationship. A temperature control device for a machine tool according to any one of claims 1 and 2,
A temperature control device for a machine tool, wherein the temperature control means (10) controls the opening degree (X) of the expansion valve (7) and the opening degree (Y) of the bypass valve (9) by PID control. A temperature control device for a machine tool according to any one of claims 1 to 3,
The expansion valve (7) and the bypass valve (9) are temperature control devices for machine tools, the opening degree of which can be controlled by digital values.

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