Servo control system

Abstract

A servo control system according to one embodiment of the present disclosure controls a servomotor, and comprises: a servo amplifier that supplies the servomotor with a pulse-width-modulated drive current, and that can change pulse frequencies; and a servo control device that gives the servo amplifier an instruction on the target speed or the target position of the servomotor and the pulse frequencies. The servo control device has: a target instruction unit that gives an instruction on the target speed or the target position; a power consumption calculation unit that calculates, on the basis of information on the servomotor and / or the servo amplifier, the total power consumption of the servomotor and the servo amplifier at each of a plurality of set frequencies set in advance as the pulse frequencies; and a frequency instruction unit that gives the servo amplifier an instruction to perform the pulse width modulation at a set frequency, among the plurality of set frequencies, at which the total power consumption becomes minimum.

Description

Servo Control System

[0001] The present invention relates to a servo control system.

[0002] For example, to control a machine tool having multiple servo motors, a servo control system is used that includes a servo amplifier that supplies drive current to the servo motors and a servo control device that commands the servo system to set target speeds, etc. of the servo motors based on a machining program, etc. In such a system, in order to suppress heat generation in the motor, a technique has been proposed that lengthens the pulse period of pulse width modulation when the drive current value is greater than a threshold level calculated from the excitation frequency (see, for example, Patent Document 1).

[0003] Japanese Patent Application Laid-Open No. 2005-33972

[0004] Heat generation in a servo motor can be a problem when the load is relatively heavy. On the other hand, even when the load is relatively light, it is desirable to reduce the power consumption of the servo system.

[0005] A servo control system according to one aspect of the present disclosure is a servo control system for controlling a servo motor, comprising: a servo amplifier that supplies a pulse-width modulated drive current to the servo motor and is capable of changing the pulse frequency; and a servo control device that commands the servo amplifier a target speed or target position of the servo motor and the pulse frequency, wherein the servo control device has a target command unit that commands the target speed or the target position; a power consumption calculation unit that calculates the total power consumption of the servo motor and the servo amplifier at each of a plurality of set frequencies that are pre-set as the pulse frequency based on information about at least one of the servo motor and the servo amplifier; and a frequency command unit that commands the servo amplifier to perform the pulse width modulation at the set frequency among the plurality of set frequencies that minimizes the total power consumption.

[0006] Fig. 1 is a schematic diagram showing a configuration of a servo control system according to an embodiment of the present disclosure; Fig. 2 is a graph showing the relationship between pulse frequency and power consumption at low speed when copper loss is dominant; Fig. 3 is a graph showing the relationship between pulse frequency and power consumption at high speed when copper loss is dominant; Fig. 4 is a graph showing the relationship between pulse frequency and power consumption at low torque when iron loss is dominant; and Fig. 5 is a graph showing the relationship between pulse frequency and power consumption at high torque when iron loss is dominant.

[0007] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present disclosure will now be described with reference to the accompanying drawings. Fig. 1 is a schematic diagram showing the configuration of a servo control system 1 according to an embodiment of the present disclosure.

[0008] The servo control system 1 includes a servo motor 10 , a servo amplifier 20 that supplies a drive current to the servo motor 10 , and a servo control device 30 that inputs a command value to the servo amplifier 20 .

[0009] The servo motor 10 rotates its shaft by a drive current supplied from the servo amplifier 20. The servo motor 10 to which the present disclosure is applied is assumed to be a motor with a relatively large output and high power consumption, a specific example of which is a spindle motor of a machine tool.

[0010] The servo amplifier 20 supplies a pulse-width modulated drive current to the servo motor 10. The servo amplifier 20 is configured to adjust the pulse width (duty ratio) of the drive current so that the speed signal or position signal fed back from the servo motor 10 matches the target speed or target position commanded by the servo control device 30. The servo amplifier 20 is also configured to be able to change the pulse frequency of the pulse-width modulation in accordance with a frequency setting command input from the servo control device 30.

[0011] The servo control device 30 can be realized by one or more computers that have a memory, a processor (CPU), an input / output interface, etc., and that execute appropriate control programs. The components of the servo control device 30 described below are classifications of the functions (operations of the processor) of the servo control device 30, and do not necessarily have to be clearly distinguishable in terms of physical configuration and program configuration.

[0012] The servo control device 30 has a target command unit 31 that commands the servo amplifier 20 to set a target speed or target position of the servo motor 10, a setting memory unit 32 that stores a plurality of preset set frequencies, a power consumption calculation unit 33 that calculates the total power consumption of the servo motor 10 and the servo amplifier 20, and a frequency command unit 34 that commands the servo amplifier 20 to set a pulse frequency.

[0013] The target command unit 31 has a well-known configuration and calculates the target speed or target position of the servo motor 10 at each time in accordance with an operation program that describes the operation of the servo motor 10, such as a machining program that describes the operation of a machine tool that includes the servo motor 10.

[0014] The setting storage unit 32 stores a plurality of set frequencies that are set in advance as pulse frequencies for pulse width modulation in the servo amplifier 20 .

[0015] The power consumption calculation unit 33 calculates the total power consumption of the servo motor 10 and the servo amplifier 20 at each of a plurality of set frequencies based on information on at least one of the servo motor 10 and the servo amplifier 20 .

[0016] The power consumption calculation unit 33 may be configured to calculate the total power consumption based on the speed and torque of the servo motor 10. The power consumption calculation unit 33 may be configured to acquire the speed and torque of the servo motor 10 from a feedback signal from the servo motor 10 or a control signal from the servo amplifier 20. If the speed and torque of the servo motor 10 can be determined, not only can the power consumption of the servo motor 10 be accurately calculated, but also the power consumption of the servo amplifier 20 can be calculated relatively accurately.

[0017] The power consumption calculation unit 33 may be configured to calculate the total power consumption based on only either the speed or torque of the servo motor 10. Furthermore, if the proportion of iron loss in the servo motor 10 in the total power consumption is sufficiently large, the error will be relatively small even if the total power consumption is calculated based only on the speed of the servo motor 10. Figures 2 and 3 show the relationship between the pulse frequency of pulse width modulation and power consumption when iron loss is dominant. Figure 2 shows the case when the speed of the servo motor 10 is relatively low, and Figure 3 shows the case when the speed of the servo motor 10 is relatively high. In each figure, three set frequencies are indicated by auxiliary lines (dashed lines).

[0018] When the proportion of the copper loss of the servo motor 10 in the total power consumption is sufficiently large, the error in calculating the total power consumption based only on the torque of the servo motor 10 is relatively small. Figures 4 and 5 show the relationship between the pulse frequency of pulse width modulation and power consumption when copper loss is dominant. Figure 4 shows the case when the torque of the servo motor 10 is relatively small, and Figure 5 shows the case when the torque of the servo motor 10 is relatively large. Thus, the pulse frequency at which the total power consumption is minimized varies not only with the speed and torque of the servo motor 10, but also with the device configuration.

[0019] The power consumption calculation unit 33 may be configured to calculate the total power consumption using a plurality of lookup tables that store in advance, for each set frequency, the correspondence relationship between the total power consumption and at least one of the speed and torque of the servo motor 10. By using the lookup tables, the total power consumption can be calculated with a relatively small calculation load, allowing for a quick response to load fluctuations.

[0020] The power consumption calculation unit 33 may be configured to calculate the total power consumption when the command from the target command unit 31 is changed. The power consumption calculation unit 33 may also be configured to calculate the total power consumption when the speed or torque of the servo motor 10 changes by a certain amount or more within a predetermined time. In this way, by calculating the total power consumption when there is a high probability that the operating state has changed, unnecessary calculation load can be reduced.

[0021] The frequency command unit 34 commands the servo amplifier 20 to perform pulse width modulation at a set frequency among the plurality of set frequencies that minimizes the total power consumption calculated by the power consumption calculation unit 33. This makes it possible to select a pulse frequency that can relatively minimize the total power consumption depending on the operating state of the servo control system 1.

[0022] The frequency command unit 34 may be configured to command the servo amplifier 20 to use a specific set frequency that is preset as a set frequency that minimizes total power consumption during pre-no-load operation of the servo motor, regardless of the calculation result of the power consumption calculation unit 33. No-load operation is, for example, operation of a machine tool to check the operation of the device without a tool or workpiece attached, and can be determined by the operating program, user input, etc. When no-load operation is clearly occurring, power consumption can be more reliably reduced by setting the pulse frequency optimal for no-load operation.

[0023] The servo control system 1 includes a servo control device 30 having a frequency command unit 34 that commands the servo amplifier 20 to perform pulse width modulation at a set frequency that minimizes the total power consumption calculated by the power consumption calculation unit 33. Therefore, the pulse frequency of the pulse width modulation of the servo amplifier 20 can be appropriately set according to the operating state, thereby suppressing the power consumption of the entire system.

[0024] The following supplementary note is further disclosed regarding the above embodiment and modified examples. (Supplementary Note 1) A servo control system (1) controls a servo motor (10), and includes: a servo amplifier (20) that supplies a pulse-width modulated drive current to the servo motor (10) and is capable of changing the pulse frequency of the pulse-width modulation; and a servo control device (30) that commands the servo amplifier (20) a target speed or target position and a pulse frequency for the servo motor (10), the servo control device (30) having a target command unit (31) that commands the target speed or target position, a power consumption calculation unit (33) that calculates the total power consumption of the servo motor (10) and the servo amplifier (20) at each of a plurality of set frequencies that are preset as pulse frequencies based on information from at least one of the servo motor (10) and the servo amplifier (20), and a frequency command unit (34) that commands the servo amplifier (20) to set the pulse frequency to the set frequency from the plurality of set frequencies that minimizes the total power consumption.

[0025] (Supplementary Note 2) In the servo control system (1) of Supplementary Note 1, the power consumption calculation unit (33) may calculate the total power consumption based on at least one of the speed and torque of the servo motor (10).

[0026] (Supplementary Note 3) In the servo control system (1) of Supplementary Note 2, the power consumption calculation unit (33) may calculate the total power consumption using a plurality of lookup tables that store in advance, for each set frequency, a correspondence relationship between at least one of the speed and torque of the servo motor (10) and the total power consumption.

[0027] (Supplementary Note 4) In the servo control system (1) of any one of Supplementary Notes 1 to 3, the power consumption calculation unit (33) may calculate the total power consumption when the command of the target command unit (31) is changed or when the speed of the servo motor (10) changes by more than a certain amount.

[0028] (Supplementary Note 5) In the servo control system (1) of any one of Supplementary Notes 1 to 4, the frequency command unit (34) may command the servo amplifier (20) to a specific preset frequency during no-load operation of the servo motor (10), regardless of the calculation result of the power consumption calculation unit (33).

[0029] Although the present disclosure has been described in detail above, the present disclosure is not limited to the individual embodiments described above. Various additions, substitutions, modifications, partial deletions, etc. are possible in these embodiments without departing from the gist of the present disclosure or the spirit of the present disclosure derived from the content of the claims and their equivalents. These embodiments can also be implemented in combination. For example, in the above-described embodiments, the order of each operation and the order of each process are shown as examples and are not limited to these. The same applies when numerical values ​​or mathematical expressions are used in the description of the above-described embodiments.

[0030] REFERENCE SIGNS LIST 1 Servo control system 10 Servo motor 20 Servo amplifier 30 Servo control device 31 Target command unit 32 Setting storage unit 33 Power consumption calculation unit 34 Frequency command unit

Claims

1. A servo control system for controlling a servo motor, a servo amplifier that supplies a pulse-width modulated drive current to the servo motor and is capable of changing a pulse frequency of the pulse-width modulation; a servo control device that commands the servo amplifier to set a target speed or a target position of the servo motor and the pulse frequency; Equipped with The servo control device a target command unit that commands the target velocity or the target position; a power consumption calculation unit that calculates the total power consumption of the servo motor and the servo amplifier at each of a plurality of preset frequencies that are set as the pulse frequency, based on information on at least one of the servo motor and the servo amplifier; a frequency command unit that commands the servo amplifier to set the set frequency that minimizes the total power consumption among the plurality of set frequencies as the pulse frequency; A servo control system having:

2. The servo control system according to claim 1 , wherein the power consumption calculation unit calculates the total power consumption based on at least one of a speed and a torque of the servo motor.

3. 3. The servo control system according to claim 2, wherein the power consumption calculation unit calculates the total power consumption using a plurality of lookup tables that store in advance, for each set frequency, a correspondence relationship between at least one of a speed and a torque of the servo motor and the total power consumption.

4. 4. The servo control system according to claim 1, wherein the power consumption calculation unit calculates the total power consumption when a command from the target command unit is changed, or when a speed or torque of the servo motor changes by a certain amount or more.

5. 4. The servo control system according to claim 1, wherein the frequency command unit commands the servo amplifier to use the predetermined specific set frequency regardless of the calculation result of the power consumption calculation unit when the servo motor is operating in no-load mode.