Servo control system

Abstract

A servo control system according to one embodiment of the present disclosure controls a servo motor, the servo control system comprising: a servo amplifier capable of changing a pulse frequency by supplying a pulse width modulated drive current to the servo motor; and a servo control device that commands the target speed or target position of the servo motor and the pulse frequency to the servo amplifier, the servo control device being provided with: a target command unit that commands the target speed or target position; a power consumption calculation unit that calculates the total power consumption of the servo motor and the servo amplifier for each of a plurality of set frequencies set in advance as the pulse frequency, on the basis of 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 setting frequency, among the plurality of setting frequencies, at which the total power consumption is minimum.

Description

Technical Field

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

[0002] For example, a servo control system is used to control a machine tool equipped with multiple servo motors. This servo control system includes a servo amplifier that supplies drive current to the servo motors, and a servo control device that instructs the servo system on target speeds for the servo motors based on a machining program. In such a system, a technique has been proposed to extend the pulse period of pulse width modulation (PWM) to suppress motor heat generation when the drive current exceeds a threshold level calculated based on the excitation frequency (see, for example, Patent Document 1).

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Application Laid-Open No. 2005-33972 Summary of the Invention

[0006] Problems to be solved by the invention

[0007] The heat generated by the servo motor becomes a problem when the load is relatively large. On the other hand, even when the load is relatively small, it is desirable to reduce the power consumption of the servo system.

[0008] Means for solving problems

[0009] A servo control system according to one embodiment of the present invention controls a servo motor, the servo control system comprising: a servo amplifier that supplies a drive current subjected to pulse width modulation to the servo motor and is capable of changing the pulse frequency; a servo control device that instructs the servo amplifier of a target speed or target position of the servo motor and the pulse frequency, the servo control device comprising: a target instruction unit that instructs the target speed or 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 from at least one of the servo motor and the servo amplifier; and a frequency instruction unit that instructs the servo amplifier to perform pulse width modulation at the set frequency at which the total power consumption is minimized among the plurality of set frequencies. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 It is a schematic diagram showing the configuration of a servo control system according to one embodiment of the present disclosure.

[0011] Figure 2This is a graph showing the relationship between the pulse frequency and power consumption at low speed when copper loss is dominant.

[0012] Figure 3 This is a graph showing the relationship between the pulse frequency and power consumption at high speed when copper loss dominates.

[0013] Figure 4 This is a graph showing the relationship between the pulse frequency and power consumption at low torque when iron loss dominates.

[0014] Figure 5 This is a graph showing the relationship between the pulse frequency and power consumption at high torque when iron loss dominates. DETAILED DESCRIPTION

[0015] Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings. Figure 1 Schematic diagram showing the configuration of a servo control system 1 according to an embodiment of the present disclosure.

[0016] 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 .

[0017] The servo motor 10 rotates its shaft by a drive current supplied from the servo amplifier 20. As an example of the servo motor 10 to which the present disclosure is applied, a motor with relatively high output and high power consumption is envisioned, and a spindle motor of a machine tool is envisioned as a specific example.

[0018] 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 cycle) 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. Furthermore, the servo amplifier 20 is configured to change the pulse frequency of the pulse-width modulation according to a frequency setting command input from the servo control device 30.

[0019] The servo control device 30 includes memory, a processor (CPU), input / output interfaces, and other components, and can be implemented by one or more computer devices executing appropriate control programs. The structural elements of the servo control device 30 described below are a classification of the functions (processor operations) of the servo control device 30 and may not be clearly distinguished in terms of physical or program structure.

[0020] The servo control device 30 includes: a target instruction unit 31, which instructs the servo motor 10 to the target speed or target position to the servo amplifier 20; a setting storage unit 32, which stores a plurality of pre-set setting frequencies; a power consumption calculation unit 33, which calculates the total power consumption of the servo motor 10 and the servo amplifier 20; and a frequency instruction unit 34, which instructs the servo amplifier 20 to have a pulse frequency.

[0021] The target command unit 31 has a well-known structure and calculates a target speed or target position of the servo motor 10 at each time according to an operation program describing the operation of the servo motor 10 , for example, a machining program describing the operation of a machine tool including the servo motor 10 .

[0022] The setting storage unit 32 stores a plurality of set frequencies that are preset as pulse frequencies of pulse width modulation in the servo amplifier 20 .

[0023] 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 .

[0024] The power consumption calculation unit 33 can 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 can be configured to obtain the speed and torque of the servo motor 10 based on 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 the power consumption of the servo motor 10 can be accurately calculated, but also the power consumption of the servo amplifier 20 can be calculated relatively accurately.

[0025] The power consumption calculation unit 33 may be configured to calculate the total power consumption based on only one of the speed and torque of the servo motor 10. Furthermore, if the ratio of the iron loss of the servo motor 10 to the total power consumption is sufficiently large, the error is relatively small even when the total power consumption is calculated based only on the speed of the servo motor 10. Figure 2 、 Figure 3 The figure shows the relationship between the pulse frequency of pulse width modulation and power consumption when iron loss dominates. Figure 2 Indicates that the speed of the servo motor 10 is relatively low. Figure 3 The figure shows a case where the speed of the servo motor 10 is relatively high. In addition, each figure shows three set frequencies with auxiliary lines (dashed lines).

[0026] When the ratio of the copper loss of the servo motor 10 to the total power consumption is sufficiently large, the error is relatively small even when the total power consumption is calculated based on only the torque of the servo motor 10 . Figure 4 、 Figure 5The figure shows the relationship between the pulse frequency of pulse width modulation and power consumption when copper loss is dominant. Figure 4 This indicates a case where the torque of the servo motor 10 is relatively small. Figure 5 This shows a case where the torque of the servo motor 10 is relatively large. The pulse frequency at which the total power consumption is minimized in this manner varies depending on the device configuration in addition to the speed and torque of the servo motor 10 .

[0027] The power consumption calculation unit 33 may be configured to calculate the total power consumption using a plurality of reference tables that pre-store a correspondence between at least one of the speed and torque of the servo motor 10 and the total power consumption at a set frequency. Using the reference tables allows calculation of the total power consumption with a relatively small computational load, thereby enabling rapid response to load fluctuations.

[0028] The power consumption calculation unit 33 may be configured to calculate the total power consumption when the command of the target command unit 31 is changed. Alternatively, the power consumption calculation unit 33 may 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 period. By calculating the total power consumption when the probability of a change in the operating state is high, unnecessary computational load can be reduced.

[0029] Frequency command unit 34 commands servo amplifier 20 to perform pulse width modulation at a frequency that minimizes the total power consumption calculated by power consumption calculation unit 33, among multiple set frequencies.

[0030] The frequency command unit 34 may also be configured to command the servo amplifier 20 a specific set frequency, which is pre-set as the set frequency that minimizes total power consumption during no-load operation, regardless of the calculation result of the power consumption calculation unit 33, when the servo motor is operating at no-load. No-load operation, for example, involves confirming the operation of a machine tool without installing a tool or workpiece. This can be determined through an operating program, user input, or the like. If no-load operation is clearly occurring, setting the pulse frequency to the optimal frequency for no-load operation can more reliably suppress power consumption.

[0031] The servo control system 1 includes a servo control device 30 having a frequency command unit 34 for instructing 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.

[0032] The following supplementary notes are further disclosed regarding the above-mentioned embodiment and modifications.

[0033] (Note 1)

[0034] A servo control system (1) is a servo control system (1) for controlling a servo motor (10), comprising: a servo amplifier (20) for supplying a drive current subjected to pulse width modulation to the servo motor (10) and capable of changing the pulse frequency of the pulse width modulation; a servo control device (30) for instructing the servo amplifier (20) on a target speed or target position and a pulse frequency of the servo motor (10); the servo control device (30) comprising: a target instruction unit (31) for instructing the target speed or target position; a power consumption calculation unit (33) for calculating the total power consumption of the servo motor (10) and the servo amplifier (20) for each of a plurality of set frequencies that are pre-set as pulse frequencies based on information of at least one of the servo motor (10) and the servo amplifier (20); and a frequency instruction unit (34) for instructing the servo amplifier (20) to set a set frequency with the smallest total power consumption among the plurality of set frequencies as the pulse frequency.

[0035] (Note 2)

[0036] 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).

[0037] (Note 3)

[0038] In the servo control system (1) of Appendix 2, the power consumption calculation unit (33) may calculate the total power consumption using a plurality of reference tables, wherein the plurality of reference tables pre-store a correspondence between at least one of the speed and torque of the servo motor (10) and the total power consumption at a set frequency.

[0039] (Note 4)

[0040] In the servo control system (1) of any one of Appendixes 1 to 3, the power consumption calculation unit (33) may calculate the total power consumption when the instruction of the target instruction unit (31) is changed or when the speed of the servo motor (10) changes by more than a certain amount.

[0041] (Note 5)

[0042] In the servo control system (1) of any one of Notes 1 to 4, the frequency instruction unit (34) may instruct the servo amplifier (20) to set a predetermined specific set frequency regardless of the calculation result of the power consumption calculation unit (33) when the servo motor (10) is operating without load.

[0043] The present disclosure has been described in detail above, but the present disclosure is not limited to the above-mentioned embodiments. These embodiments can be variously added, replaced, changed, partially deleted, etc. without departing from the scope of the main purpose of the present disclosure, or without departing from the scope of the main purpose of the present disclosure derived from the contents recorded in the claims and their equivalents. In addition, these embodiments can also be implemented in combination. For example, in the above-mentioned embodiments, the order of each action and the order of each processing are shown as an example and are not limited to this. In addition, the same applies to the case where numerical values or mathematical formulas are used in the description of the above-mentioned embodiments.

[0044] Description of Reference Numerals

[0045] 1 Servo control system

[0046] 10 Servo motor

[0047] 20 Servo amplifier

[0048] 30 Servo control device

[0049] 31 Target Command Unit

[0050] 32 Setting storage unit

[0051] 33 Power consumption calculation unit

[0052] 34 Frequency command unit.

Claims

1. A servo control system for controlling a servo motor, characterized in that: The servo control system has: 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 for instructing the servo amplifier on the target speed or target position of the servo motor and the pulse frequency, The servo control device comprises: a target instruction unit for instructing 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 preset as the pulse frequency based on information on at least one of the servo motor and the servo amplifier; A frequency instruction unit instructs the servo amplifier to set the set frequency with the smallest total power consumption among the plurality of set frequencies as the pulse frequency.

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

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

4. The servo control system according to any one of claims 1 to 3, characterized in that: The power consumption calculation unit calculates the total power consumption when the command of the target command unit is changed or when the speed or torque of the servo motor changes by a certain amount or more.

5. The servo control system according to any one of claims 1 to 4, characterized in that: The frequency command unit commands the preset specific set frequency to the servo amplifier regardless of the calculation result of the power consumption calculation unit when the servo motor is in no-load operation.

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