Servo driver and injection molding system

Abstract

Provide is a servo driver capable of coping with motors of various capacities. This servo driver comprises: a supply unit that supplies a drive current to a motor; a detection unit that detects a current value of the drive current with a resolution corresponding to a clock frequency of a supplied clock signal; and a control unit that supplies the clock signal to the detection unit. The control unit can change the clock frequency.

Description

Servo drivers and injection molding systems

[0001] The present invention relates to a servo driver and an injection molding system.

[0002] In a servo system, the position of a motor is counted by an encoder having slits and notified to a servo driver as a feedback signal. Patent Document 1 proposes a technology for increasing the resolution of an encoder by supplying a high-speed clock to a counter that counts the slit intervals of the encoder.

[0003] Japanese Patent Application Laid-Open No. 2005-091047

[0004] The servo driver is provided with a detector that detects the current value of the drive current supplied to the motor. Conventionally, the resolution of drive current detection is determined by the combination of resistors and A / D converters that make up the detector, so different servo drivers are used depending on the desired resolution of drive current detection.

[0005] One aspect of the disclosed technology aims to provide a servo driver and an injection molding system that can change the resolution of drive current detection by a detection unit.

[0006] One aspect of the disclosed technology is exemplified by the following servo driver: The servo driver includes a supply unit that supplies a drive current to a motor, a detection unit that detects the current value of the drive current with a resolution according to the clock frequency of a supplied clock signal, and a control unit that supplies the clock signal to the detection unit, and the control unit is capable of changing the clock frequency.

[0007] The resolution of the detection unit's detection of the drive current value varies depending on the clock frequency of the supplied clock signal. The current value of the motor's rated current also varies depending on the motor's capacity. In the servo driver described above, the resolution of the detection unit can be changed by varying the clock frequency of the clock signal supplied from the control unit.

[0008] The servo driver may further include the following feature: the control unit sets the clock frequency higher as the current value of the drive current decreases. A servo driver with such a feature can suppress a decrease in accuracy of position control of the motor, which is finely controlled due to a low current value of the drive current, by detecting the current value with higher resolution.

[0009] The servo driver may further include the following feature: the motor stores motor information including information related to a current value of a rated current of the motor, and the control unit acquires the motor information from the motor and varies the clock frequency in accordance with the acquired motor information. By including such a feature, the servo driver can supply the detection unit with the clock frequency appropriate for the current value of the rated current indicated by the motor information acquired from the motor.

[0010] The servo driver may further include the following feature: the control unit sets the clock frequency higher as the current value of the rated current indicated by the motor information becomes lower. A servo driver with such a feature can suppress a decrease in accuracy of position control of the motor, which is finely controlled due to a low current value of the rated current, by detecting the current value with higher resolution.

[0011] The servo driver may further include the following feature: the control unit receives information on options related to the clock frequency, and supplies the clock signal of the clock frequency selected from the options to the detection unit. By including such a feature, the servo driver can cause the detection unit to detect the drive current with a user-desired resolution.

[0012] The servo driver may further include the following feature: The servo driver further includes a storage unit that stores a correspondence relationship between the current value of the drive current and the clock frequency. The control unit acquires the current value of the drive current detected by the detection unit, acquires the clock frequency corresponding to the acquired current value of the drive current from the correspondence relationship, and supplies the clock signal of the clock frequency acquired from the correspondence relationship to the detection unit. By having such a feature, the servo driver can determine the clock frequency suitable for detecting the current value of the drive current by referring to the correspondence relationship.

[0013] The disclosed technology can also be understood from the perspective of an injection molding system. The injection molding system includes an injection molding machine and a servo driver. The injection molding machine includes a cylinder having an injection port and filled with a plastic material, a motor receiving a drive current from the servo driver, and an injection unit driven by the motor to inject the plastic material in the cylinder through the injection port. The servo driver includes a supply unit that supplies the drive current to the motor, a detection unit that detects the current value of the drive current with a resolution corresponding to the clock frequency of a supplied clock signal, and a control unit that supplies the clock signal to the detection unit, and the control unit is capable of changing the clock frequency.

[0014] According to this injection molding system, the detection accuracy of the drive current by the detector can be changed by changing the clock frequency of the clock signal supplied to the detector, so that the drive current can be detected with suitable detection accuracy at each stage from the start to the end of injection of the plastic member.

[0015] Furthermore, in the injection molding system, when the control unit is injecting the plastic member, if the absolute value of the fluctuation range per unit time of a torque command value instructed by a host device is equal to or greater than a threshold value, the control unit may supply the clock signal having a first clock frequency to the detection unit, and if the absolute value of the fluctuation range of the torque command value is less than the threshold value, the control unit may supply the clock signal having a second clock frequency higher than the first clock frequency to the detection unit. In this injection molding system, if the absolute value of the fluctuation range of the torque command value is less than the threshold value, the clock frequency of the clock signal supplied to the detection unit is set higher, thereby monitoring torque fluctuations more closely. Therefore, this injection molding system monitors motor torque fluctuations more closely, thereby suppressing torque ripple and stabilizing injection of the plastic member. Consequently, this injection molding system enables the production of more stable molded products.

[0016] According to the disclosed technology, the servo driver can change the resolution of the drive current detection by the detection unit.

[0017] FIG. 1 is a diagram illustrating an example of a servo system according to an embodiment. FIG. 2 is a diagram illustrating an example of a processing block of a control unit included in a servo driver according to an embodiment. FIG. 3 is a diagram illustrating an example of a management table stored in a storage unit according to an embodiment. FIGS. 4A and 4B are diagrams illustrating an example of a relationship between a position command value from a servo driver 1 and a detected position of an output shaft detected by an encoder when the clock frequency of a clock signal supplied to a resistor is changed. FIG. 5 is a diagram illustrating an example of a processing flow of a servo driver according to an embodiment. FIG. 6 is a diagram illustrating an example of a processing flow of a presetting process according to an embodiment. FIG. 7 is a diagram illustrating an example of a processing flow of an in-operation setting process according to an embodiment. FIG. 8 is a diagram illustrating an example of an injection molding system according to a first modified example. FIG. 9 is a diagram illustrating an example of a processing block of a control unit included in a servo driver according to the first modified example. FIG. 10 is a diagram illustrating an example of a management table stored in a storage unit according to the first modified example. FIG. 11 is a diagram schematically illustrating a time-series change in a torque command value for a motor implemented in an injection molding machine.

[0018] 1, a servo driver 1 according to this application example detects the current value of a drive current supplied from a supply unit 12 to a motor 2 using a detection unit 13. The detection unit 13 includes a resistor 131 disposed on a power line 7 that supplies the drive current, and a detection IC 132 that detects the current flowing through the resistor 131.

[0019] In this application example, the detection unit 13 detects the current value of the drive current supplied from the supply unit 12 to the motor 2 with a resolution corresponding to the clock frequency of the clock signal supplied from the control unit 11. The control unit 11 can change the clock frequency of the clock signal supplied to the detection unit 13 (detection IC 132). Changing the clock frequency of the clock signal supplied to the detection IC 132 changes the resolution for detecting the current value of the drive current. Therefore, even when a low-capacity motor 2 is connected, a decrease in the accuracy of position control, etc. for the low-capacity motor 2 can be suppressed by setting the clock frequency of the clock signal high. In other words, according to this application example, the resolution of drive current detection by the detection unit 13 can be changed.

[0020] 1 is a diagram showing an example of a servo system 100 according to an embodiment. The servo system 100 includes a servo driver 1 and a motor 2.

[0021] The servo driver 1 has a control unit 11, a supply unit 12, and a detection unit 13. The control unit 11 is connected to the supply unit 12 by a signal line 14. The control unit 11 is connected to a detection IC 132 of the detection unit 13 by a signal line 15 and a clock signal supply line 16. The supply unit 12 is connected to the motor main body 21 by a power line 7. A resistor 131 is arranged on the power line 7 between the supply unit 12 and the motor main body 21, and inside the servo driver 1.

[0022] The control unit 11 receives a command signal from a higher-level device (not shown) such as a PLC. The control unit 11 also receives a feedback signal from the encoder 23 of the motor 2 via the encoder cable 8. Based on the command signal and the feedback signal, the control unit 11 instructs the supply unit 12 via the signal line 14 on the value of the drive current to be supplied to the motor 2. The control unit 11 may also receive a specification as to whether the clock frequency of the clock signal supplied to the detection IC 132 (described below) via the clock signal supply line 16 should be changed in advance (before the motor 2 is put into operation) or while the motor 2 is in operation (while the motor 2 is in operation).

[0023] The supply unit 12 supplies a drive current to the motor body 21 of the motor 2 via the power line 7 based on power supplied from a commercial power source. The detection unit 13 includes a resistor 131 arranged on the power line 7 and a detection IC 132 connected to the resistor 131. The resistor 131 is a resistor used to detect the drive current flowing through the power line 7. The detection IC 132 measures the current value of the drive current flowing through the resistor 131 with a resolution according to the clock signal supplied from the control unit 11. The detection IC 132 includes a ΔΣ A / D converter.

[0024] The servo driver 1 is formed with a servo system that performs feedback control using a speed detector, a torque detector, a power generator, etc., and these signals are used to servo-control and drive the motor 2.

[0025] The motor 2 is, for example, a three-phase AC servo motor. The motor 2 includes a motor main body 21 and an encoder 23. The motor main body 21 receives a drive current from the servo driver 1 via a power line 7. The encoder 23 detects the operation of the motor main body 21 and generates a feedback signal indicating the detected operation. The encoder 23 stores motor information including information related to the rated current value of the motor 2, and the encoder 23 may include the motor information in the feedback signal. The information related to the rated current value may be the rated current value itself or the rated capacity. The rated current of the motor 2 varies depending on the capacity of the motor 2. The feedback signal is output to the servo driver 1 via an encoder cable 8. The feedback signal includes information related to the displacement of the output shaft 22, such as information about the rotational position (angle) of the output shaft 22 of the motor main body 21, information about the rotational speed of the output shaft 22, and information about the rotational direction of the output shaft 22. The encoder 23 may be configured as a known incremental or absolute type.

[0026] <Processing Blocks of Control Unit 11> The control unit 11 can be considered as a computer including a processor and a memory. Fig. 2 is a diagram showing an example of a processing block of the control unit 11 included in the servo driver 1 according to the embodiment. The control unit 11 includes a first acquisition unit 111, a second acquisition unit 112, a clock control unit 113, a storage unit 114, and an instruction unit 115. The control unit 11 executes a predetermined program stored in the memory to perform processing as each unit, such as the first acquisition unit 111, the second acquisition unit 112, the clock control unit 113, the storage unit 114, and the instruction unit 115.

[0027] The first acquisition unit 111 acquires the current value of the drive current detected by the detection unit 13 from the detection IC 132 via the signal line 15. The second acquisition unit 112 receives a feedback signal from the encoder 23 via the encoder cable 8. The second acquisition unit 112 acquires motor information from the received feedback signal.

[0028] The clock control unit 113 controls the clock frequency of the clock signal supplied to the detection IC 132 via the clock signal supply line 16. The clock control unit 113 controls the clock frequency of the clock signal supplied to the detection IC 132, for example, in accordance with the current value of the drive current acquired from the detection IC 132. For example, when the current value of the drive current is halved, the clock control unit 113 may double the clock frequency of the clock signal supplied to the detection IC 132.

[0029] The clock control unit 113 may also control the clock frequency of the clock signal supplied to the detection IC 132 based on, for example, motor information acquired from the encoder 23. The clock control unit 113 may also receive a clock frequency designated by a user, and control the clock frequency of the clock signal supplied to the detection IC 132 to the received clock frequency.

[0030] The storage unit 114 stores the current value of the drive current and the clock frequency in association with each other. The storage unit 114 is implemented, for example, in a non-volatile storage device. FIG. 3 is a diagram illustrating an example of a management table 1141 stored in the storage unit 114 in this embodiment. The management table 1141 includes fields for "drive current" and "clock frequency." In the management table 1141, the current value of the drive current and the clock frequency are associated with each other. In the example of FIG. 3, a lower drive current is associated with a higher clock frequency. In the example of FIG. 3, three patterns of "drive current" are illustrated: "large," "medium," and "small." However, specific drive current values ​​such as "10 A," "5 A," and "1 A" may also be stored in the management table 1141. Furthermore, in the example of FIG. 3, three patterns of "clock frequency" are illustrated: "high," "medium," and "low." However, specific clock frequency values ​​such as "10 MHz," "5 MHz," and "1 MHz" may also be stored in the management table 1141.

[0031] Here, by referring to the management table 1141, it can be seen that the larger the drive current, the lower the clock frequency. This is because, for example, when driving a small-capacity motor 2, it is considered preferable for servo control of the motor 2 to detect fluctuations in the drive current value more precisely (to have a higher clock frequency for the clock signal supplied to the detection IC 132). The clock control unit 113 may refer to the management table 1141 and determine the clock frequency of the clock signal to be supplied to the detection IC 132 based on, for example, the current value of the rated current indicated by the motor information from the encoder 23 or the current value of the drive current detected by the detection unit 13.

[0032] Returning to Figure 2, the instruction unit 115 determines the current value of the drive current to be supplied to the motor 2 based on a command signal from a higher-level device such as a PLC and a feedback signal received by the second acquisition unit 112, and instructs the supply unit 12 to supply the drive current of the determined current value.

[0033] 4A and 4B are diagrams illustrating the relationship between the position command value from the servo driver 1 and the detected position of the output shaft 22 detected by the encoder 23 when the clock frequency of the clock signal supplied to the resistor 131 is changed. In FIGS. 4A and 4B, the solid lines illustrate the detected position of the output shaft 22, and the dotted lines illustrate the position command value from the servo driver 1. FIG. 4B illustrates a case where a clock signal with a higher clock frequency than that of FIG. 4A is supplied to the detection IC 132. As can be seen by comparing FIGS. 4A and 4B, the clock frequency of the clock signal supplied to the detection IC 132 affects the accuracy of position control. By appropriately setting the clock frequency, the servo driver 1 can more stably obtain the position of the output shaft 22. Consequently, the servo driver 1 can reflect the stably detected position of the output shaft 22 in the position command, thereby achieving more accurate position control.

[0034] <Processing Flow> Fig. 5 is a diagram showing an example of a processing flow of the servo driver 1 according to the embodiment. Hereinafter, an example of the processing flow of the servo driver 1 will be described with reference to Fig. 5 .

[0035] In step S1, the control unit 11 accepts a designation of either pre-setting or in-operation setting. If pre-setting is designated ("pre-setting" in step S1), the process proceeds to step S2. If in-operation setting is designated ("in-operation setting" in step S1), the process proceeds to step S3.

[0036] In step S2, a clock frequency of the clock signal supplied to the detection IC 132 is determined by a presetting process. Details of step S2 will be described later with reference to Fig. 6. In step S3, a clock frequency of the clock signal supplied to the detection IC 132 while the motor 2 is operating is determined. Details of step S3 will be described later with reference to Fig. 7.

[0037] Fig. 6 is a diagram illustrating an example of a processing flow of the presetting processing in the embodiment. The processing in Fig. 6 is an example of the processing executed in step S2 in Fig. 5. Hereinafter, an example of the processing flow of the presetting processing will be described with reference to Fig. 6.

[0038] In step S21, the control unit 11 accepts a designation of automatic setting or manual setting. If automatic setting is designated ("automatic setting" in step S21), the process proceeds to step S22. If manual setting is designated ("manual setting" in step S21), the process proceeds to step S24.

[0039] In step S22, the second acquisition unit 112 acquires motor information of the motor 2 from the encoder 23. In step S23, the clock control unit 113 acquires the current value of the drive current of the motor 2 from the motor information acquired in step S22. The clock control unit 113 acquires the clock frequency corresponding to the current value of the drive current acquired from the motor information, for example, by referring to the management table 1141. The clock control unit 113 determines the clock frequency acquired from the management table 1141 as the clock frequency of the clock signal to be supplied to the detection IC 132.

[0040] The clock control unit 113, for example, displays a menu for selecting a clock frequency on a display device or the like of the servo driver 1. The clock control unit 113, for example, refers to the management table 1141, acquires clock frequencies associated with drive currents in the management table 1141 ("low," "medium," and "high" in the example of FIG. 3) as options, and displays the acquired options on a display device or the like of the servo driver 1. The clock control unit 113 determines a clock frequency selected from the displayed options as the clock frequency of the clock signal to be supplied to the detection IC 132. The selected clock frequency is an example of a "first frequency."

[0041] Fig. 7 is a diagram showing an example of a processing flow of the in-operation setting processing in the embodiment. The processing in Fig. 7 is an example of the processing executed in step S3 in Fig. 5. Hereinafter, an example of the processing flow of the pre-setting processing will be described with reference to Fig. 7.

[0042] In step S31, the first acquisition unit 111 acquires the current value of the drive current from the detection IC 132. In step S32, the clock control unit 113 acquires a clock frequency corresponding to the current value of the drive current acquired in step S31, for example, by referring to the management table 1141. The clock control unit 113 determines the clock frequency acquired from the management table 1141 as the clock frequency of the clock signal to be supplied to the detection IC 132. The processing from step S31 to step S32 may be repeatedly executed at predetermined intervals while the motor 2 is in operation.

[0043] <Effects of the embodiment> One method for detecting drive currents of various current values ​​is to prepare a combination of a resistor with a resistance value corresponding to the current value of the drive current and a detection IC that reads the current value using the resistor. In this method, a servo driver including a resistor and detection IC that are suitable for the current value of the drive current must be prepared to drive the motor 2, making it difficult to drive motors 2 of various drive current values ​​with a single servo driver.

[0044] Here, the resolution of drive current detection by the detector 13 varies depending on the clock frequency of the clock signal supplied from the controller 11. Furthermore, the resolution of drive current detection suitable for servo control also varies depending on the current value of the drive current. In this embodiment, by varying the clock frequency of the clock signal supplied from the controller 11 to the detector IC 132, one servo driver 1 can be used with motors 2 of various capacities. Furthermore, by varying the clock frequency of the clock signal supplied from the controller 11 to the detector IC 132, it becomes possible to maintain the accuracy of position control, torque control, and speed control for motors 2 of various capacities within a predetermined range. For example, the controller 11 sets a higher clock frequency of the clock signal supplied to the detector 13 as the current value of the drive current supplied to the motor 2 decreases. This allows the controller 11 to detect the current value with higher resolution, thereby suppressing a decrease in the accuracy of position control for the motor 2, which is controlled finely due to the low current value of the drive current. In other words, according to this embodiment, by changing the clock frequency of the clock signal supplied to the detector IC 132, the resolution of drive current detection by the detector IC 132 can be changed to a desired resolution.

[0045] In this embodiment, motor information is stored in the motor main body 21 of the motor 2. The motor information includes, for example, information indicating the current value of the rated current of the motor 2. The second acquisition unit 112 acquires the motor information from the motor main body 21 via the encoder cable 8, and the clock control unit 113 determines the clock frequency of the clock signal to be supplied to the detection IC 132 based on the current value of the drive current acquired by the second acquisition unit 112. Therefore, this embodiment reduces the burden on the user associated with determining the clock frequency according to the drive current of the motor 2. For example, the control unit 11 sets a higher clock frequency of the clock signal to be supplied to the detection unit 13 as the current value of the rated current of the motor 2 decreases. This allows the control unit 11 to detect the current value with higher resolution, thereby suppressing a decrease in the accuracy of position control of the motor 2, which is controlled more precisely due to a low current value of the rated current.

[0046] In this embodiment, the clock control unit 113 displays the clock frequencies associated with the drive current in the management table 1141 ("low," "medium," and "high" in the example of FIG. 3) as options on a display device or the like of the servo driver 1, and allows the user to specify a clock frequency from the displayed options. Therefore, according to this embodiment, the drive current can be detected with the resolution desired by the user.

[0047] In this embodiment, the clock control unit 113 can determine the clock frequency of the clock signal to be supplied to the resistor 131 in accordance with the current value of the drive current detected by the detection unit 13. Therefore, according to this embodiment, the drive current can be detected with a resolution in accordance with the drive current of the motor 2 while the motor 2 is in operation.

[0048] <First Modification> The servo system 100 according to the embodiment described above can be applied to, for example, an injection molding machine. In the first modification, a case where the servo system 100 according to the embodiment is applied to an injection molding machine will be described. The same components as those in the embodiment will be assigned the same reference numerals, and their description will be omitted. The first modification will be described below with reference to the drawings.

[0049] 8 is a diagram showing an example of an injection molding system 500 according to a first modified example. The injection molding system 500 includes an injection molding machine 50 and a servo system 100A. The injection molding machine 50 includes a motor 2 and a cylinder 51. The motor 2 is connected to a servo driver 1A by a power line 7 and an encoder cable 8.

[0050] The servo system 100A differs from the servo system 100 according to the embodiment in that it includes a servo driver 1A. A programmable logic controller (PLC) 500 is connected to the servo driver 1A via an industrial network N1. An output shaft 22 of a motor 2 is connected to a cylinder 51, and when the output shaft 22 is driven, a resin (plastic member) plasticized in the cylinder 51 is injected from an injection port 52 of the cylinder 51.

[0051] 9 is a diagram showing an example of a processing block of a control unit 11A included in a servo driver 1A according to the first modification. The control unit 11A differs from the control unit 11 according to the embodiment in that it includes a clock control unit 113A instead of the clock control unit 113 and further includes a third acquisition unit 116.

[0052] The third acquisition unit 116 acquires a torque command value from a command signal from the PLC 500. The clock control unit 113A controls the clock frequency of the clock signal supplied to the detection IC 132 via the clock signal supply line 16 based on the torque command value acquired by the third acquisition unit 116. For example, when the torque command value gradually increases or decreases, the clock control unit 113A lowers the clock frequency supplied to the detection IC 132. Furthermore, for example, when the torque command value is constant, the clock control unit 113A increases the clock frequency compared to when the torque command value gradually increases or decreases. For example, when the torque command value is constant, the clock control unit 113A may set the clock frequency supplied to the detection IC 132 to the highest clock frequency that can be supplied to the detection IC 132.

[0053] FIG. 10 is a diagram showing an example of a management table 1142 stored in the storage unit 114 in the first modified example. The management table 1142 includes fields for "torque command value" and "clock frequency." In the management table 1142, the torque command value from the PLC 500 is associated with the clock frequency. In the example of FIG. 10, a constant torque command value is associated with a high clock frequency. Also, in the example of FIG. 10, an increasing or decreasing torque command value is associated with a low clock frequency. Here, a constant torque command value can be defined as, for example, a case where the absolute value of the fluctuation range of the torque command value per unit time is less than a predetermined threshold. Also, an increase or decrease in the torque command value can be defined as a case where the absolute value of the fluctuation range of the torque command value per unit time is equal to or greater than a predetermined threshold.

[0054] Here, by referring to the management table 1142, it can be seen that the clock frequency becomes high when the torque command value is constant. This is because, for example, it is considered preferable to detect fluctuations in the current value of the drive current in detail in order to control the torque of the motor 2 to be constant. The clock control unit 113A may refer to the management table 1142 based on, for example, fluctuations in the torque command value acquired by the third acquisition unit 116, and determine the clock frequency of the clock signal to be supplied to the detection IC 132.

[0055] FIG. 11 is a diagram schematically illustrating time-series changes in the torque command value for the motor 2 mounted in the injection molding machine 50. In FIG. 10, the vertical axis represents the torque command value, and the horizontal axis represents time. From time T0 to time T1, the torque command value gradually (linearly) increases in order to bring the amount of resin injected per unit time closer to the target value. From time T2 to time T3, the amount of resin injected per unit time reaches the target value, and the torque command value remains constant. From time T2 to time T3, the torque command value gradually (linearly) decreases in order to reduce the amount of resin injected per unit time toward the end of resin injection.

[0056] From time T0 to time T1, the torque command value from the PLC 500 increases, so the clock control unit 113A lowers the clock frequency of the clock signal supplied to the detection IC 132. From time T1 to time T2, the torque command value from the PLC 500 remains constant, so the clock control unit 113A raises the clock frequency of the clock signal supplied to the detection IC 132. Furthermore, from time T2 to time T3, the torque command value from the PLC 500 decreases, so the clock control unit 113A lowers the clock frequency of the clock signal supplied to the detection IC 132.

[0057] According to the first modification, the detection accuracy of the drive current by the detection IC 132 can be changed by changing the clock frequency of the clock signal supplied to the detection IC 132. Therefore, the drive current can be detected with suitable detection accuracy at each stage from the start to the end of resin injection.

[0058] According to the first modification, when the torque command value from the PLC 500 is constant, the clock frequency of the clock signal supplied to the detection IC 132 is set high. This makes it possible to monitor torque fluctuations of the motor 2 more precisely, thereby suppressing torque ripple and stabilizing resin injection, thereby enabling the production of more stable molded products.

[0059] <Other Modifications> In the embodiment described above, the management table 1141 associates the current value of the drive current with the clock frequency of the clock signal. However, the management table 1141 is not limited to this form. For example, the management table 1141 may associate the model number that identifies the model of the motor 2 with the clock frequency of the clock signal. In such a case, the model number of the motor 2 is stored in the motor main body 21 as motor information, and the second acquisition unit 112 acquires this model number from the motor main body 21. The clock control unit 113 then refers to the management table 1141 and determines the clock frequency of the clock signal to be supplied to the detection IC 132 based on the model number acquired by the second acquisition unit 112.

[0060] In the embodiment described above, the larger the drive current supplied to the motor 2, the lower the clock frequency of the clock signal supplied to the detection IC 132. However, even when the drive current is large, a clock signal with a high clock frequency may be supplied to the detection IC 132. For example, when it is desired to achieve torque control with higher accuracy, the clock control unit 113 may achieve torque control with higher accuracy by setting the clock frequency of the clock signal supplied to the detection IC 132 to a higher frequency.

[0061] In the embodiment described above, either the pre-setting or the setting during operation is selected, but such a selection may be omitted. In such a case, the second acquisition unit 112 acquires motor information from the motor main body 21 before the motor 2 starts operating, and the clock control unit 113 determines the clock frequency of the clock signal to be supplied to the detection IC 132 based on the acquired motor information.

[0062] The embodiments and modifications disclosed above can be combined with each other.

[0063] <Supplementary Note 1> A servo driver (1) comprising: a supply unit (12) that supplies a drive current to a motor (2); a detection unit (13) that detects a current value of the drive current with a resolution corresponding to a clock frequency of the supplied clock signal; and a control unit (11) that supplies the clock signal to the detection unit (13), wherein the control unit (11) is capable of changing the clock frequency. <Supplementary Note 2> The servo driver according to Supplementary Note 1, wherein the control unit sets the clock frequency higher as the current value of the drive current decreases. <Supplementary Note 3> The servo driver (1) according to Supplementary Note 1 or 2, wherein the motor (2) stores motor information including information related to a current value of a rated current of the motor (2), and the control unit (11) acquires the motor information from the motor (2) and varies the clock frequency in accordance with the acquired motor information. <Supplementary Note 4> The servo driver according to Supplementary Note 3, wherein the control unit sets the clock frequency higher as the current value of the rated current indicated by the motor information decreases. <Supplementary Note 5> The servo driver (1) according to any one of Supplementary Notes 1 to 4, wherein the control unit (11) receives information on options related to the clock frequency, and supplies the detection unit with the clock signal of the clock frequency selected from the options. <Supplementary Note 6> The servo driver (1) according to any one of Supplementary Notes 1 to 5, further comprising a memory unit (114) that stores a correspondence relationship (1141) between the current value of the drive current and the clock frequency, wherein the control unit (11) acquires the current value of the drive current detected by the detection unit (13), acquires the clock frequency corresponding to the acquired current value of the drive current from the correspondence relationship (1141), and supplies the detection unit (13) with the clock signal of the clock frequency acquired from the correspondence relationship (1141).<Supplementary Note 7> An injection molding system (500) comprising an injection molding machine (50) and a servo driver, wherein the injection molding machine (50) comprises: a cylinder (51) having an injection port (52) and filled with a plastic material; a motor (2) receiving a supply of drive current from the servo driver (1A); and an injection unit (22) driven by the motor (2) and injecting the plastic material in the cylinder (51) from the injection port (52), wherein the servo driver (1A) comprises: a supply unit (12) supplying the drive current to the motor (2); a detection unit (13) detecting a current value of the drive current with a resolution according to a clock frequency of a supplied clock signal; and a control unit (11A) supplying the clock signal to the detection unit (13), wherein the control unit (11A) is capable of changing the clock frequency. <Supplementary Note 8> The injection molding system (500) according to Supplementary Note 7, wherein the control unit (11A) supplies the clock signal of a first clock frequency to the detection unit (13) when an absolute value of a fluctuation range per unit time of a torque command value instructed by a higher-level device (500) is equal to or greater than a threshold value while injecting the plastic member, and supplies the clock signal of a second clock frequency higher than the first clock frequency to the detection unit (13) when the absolute value of the fluctuation range of the torque command value is less than the threshold value.

[0064] DESCRIPTION OF SYMBOLS 1. Servo driver 2. Motor 7. Power line 8. Encoder cable 11. Control unit 11A. Control unit 12. Supply unit 13. Detection unit 14. Signal line 15. Signal line 16. Clock signal supply line 100. Servo system 111. First acquisition unit 112. Second acquisition unit 113. Clock control unit 114. Memory unit 115. Instruction unit 116. Third acquisition unit 131. Resistor 132. Detection IC 21. Motor body 22. Output shaft 23. Encoder 500. Injection molding system 1141. Management table

Claims

1. A servo driver comprising: a supply unit that supplies a drive current to a motor; a detection unit that detects a current value of the drive current with a resolution corresponding to a clock frequency of a supplied clock signal; and a control unit that supplies the clock signal to the detection unit, wherein the control unit is capable of changing the clock frequency.

2. The servo driver according to claim 1, wherein the control unit sets the clock frequency higher as the current value of the drive current becomes lower.

3. A servo driver as described in claim 1, wherein the motor stores motor information including information relating to a current value of the rated current of the motor, and the control unit acquires the motor information from the motor and varies the clock frequency in accordance with the acquired motor information.

4. The servo driver according to claim 3, wherein the control unit sets the clock frequency higher as the current value of the rated current indicated by the motor information becomes lower.

5. The servo driver according to claim 1, wherein the control unit receives information on options regarding the clock frequency, and supplies the clock signal of the clock frequency selected from the options to the detection unit.

6. A servo driver as described in any one of claims 1 to 5, further comprising a memory unit that stores a correspondence relationship between the current value of the drive current and the clock frequency, wherein the control unit acquires the current value of the drive current detected by the detection unit, acquires the clock frequency corresponding to the acquired current value of the drive current from the correspondence relationship, and supplies the clock signal of the clock frequency acquired from the correspondence relationship to the detection unit.

7. An injection molding system comprising an injection molding machine and a servo driver, wherein the injection molding machine comprises: a cylinder having an injection port and filled with a plastic material; a motor receiving a drive current from the servo driver; and an injection unit driven by the motor and injecting the plastic material in the cylinder from the injection port, wherein the servo driver comprises: a supply unit supplying the drive current to the motor; a detection unit detecting a current value of the drive current with a resolution according to a clock frequency of a supplied clock signal; and a control unit supplying the clock signal to the detection unit, wherein the control unit is capable of changing the clock frequency.

8. The injection molding system according to claim 7, wherein the control unit, when injecting the plastic member, supplies the clock signal of a first clock frequency to the detection unit if an absolute value of a fluctuation range per unit time of a torque command value instructed by a higher-level device is equal to or greater than a threshold value, and supplies the clock signal of a second clock frequency higher than the first clock frequency to the detection unit if the absolute value of the fluctuation range of the torque command value is less than the threshold value.

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