SERVO SYSTEM AND METHOD FOR CONTROLLING SERVO SYSTEM

Abstract

To provide a highly reliable servo system with little increase in cost and a method for controlling the same.SOLUTION: A servo system includes a servo motor, an encoder for detecting rotation information of a position and speed of the servo motor, and a servo amplifier for performing drive control of the servo motor using the rotation information. The servo amplifier includes: an encoder communication interface configured by hardware; a processor for computing a control command for controlling the servo motor based on an operation command and rotation information input via the encoder communication interface; and a control unit for performing drive control of the servo motor based on the control command. Then, the processor compares the rotation information received directly from the encoder with the rotation information input via the hardware communication interface to diagnoses as failure when not being matched.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a servo system and a control method for a servo system. [Background technology]

[0002] A servo system is equipped with an encoder that detects the rotation information (rotation speed, rotation position) of a servo motor, and a servo amplifier that takes in (feeds back) the rotation information from the encoder, determines a control command for the servo motor based on the drive command information (operation command) for the servo motor and the fed back rotation information, and drives and controls the servo motor using that control command. A servo amplifier often consists of a processor such as a microprocessing unit (MPU) and a control unit that operates according to control commands from the processor.

[0003] Incidentally, in order to improve the control accuracy in a servo system, it is necessary to generate and control control signals at high frequency, and it is necessary to feed back rotation information from an encoder to a servo amplifier more quickly and reliably. However, when the fed-back rotation information (output signal of the encoder) is taken into the servo amplifier through an interface using software, the rotation information may not be taken in at high speed. For this reason, hardware such as a field-programmable gate array (FPGA) or an application specific integrated circuit (ASIC) is used as an interface (encoder communication interface) for inputting rotation information. For example, Japanese Patent Application Laid-Open Publication No. 2015-231255 (Patent Document 1) discloses a configuration in which the output (rotation information) of an encoder is fed back to an MPU, which is a processor, through a field programmable gate array (FPGA). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2015-231255 A Summary of the Invention [Problem to be solved by the invention]

[0005] As shown in Patent Document 1, by using an encoder communication interface that uses hardware such as FPGA or ASIC as the communication interface, rotation information can be input at high speed, enabling high-speed processing and achieving precise servo control.

[0006] However, when using an encoder communication interface that uses hardware such as FPGA or ASIC, it can be difficult to detect all hardware failures (such as soft errors), and this poses a problem when applied to functional safety with a high level of safety.In such cases, in order to ensure functional safety with a high level of safety, it is possible to consider making the encoder communication interface using hardware redundant, that is, providing two or more encoder communication interfaces and detecting whether the information between them matches to increase the reliability of hardware failure detection and increase the reliability of the entire servo system.

[0007] However, such a method of making the encoder communication interface redundant using hardware raises problems such as an increase in the cost of the servo system and an increase in the installation area.

[0008] SUMMARY OF THE PRESENT EMBODIMENTS An object of the present invention is to provide a servo system and a control method for a servo system that are highly reliable and involve little increase in cost. [Means for solving the problem]

[0009] One example of the present invention is a servo system having a servo motor, an encoder that detects rotation information of the servo motor, and a servo amplifier that drives and controls the servo motor using the rotation information, wherein the servo amplifier includes an encoder communication interface configured by hardware, a processor that calculates a control command to control the servo motor based on an operation command and the rotation information input via the encoder communication interface, and a control unit that drives and controls the servo motor based on the control command, and the processor compares the rotation information received directly from the encoder with the rotation information input via the encoder communication interface, and diagnoses the presence or absence of a malfunction of the encoder communication interface based on the comparison result of both pieces of rotation information.

[0010] Another example of the present invention is a control method for a servo system having a servo motor and an encoder that detects rotation information of the servo motor, and driving the servo motor based on the rotation information of the encoder, the control method driving the servo motor based on an operation command and the rotation information inputted via an encoder communication interface using hardware, comparing the rotation information inputted via the encoder communication interface with the rotation information inputted directly from the encoder, and diagnosing the presence or absence of a fault in the encoder communication interface based on the comparison result of both pieces of rotation information. Effect of the Invention

[0011] According to the present invention, it is possible to provide a servo system and a method for controlling a servo system that can realize a highly reliable servo system with little increase in cost, even when the servo system is driven by an encoder communication interface using hardware. [Brief description of the drawings]

[0012] [Figure 1]FIG. 1 is a diagram illustrating a servo system according to a first embodiment of the present invention. [Diagram 2] FIG. 4 is an operation flow diagram of the servo system in the embodiment. [Diagram 3] 10A to 10C are diagrams illustrating data thinning when comparing two types of rotation information in the first embodiment. [Figure 4] FIG. 11 is a configuration diagram showing a servo system according to a second embodiment of the present invention. [Diagram 5] FIG. 2 is a diagram illustrating an example of a connection configuration between an encoder and a processor. [Figure 6] FIG. 6 is a configuration diagram showing a servo system in the connection configuration of FIG. 5. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] The present invention will be described in detail below with reference to specific examples. Note that the present invention is not limited to the examples described below. That is, the present invention can be modified in various ways, including the examples described below. In addition, in the drawings used in the following description, the same parts and components are designated by the same reference symbols (numbers), and descriptions of parts and components that have already been described may be omitted.

[0014] Example 1 Next, a first embodiment of the present invention will be described with reference to Figs. 1 to 3. Fig. 1 is a diagram showing an overall configuration of a servo system in the first embodiment of the present invention. Fig. 2 is a diagram showing an operation flow of the embodiment. Fig. 3 is a diagram for explaining data thinning when comparing two types of rotation information in the first embodiment.

[0015] As shown in Fig. 1, the servo system 1 is composed of a servo amplifier 2, a servo motor 3, and an encoder 4 that detects rotation information (rotation position, rotation speed, etc.) of the servo motor 3. The encoder 4 receives requests from the servo amplifier 2 according to a communication protocol, and transmits rotation information corresponding to the request to the servo amplifier 2 in response to the request. The servo amplifier 2 takes in (feeds back) the rotation information obtained by communication with the encoder 4, determines a control command for the servo motor based on the servo motor command information (operation command) and the taken-in rotation information, and drives and controls the servo motor according to the control command.

[0016] Here, the servo amplifier 2 includes a microcontroller unit (MCU) 5, which is a control IC based on a microprocessor, a control unit 6 that controls the servo motor 3, and an encoder communication interface 7 that receives and processes feedback data of rotation information (rotation position, speed) transmitted from the encoder 4. This encoder communication interface 7 uses hardware such as an FPGA or an ASIC.

[0017] In this embodiment, the MCU 5 includes a serial communication interface (SCI) 51, a safety diagnosis unit 52 including a function for performing abnormality diagnosis (fault diagnosis) of the encoder communication interface 7, a control command generation unit 53 for calculating and generating control commands to the control unit 6, a request generation unit 54 for outputting a request to the encoder 4, and a fault handling unit 55 for handling a fault (abnormality) diagnosed by the safety diagnosis unit 52. The SCI 51 may be attached externally to the MCU 5, but here it is provided at the input end within the MCU 5 to make it more compact.

[0018] To realize precise servo control, the control command generating unit 53 generates a control command using the rotation information FB2 obtained from the encoder communication interface 7 which inputs the rotation information of the encoder 4 at high speed.

[0019] The SCI 51 is an interface that receives serial data transmitted from the encoder communication protocol. The SCI 51 can perform full-duplex communication, receives data (rotation information) transmitted serially from the encoder 4, stores the rotation information in a register of the SCI 51, and transmits the data stored in the register in FIFO order to the MCU 5 and the encoder communication interface 7. In this way, by sharing the rotation information to the MCU 5 and the encoder communication interface 7 with one SCI 51, the circuit is simplified, which is preferable in terms of cost and control.

[0020] The safety diagnosis unit 52 performs a safety diagnosis to ensure the safety of the servo amplifier 2. The safety diagnosis detects faults in the hardware circuits of the servo amplifier 2, faults related to the internal software of the MCU 5, and fault diagnosis of the encoder communication interface 7. Of these safety diagnoses, the fault diagnosis of the encoder communication interface 7 is performed by comparing the rotation information FB1 directly input (fed back) to the MCU 5 via the SCI 51 with the rotation information FB2 input to the MCU 5 via the encoder communication interface 7. The fault handling unit 55 takes appropriate measures, such as an emergency stop of the servo motor, based on the diagnosis result of the safety diagnosis unit 52.

[0021] The control command generator 53 generates control commands for the position controller 61, the speed controller 62, and the motor controller 63 of the controller 6. The control commands are generated based on the operation command and the rotation information FB2 obtained via the encoder communication interface 7. Specifically, the control command generator 53 generates (calculates) a control command that eliminates the difference between the operation command and the rotation information.

[0022] The request generator 54 generates a request corresponding to the data to be received according to the encoder protocol, and transmits it to the encoder 4 via the SCI 51. The requests include requests to transmit rotation information for normal control, as well as requests to transmit test information. The encoder 4 transmits the rotation information corresponding to this request to the servo amplifier 2. Specifically, it transmits it to the SCI 51 provided at the input end of the MCU 5.

[0023] The control unit 6 includes a position control unit 61, a speed control unit 62, and a motor control unit 63. The position control unit 61, the speed control unit 62, and the motor control unit 63 input the control commands generated by the control command generation unit 53 of the MCU 5, and control the position, speed, and torque of the servo motor 3.

[0024] The encoder communication interface 7 includes an encoder data receiving unit 71 and an encoder data transmitting unit 72. The encoder data receiving unit 71 receives rotation information data transmitted from the encoder. The encoder data transmitting unit 72 transmits the received rotation information FB1 to the MCU 5 via an I / O port of an FPGA, ASIC, or the like. The MCU 5 stores this rotation information FB1 in a memory (not shown) in the order in which it is input.

[0025] In FIG. 1, the configuration of the MCU 5 is shown in the form of functional blocks for ease of understanding, but in reality, the MPU and CPU control the motor and perform fault diagnosis in accordance with a program stored in the ROM.

[0026] Next, a fault diagnosis of the encoder communication interface 7 using the hardware in the first embodiment will be described with reference to the operation flow shown in Fig. 2. Fig. 2 is a flow diagram showing the operation of the fault diagnosis process of the MCU 5.

[0027] In FIG. 2, in step S01, the request generating unit 54 generates a request R for obtaining rotation information required for controlling the motor.

[0028] Next, in step S02, the request generation unit 54 transmits the request R to the encoder 4 via the SCI 51. As a result, the encoder 4 transmits rotation information corresponding to the request to the servo amplifier 2. In step S03, the rotation information (rotational position, speed, etc.) transmitted from the encoder 4 is received by the SCI.

[0029] Next, in step S04, the rotation information accumulated in the register in SCI 51 is transmitted to encoder communications interface 7 in FIFO order. At the same time, the same rotation information is also fetched into MCU 5. Here, the rotation information transmitted to encoder communications interface 7 and output from encoder data transmitter 72 is designated as FB2, and the rotation information directly fetched and stored in the MCU is designated as FB1.

[0030] Next, in step S05, the safety diagnosis unit 52 compares the rotation information FB2 obtained via the encoder communication interface 7 with the rotation information FB1 received by the SCI 51 and loaded into the MCU 5. Then, in step S05, if FB1 and FB2 match, the safety diagnosis unit 52 determines that there is no failure (abnormality) in the encoder communication interface 7, and returns to step S01. The failure diagnosis routine shown in steps S01 to S05 continues while the servo motor is in operation.

[0031] In step S05, if a state occurs in which the compared data (rotation information FB1 and FB2) do not match, the safety diagnosis unit 52 determines that the encoder communication interface 7 has failed, and proceeds to the next step S06.

[0032] In step S 06 , a failure signal of the encoder communication interface 7 is sent to the failure handling unit 55 .

[0033] Then, in step S07, the failure handling unit 55 takes appropriate emergency measures for the servo system based on the failure signal. For example, the failure handling unit 55 cuts off the power supplied to the servo motor 3 to stop the servo motor. At the same time, the failure handling unit 55 takes measures such as notifying a host device that manages the entire system that the system is in a failure state.

[0034] In this way, while the servo system is in operation (driving), the system continues to perform fault diagnosis operations in accordance with the operation control of the servo motor. If a fault is detected (when the data in FB1 and FB2 do not match), the system can diagnose the fault and take emergency measures.

[0035] Next, a method for comparing rotation information output by the encoder 4 at the same timing when comparing FB1 and FB2 in the diagnostic operation (comparison judgment operation in step S05) in the safety diagnostic unit 52 will be described. As described above, the hardware-based encoder communication interface 7 operates at a higher speed, so the number of rotation information FB2 that can be obtained per unit time is greater than that of FB1 that is directly input to the MCU 45. Therefore, in order to compare FB1 and FB2 more accurately, more accurate diagnosis can be achieved by comparing the FB2 data with FB2 at the same time as thinning out the data. FIG. 3 is a diagram for explaining this thinning out process and data comparison.

[0036] In FIG. 3, the lower side shows rotation information FB2 which is the output of the encoder communication interface 7, and the upper side shows rotation information FB1 which is input directly from the SCI 51 to the MPU 5.

[0037] As shown in Fig. 3, in order to match the timing of comparing these two pieces of data, the rotation information FB2 output from the encoder communication interface 7 is thinned out at a thinning rate set by the ratio of the data communication cycle time to the multiple cycle time for the rotation information FB1 directly input to the MPU 5. Then, after a time has elapsed from the set thinning rate, the thinned out rotation information FB2 is compared with FB1. By performing such thinning out, it is possible to more accurately determine a failure of the encoder communication interface 7. The thinning out process for FB2 can be set in advance. Fig. 3 shows an example where the thinning out rate is 1:3, and the rotation information FB2 from one cycle out of three cycles is used for comparison with FB1.

[0038] According to the first embodiment of the present invention described above, even when the servo system is driven by an encoder communication interface using hardware, a highly reliable servo system can be realized with little increase in cost.

[0039] Example 2 Next, a second embodiment of the present invention will be described with reference to Fig. 4. Fig. 4 is a configuration diagram of a servo system in the second embodiment. The basic configuration of the second embodiment is similar to that of the first embodiment already described, so a description thereof will be omitted, and the following mainly describes the configuration parts that differ from the first embodiment.

[0040] In the second embodiment shown in FIG. 4, instead of the encoder communication interface 7 using the hardware in FIG. 1, an encoder communication interface 70 having the same function is provided in the MCU 5. That is, the encoder communication interface 70 built into the MCU 5 uses a DRP (Dynamically Reconfigurable Processor), which is a dynamic reconfigurable processor. The DRP (Dynamically Reconfigurable Processor) is hardware that executes an application while dynamically switching the connection between the arithmetic units. The circuit inside a general DRP includes an 8-bit PE (Processor Element) array arranged in a lattice, an STC (State Transition Controller) that dynamically selects them, and a RAM and a memory controller that supply data to the PE. Note that the configuration of the DRP itself is publicly known, so a detailed description will be omitted here.

[0041] The operation of this embodiment 2 is similar to that of embodiment 1, and overlaps with the contents already described, so detailed description thereof will be omitted here. Also, since the operation flow of embodiment 2 is similar to the operation flow shown in FIG. 2, description of the operation will also be omitted. Also, in the diagnostic operation of safety diagnostic unit 52, when comparing FB1 and FB2, in order to compare rotation information output by encoder 4 at the same timing, data thinning is performed in the same manner as in embodiment 1. That is, thinning processing as shown in FIG. 3 is also performed in embodiment 2. Therefore, description thereof will also be omitted.

[0042] In FIG. 4, the encoder communication interface 70 configured as a DRP is built into the MCU 5, and has high processing capacity of hardware logic and high flexibility and functional expandability like a CPU.

[0043] In this second embodiment, similarly to the first embodiment, the encoder communication interface 70 configured by the DRP does not have an SCI for taking in rotation information and an SCI for taking in the rotation information into the MCU 5 separately provided, but uses one common SCI 51. Also, by incorporating the encoder communication interface 70 compatible with the encoder protocol by the DRP, external hardware (such as FPGA or ASIC) is not required, making it compact and reducing the cost of some of the hardware.

[0044] 5 shows an example of a connection with an encoder using clock-synchronized serial communication. For example, a differential signal such as RS-485 standard is used for the connection between the encoder 4 and the microcontroller unit 5, and the influence of noise can be reduced by wiring with a twisted pair cable 41. The microcontroller unit 5 is provided with input / output pins corresponding to both the DRP and SCI functional blocks, and each signal (SCL, Rx, Tx) of the RS-485 transceiver may be connected in parallel to both of these input / output pins.

[0045] FIG. 6 is a configuration diagram in which the microcomputer controller 5 shown in FIG. 5 is provided with input / output pins for DRP and SCI, and each signal (SCL, Rx, Tx) of the RS-485 transceiver is connected in parallel to both input / output pins.

[0046] According to the second embodiment of the present invention described above, it is possible to provide a compact and less expensive servo system that has the same effects as the first embodiment. [Explanation of symbols]

[0047] 1...Servo system, 2...Servo amplifier, 3...Servo motor, 4...Encoder, 5...Microcontroller unit, 6...Control unit, 7...Encoder communication interface, 41...Twisted pair cable, 51...Serial communication interface, 52...Safety diagnosis unit, 53...Control command generation unit, 54...Request generation unit, 55...Fault handling unit, 61...Position control unit, 62...Speed ​​control unit, 63...Motor control unit, 70...Encoder communication interface, 71...Encoder data receiving unit, 72...Encoder data transmitting unit

Claims

1. A servo system including a servo motor, an encoder that detects rotation information of the servo motor, and a servo amplifier that drives and controls the servo motor using the rotation information, The servo amplifier includes an encoder communication interface configured by hardware, a processor that calculates a control command for controlling the servo motor based on an operation command and the rotation information input via the encoder communication interface, and a control unit that drives and controls the servo motor based on the control command, The processor compares the rotation information directly received from the encoder with the rotation information input via the encoder communication interface, and diagnoses whether or not the encoder communication interface has a failure based on a comparison result of both pieces of rotation information; the processor includes a serial communication interface that receives and accumulates the serial rotation information transmitted from the encoder and transmits the accumulated data in FIFO order to the processor and the encoder communication interface, a request generation unit that generates a request for determining which data of the rotation information should be received, a safety diagnosis unit that performs a fault diagnosis on the encoder communication interface, and a control command generation unit that generates the control command to the control unit; the request generation unit transmits the request to the encoder via the serial communication interface, whereby the encoder transmits the rotation information corresponding to the request to the serial communication interface; the control command generation unit generates the control command by using the rotation information input via the encoder communication interface; The safety diagnosis unit is a servo system that diagnoses whether or not there is a malfunction in the encoder communication interface by comparing the rotation information received directly from the encoder via the serial communication interface with the rotation information input via the encoder communication interface.

2. 2. The servo system according to claim 1, wherein the processor is a microcontroller unit.

3. 2. The servo system according to claim 1, wherein said serial communication interface is provided at an input end of said processor.

4. 2. The servo system according to claim 1, wherein the encoder communication interface is built into the processor.

5. 5. The servo system according to claim 4, wherein a dynamically reconfigurable processor is used as the encoder communication interface.

6. 6. The servo system according to claim 5, further comprising a serial communication interface built into the processor for receiving and storing the serial rotation information transmitted from the encoder and transmitting the stored data in FIFO order to the processor and the encoder communication interface.

7. 2. The servo system according to claim 1, further comprising: a servo system for comparing the rotation information input via the encoder communication interface with thinned-out information and the rotation information directly received from the encoder.

8. 2. The servo system according to claim 1, wherein when said fault is diagnosed, an emergency response is taken for the servo system.

9. A control method for a servo system having a servo motor and an encoder that detects rotation information of the servo motor, the control method comprising the steps of: Driving the servo motor based on an operation command and the rotation information input via an encoder communication interface using hardware; comparing the rotation information input via the encoder communication interface with the rotation information directly input from the encoder, and diagnosing the presence or absence of a failure in the encoder communication interface based on a comparison result of both pieces of rotation information; The rotation information is input to an encoder communication interface via a serial communication interface that receives and stores the serial rotation information transmitted from the encoder and transmits the stored data in FIFO order; generating a request determining data to be received from the encoder, transmitting the request to the encoder via the serial communications interface, and receiving the rotation information from the encoder corresponding to the request; A servo system control method for diagnosing the presence or absence of a malfunction in the encoder communication interface by comparing the rotation information input via the encoder communication interface with the rotation information input directly from the encoder via the serial communication interface.

10. 10. The control method for a servo system according to claim 9, further comprising the step of comparing thinned information of the rotation information input via the encoder communication interface with the rotation information directly received from the encoder.

11. 10. A method for controlling a servo system according to claim 9, further comprising the steps of: A method for controlling a servo system, comprising the steps of: when the fault is diagnosed, taking emergency measures against the servo system.

12. 2. The servo system according to claim 1, wherein the processor is provided with input / output pins corresponding to the functions of a dynamic reconfigurable processor and a serial communication interface, and the serial rotation information transmitted from the encoder is received by the input / output pins.

Images