Servo amplifier

Abstract

To reduce malfunction caused by inflow noise and degradation of EMC characteristic regardless of a form of grounding in another device in a servo amplifier connected to the another device via a communication cable.SOLUTION: A servo amplifier 10 has: a connector 11 to which a communication cable is connectable; and a signal ground 15 independently installed from a frame ground 13 set to a housing to provide a grounding potential to an internal circuit such as a physical layer transceiver 14. The connector 11 is provided with a shielding conductor part (e.g., metal shell 12) that electrically connects to a shield of the communication cable when the communication cable is a shielded cable. The shielding conductor part is floated from the frame ground 13 to electrically connect to the signal ground 15 via a coupling capacitor 17.SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] The present invention relates to a servo amplifier that controls a servo motor.

Background Art

[0002] When servo motors are provided at multiple locations in a factory or the like, a host device is provided to centrally manage and control these servo motors, and a servo amplifier provided for each location or each motor drives each motor based on a command from the host device. In many cases, a master-slave configuration is adopted in which the host device is the master device and each servo amplifier is the slave device. Examples of communication protocols used to connect the host device and the servo amplifier include EtherCAT (registered trademark), an industrial protocol based on Ethernet (registered trademark), and CC-Link (registered trademark). These protocols are high-speed serial communication protocols that enable a plurality of servo amplifiers to be connected to the host device in a daisy-chain form. As a communication cable used for connection between devices, a 4-pair 8-wire twisted pair cable, which is a general LAN (Local Area Network) cable based on Ethernet (registered trademark), is widely used. The signal lines of each twisted pair (twisted pair) of the twisted pair cable form a balanced line. When such a twisted pair cable is used, RJ45-type plugs are attached to both ends of the twisted pair cable, and corresponding RJ45-type jacks are provided on the device side, so that the cable can be detachably connected to the device. On the device side, a pulse transformer is provided between the RJ45-type jack and the physical layer transceiver corresponding to each signal line pair of the cable, and a termination resistor is connected to the center tap of the pulse transformer.

[0003] The factory and other spaces where servo amplifiers are installed are environments with high levels of electromagnetic noise. Therefore, shielded cables, such as STP (Shielded Twisted Pair) cables, are used for communication cables connecting the higher-level equipment and the servo amplifier. When using shielded cables, the connector, or jack, on the equipment side must also be compatible with shielded cables. The shield of a shielded cable is electrically connected to a shield connection point on the plug at the end of the cable. In a shielded jack, a shielding conductor is provided at a position corresponding to the shield connection point on the plug side. When the cable is connected to the equipment, the shield connection point on the cable side comes into contact with the shielding conductor on the equipment side, thereby electrically connecting the cable's shield to the ground point on the equipment side. In a shielded RJ45 type jack, the outer shell is formed of metal to serve as the shielding conductor and is configured to come into contact with the shield connection point on the plug side. When the plug at the end of the cable is inserted into the jack, the shield inside the cable is electrically connected to the shell, which is the shielding conductor on the jack side. The termination resistor connected to the center tap of the pulse transformer is electrically connected to the jack's shell, for example, via a capacitor. The jack's shell is typically connected to the device's frame ground (FG; a grounding point in the device's enclosure, generally used for safety grounding, etc.).

[0004] When two devices have different ground potentials, and these two devices are connected with a shielded cable, and the cable's shield is connected to the frame ground at each device, current may flow through the cable's shield, causing noise to be superimposed on the signal lines within the cable. To prevent such problems, Patent Document 1 discloses that in a switching hub device to which an STP cable is connected, a switchable changeover switch is provided in the path to the frame ground to prevent current from flowing through the STP cable's shield when the shell of the RJ45 jack on the device side is connected to the frame ground. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2013-255139 [Overview of the project] [Problems that the invention aims to solve]

[0006] Servo amplifiers are devices used in environments with high levels of electromagnetic noise, and due to their function of driving and controlling motors, they themselves have the potential to generate noise. Therefore, servo amplifiers are carefully designed to be unaffected by external noise and to have good EMC (electromagnetic compatibility) characteristics. Accordingly, connectors used for connecting to higher-level devices, such as RJ45 jacks, are configured in such a way that the points where they should be connected to the frame ground are as described above. However, higher-level devices are not necessarily used in environments with high levels of electromagnetic noise, so sufficient consideration may not be given to the impact on EMC characteristics and grounding, and various devices may be used as higher-level devices. Therefore, in higher-level devices to which servo amplifiers are connected via cables, the grounding configuration at the connection point between the cable and the higher-level device may vary, and the cable shielding may not be properly handled. If the cable shield is electrically connected to the frame ground on the servo amplifier side, this can actually cause malfunctions due to noise or a decrease in EMC characteristics. The same applies when there are slave devices in a daisy-chain connection that have insufficient shielding.

[0007] The object of the present invention is to provide a servo amplifier that is connected to another device by a communication cable and can suppress malfunctions due to incoming noise and deterioration of EMC characteristics, regardless of the grounding configuration of the other device. [Means for solving the problem]

[0008] According to one aspect of the present invention, the servo amplifier is a servo amplifier that controls a servo motor and is connected to another device by a communication cable, comprising: a connector to which a communication cable can be connected; a physical layer transceiver that performs transmission and reception processing at the physical layer with respect to communication with the other device via the communication cable; a control circuit that generates internal commands for the servo motor based on commands input via the physical layer transceiver; a driver circuit that is supplied with a power supply voltage to drive the servo motor and drives the servo motor in accordance with the internal commands; and a signal ground that is provided separately from the frame ground set in the housing of the servo amplifier and provides a ground potential to the physical layer transceiver and the control circuit, wherein the connector comprises a shielding conductor portion that is electrically connected to the shield of the communication cable when the communication cable is a shielded cable, and the shielding conductor portion is floating relative to the frame ground and is electrically connected to the signal ground via a first capacitor.

[0009] When using a shielded cable to connect a servo amplifier to other devices such as a host system via a communication cable, depending on the grounding configuration on the other device side, connecting the cable shield to the frame ground on the servo amplifier side may actually make it more susceptible to external noise or degrade its EMC characteristics. To solve this problem, the cable shield is made floating on the servo amplifier side. However, simply making it floating is insufficient, as the cable effectively functions as an antenna, becoming a source of noise and making it more susceptible to external noise. Therefore, in this embodiment, the cable shield is electrically connected to the shielding conductor portion of the connector, and the shielding conductor portion is connected via a coupling capacitor (i.e., a first capacitor) to a signal ground, which is provided separately from the frame ground and provides a ground potential to the signal system circuit in the servo amplifier. As a result, in one embodiment of the present invention, a servo amplifier can suppress malfunctions due to noise and degradation of EMC characteristics, regardless of the grounding configuration on the other device side. The signal system circuit refers to circuits that handle signals with relatively small voltage amplitudes, such as physical layer transceivers and control circuits.

[0010] A servo amplifier typically has a configuration in which the circuits constituting the servo amplifier are housed in a chassis, and a frame ground is provided in the chassis. In one embodiment of the present invention, it is preferable to connect the signal ground to the frame ground via a parallel circuit consisting of a second capacitor different from the first capacitor and a resistor. By configuring it in this way, the ground potential of the signal system circuits constituting the servo amplifier can be made more stable. In this case, the shielding conductor portion of the connector is electrically connected to the signal ground without going through the frame ground.

[0011] The communication cable is, for example, a cable having a balanced line, such as a twisted-pair cable. When the communication cable has a balanced line, a pulse transformer may be provided in the servo amplifier between the pair of contacts to be connected to the balanced line in the connector and the physical layer transceiver. If a pulse transformer is provided, it is preferable that the center tap of the pulse transformer is electrically connected to the shielding conductor via at least a termination resistor. Alternatively, the center tap of the pulse transformer may be connected to the signal ground via a termination resistor and a second capacitor different from the first capacitor. By configuring it in this way, the zero potential in the balanced line is stabilized, further improving immunity to noise and further suppressing the deterioration of EMC characteristics. When the communication cable is a twisted-pair cable, for example, an RJ45 type connector is used to connect the communication cable to the servo amplifier. When an RJ45 type connector is used, an RJ45 type jack is used as the connector provided in the servo amplifier, and the metal shell provided in this jack functions as the shielding conductor.

[0012] The communication cable may be a USB (Universal Serial Bus) cable, in which case the servo amplifier is provided with a USB connector. Alternatively, a general-purpose input / output (I / O) standard such as RS-232, RS-422, or RS-485 can be used as the communication cable, in which case the servo amplifier is provided with an I / O connector that conforms to the protocol used by the communication cable. In any case, in each embodiment of the present invention, there are no restrictions on the type of communication cable or the communication protocol used for communication with other devices. However, since the present invention aims to solve the problems that arise when a shielded cable is used as the communication cable, it is preferable to use a shielded cable as the communication cable.

[0013] In yet another aspect of the present invention, the servo amplifier is configured to have multiple connectors so that it can be daisy-chained with other servo amplifiers. Enabling daisy-chaining significantly reduces the number of input / output ports in the host device and the overall wiring length when the host device is the master device and each servo amplifier is the slave device, and also makes it possible to avoid congestion of communication cables around the host device. [Effects of the Invention]

[0014] According to the present invention, in a servo amplifier connected to another device by a communication cable, it becomes possible to suppress malfunctions and deterioration of EMC characteristics due to incoming noise, regardless of the grounding configuration of the other device. [Brief explanation of the drawing]

[0015] [Figure 1] This diagram illustrates the daisy-chain connection between a master device and a slave device. [Figure 2] This is a block diagram showing the configuration of the input and output sections of a conventional servo amplifier. [Figure 3] This diagram shows an example of connecting a higher-level controller to a servo amplifier. [Figure 4] This is a block diagram showing a servo amplifier as one embodiment of the present invention. [Figure 5] This diagram shows the details of the input and output sections of the servo amplifier shown in Figure 4. [Figure 6] This figure shows a detail of another example of the input / output section of the servo amplifier shown in Figure 4. [Figure 7] This is a block diagram showing the configuration of the input / output section of a servo amplifier in another embodiment. [Modes for carrying out the invention]

[0016] Next, embodiments for carrying out the present invention will be described with reference to the drawings. A servo amplifier based on the present invention can be connected to a higher-level device in a daisy-chain configuration via a communication cable, for example, based on the EtherCAT® standard.

[0017] Figure 1 illustrates a typical daisy-chain connection. In a daisy-chain connection, multiple slave devices 72 are connected in series to a single master device 71. The first of the series-connected slave devices 72 is connected to the master device 71 and the second slave device 72 via a communication cable 73, while the second slave device 72 is connected to both the first and third slave devices 72. Therefore, the master device 71 only needs to have one connector 74 to which the communication cable 73 is connected, but the slave devices 72 generally need to have two or more connectors 74. In this embodiment, when using a daisy-chain connection, the upper-level controller, which is a higher-level device for the servo amplifiers, becomes the master device 71, and multiple servo amplifiers are daisy-chained to the upper-level controller, with each servo amplifier becoming a slave device 72. For example, an STP cable is used for the communication cable 83 used to connect the upper-level controller to the servo amplifiers and to connect the servo amplifiers to each other.

[0018] For reference, a configuration example of an input / output section in a conventional servo amplifier 90 will be described using FIGS. 2(a) and 2(b). In these figures, only the part related to one connector 91 to which a communication cable is connected is depicted, but in the servo amplifier 90 that performs daisy chain connection, two or more connectors 91 for communication cables are provided. Also, the wiring related to grounding is indicated by a broken line. Here, assuming that an STP cable is used for the communication cable, the connector 91 uses a shield type RJ45 type jack, and the shell 92 of the connector 91 is made of metal and is electrically connected to the shield conductor in the STP cable when the STP cable is connected to the connector 91. A frame ground (FG) 93 is set in the housing of the servo amplifier 90. Also, in the servo amplifier 90, a physical layer transceiver 94 that performs transmission / reception processing at the physical layer for communication via the communication cable, and a signal ground (SG) 95 that gives a ground potential to the signal system circuits in the servo amplifier 90 including the physical layer transceiver 94 are provided.

[0019] In the servo amplifier 90 shown in FIG. 2(a), the shell 92 of the connector 91 is directly connected to the frame ground 93, and the signal ground 95 is connected to the frame ground 93 via an RC parallel circuit 96 configured as a parallel circuit of a resistor and a capacitor. Also, in the example shown in FIG. 2(b), the shell 92 of the connector 91 is connected to the frame ground 93 via the RC parallel circuit 96, and the signal ground 95 is connected to this RC parallel circuit 96 via a capacitor 97. The shell 92 of the connector 91 is connected to the frame ground 93 directly in the case of FIG. 2(a) and via the resistor in the RC parallel circuit 96 in the case of FIG. 2(b), so it is not floating with respect to the frame ground 93. Therefore, when the communication cable connected to the connector 91 is a shielded cable, the shield of the cable does not become floating either.

[0020] When connecting the servo amplifier 90 shown in Fig. 2(a) or Fig. 2(b) to the host controller 80 which is the host device, the connection form will be described using Fig. 3. In the servo amplifier 90, assume that the shell 92 of the connector 91 (not shown explicitly in Fig. 3) is directly connected to the frame ground 93, and the frame ground 93 is grounded to the earth E. And assume that a shielded cable is used as the communication cable 85 for connecting the servo amplifier 90 to the host controller 80. In the figure, the shield of the communication cable 85 is indicated by the reference numeral 86. Also, the dashed lines indicate the wirings related to grounding.

[0021] Fig. 3(a) shows the case where the frame ground 83 is set in the host controller 80, the frame ground 83 is grounded to the earth E, and the shell of the connector 81 is also connected to the frame ground 83, which is the original grounding form of the host controller 80. In this case, the frame ground 83 of the host controller 80 and the frame ground 93 of the servo amplifier 90 are connected via the shield 86 of the communication cable 85, and since the frame grounds 83 and 93 are grounded to the earth E, the shield 86 of the communication cable 85 is also kept at the same potential as the earth E, becoming less susceptible to external noise and showing good EMC characteristics. Here, if the shield 86 of the communication cable 85 is not grounded on the host controller 80 side, that is, a so-called single-sided grounding, the communication cable 85 will function as an antenna and the EMC characteristics will deteriorate.

[0022] When the shell of the connector 81 of the host controller 80 is not connected to the frame ground of the host controller 80, as shown in Fig. 3(b), in order to prevent the deterioration of the EMC characteristics, it is necessary to provide a wiring for directly grounding the shell of the connector 81 to the earth E.

[0023] If the shell of connector 81 is connected to the signal ground of the upper-level controller 80, the relationship between the signal ground and frame ground within the upper-level controller 80 is unknown, and there is a risk that malfunction may occur due to noise inflow when the shield 86 of communication cable 85 is electrically connected to the shell of connector 81 as is. In that case, the upper-level controller 80 should be configured so that the end of the shield 86 of communication cable 85 is not electrically connected to the shell of connector 81, and instead the end of the shield 86 should be directly grounded to earth E as shown in Figure 3(c).

[0024] If there is a potential difference in the ground E between the installation location of the upper-level controller 80 and the installation location of the servo amplifier 90, and the shield 86 of the communication cable 85 is grounded to the ground E on both the upper-level controller 80 side and the servo amplifier 90 side, current will flow through the shield 86, making it more susceptible to noise and degrading the EMC characteristics. In that case, as shown in Figure 3(d), it is unavoidable to use the aforementioned one-sided grounding method, or to use a cable without shielding as the communication cable 85, such as a UTP (Unshielded Twisted Pair) cable.

[0025] From the perspective of the servo amplifier 90, the grounding configuration of the higher-level controller 80 is often unknown. For example, it may be unclear whether the higher-level controller 80 employs one of the grounding configurations shown in Figures 3(a) to (d), or whether grounding is even considered at all in the higher-level controller 80. In such cases, connecting the shield 86 of the communication cable 85 to the frame ground 93 on the servo amplifier 90 side may actually make it more susceptible to external noise or degrade its EMC characteristics. One embodiment of the present invention is a servo amplifier that is connected to the higher-level device by, for example, a shielded communication cable, and is designed to suppress malfunctions due to incoming noise and degradation of EMC characteristics regardless of the grounding configuration of the higher-level device. Figure 4 shows the configuration of one embodiment of the present invention.

[0026] The servo amplifier 10 shown in Figure 4 performs servo control of the motor 30 based on commands from a higher-level device such as a higher-level controller. The servo amplifier 10 is connected to the higher-level device by an STP cable (shielded twisted pair cable), which is a communication cable, and is equipped with a connector 11, which is an RJ45 type jack, for connection to the STP cable, and communicates with the higher-level device based on the EtherCAT® standard. The servo amplifier 10 is equipped with multiple connectors 11 to enable daisy-chain connection to the higher-level device in the configuration shown in Figure 1, but only one connector 11 is depicted here for illustrative purposes. The connector 11 is a shielded connector and is equipped with a metal shell 12 which is a shielding conductor part, and is configured so that when an STP cable is connected, the shield of the STP cable is electrically connected to the shell 12. Each twisted pair of the STP cable forms a balanced line and is connected to the physical layer transceiver 14 via a pair of contacts in the connector 11. Between the contact pair of connector 11 and the physical layer transceiver 14, pulse transformers 41 and 42 (not shown in Figure 4, see Figure 5) are provided.

[0027] The servo amplifier 10's enclosure is equipped with a frame ground (FG) 13 for safety grounding. The servo amplifier 10 also includes a physical layer transceiver 14 that performs physical layer transmission and reception processing for communication with a higher-level device, a control circuit 21 connected to the physical layer transceiver 14 that performs calculations necessary for servo control of the motor 30 based on commands from the higher-level device, and a drive circuit 22 that actually drives the motor 30 based on internal commands from the control circuit 21. The motor 30 is an encoder-equipped motor, and the motor position detected by the encoder is fed back to the control circuit 21. The drive circuit 22 is equipped with a power circuit such as an inverter circuit, and supplies the power supply voltage (drive power supply voltage) necessary to drive the motor 30. The drive circuit 22 is connected to the frame ground 13 for grounding.

[0028] The physical layer transceiver 14 and the control circuit 21 are signal system circuits that handle relatively small signal voltages, and the servo amplifier 10 is provided with a signal ground (SG) 15 to provide a ground voltage to these circuits. Typically, the signal ground 15 is realized by a wiring layer that serves as the ground plane on a multilayer printed circuit board on which circuits such as the physical layer transceiver 14 and the control circuit 21 are mounted. The signal ground 15 is provided separately from the frame ground 13 and is connected to the frame ground 13 via an RC parallel circuit 16 configured as a parallel circuit of a resistor and a capacitor.

[0029] In the servo amplifier 10 of this embodiment, the shield of the STP cable is made floating so that it can handle any grounding condition on the higher-level device. However, simply making it floating would cause the STP cable to function as an antenna, becoming a source of noise and making it susceptible to external noise. Therefore, the shield of the STP cable is connected to the signal ground 15 via a coupling capacitor. To this end, in the servo amplifier 10 shown in Figure 4, the shell 12 that is electrically connected to the shield of the STP cable at the connector 11 is connected to the signal ground 15 via a capacitor 17. By connecting the shield of the STP cable to the signal ground 15 via the capacitor 17 in this way, the servo amplifier 10 can suppress malfunctions due to noise and deterioration of EMC characteristics, regardless of the grounding configuration of the higher-level device.

[0030] Figure 5 is a detailed diagram showing the circuit configuration around the connector 11 in the servo amplifier 10 shown in Figure 4. As mentioned above, the connector 11 is an RJ45 type jack and has eight contacts corresponding to a 4-pair, 8-wire STP cable. In Figure 5, the eight squares drawn within the connector 11 represent contacts, and the numbers within the squares represent contact numbers. TX+ and TX- represent a pair of transmit signal lines, and RX+ and RX- represent a pair of receive signal lines. A pulse transformer 41 is provided between the transmit pair of contacts in the connector 11 and the physical layer transceiver 14, and similarly, a pulse transformer 42 is provided between the receive pair of contacts and the physical layer transceiver 14. Furthermore, the servo amplifier 10 is provided with a termination circuit 43 consisting of resistors R1 to R4 and a capacitor C1. Resistors R1 to R4 are termination resistors. One end of resistors R1 and R2 are connected to the center taps of pulse transformers 41 and 42, respectively. Pins 4 and 5 of connector 11 are connected in common to one end of resistor R3, and pins 7 and 8 of connector 11 are connected in common to one end of resistor R4. The other ends of resistors R1 to R4 are interconnected, and one end of capacitor C1 is connected to them. The other end of capacitor C1 is connected to the shell 12 of connector 11. As described above, the shell 12 of connector 11 is connected to the signal ground 15 of the servo amplifier 10 via a coupling capacitor 17. Therefore, the signal wire pairs in the STP cable are terminated by termination resistors R1 to R4, which are high-frequency grounded to the signal ground 15 of the servo amplifier 10.

[0031] In the circuit shown in Figure 5, the other end of capacitor C1 in the termination circuit 43 is connected to the shell of connector 11. This is a common method of providing a ground point to the termination circuit in conventional circuits that assume the shell 12 of connector 11 is connected to the frame ground 15, and it facilitates modifying existing servo amplifiers to create servo amplifiers according to the present invention. However, in the circuit shown in Figure 5, since capacitor C1 and the coupling capacitor 17 are connected in series, the effective capacitance between the other end of the termination resistors R1 to R4 and the signal ground 15 becomes smaller than the capacitance of the coupling capacitor 17, reducing the flexibility of the circuit. Therefore, as shown in Figure 6, the other end of capacitor C1 may be connected directly to the signal ground 15 instead of being connected to the shell of connector 11. By configuring as shown in Figure 6, the range of constant selection for capacitor C1 and the coupling capacitor 17 can be widened.

[0032] In the servo amplifier 10 of this embodiment, by connecting the shield of the STP cable used for connection with the host device to the signal ground 15 instead of the frame ground 13 via the capacitor 17, malfunctions due to incoming noise and deterioration of EMC characteristics can be suppressed regardless of the grounding configuration of the host device.

[0033] In the above explanation, the case in which the servo amplifier 10 is connected to a higher-level device via an STP cable was used as an example. However, the device to which the servo amplifier 10 is connected is not limited to a higher-level device; it may be other servo amplifiers connected in a daisy-chain configuration. In any case, when the servo amplifier 10 is connected to another device via an STP cable, by ensuring that the shield of the STP cable is connected to the signal ground 15 via a capacitor, malfunctions due to incoming noise and deterioration of EMC characteristics can be suppressed regardless of the grounding configuration of the other device.

[0034] Furthermore, the servo amplifier 10 according to the present invention can use cables other than STP cables as communication cables for connection to other devices. Figure 6 shows the configuration of the main parts of a servo amplifier 10 of another embodiment of the present invention. For the sake of clarity, Figure 6 does not show the control circuit 21 and drive circuit 22 that should be provided in the servo amplifier 10. The servo amplifier 10 shown in Figure 6 is similar to the one shown in Figure 4, but in addition to STP cables, it can also connect to general-purpose input / output (I / O) cables (e.g., RS-485 standard cables) and USB cables. These cables generally have an outer shield. The servo amplifier 10 shown in Figure 6 has an RJ45 type jack connector 11, as well as an I / O connector 41 to which input / output cables are connected and a USB connector 51 to which USB cables are connected. A physical layer transceiver 44 that processes communication according to the RS-485 standard is provided corresponding to the I / O connector 41, and a physical layer transceiver 54 that processes physical layer transmission and reception of communication by USB interface is provided corresponding to the USB connector 51. Similar to the physical layer transceiver 14, the physical layer transceivers 44 and 54 are also connected to the signal ground 15 of the servo amplifier 10. As shown in Figure 4, the signal ground 15 is connected to the frame ground 13 of the servo amplifier 10 via the RC parallel circuit 16.

[0035] When an input / output cable is connected to the I / O connector 41, the shield of this input / output cable is electrically connected to the shell 42 of the I / O connector 41. Similarly, when a USB cable is connected to the USB connector 51, the shield of this USB cable is electrically connected to the shell 52 of the USB connector 51. The shells 42 and 52 of these connectors 41 and 51 are connected to the signal ground 15 via coupling capacitors 47 and 57, respectively, just as in the case of the shell 12 of the RJ45 type jack connector 11. The servo amplifier 10 shown in Figure 6 achieves the same effect as the servo amplifier 10 shown in Figure 4, and can suppress malfunctions due to incoming noise and deterioration of EMC characteristics, regardless of the grounding status of other devices connected by the input / output cable or the USB cable. [Explanation of symbols]

[0036] 10...Servo amplifier; 11, 41, 51...Connectors; 12, 42, 52...Shell; 13...Frame ground; 14, 44, 54...Physical layer transceiver; 15...Signal ground; 16...RC parallel circuit; 17, 47, 57...Capacitor; 30...Motor; 41, 42...Pulse transformer; 43...Termination circuit.

Claims

1. A servo amplifier that is connected to other devices by a communication cable to control a servo motor, A connector to which the aforementioned communication cable can be connected, A physical layer transceiver that performs transmission and reception processing at the physical layer with respect to communication with the other device via the aforementioned communication cable, A control circuit that generates internal commands for the servo motor based on commands input via the physical layer transceiver, A driver circuit that receives a power supply voltage to drive the servo motor and drives the servo motor according to the internal command, A signal ground is provided separately from the frame ground set in the housing of the servo amplifier, and provides a ground potential to the physical layer transceiver and the control circuit. It has, The connector includes a shielding conductor portion that electrically connects to the shield of the communication cable when the communication cable is a shielded cable. A servo amplifier in which the shielding conductor is floating relative to the frame ground and connected to the signal ground via a first capacitor.

2. The signal ground is connected to the frame ground via a parallel circuit consisting of a second capacitor and a resistor, which are different from the first capacitor. The servo amplifier according to claim 1, wherein the shielding conductor is connected to the signal ground without passing through the frame ground.

3. The aforementioned communication cable has a balanced line, In the servo amplifier, a pulse transformer is provided between the pair of contacts to be connected to the balanced line in the connector and the physical layer transceiver. The servo amplifier according to claim 1 or 2, wherein the center tap of the pulse transformer is connected to the shielding conductor portion at least via a termination resistor.

4. The aforementioned communication cable has a balanced line, In the servo amplifier, a pulse transformer is provided between the pair of contacts to be connected to the balanced line in the connector and the physical layer transceiver. The servo amplifier according to claim 1 or 2, wherein the center tap of the pulse transformer is connected to the signal ground via a termination resistor and a second capacitor different from the first capacitor.

5. The servo amplifier according to claim 1 or 2, wherein the connector is an RJ45 type jack and the shielding conductor is the shell of the jack.

6. The servo amplifier according to claim 1 or 2, wherein the connector is a USB connector.

7. The servo amplifier according to claim 1 or 2, wherein the connector is an I / O connector.

8. The servo amplifier according to claim 1 or 2, further comprising a plurality of the aforementioned connectors, enabling daisy-chain connection with other servo amplifiers.

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