DRIVER

A driver supplies driving power to a motor including an extractor that extracts a part of externally supplied power and a supply unit that supplies the power extracted by the extractor to an external device. The driver includes an output unit that outputs, to the motor, driving power for the motor on which first power to be supplied to the external device is superimposed. The output unit adjusts the first power to be superimposed by controlling a d-axis current value in a driving current for the motor. This structure allows stable power supply to the external device associated with the motor.

FIELD

The present invention relates to a driver.

BACKGROUND

Motors are to be controlled accurately to drive loads for various uses. To achieve this, the states of the motors are determined typically using detectors such as encoders. Encoders are driven with power that can typically be supplied through cables connecting the encoders and servo systems (e.g., drivers). In another example, Patent Literature 1 describes an encoder that receives power from a power supply other than a servo system. More specifically, Patent Literature 1 describes an auxiliary power supply for the encoder that operates when the power supplied to the encoder from the system is reduced for some reason.

As another example of power supply to encoders, Patent Literature 2 describes an encoder that wirelessly communicates with a servo system using power externally supplied wirelessly. Further, Patent Literature 3 describes an encoder that wirelessly communicates with a servo system using power externally supplied with a wire.

CITATION LIST

Patent Literature

Patent Literature 1: Japanese Unexamined Patent Application Publication No. 8-251817Patent Literature 2: Japanese Unexamined Patent Application Publication No. 2001-297389Patent Literature 3: Japanese Unexamined Patent Application Publication No. 2002-197581

SUMMARY

Technical Problem

An encoder attached to a motor is to receive stable power to constantly monitor the state of the motor to be driven, although the encoder consumes lower power than the motor. Power is supplied to the encoder typically through a cable connected to a driver for the motor. However, this involves cabling for the encoder in addition to installing power lines for the motor, possibly increasing the workload and the cost for cabling.

Techniques have been developed for supplying power wirelessly to encoders, but can be unpractical. A motor is typically incorporated in equipment as a power source for a drive axis in the equipment. In such equipment, the encoder can receive power much less efficiently in a wireless manner than in a wired manner, with the encoder at a distance from a wireless transmission device (antenna). For equipment being a movable machine (e.g., a robot), the encoder cannot reliably receive stable power when obstacles interfere with wireless power transmission or when the machine is positioned or oriented in a certain manner. Such equipment includes various devices that use power around the motor, such as sensors.

In response to the above issue, one or more aspects of the present invention are directed to a technique for stable power supply to an external device associated with a motor.

Solution to Problem

A motor according to one aspect of the present invention receives power from a driver external to the motor through a power line. The motor includes an extractor that extracts a part of power supplied from the driver to the motor, and a supply unit that supplies the power extracted by the extractor to an external device. The above motor may be either a single-phase alternating current (AC) motor or a three-phase AC motor. The coils in a winding unit in the motor may be either delta-connected or star-connected (or Y-connected). The coils in the winding unit may be wound around a stator in the motor with either distributed winding or concentrated winding. In other words, the motor according to one or more aspects of the present invention may include a winding unit with any structure. The above motor may further include a power input unit that allows power from the driver through the power line to be input into a winding unit in the motor. In this case, the extractor may extract a part of power in the winding unit. In another aspect, the extractor may extract a part of power in the power line.

The above motor may further include a transformer located in the winding unit. The transformer may include a primary coil to receive a part of power in the winding unit. The extractor may extract a part of the power in the winding unit using the transformer. In the motor with this structure, the extractor uses the transformer located in the winding unit in the motor and extracts, as power for the external device, a part of the driving power supplied to the motor through the power line. The transformer is located in the motor to receive, at its primary coil, a part of the AC flowing through the winding unit. The transformer may be either an autotransformer or a two-winding transformer. In an autotransformer, the primary coil includes a portion that also serves as a secondary coil. In a typical motor including coils wound around the stator core, the coils protrude from the stator core by a certain distance at the coil end. The transformer may thus be located in the winding unit at the coil end. In another aspect, the secondary coil in the transformer may be wound around the stator core together with the coils in the motor.

The AC extracted from the secondary coil in the transformer is determined based on the AC flowing through the primary coil and on the ratio of turns of the transformer (the ratio of the number of turns of the secondary coil to the number of turns of the primary coil). The supply unit rectifies the extracted AC and supplies the AC to the external device. The supply unit may transform, as appropriate, the voltage resulting from rectification to a voltage appropriate for driving the external device. The supply unit may also include a secondary battery that stores power resulting from rectification. This allows more stable power supply to the external device.

The motor with the above structure extracts, as power for the external device, a part of the power supplied to the motor through the power line, and supplies the extracted power to the external device. This allows stable power supply to the external device independently of the position and the orientation of the motor. The structure also eliminates cabling for power supply to the external device, thus greatly reducing the workload. The external device may be an encoder attached to the motor. In another aspect, the external device may be a temperature sensor, a vibration sensor, or another sensor located inside or outside the motor.

Specific aspects of the transformer in the above motor will now be described. In a first aspect, the transformer may include the primary coil connected in series to a winding portion for at least one phase of one or more phases included in the winding unit, and a secondary coil connected to the supply unit. In a second aspect, the transformer may include the primary coil connected in parallel to a winding portion for at least one phase of one or more phases included in the winding unit, and a secondary coil connected to the supply unit. In a third aspect, the transformer may include the primary coil being a winding portion for at least one phase of one or more phases included in the winding unit, and a secondary coil wound together with the winding portion in the motor and connected to the supply unit. The transformer may have any structure other than the structures in the above aspects.

The above motor may eliminate the above transformer. In this case, the extractor may be located in parallel to a winding portion for at least one phase of one or more phases included in the winding unit, and also connected to the supply unit. The extractor in this aspect extracts, as power for the encoder, a part of the power in the winding portion directly from the winding portion, or in other words, without using the transformer. This structure also allows stable power supply to the encoder and eliminates cabling for power supply to the encoder, thus greatly reducing the workload.

Any of the above motors may further include a signal exchanger that causes a predetermined signal to be transmitted or received between the winding unit and the encoder using the transformer. This structure uses the operation of the transformer also to transmit or receive the predetermined signal between the encoder and the winding unit in the motor. This allows communication between the encoder and the external driver through the transmission or reception of the predetermined signal using the signal exchanger, with the winding unit in the motor being connected to the driver through the power line.

One or more aspects of the present invention may be directed to a driver that supplies a driving current to any of the above motors. The driver may calculate the power supplied by the supply unit. In response to the calculated power being lower than a threshold associated with driving power for the encoder, the driver may increase the power to be supplied to the motor by increasing the d-axis current value in the driving current for the motor. For the motor being driven and controlled, the d-axis current does not contribute to the torque of the motor, specifically in an area with a lower driving current for the motor. In this lower-current area, the extractor extracts lower power that can be insufficient to drive the encoder. The d-axis current value is increased in the driving current for the motor when the power supplied to the encoder is estimated to be lower than the threshold, allowing sufficient power supply to the encoder without greatly affecting the motor operation.

In another aspect of the present invention, when the motor is stopped, the driver may supply power to the motor by controlling the q-axis current value at a constant value that causes the motor to stop and by controlling the d-axis current value to vary over time. This structure allows sufficient power supply to the encoder when the motor is stopped or is to be stopped. In this case, the d-axis current value may vary as, for example, a sine wave, a square wave, or a triangular wave.

In another aspect of the present invention, the driver may include an inverter circuit connected to the winding unit to supply the driving current to the winding unit, and a superimposition unit connected to the winding unit to be in parallel to the inverter circuit to superimpose power on the driving current flowing through the winding unit. This structure allows AC power appropriate for the external device to be transmitted to the winding unit in the motor.

One or more aspects of the present invention may further be directed to a driver that supplies driving power to a motor including an extractor that extracts a part of externally supplied power and a supply unit that supplies the power extracted by the extractor to an external device. Any of the technical ideas described above may be applicable to the motor. The driver may include an output unit that outputs, to the motor, driving power for the motor on which first power to be supplied to the external device is superimposed. In this case, the output unit may adjust the first power to be superimposed by controlling the d-axis current value in the driving current for the motor. The output unit may generate the first power by controlling the d-axis current value and the q-axis current value in the driving current for the motor. In one or more aspects of the present disclosure, the control of the d-axis current value and the q-axis current value includes an increase and a decrease of these values. The first power to be superimposed may be adjusted by combining an increase and a decrease of the d-axis current value and the q-axis current value as appropriate for the type of the motor (e.g., a surface permanent magnet motor or an SPM, or an internal permanent magnet or an IPM). The driver with this structure can supply power to the external device using the extractor and the supply unit at the same time as supplying driving power to the motor. This simplifies the structure of, for example, the power supply and power cables for the external device.

In the above driver, the output unit may generate the first power by controlling the d-axis current value within an allowable range of a current to be output from the driver to the motor. The d-axis current may be controlled in this manner to achieve both stable drive of the motor and appropriate power supply to the external device.

In the above driver, the output unit may control the d-axis current value in the driving current for the motor based on a rotational speed of the motor. The efficiency of power extraction performed by the extractor in the motor can depend on the electrical angular frequency of the driving current, which is associated with the rotational speed of the motor. When the extractor uses the above transformer to extract power, for example, the extraction efficiency tends to be higher for the driving current having a higher electrical angular frequency. The output unit can reflect such power extraction characteristics in controlling the d-axis current value to achieve appropriate power supply to the external device.

For example, in response to the rotational speed of the motor being higher than a predetermined threshold, the output unit may generate the first power by controlling the d-axis current value not to vary over time, and superimpose the first power on the driving power for the motor. The predetermined threshold is the rotational speed of the motor corresponding to the electrical angular frequency of the driving current that causes the extractor to extract power at relatively high efficiency. When the rotational speed of the motor is higher than the predetermined threshold, the extractor is expected to extract power at relatively high efficiency. In this case, the d-axis current value may be controlled not to vary over time.

In response to the rotational speed of the motor being less than or equal to a predetermined threshold, the extractor is not expected to extract power at high efficiency. In this case, the output unit may generate the first power by controlling the d-axis current value to vary over time, and superimpose the first power on the driving power for the motor. To control the d-axis current value to vary over time, for example, the output unit may cause the d-axis current value to vary at a frequency higher than an electrical angular frequency corresponding to the rotational speed of the motor. The d-axis current value may vary over time as, for example, a sine wave, a square wave, or a triangular wave.

In the above driver, in response to the power supplied by the supply unit being lower than a threshold associated with driving power for the external device, the output unit may generate the first power by controlling the d-axis current value in the driving current for the motor, and output the first power to the motor.

In the above driver, the output unit may generate the first power by controlling the q-axis current value at a constant value and by controlling the d-axis current value to vary over time, and output the first power to the motor. This structure can appropriately supply power to the external device using the extractor and the supply unit. When the motor is stopped or is to be stopped, this structure may be used to generate the first power and output the first power to the motor.

In any of the above drivers, the output unit may perform feedback control of the d-axis current value based on the power extracted by the extractor in the motor and based on power to be supplied to the external device. This structure allows more appropriate power supply to the external device using the extractor and the supply unit in the motor.

Advantageous Effects

The technique achieves stable power supply to the external device associated with the motor.

DETAILED DESCRIPTION

First Embodiment

FIG.1is a schematic diagram of a control system for driving and controlling motors. The control system will now be described. The control system includes a programmable logic controller (PLC)5as a host controller connected to a network1. The network1is connected to multiple servo drivers4that can transmit or receive signals to or from the PLC5. AlthoughFIG.1shows the functional components of a servo driver4in detail as a typical example, other servo drivers4aand4balso include functional components equivalent to those of the servo driver4. A motor2is connected to the servo driver4with a power line11and receives driving power from the servo driver4. Similarly, a motor2areceives driving power from the servo driver4athrough a power line11a. A motor2breceives driving power from the servo driver4bthrough a power line11b. The structures of the motor and the servo driver are described below with reference to the motor2and the servo driver4as typical examples.

The motor2is driven and controlled in accordance with commands from the PLC5to drive a predetermined load device. Examples of the load device include various machines (e.g., industrial robotic arms and conveyors). The motor2is incorporated in the load device as an actuator for driving the load device. The motor2is an AC servo motor. In another embodiment, the motor2may be an induction motor or a direct current (DC) motor. The motor2includes a motor body21and an encoder22. The motor body21includes a stator and a rotor. The stator includes a winding unit including a stator core and coils wound around the stator core. The rotor incorporates permanent magnets. The encoder22includes a detection disk rotatable as the rotor rotates to detect the rotation of the rotor. The encoder22may detect the rotation in an incremental manner or an absolute manner.

The detection signal from the encoder22is transmitted wirelessly to the servo driver4through a communicator42(described later) included in the servo driver4. The transmitted detection signal is used for servo control in a control unit41(described later) included in the servo driver4. The detection signal from the encoder22includes, for example, positional information about the rotational position (angle) of the rotational axis of the motor2and information about the rotational speed of the rotational axis.

The servo driver4includes the control unit41, the communicator42, and a power converter43. The control unit41is a functional unit for performing servo control of the motor2based on commands from the PLC5. The control unit41receives motion command signals about the motion of the motor2from the PLC5with the network1, and receives detection signals from the encoder22. The control unit41then performs servo control for driving the motor2, or specifically, calculates command values about the motion of the motor2. The control unit41performs, for example, feedback control using a position controller, a speed controller, and a current controller. The control unit41also performs control in the servo driver4other than the servo control of the motor2.

The communicator42is a functional unit for performing wireless communication between the encoder22and the servo driver4. To start wireless communication, the communicator42in the servo driver4identifies its communication target encoder, thus identifying the encoder22as a target of wireless communication. Thus, the communicator42performs wireless communication with the target encoder without crosstalk with the encoder in the motor2aor with the encoder in the motor2b. Similarly, the encoder in the motor2aperforms wireless communication with the servo driver4aalone, and the encoder in the motor2bperforms wireless communication with the servo driver4balone. The power converter43supplies driving power to the motor2through the power line11based on the command value about the motion of the motor2calculated by the control unit41. The supply power is AC power from an AC power supply7to the servo driver4. Although the servo driver4receives a three-phase AC in the present embodiment, the servo driver4may receive a single-phase AC. In another embodiment, the servo driver4may receive a DC.

The schematic structure of the motor2will now be described with reference toFIG.2. The motor2is a three-phase (U phase, V phase, and W phase) AC motor and includes the motor body21and the encoder22. The motor body21includes a rotor212and a stator213. The rotor212incorporates permanent magnets and is supported in a rotatable manner. The stator213includes a winding unit25including the stator core formed from magnetic steel and the coils wound around the stator core. In the winding unit25in the present embodiment, the winding portions for the respective phases are Y-connected, but the winding portions may be delta-connected instead. The coils may be wound around the stator core with either distributed winding or concentrated winding in the present embodiment. The structure shown inFIG.2is schematic. The technical concept of the present invention is applicable to a motor with any structure.

The power line11for supplying driving power from the servo driver4is connected to a connector211. The connector211corresponds to a power input unit in one or more aspects of the present invention. The connector211is connected to the winding portions for the respective phases in the winding unit25. The motor2includes transformers (refer to53,63, and73inFIGS.3to5, described in detail later) located in the winding unit25. The motor2also includes an extractor214that uses the transformers to extract, as power for the encoder, a part of the driving power supplied to the coils in the winding unit25. More specifically, the extractor214supplies the AC flowing through the winding unit25in the motor body21to the primary coils in the transformers, and extracts a current at the secondary coils as a driving current for the encoder22. In the examples ofFIGS.3and4, the transformers are located in the winding unit25at the coil end in the stator213. In the example ofFIG.5, the transformers have their primary coils wound around the stator core together with the coils in the winding unit25. The transformers may be at a position other than the coil end.

The extractor214extracts, as power for the encoder22, the AC power output from the secondary coils in the transformers. The power is rectified by a supply unit215and stepped up or down as appropriate into a DC voltage appropriate for driving the encoder22using a DC-DC converter included in the supply unit215. The supply unit215is electrically connectable to the encoder22attached to the motor body21to supply DC power to the encoder22, or more specifically, to a processor221that detects rotation of the rotor212. The supply unit215may include a secondary battery that can store DC power resulting from rectification. The secondary battery can supply power to the encoder22with no or very low driving current flowing through the winding unit25.

In the motor2in the present embodiment, a predetermined signal is transmitted or received between the winding unit25in the motor body21and the processor221in the encoder22through the power extraction with the extractor214. The predetermined signal is transmitted or received with a signal exchanger216using the above transformers. To transmit the predetermined signal from the winding unit25to the processor221, a current including the predetermined signal being superimposed is applied to the coils in the winding unit25to flow through the primary coils in the transformers. The extractor214can thus generate a current corresponding to the predetermined signal at the secondary coils in the transformers. The extracted corresponding current can then be transmitted to the processor221with the signal exchanger216. To accurately transmit information about the predetermined signal, the signal exchanger216transmits the predetermined signal without rectifying the corresponding current extracted by the extractor214. For the extracted corresponding current being weak, the signal exchanger216may perform predetermined amplification.

To transmit the predetermined signal from the processor221to the winding unit25, a current including the predetermined signal is applied to the secondary coils in the transformers through the signal exchanger216. The extractor214can thus generate a current corresponding to the predetermined signal at the primary coils in the transformers and cause the current to flow through the coils in the winding unit25. In this case as well, the signal exchanger216may perform predetermined amplification of the predetermined signal. The encoder22can transmit the predetermined signal from the processor221to the servo driver4through a current corresponding to the predetermined signal, with the coils in the winding unit25being electrically connected to the servo driver4with the power line11. As described above, the communication between the encoder22and the servo driver4is performed wirelessly through the communicator42. The communication of the predetermined signal through the signal exchanger216is performed in a manner usable under a predetermined condition, such as before the above wireless communication is enabled.

Example structures of the winding unit25in the motor body21and the transformers located in the winding unit25will now be described. A first example will be described first with reference toFIG.3. The winding unit25includes three-phase winding portions L5, L6, and L7for the U, V, and W phases. The winding portions for the respective phases are Y-connected and have a connection being a neutral point. InFIG.3, the U-phase winding portion L5has an inductance component51and a resistance component52. Similarly, the V-phase winding portion L6has an inductance component61and a resistance component62. The W-phase winding portion L7has an inductance component71and a resistance component72.

The structure includes transformers for the respective phases to form the extractor214. More specifically, for the U phase, the winding portion L5is connected in series to a primary coil531in a U-phase transformer53. For the V phase, the winding portion L6is connected in series to a primary coil631in a V-phase transformer63. For the W phase, the winding portion L7is connected in series to a primary coil731in a W-phase transformer73. A secondary coil532in the transformer53for the U phase, a secondary coil632in the transformer63for the V phase, and a secondary coil732in the transformer73for the W phase are connected to the supply unit215. The secondary coils532,632, and732are also connected to the signal exchanger216.

The transformers for the respective phases basically have the same ratio of turns (the ratio of the number of turns of the secondary coil to the number of turns of the primary coil), but may have different ratios of turns. In the example ofFIG.3, the structure includes transformers for all the three phases, and each transformer has the secondary coil connected to the supply unit215and to the signal exchanger216. In some embodiments, the structure may include one or more transformers for one or two of the three phases, and the transformer(s) may have the secondary coil connected to the supply unit215and to the signal exchanger216. In another embodiment, the structure may include transformers for all the three phases, and one or more of the transformers may have the secondary coil connected to the supply unit215with the remaining transformer(s) having the secondary coil connected to the signal exchanger216. In this case, the transformer(s) connected to the supply unit215to supply power to the encoder22may have a ratio of turns selected as appropriate. The transformer(s) connected to the signal exchanger216to transmit or receive the predetermined signal to or from the encoder22may have a ratio of turns selected as appropriate.

The winding unit25and the transformers53,63, and73with the above structure allow the extractor214to extract, as the driving power for the encoder22, a part of the power supplied to the motor2through the power line11. This structure can constantly and stably supply power to the encoder22while the motor2is being driven. The structure also eliminates cabling for the encoder22, greatly reducing the work and the cost for cabling. In the first example, the transformer for each phase may be located at the coil end in the stator213.

A second example will now be described with reference toFIG.4. The winding unit25in the motor body21in this example has the same structure as in the first example, and will not be described in detail. In the second example, the winding portion L5is connected in parallel to the primary coil531in the transformer53for the U phase. The winding portion L6is connected in parallel to the primary coil631in the transformer63for the V phase. The winding portion L7is connected in parallel to the primary coil731in the transformer73for the W phase. More specifically, the structure includes a line L50including the primary coil531, a line L60including the primary coil631, and a line L70including the primary coil731. The line L50, the line L60, and the line L70are Y-connected and have their other ends respectively connected to the winding portion L5for the U phase, the winding portion L6for the V phase, and the winding portion L7for the W phase. The secondary coil532in the transformer53, the secondary coil632in the transformer63for the V phase, and the secondary coil732in the transformer73for the W phase are connected to the supply unit215. The secondary coils532,632, and732are also connected to the signal exchanger216.

In the second example as well, the transformers for the respective phases basically have the same ratio of turns, but may have different ratios of turns. In the example ofFIG.4, the structure includes transformers for all the three phases, and each transformer has the secondary coil connected to the supply unit215and to the signal exchanger216. In some embodiments, the structure may include one or more transformers for one or two of the three phases, and the transformer(s) may have the secondary coil connected to the supply unit215and to the signal exchanger216. In another embodiment, the structure may include transformers for all the three phases, and one or more of the transformers may have the secondary coil connected to the supply unit215with the remaining transformer(s) having the secondary coil connected to the signal exchanger216. In this case, the transformer(s) connected to the supply unit215to supply power to the encoder22may have a ratio of turns selected as appropriate. The transformer(s) connected to the signal exchanger216to transmit or receive the predetermined signal to or from the encoder22may have a ratio of turns selected as appropriate.

The winding unit25and the transformers53,63, and73with the above structure allow the extractor214to extract, as the driving power for the encoder22, a part of the power supplied to the motor2through the power line11. This structure can constantly and stably supply power to the encoder22while the motor2is being driven. The structure also eliminates cabling for the encoder22, greatly reducing the work and the cost for cabling. In the second example as well, the transformer for each phase may be located at the coil end in the stator213, similarly to the first example.

A third example will now be described with reference toFIG.5. The winding unit25in the motor body21in this example has the same structure as in the first example, and will not be described in detail. In the third example, the winding portions L5, L6, and L7have coil components51,61, and71that serve as the primary coils531,631, and731in the transformers53,63, and73for the respective phases. More specifically, the transformer53includes the coil component51serving as the primary coil531for the U phase. The transformer63includes the coil component61serving as the primary coil631for the V phase. The transformer73includes the coil component71serving as the primary coil731for the W phase. Thus, in the third example, the transformers53,63, and73for the respective phases include the secondary coils532,632, and732wound around the stator core, with the main coils in the winding unit that serve as the primary coils also being wound around the stator core. The secondary coil532in the transformer53, the secondary coil632in the transformer63for the V phase, and the secondary coil732in the transformer73for the W phase are connected to the supply unit215. The secondary coils532,632, and732are also connected to the signal exchanger216.

In the third example as well, the transformers for the respective phases basically have the same ratio of turns, but may have different ratios of turns. In the example ofFIG.5, the structure includes transformers for all the three phases, and each transformer has the secondary coil connected to the supply unit215and to the signal exchanger216. In some embodiments, the structure may include one or more transformers for one or two of the three phases, and the transformer(s) may have the secondary coil connected to the supply unit215and to the signal exchanger216. In another embodiment, the structure may include transformers for all the three phases, and one or more of the transformers may have the secondary coil connected to the supply unit215with the remaining transformer(s) having the secondary coil connected to the signal exchanger216. In this case, the transformer(s) connected to the supply unit215to supply power to the encoder22may have a ratio of turns selected as appropriate. The transformer(s) connected to the signal exchanger216to transmit or receive the predetermined signal to or from the encoder22may have a ratio of turns selected as appropriate.

The winding unit25and the transformers53,63, and73with the above structure allow the extractor214to extract, as the driving power for the encoder22, a part of the power supplied to the motor2through the power line11. This structure can constantly and stably supply power to the encoder22while the motor2is being driven. The structure also eliminates cabling for the encoder22, greatly reducing the work and the cost for cabling. In the third example, the secondary coils in the transformers are wound around the stator core, and thus allow the stator213to have a smaller coil end.

The transformers53,63, and73shown inFIGS.3to5are two-winding transformers, but may be replaced with autotransformers in modifications. For the transformers shown inFIG.5being autotransformers, for example, each of the transformers53,63, and73includes a primary coil being the winding unit25in the motor2and a secondary coil being a portion of the winding unit25. In other words, the winding unit25includes portions that serve as both the primary coils and the secondary coils.

A modification of the example ofFIG.4will now be described with reference toFIG.6. In the example ofFIG.4, the transformers53,63, and73are respectively located in parallel to the winding portions L5, L6, and L7for the three phases, as described above. In another example, power may be extracted from between the winding portions L5, L6, and L7for the respective phases, and the extracted power may be transmitted to a rectifier, a smoothing circuit, and a step-up or step-down circuit including a DC-DC converter. In this example, the extractor214extracts power directly from the winding unit25, rather than extracting power from the winding unit25using transformers. This structure is also within the scope of the present invention.

A fourth example will now be described with reference toFIG.7. The winding unit25in the motor body21in this example has the same structure as in the first example, and will not be described in detail. In the fourth example, the primary coil531in the transformer53is connected between the U phase and the V phase in parallel to the winding portions L5and L6for the U and V phases. The primary coil631in the transformer63is connected between the V phase and the W phase in parallel to the winding portions L6and L7for the V and W phases. The primary coil731in the transformer73is connected between the W phase and the U phase in parallel to the winding portions L7and L5for the W and U phases. The secondary coil532in the transformer53, the secondary coil632in the transformer63, and the secondary coil732in the transformer73are connected to the supply unit215. The secondary coils532,632, and732are also connected to the signal exchanger216.

In the fourth example as well, the transformers for the respective phases basically have the same ratio of turns, but may have different ratios of turns. In the example ofFIG.7, the structure includes a transformer between every pair of phases of the three phases, and each transformer has the secondary coil connected to the supply unit215and to the signal exchanger216. In some embodiments, the structure may include one or more transformers between two or more of the three phases, and the transformer(s) may have the secondary coil connected to the supply unit215and to the signal exchanger216. In another embodiment, the structure may include a transformer between every pair of phases of the three phases, and one or more of the transformers may have the secondary coil connected to the supply unit215with the remaining transformer(s) having the secondary coil connected to the signal exchanger216. In this case, the transformer(s) connected to the supply unit215to supply power to the encoder22may have a ratio of turns selected as appropriate. The transformer(s) connected to the signal exchanger216to transmit or receive the predetermined signal to or from the encoder22may have a ratio of turns selected as appropriate. The winding unit25and the transformers53,63, and73with the above

structure allow the extractor214to extract, as the driving power for the encoder22, a part of the power supplied to the motor2through the power line11. This structure can constantly and stably supply power to the encoder22while the motor2is being driven. The structure also eliminates cabling for the encoder22, greatly reducing the work and the cost for cabling. In the fourth example as well, the transformer for each phase may be located at the coil end in the stator213, similarly to the first example.

Power Supply Control

The motor2including the winding unit25and the transformers in the first to third examples above can extract power for the encoder22from the driving power supplied to the motor2. However, when the motor2receives low driving power, such as when the motor2operates at low speed and light load, the motor2cannot supply sufficient power with the supply unit215to drive the encoder22, possibly affecting the operation of the encoder22. To avoid such unstable power supply to the encoder22, power supply control shown inFIG.8is performed.

The power supply control shown inFIG.8is repeatedly performed by the control unit41in the servo driver4for supplying power to the motor2. Power is supplied to the motor2using known vector control, which is not described in detail herein. First, in S101, the power to be supplied to the encoder22by the supply unit215is calculated. The power to be supplied results from extracting a part of power actually supplied to the motor2through the power line11, and can thus be calculated by reflecting, for example, the voltage applied for each phase, the induced voltage and the impedance of the motor body21, and the impedances of the transformers.

In S102, the determination is performed as to whether the power to be supplied that is calculated in S101is lower than a threshold associated with the driving power for the encoder22. The threshold may be the maximum value of the driving power in the range of variation occurring during the operation of the encoder22, or may be any other value (e.g., the minimum value or the middle value in the range of variation). In response to an affirmative determination result in S102, the processing advances to S103. In S103, the d-axis current value is increased in the vector control for supplying power to the motor2. The drive of the motor2is less susceptible to the increase in the d-axis current value in S103, with the d-axis current value indicating a current that does not contribute to the torque of the motor2. When the current to the motor2is lowered, the current can also be increased through current control performed by the control unit41. The degree of increase in the d-axis current value may be adjusted to be greater for a greater difference between the power to be supplied that is calculated in S101and the above threshold. In response to a negative determination result in S102, the control process is complete.

The power supply control shown inFIG.8allows appropriate power supply to the encoder22independently of the operating state of the motor2.

First Modification of Power Supply Control

Power supply control using the d-axis current value will now be described in detail with reference toFIGS.9to11. In the present modification, the servo driver4includes an output unit that outputs, to the motor2, driving power for the motor2on which first power for driving the encoder22is superimposed. The output unit corresponds to the power converter43shown inFIG.1, or is a functional unit incorporated in the power converter43. The output unit controls the d-axis current value in the driving current for the motor2to adjust the first power to be superimposed on the driving power for the motor2. The superimposition of the first power will be mainly described below.

FIG.9is a graph of the correlation between the rotational speed of the motor2and the current applied by the servo driver4. In a lower-speed area of the motor2(e.g., the area with the rotational speed being less than or equal to V0), the motor2is driven and controlled with a driving current including substantially a q-axis current alone without a d-axis current. In a higher-speed area of the motor2(e.g., the area with the rotational speed being greater than V0), the motor2receives a driving current having a higher d-axis current value at a higher rotational speed. The maximum current that substantially contributes to the torque of the motor2is indicated by a line L100. The area inside the line L100(the area including the origin) includes a lower-speed area R2in which the upper limit of the current is substantially constant, or specifically at a rated current Ir, and a higher-speed area R1in which the upper limit of the current decreases as the rotational speed increases. The area outside the line L100is an area R0in which the driving current is not allowed to or cannot be applied to the motor2by the servo driver4. The above power supply control using the d-axis current value is thus performed within the area R1and the area R2.

The power supply control for the motor2in the state indicated by a point P1in the area R1will now be described with reference toFIGS.10A and10B. In the state indicated by the point P1, as shown inFIG.10A, the driving current output to the motor2from the servo driver4has the q-axis current value being Iq1(a line L102) and the d-axis current value being Id1(a line L101). For the motor2being in an unchanged drive state, the q-axis current value and the d-axis current value are unchanged over time. When the driving power for the motor2on which the driving power (first power) for the encoder22is superimposed is output to the motor2, the d-axis current value is increased from Id1up to Id1′ (a line L101′) while the q-axis current value is maintained at Iq1. As shown inFIG.10B, the d-axis current value can be increased up to Idt at which the current output to the motor2reaches a point P1′ on the line L100inFIG.9when the q-axis current value is Iq1. The circle inFIG.10Bhas the radius indicating the rated current Ir.

In the motor2having a relatively high rotational speed greater than V0, the above extractor214extracts power with the transformers at higher efficiency, with a higher electrical angular frequency of the current flowing through the windings in the motor2. In this case, as shown inFIG.10A, the d-axis current value is increased from Id1up to Idt and not to vary over time. The driving power (first power) for the encoder22is thus superimposed on the driving power for the motor2and output from the servo driver4to the motor2. A part of the output power, or specifically, the power corresponding to the increase in the d-axis current value, is extracted by the extractor214and supplied to the encoder22.

The power supply control for the motor2in the state indicated by a point P2in the area R2will now be described with reference toFIGS.11A and11B. In the state indicated by the point P2, as shown inFIG.11A, the driving current output to the motor2from the servo driver4has the q-axis current value being Iq1(the line L102) and the d-axis current value being Id1(the line L101, Id1=0). For the motor2being in an unchanged drive state, the q-axis current value and the d-axis current value are unchanged over time.

In the motor2having a relatively low rotational speed less than or equal to V0, the above power extraction with the transformers is performed at lower efficiency, with a lower electrical angular frequency of the driving current flowing through the windings in the motor2. When the driving power for the motor2on which the driving power (first power) for the encoder22is superimposed is output to the motor2, the d-axis current value is increased from Id1to Idt while the q-axis current value is maintained at Iq1. In this case, as shown inFIG.11A, the d-axis current value is increased to Idt to vary over time with a predetermined offset of a DC component, unlike the example ofFIG.10A. In other words, the increased d-axis current value is not constant but varies over time at a predetermined amplitude and at a predetermined frequency. When the increased d-axis current value is expressed as an effective value as shown inFIG.11B, the current output to the motor2reaches a point P2′ on the line L100inFIG.9. InFIG.11B, the d-axis current Idt varies over time by an amount Aid.

The increased d-axis current value may vary as a sine wave oscillating at a predetermined frequency. The predetermined frequency is, for example, higher than the electrical angular frequency of the driving current associated with the rotational speed of the motor2. The increased d-axis current value may vary as a square wave or a triangular wave. The offset of the DC component above can be adjusted as appropriate based on the power to be supplied to the encoder22.

Thus, for the motor2being in the drive state within the area R2, the d-axis current value is increased from Id1up to Id1′ and to vary over time. The driving power (first power) for the encoder22is thus superimposed on the driving power for the motor2and output from the servo driver4to the motor2. When the driving current through the motor2has a low electrical angular frequency, the extractor214can thus appropriately extract a part of the output power, or specifically, the power corresponding to the increase in the d-axis current value, and supply the extracted power to the encoder22.

To control the d-axis current value as described above, feedback control may be performed based on the power actually extracted by the extractor214in the motor2and on the power to be supplied to the encoder22. In the feedback control, information about the power actually extracted by the extractor214and about the power to be supplied to the encoder22is transmitted wirelessly from the motor2to the servo driver4. In another embodiment, predetermined information about the power to be supplied to the encoder22may be stored in the servo driver4.

As described above, in the present modification, the d-axis current is controlled to superimpose the driving power (first power) for the encoder22based on the rotational speed of the motor2to allow efficient power extraction by the extractor214with the transformers. In the present modification, the rotational speed V0is at the boundary between the higher-speed area and the lower-speed area. However, the rotational speed V0may be set as appropriate to allow efficient power extraction with the transformers, rather than matching the changing point of the boundary value of the current indicated by the line L100(the point at which the current starts to decrease as the rotational speed increases).

In the control of the d-axis current value described above, the first power to be generated and superimposed is increased by increasing the d-axis current. However, the first power to be superimposed may be adjusted by combining an increase and a decrease of the d-axis current value and the q-axis current value as appropriate for the type of the motor (e.g., an SPM or an IPM). Thus, the first power to be generated may be adjusted by controlling the d-axis current value and the q-axis current value to increase or decrease these current values as appropriate.

Second Modification of Power Supply Control

When the motor2(or specifically the rotor212in the motor2) is stopped or is to be stopped, no power is typically supplied to the motor2. This can cause insufficient power supply to the encoder22. In the present modification, when the motor2is stopped, power supply to the motor2is performed by controlling the q-axis current value at a constant value that causes the motor2to stop and by controlling the d-axis current value to vary over time (e.g., to vary as a sine wave). With such power supplied, the motor2is stopped without rotating, with the q-axis current value being a constant value that causes the motor2to stop. When the motor2is stopped, the q-axis current value may typically be set to zero under a substantially zero external force applied to the motor2. Under any external force such as an unbalanced load, the q-axis current value may be set to a value that generates torque to resist the external force.

In this state, the d-axis current varying over time is applied to the motor2. Thus, the motor2being stopped can supply a part of the received power to the encoder22using the transformers. The value of the d-axis current to be applied may vary as a sine wave, or as any other wave such as a square wave or a triangular wave.

For the motor2in the example ofFIG.3with single-phase transformers, the circuit equations will now be described. The transformers for the respective phases have the same characteristics. In the formulas below, Vu, Vv, and Vw are the output voltages of the driver4for the respective phases, and lu, Iv, and lw are the currents of the driver4for the respective phases. Lu, Lv, and Lw are the self-inductances of the motor2for the respective phases, and Muv, Mvw, and Mwu are the mutual inductances between the phases of the motor2. In the formulas below, we is the electrical angular frequency, ϕuvw is the maximum number of flux linkages of the mature windings, R is the winding resistance, Ke is the induced voltage constant, and s is the differential operator. Vux2, Vvx2, and Vwx2are the output voltages of the secondary portions of the transformers, and Iux2, Ivx2, and Iwx2are the currents of the secondary portions of the transformers. Lx1, Lx2, and Mx are respectively the primary inductance, the secondary inductance, and the mutual inductance of the transformers. Rx1and Rx2are respectively the primary winding resistance and the secondary winding resistance of the transformers. In the formulas below, ee is the electrical angle.

The circuit equations for the motor2are expressed as Formulas 1 and 2 below.

The above formulas are further transformed to the circuit equations expressed as Formulas 3 and 4 below through the transformation from the three phases U, V, and W to the two phases d and q and the transformation from a fixed coordinate system to a rotating coordinate system.

Formulas 3 and 4 will now be verified.FIG.13A(upper figure) is a schematic diagram of a circuit model for verifying the formulas. An inverter (corresponding to the driver4) receives power from a DC power supply and supplies a driving current to the motor2through a power line to drive the motor2. The model shown inFIG.13Aincludes a transformer between the power line and the motor body, and a load RL (e.g., a sensor) connected to the secondary portion of the transformer. The inverter has the outputs for the three phases each connected to a single-phase transformer, to which the motor is connected in the subsequent stage. The inverter supplies the driving current to drive the motor with current control and speed control. In the current control, for example, parameters associated with the motor characteristics are fed back as appropriate to the inverter, which then uses the parameters to generate the driving current.FIG.13B(lower figure) is a diagram of the single-phase transformer and the load. The parameters for the motor and the transformer in the circuit model are shown in Tables 1 and 2 below.

Parameters for Motor

Parameters for Transformer

FIG.13Ashows three measurement points Pa, Pb, and Pc at which voltages and currents are measured for the three phases. In the simulation using the circuit model, voltages and currents are measured at the measurement points Pa, Pb, and Pc for the three phases. The measured values are used to calculate voltages and currents for the d-axis and the q-axis. At the measurement point Pa, the voltage and the current of a terminal in the motor are calculated. At the measurement point Pb, the voltage and the current output from the inverter are calculated. At the measurement point Pc, the voltage and the current output from the transformer are calculated. At each measurement point, these calculated values are compared with the values calculated using the above circuit equations for each of the d-axis voltage and the q-axis voltage. The calculation and the comparison are performed with the motor having a fixed rotational speed.

Tables 3 to 5 below show the comparison results.

Comparison Results at Measurement Point Pa

Comparison Results at Measurement Point Pb

Comparison Results at Measurement Point Pc

The above comparison results reveal that the values calculated using the circuit equations are within an error of 1% as compared with the values calculated using the circuit model. The above circuit equations, or Formulas 3 and 4, are thus verified. The above results also reveal that the current control and the speed control are unlikely to be affected by the transformer for power extraction incorporated in the motor. Thus, the above circuit equations can be used to design the motor incorporating the transformer.

For the motor2in the example ofFIG.3with three-phase transformers, the circuit equations are expressed as Formulas 5 and 6 below. These formulas may also be used to design the motor.

For the motor2in the example ofFIG.5with transformers, the circuit equations are expressed as Formulas 7 and 8 below. These formulas may also be used to design the motor.

Modification of Driver4

In the above embodiments, the inverter circuit in the power converter43in the driver4is used to supply power to the winding unit25in the motor2. More specifically, the driving current generated by the inverter circuit is supplied to the winding unit25in the motor2, and a part of the supplied power is extracted by the extractor214for the encoder22. In the present modification, as shown inFIG.12, the power converter43includes a power superimposition unit432, separate from an inverter circuit431, to supply power. Although the winding unit25shown inFIG.12corresponds to the winding unit25in the example ofFIG.5, the winding unit25in the present modification may be replaced with the winding unit25in the example ofFIG.3orFIG.5.

The inverter circuit431includes, between a positive power line and a negative power line, a U-phase leg, a V-phase leg, and a W-phase leg connected in parallel. Each leg has the output connected to the winding portion in the motor2for the corresponding phase with the power line. The power converter43includes the power superimposition unit432connected in parallel to the inverter circuit431with the power line, through which the power superimposition unit432superimposes power on the driving current for the motor2flowing in the winding unit25. The power superimposition unit432allow high-frequency power to be superimposed using the transformers for the U phase, the V phase, and the W phase. This structure allows AC power appropriate for the encoder22to be transmitted to the extractor214, separately from power for operating the motor2. In another embodiment, the power superimposition unit432may be connected in series to the inverter circuit431.

Modification of Device to Which Extracted Power is Supplied

In the above embodiments, the power extracted by the extractor214is supplied to the encoder22. However, the extracted power may be supplied to a device other than the encoder22. For example, the power may be supplied to a sensor (e.g., a temperature sensor or a vibration sensor) located inside or outside the motor2. In this case, the motor body21may include a port to connect to the sensor with a cable for power supply.

Modification of Power Extraction

A modification will now be described with reference toFIG.14.FIG.14is a schematic diagram of a motor2according to the present modification. Similarly to the example ofFIG.2, the motor2in the present modification includes an extractor214with transformers located in the winding unit25. The transformers for the extractor214may have substantially the same structure as the transformers shown inFIG.3,4, or7. The structure in the present modification further includes an extractor214bon the power line11connected to the connector211to extract power. The extractor214bextracts power also using transformers electrically identical to the transformers shown inFIG.3orFIG.4incorporated in the power line11.

The power extracted by the extractor214bmay be, for example, rectified in a predetermined manner and supplied to a device located outside the motor2, such as a temperature sensor or a vibration sensor. The extracted power is stored in a secondary battery for stable power supply to, for example, the temperature sensor. In the motor2shown inFIG.14, the power to be supplied to the encoder22is extracted by the extractor214. In some embodiments, the power to be supplied to the encoder22may be extracted by the extractor214b. In some embodiments, the power to be supplied to the encoder22may be extracted by both the extractors214and214b. The motor2may eliminate the extractor214, and the encoder22may receive power from a built-in battery or from the servo driver4.

The motor2according to one or more embodiments of the present disclosure can extract power from the winding unit25and also from the power line11and supply the extracted power to, for example, the encoder22and an external sensor. This greatly reduces the load for cabling for power supply in the servo system.

Modification of Power Supply and Signal Relay

A modification will now be described with reference toFIG.15.FIG.15is a schematic diagram of a motor2according to the present modification. In the present modification, the extractor214bshown inFIG.14can communicate with the processor221in the encoder22. The extractor214bcommunicates with the processor221through wireless communication using power extracted from the power line11by the extractor214b. The processor221in the encoder22uses power extracted by the extractor214and supplied from the motor body21with the supply unit215.

The extractor214bin the present modification includes a first communicator2141and a second communicator2142. The first communicator2141can perform wireless communication with the processor221. More specifically, the first communicator2141can receive a detection signal from the encoder22and transmit a signal to the encoder22through wireless communication. The first communicator2141may use any wireless communication scheme. The extractor214bincludes the transformers for power extraction as described above. The transformers are also used by the second communicator2142to serve as an interface to communicate with the servo driver4. For example, the second communicator2142can receive the detection signal from the encoder22through the first communicator2141, and superimpose the detection signal on a current flowing through the power line11. More specifically, the second communicator2142can transmit a signal to the secondary coils in the transformers, obtain a signal output from the primary coils, and superimpose the output signal on the current flowing through the power line11. The second communicator2142is thus used to transmit or receive a signal between the power line11and the processor221in the encoder22, and is also used to transmit the signal to the servo driver4through the power line11.

The second communicator2142can also receive a predetermined signal from the servo driver4through the transformers and transmit the signal to the first communicator2141, which can then transmit the signal to the processor221in the encoder22through wireless communication. In other words, the extractor214band the processor221can communicate with each other.

In this structure, the motor2receiving power through the power line11supplies a part of the power to the attached encoder22, and also serves as a repeater for information between the servo driver4and the encoder22. The extractor214bmay be installed at a position on the power line11to allow wireless communication with the encoder22. The extractor214bis easy to install, with the encoder22and the power line11both typically located near the motor body21. The structure in the example ofFIG.15eliminates cabling for power supply and signal transmission to the encoder22, thus greatly reducing the workload for constructing the servo system. In another modification, the extractor214bmay receive a detection signal

from a power supply target (e.g., a temperature sensor or a vibration sensor) with the first communicator2141through wireless communication, superimpose the received signal on the power line11with the second communicator2142, and transmit the resultant signal to the servo driver4. The extractor214bmay relay the detection signals from the above sensor and from the encoder22to the servo driver4. The first communicator2141may perform wired communication with, for example, the encoder22and the sensor.

A driver (4) for supplying driving power to a motor (2) including an extractor (214) to extract a part of externally supplied power and a supply unit (215) to supply the power extracted by the extractor (214) to an external device, the driver (4) comprising:

an output unit configured to output, to the motor (2), driving power for the motor (2) on which first power to be supplied to the external device is superimposed, wherein the output unit adjusts the first power to be superimposed by controlling a d-axis current value in a driving current for the motor (2).

DESCRIPTION OF SYMBOLS