Transport System

Abstract

Each of the one or more transport path units (11) included in the transport system (1) includes one or more coils (20) that generate power, one or more inverter circuits (21) that are provided corresponding to the respective coils (20) and apply voltage to the coils (20), and an inverter circuit control unit (50) that controls switching of four switching elements (40A-40D) included in the inverter circuit (21). When a carriage (16) is present in a portion of the transport path (10) that is formed by a first transport path unit among the one or more transport path units (11), switching of at least one switching element (40) of at least one inverter circuit (21) among the one or more inverter circuits (21) included in the first transport path unit is forcibly stopped.

Description

[Technical Field]

[0001] The present disclosure relates to a transport system for transporting objects. [Background technology]

[0002] In production lines where factory automation is implemented, such as production lines for assembling industrial products or for packaging food, conveyor systems are commonly used to transport workpieces. In recent years, conveyor systems have been widely used in which the conveyor path for transporting workpieces is divided into multiple zones, and carts carrying the workpieces are driven by control devices located in each zone. This type of conveyor system is known as one of the conveyor systems with excellent production efficiency.

[0003] Patent Document 1 below discloses a conveyance system using a linear motor. The conveyance system disclosed in Patent Document 1 comprises a plurality of conveyance path units that form a conveyance path along which a conveyance body moves and that move the conveyance body by applying power to the conveyance body. Each of the plurality of conveyance path units comprises a drive unit that generates power and an inverter circuit that has a switching element and supplies power to the drive unit after undergoing power conversion by switching the switching element. At least one of one or more conveyance path units in a portion of the conveyance path where no conveyance body is present stops switching. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 7258265 Summary of the Invention [Problem to be solved by the invention]

[0005] The conveyance system disclosed in Patent Document 1 can reduce energy loss in conveyance path units where no conveyance body is present on the conveyance path unit. However, Patent Document 1 only allows the selection of whether or not to stop switching for the entire conveyance path unit. Therefore, the method of Patent Document 1 is unable to select an inverter circuit to stop switching even when the ratio of the length of the conveyance path unit to the length of the conveyance body becomes large, and therefore is not effective in reducing energy loss. In other words, the method of Patent Document 1 has the problem that the greater the ratio of the length of the conveyance path unit to the length of the conveyance body, the smaller the effect of reducing energy loss.

[0006] The present disclosure has been made in consideration of the above, and aims to provide a conveying system that can achieve the effect of reducing energy loss even when the ratio of the length of the conveying path unit to the length of the conveying body becomes large. [Means for solving the problem]

[0007] In order to solve the above-mentioned problems and achieve the object, a conveying system according to the present disclosure includes a plurality of conveying path units that form a conveying path along which one or more conveyed bodies move and that move the conveyed bodies by applying power to the conveyed bodies. Each conveying path unit includes one or more drive units that generate power, one or more inverter circuits that are provided corresponding to each drive unit and apply voltage to the drive units, and an inverter circuit control unit that controls switching of a plurality of switching elements provided in the inverter circuits. When a conveyed body is present in a portion of the conveying path formed by a first conveying path unit of the one or more conveying path units, switching of at least one switching element of at least one inverter circuit of the one or more inverter circuits provided in the first conveying path unit is forcibly stopped. [Effects of the Invention]

[0008] According to the transport system according to the present disclosure, it is possible to obtain an effect of reducing energy loss even when the ratio of the length of the transport path unit to the length of the transport body is large. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a diagram showing a configuration example of a transport system according to a first embodiment; [Figure 2] FIG. 1 is a diagram showing an example of the configuration of a transport path unit according to the first embodiment; [Figure 3] FIG. 10 is a diagram showing a configuration example of an inverter circuit provided in the transport path unit according to the first embodiment; [Figure 4] FIG. 10 is a diagram illustrating the current distribution of currents flowing through the coils in the transport path unit according to the first embodiment; [Figure 5] FIG. 10 is a diagram illustrating current commands and voltage commands given to each coil in the transport path unit according to the first embodiment. [Figure 6] 10 is a timing chart illustrating an operation when a dead time period is set in the inverter circuit according to the first embodiment; [Figure 7] 1 is a first time chart illustrating the operation of the inverter circuit control unit according to the first embodiment; [Figure 8] 10 is a second time chart illustrating the operation of the inverter circuit control unit according to the first embodiment; [Figure 9] FIG. 10 is a block diagram showing another example of the configuration of the inverter circuit control unit according to the first embodiment. [Figure 10] FIG. 1 is a diagram illustrating an example of a hardware configuration for realizing the functions of a control device according to a first embodiment. [Figure 11] FIG. 10 is a diagram showing another example of a hardware configuration for realizing the functions of the control device according to the first embodiment. [Figure 12] 10 is a time chart illustrating a single-phase modulation method used in the second embodiment. [Figure 13] 10 is a time chart illustrating the operation of the inverter circuit control unit according to the second embodiment; [Figure 14]10 is a time chart illustrating the operation of the inverter circuit control unit according to the third embodiment; DETAILED DESCRIPTION OF THE INVENTION

[0010] A transport system according to an embodiment of the present disclosure will be described in detail below with reference to the accompanying drawings.

[0011] Embodiment 1 FIG. 1 is a diagram showing an example of the configuration of a conveyance system 1 according to a first embodiment. The conveyance system 1 is a system used to convey objects. In the first embodiment, the conveyance system 1 conveys objects by moving conveyance bodies on which the objects are placed. The number of conveyance bodies is one or more.

[0012] The transport system 1 includes a plurality of transport path units 11A, 11B, 11C, 11D, 11E, 11F, 11G, and 11H, a control device 12, a DC (Direct Current) power supply 13, and carts 16A, 16B, and 16C. In the following description, the transport path units 11A, 11B, 11C, 11D, 11E, 11F, 11G, and 11H will be referred to collectively as "transport path unit 11" without distinction between them. Furthermore, the carts 16A, 16B, and 16C will be referred to collectively as "cart 16" without distinction between them.

[0013] The plurality of transport path units 11 are connected to one another to form a transport path 10 along which a carriage 16, which is a transport body, moves. The plurality of transport path units 11 applies power to the carriage 16, thereby moving the carriage 16.

[0014] The conveying path 10 shown in Fig. 1 is circular. That is, the conveying path 10 shown in Fig. 1 is a closed path. The conveying path 10 of the conveying system 1 may also be an open path, that is, a path having a start point and an end point.

[0015] The transport path units 11A, 11B, 11E, and 11F are linear transport path units 11 that form a linear path. The transport path units 11C, 11D, 11G, and 11H are curved transport path units 11 that form a curved path and change the traveling direction of the carriage 16. In FIG. 1, the transport path 10 is formed by combining linear transport path units 11 and curved transport path units 11, but the overall shape of the transport path 10 is arbitrary. For example, the transport path 10 may be formed only by transport path units 11 that form a curved path, without including any transport path units 11 that form a linear path.

[0016] The carriage 16 is attached to the side of the conveying path 10. The carriage 16 moves along a guide rail provided on the side of the conveying path 10. The carriage 16 moves along the side of the conveying path 10 and stops at the side of the conveying path 10. The conveying system 1 according to the first embodiment is a moving magnet type linear motor. The carriage 16 may move along a guide rail provided on the upper surface of the conveying path 10. The carriage 16 includes a permanent magnet as a mover, a permanent magnet for a linear scale, and a guide roller that moves on the guide rail by rotation. In FIG. 1, the guide rail, guide roller, permanent magnet as a mover, and permanent magnet for the linear scale are not shown.

[0017] In the example shown in Fig. 1, the conveyance system 1 includes eight conveyance path units 11 and three carriages 16. However, the number of conveyance path units 11 included in the conveyance system 1 is arbitrary. That is, the conveyance system 1 can include a plurality of conveyance path units 11. The number of carriages 16 that move on the conveyance path 10 is arbitrary. That is, the conveyance system 1 can include one or a plurality of carriages 16.

[0018] The conveying system 1 is not limited to a system equipped with a linear motor, but may also be a system equipped with a rotary motor. The conveying system 1 may also be a belt conveyor equipped with a rotary motor and a belt rotated by the rotary motor. The belt conveyor moves workpieces placed on the belt. The conveying system 1 may also be a roller conveyor equipped with multiple rollers and a rotary motor that rotates the rollers. The roller conveyor moves workpieces placed on the rollers.

[0019] The DC power supply 13 is connected to each transport path unit 11 via a DC power bus 15. The DC power supply 13 is a power supply device or power supply circuit that outputs a DC voltage. The DC power supply 13 supplies power to each transport path unit 11. Each transport path unit 11 shares the DC power supply 13. The transport system 1 has a configuration in which each transport path unit 11 is connected to the DC power supply 13 by a multi-drop connection. The connection between each transport path unit 11 and the DC power supply 13 is not limited to a multi-drop connection, and may be a daisy chain connection. In the example shown in FIG. 1, the transport system 1 is provided with one DC power supply 13, but the transport system 1 may be provided with multiple DC power supplies 13. In other words, the transport system 1 may be configured with multiple power supply domains.

[0020] The control device 12 is connected to each of the transport path units 11 via a data communication line 14. The control device 12 controls each of the multiple transport path units 11. The data communication line 14 is composed of a communication line connecting the control device 12 to one of the multiple transport path units 11, that is, transport path unit 11A, and a communication line connecting adjacent transport path units 11. In the transport system 1, each of the transport path units 11 is connected to the control device 12 in a daisy chain manner, thereby enabling communication therebetween. Note that the connection between each of the transport path units 11 and the control device 12 is not limited to a daisy chain connection. The connection between each of the transport path units 11 and the control device 12 may also be a star connection in which each of the transport path units 11 is connected to the control device 12 via a communication hub. Alternatively, the transport system 1 may be configured to include multiple data communication lines 14, and each of the transport path units 11 and the control device 12 may be directly connected by the data communication line 14. Furthermore, the data communication line 14 may not be a physical communication line, but may be a communication path that allows wireless communication.

[0021] The control device 12 generates a position command indicating a position to which the carriage 16 should be moved, and also generates a coil drive command based on the position command. The control device 12 outputs the coil drive command to each transport path unit 11. Each transport path unit 11 drives its respective coil in accordance with the coil drive command. The control device 12 controls the movement of each carriage 16 by outputting the coil drive command to each transport path unit 11. Alternatively, the control device 12 may generate a position command indicating a position to which the carriage 16 should be moved, and output the position command to each transport path unit 11. In this case, each transport path unit 11 generates a coil drive command based on the position command, and drives its respective coil in accordance with the coil drive command.

[0022] The traveling direction of each carriage 16 is either clockwise in Fig. 1 or counterclockwise in Fig. 1. Of the traveling directions, the clockwise direction in Fig. 1 is the forward direction, and the counterclockwise direction in Fig. 1 is the reverse direction. Arrow 17A indicates the forward direction, and arrow 17B indicates the reverse direction.

[0023] The control device 12 may be connected to a higher-level control device such as a programmable logic controller. The higher-level control device outputs commands for sequence control to the control device 12. A human-machine interface may be connected to the control device 12. The human-machine interface accepts input from an operator. The human-machine interface also outputs information indicating the status of the conveyance system 1 by display or the like. The control device 12 may acquire operation information of the carriages 16 from the higher-level control device or the human-machine interface and generate a position command based on the operation information. The operation information is information indicating a schedule for the movement of each of the multiple carriages 16 on the conveyance path 10.

[0024] Next, the configuration of the transport path unit 11 will be described. Here, the configuration of the transport path unit 11 will be described using a straight-type transport path unit 11 as an example. In the curved-type transport path unit 11, the coil arrangement is different from that in the case of the straight-type transport path unit 11. The configuration of the curved-type transport path unit 11 is the same as the configuration of the straight-type transport path unit 11, except for the difference in the coil arrangement.

[0025] Fig. 2 is a diagram showing an example of the configuration of the transport path unit 11 according to the first embodiment. In addition to the transport path unit 11, Fig. 2 also shows the carriage 16 having a permanent magnet 30 and a scale magnet 31. The permanent magnet 30 is a permanent magnet that is a mover and contributes to driving the carriage 16. The scale magnet 31 is a permanent magnet for a linear scale.

[0026] The transport path unit 11 is provided with a plurality of coils 20. Each coil 20 functions as a drive unit that generates power. In the example shown in FIG. 2, the transport path unit 11 is provided with nine coils 20. However, the number of coils 20 provided in the transport path unit 11 is arbitrary. That is, the number of coils 20 is one or two or more. When the transport path unit 11 is provided with a plurality of coils 20, the plurality of coils 20 are arranged in a linear direction in a linear transport path unit 11, and are arranged in a curved direction in a curved transport path unit 11.

[0027] An inverter circuit 21 is connected to each coil 20 in the conveying path unit 11. The inverter circuit 21 is provided corresponding to each coil 20, and controls the current flowing through the corresponding coil 20 by applying a voltage to the coil 20. The inverter circuit 21 is a single-phase full-bridge inverter circuit or a single-phase half-bridge inverter circuit. The inverter circuit 21 may also be a three-phase inverter circuit connected to three coils 20. In this paper, the single-phase full-bridge inverter circuit and the single-phase half-bridge inverter circuit are collectively referred to as a "single-phase inverter circuit."

[0028] The coils 20 generate electromagnetic force, which is the power that moves the cart 16, when power is supplied from the inverter circuit 21. A current detector 22 is connected to each coil 20 of the transport path unit 11. The current detector 22 detects the actual coil current value, which is the current value of the current flowing through the coils 20.

[0029] An inverter circuit control unit 50 is connected to the inverter circuit 21. The inverter circuit control unit 50 controls the switching of the multiple switching elements 40 included in the inverter circuit 21.

[0030] The inverter circuit control unit 50 includes a PWM (Pulse Width Modulation) signal generator 29 and a current controller 24. The PWM signal generator 29 is connected to the inverter circuit 21, and the PWM signal generator 29 is connected to the current controller 24. The current controller 24 calculates a voltage value to be applied to the coil 20 based on a current command value of a current to be passed through the coil 20 and an actual coil current value detected by a current detector 22. The calculated voltage value is output to the PWM signal generator 29, which compares the calculated voltage value with a carrier signal and transmits a PWM signal to the inverter circuit 21. The PWM signal is a control signal that controls switching of a plurality of switching elements 40.

[0031] The PWM signal generator 29 transmits a PWM signal to the inverter circuit 21, causing the inverter circuit 21 to perform switching. As a result, the inverter circuit 21 applies a voltage to the coil 20 for causing a current of a desired value to flow through the coil 20. The current controller 24 may calculate the voltage value of the voltage to be applied to the coil 20 by performing PID (Proportional Integral Differential) control of the voltage to be applied to the coil 20 based on the deviation between a current command value and an actual coil current value. The current controller 24 and the PWM signal generator 29 can be realized by an FPGA (Field Programmable Gate Array), a microprocessor, or the like.

[0032] The inverter circuit 21 is connected to the positive wiring of the DC power supply bus 15 and the negative wiring of the DC power supply bus 15. The positive wiring is the wiring connected to the positive electrode of the DC power supply 13. The negative wiring is the wiring connected to the negative electrode of the DC power supply 13. A capacitor 23 is connected between the wiring on the positive side of the DC power supply 13 and the wiring on the negative side of the DC power supply 13. In this paper, the voltage applied to both ends of the inverter circuit 21 by the positive wiring and negative wiring of the DC power supply bus 15 is called the "bus voltage."

[0033] The transport path unit 11 includes a linear scale 25 and a processor 27. The linear scale 25 is a detection unit that detects the position of the carriage 16 on the transport path unit 11. The linear scale 25 is provided on the transport path 10 when a plurality of transport path units 11 are connected to each other to form the transport path 10. The processor 27 is an example of a calculation means. The processor 27 may be a calculation means called a microprocessor, a microcomputer, a CPU (Central Processing Unit), or a DSP (Digital Signal Processor).

[0034] The linear scale 25 includes a plurality of position sensors 26. The position sensors 26 are sensors that detect magnetic fields, such as Hall sensors or magnetoresistive sensors. Each position sensor 26 detects the magnetic field of the permanent magnet 30 or the magnetic field of the scale magnet 31. In this example, the position sensor 26 is a Hall sensor equipped with two Hall elements. The distance between the two Hall elements corresponds to half the magnetic pole pitch of the scale magnet 31. The two Hall elements convert the magnetic field into an electric signal and output the electric signal. The electric signal output by each Hall element changes as the carriage 16 moves. The waveform of the electric signal output by one Hall element is a sine wave. The waveform of the electric signal output by the other Hall element is a cosine wave.

[0035] An AD (Analog to Digital) converter (not shown) provided in the processor 27 detects the sine wave and the cosine wave. The processor 27 calculates the arctan based on the sine wave information and the cosine wave information to detect the position of the dolly 16 relative to the position sensor 26. In this way, the processor 27 obtains position information indicating the position of the dolly 16.

[0036] The transport path unit 11 includes a communication slave station 28. The communication slave station 28 is a communication slave station on the transport path unit 11 side. The data communication line 14 is connected to the communication slave station 28. When each transport path unit 11 and the control device 12 are connected by a daisy chain connection, the communication slave station 28 is configured to be able to connect two data communication lines 14. The communication slave station 28 receives, for each of the multiple coils 20 provided in the transport path unit 11, a current command indicating a current command value for the current to be passed through the coil 20 from the control device 12. The communication slave station 28 acquires position information acquired by the position sensor 26 from each of the multiple position sensors 26 provided in the linear scale 25. The communication slave station 28 transmits the acquired position information to the control device 12.

[0037] The communication slave station 28 performs, for example, periodic communication, in which it receives a current command at a fixed period and transmits position information. Instead of periodic communication, the communication slave station 28 may perform non-periodic communication, in which it receives a current command and transmits position information non-periodically.

[0038] As described above, the transport path unit 11 mainly has the function of controlling the energization of the coil 20 and the function of acquiring position information. All of the multiple transport path units 11 constituting the transport path 10 similarly control the energization of the coil 20 and similarly acquire position information.

[0039] Next, a description will be given of the configuration of the inverter circuit 21. Fig. 3 is a diagram showing an example of the configuration of the inverter circuit 21 provided in the transport path unit 11 according to the first embodiment.

[0040] The inverter circuit 21 includes four switching elements 40A, 40B, 40C, and 40D, four insulated gate drivers 41A, 41B, 41C, and 41D, two bootstrap circuits 42A and 42C, and a secondary power supply 44. The inverter circuit 21 also includes a positive wiring 45, a negative wiring 46, and a signal line 47. The positive wiring 45 is connected to the positive side of the DC power supply bus 15. The negative wiring 46 is connected to the negative side of the DC power supply bus 15. The signal line 47 is a signal line to which a PWM signal from the PWM signal generator 29 is input.

[0041] The switching elements 40A and 40C are connected to a positive wiring 45. The switching elements 40A and 40C are switching elements connected between the positive electrode of the DC power supply 13 and the coil 20. The switching elements 40B and 40D are connected to a negative wiring 46. The switching elements 40B and 40D are switching elements connected between the negative electrode of the DC power supply 13 and the coil 20. In this document, the switching elements 40A and 40C connected to the positive electrode side of the DC power supply 13 may be referred to as "upper arm switching elements," and the switching elements 40B and 40D connected to the negative electrode side of the DC power supply 13 may be referred to as "lower arm switching elements."

[0042] Switching elements 40A and 40B form a half bridge 49AB, and switching elements 40C and 40D form a half bridge 49CD. Switching elements 40A, 40B, 40C, and 40D form a full-bridge circuit. In this paper, with respect to switching elements 40A and 40B forming half bridge 49AB, switching element 40A, which is the upper arm switching element, is sometimes referred to as the "first switching element," and switching element 40B, which is the lower arm switching element, is sometimes referred to as the "second switching element." Furthermore, with respect to switching elements 40C and 40D forming half bridge 49CD, switching element 40C, which is the upper arm switching element, is sometimes referred to as the "third switching element," and switching element 40D, which is the lower arm switching element, is sometimes referred to as the "fourth switching element." Each of switching elements 40A, 40B, 40C, and 40D is, for example, a field effect transistor (FET). Each of the switching elements 40A, 40B, 40C, and 40D may be an IGBT (Insulated Gate Bipolar Transistor) or the like.

[0043] One end of the coil 20 is connected to a connection end 51 via a current detector 22. The connection end 51 to which the one end of the coil 20 is connected is a connection end of the switching elements 40A and 40B, and is also referred to herein as "coil end AB." The other end of the coil 20 is connected to a connection end 52. The connection end 52 to which the other end of the coil 20 is connected is a connection end of the switching elements 40C and 40D, and is also referred to herein as "coil end CD."

[0044] The isolated gate drivers 41A and 41C are isolated switching driver circuits for driving the upper arm, and the isolated gate drivers 41B and 41D are isolated switching driver circuits for driving the lower arm. The gate signal line of the isolated gate driver 41A is connected to the switching element 40A, and the gate signal line of the isolated gate driver 41C is connected to the switching element 40C. The gate signal line of the isolated gate driver 41B is connected to the switching element 40B, and the gate signal line of the isolated gate driver 41D is connected to the switching element 40D.

[0045] When switching elements 40A and 40D are turned on and switching elements 40B and 40C are turned off, current flows through coil 20 in the direction indicated by arrow 48. On the other hand, when switching elements 40A and 40D are turned off and switching elements 40B and 40C are turned on, current flows through coil 20 in the direction opposite to that indicated by arrow 48. In this way, inverter circuit 21 switches the positive and negative polarities of the current flowing through coil 20. Furthermore, inverter circuit 21 turns on or off the gate signals of isolated gate drivers 41A, 41C, 41B, and 41D at a high frequency in accordance with the PWM signal. Inverter circuit 21 adjusts the current flowing through coil 20 by turning the gate signals on and off.

[0046] When all of the switching elements 40A, 40B, 40C, and 40D of the inverter circuit 21 are turned off, the coil 20 is put into an open state, and current to the coil 20 is cut off. When the switching elements 40A and 40D are turned on and the switching elements 40B and 40C are turned off, the coil 20 forms a closed circuit. When the switching elements 40A and 40D are turned off and the switching elements 40B and 40C are turned on, the coil 20 forms a closed circuit.

[0047] Each of the switching elements 40A, 40B, 40C, and 40D generates energy loss when switching from off to on or from on to off.

[0048] A secondary-side power supply 44 is connected to the secondary sides of the isolated gate drivers 41B and 41D. A bootstrap circuit 42A is connected to the secondary side of the isolated gate driver 41A. The bootstrap circuit 42A is a bootstrap power supply circuit that drives the isolated gate driver 41A. The bootstrap circuit 42A includes a capacitor 54 that is charged when the switching element 40B is turned on. A bootstrap circuit 42C is connected to the secondary side of the isolated gate driver 41C. The bootstrap circuit 42C is a bootstrap power supply circuit that drives the isolated gate driver 41C and is configured similarly to the bootstrap circuit 42A. By including the bootstrap circuits 42A and 42C that drive the isolated gate drivers 41A and 41C, the inverter circuit 21 can reduce the number of secondary-side power supplies 44 to one. This enables the inverter circuit 21 to have lower manufacturing costs than when two secondary-side power supplies 44 are included.

[0049] The PWM signal generator 29 generates a PWM signal by comparing the voltage command calculated by the current controller 24 with the carrier signal. The on / off of the switching elements 40A, 40B, 40C, and 40D is controlled by the PWM signal. Here, in the half bridge 49AB, if the upper arm switching element 40A and the lower arm switching element 40B are simultaneously turned on, the positive electrode wiring 45 and the negative electrode wiring 46 are short-circuited, causing a large amount of power to flow through the switching elements 40A and 40B, potentially burning out the inverter circuit 21 and its peripheral circuits. Therefore, when the upper arm switching element 40A is on, the lower arm switching element 40B is turned off, and conversely, when the upper arm switching element 40A is off, the lower arm switching element 40B is turned on. Furthermore, even if the upper-arm switching element 40A and the lower-arm switching element 40B are controlled so that they are not turned on simultaneously, the upper-arm switching element 40A and the lower-arm switching element 40B may unintentionally be turned on simultaneously due to variations in the circuit elements of the isolated gate drivers 41A and 41B. To prevent this phenomenon, a dead time period is intentionally provided to ensure that the upper-arm switching element 40A and the lower-arm switching element 40B are turned off simultaneously. The dead time period prevents the upper-arm switching element 40A and the lower-arm switching element 40B from being simultaneously turned on. In other words, the dead time period ensures that both the upper-arm switching element 40A and the lower-arm switching element 40B are open. Note that while the switching elements 40A and 40B in the half bridge 49AB have been described above, the same applies to the switching elements 40C and 40D in the half bridge 49CD, and similar dead time periods are provided.

[0050] FIG. 4 is a diagram illustrating the current distribution of the current flowing through each coil 20 in the transport path unit 11 according to the first embodiment. The horizontal axis of FIG. 4 represents the center position of the carriage 16 relative to the center position of the coil 20 when a thrust N is applied to the carriage 16, and the vertical axis represents the current flowing through the coil 20. If the overall length of the permanent magnet 30 in the transport direction is L, when the center position of the carriage 16 relative to the center position of the coil 20 is approximately L / 2 or more, flowing a current through the coil 20 does not contribute to the thrust of the carriage 16. Therefore, in the transport path unit 11 according to the first embodiment, as shown in FIG. 4, when the center position of the carriage 16 relative to the center position of the coil 20 is approximately L / 2 or more, the coil 20 is driven so that the current flowing through the coil 20 is zero.

[0051] FIG. 5 is a diagram illustrating the current commands and voltage commands given to each coil 20 in the transport path unit 11 according to the first embodiment. FIG. 5 shows an example of the current commands and voltage commands given to each coil 20 when the transport path unit 11 and the carriage 16 are in the positional relationship shown in FIG. 5. Specifically, in FIG. 5, the carriage 16 is located directly above the coils 20A, 20B, and 20C, and current commands and voltage commands other than 0 are given to the coils 20A, 20B, and 20C. At this time, the carriage 16 receives a thrust N in the direction of the arrow. Meanwhile, current commands and voltage commands of 0 are given to the coils 20D, 20E, 20F, 20G, 20H, and 20I. Therefore, in the inverter circuit 21 connected to the coils 20D, 20E, 20F, 20G, 20H, and 20I to which a current command and a voltage command of 0 are given, there is no need to control the voltage applied to each coil 20, and therefore the switching of the switching elements 40A, 40B, 40C, and 40D can be stopped.

[0052] The position of the carriage 16 on the conveying path can be measured and calculated using the linear scale 25 and the magnetic field of the scale magnet 31. Therefore, it is possible to identify the coils 20 where the carriage 16 is not present, and control the inverter circuits 21 connected to the identified coils 20 to stop switching. However, with this method, when the carriage 16 is stopped, it is not possible to stop switching in the inverter circuits 21 connected to the coils 20 where the carriage 16 is present, and switching continues. Therefore, in the first embodiment, the following method different from this method is proposed.

[0053] First, information on a switching stop voltage command upper limit value Vstopu and a switching stop voltage command lower limit value Vstopl is held in the PWM signal generator 29. The PWM signal generator 29 operates to stop the switching of the inverter circuit 21 when the inter-coil voltage command Vcmd is within a range that satisfies the following formula (1):

[0054] Vstopl <Vcmd<Vstopu …(1)

[0055] The coil-to-coil voltage command Vcmd is a voltage command value input to the PWM signal generator 29. Details of the coil-to-coil voltage command Vcmd will be described later. The switching stop voltage command upper limit value Vstopu and the switching stop voltage command lower limit value Vstopl are set based on the dead band voltage Vdead, which will be described later. The method of setting the switching stop voltage command upper limit value Vstopu and the switching stop voltage command lower limit value Vstopl will also be described later.

[0056] The inverter circuit 21 connected to the coils 20D to 20I stops switching, thereby stopping the supply of current to the coils 20D to 20I. With this method, switching can be stopped even when the carriage 16 is on the conveying path and the thrust N=0, i.e., when the carriage 16 is stopped. Therefore, in the conveying system 1, when there are a large number of carriages 16 and the carriages 16 stop frequently, or when there are a large number of carriages 16 and the carriages 16 are stuck, the effect of reducing switching loss can be further enhanced.

[0057] When stopping the switching of the inverter circuit 21, for example, all of the switching elements 40A, 40B, 40C, and 40D are fixed to an open state, so that no voltage is applied to the coil 20 connected to the switching elements 40 fixed to an open state.

[0058] Alternatively, the switching elements 40A and 40C may be fixed in an open state and the switching elements 40B and 40D may be fixed in a conducting state when stopping switching of the inverter circuit 21. In this case, the switching elements 40A and 40C, which are the switching elements of the upper arm, are in an open state to stop switching, and the switching elements 40B and 40D, which are the switching elements of the lower arm, are in a conducting state to stop switching.

[0059] In a configuration including the bootstrap circuits 42A and 42C, fixing the switching elements 40B and 40D to the on state allows the capacitors 54 of the bootstrap circuits 42A and 42C to continue to be charged. Therefore, when the latter method is used, the inverter circuit 21 can charge the bootstrap circuits 42A and 42C using the period in which switching is stopped.

[0060] As a result of the charge being charged, the inverter circuit 21, whose voltage command was 0, can immediately activate the insulated gate drivers 41A and 41C when the voltage command becomes a value other than 0. If the insulated gate drivers 41A and 41C are immediately activated, control of the current flowing to the coil 20 immediately begins. This allows the conveyance system 1 to move the cart 16 smoothly.

[0061] FIG. 6 is a time chart illustrating the operation of the inverter circuit 21 according to the first embodiment when a dead time period is set. From top to bottom, FIG. 6 shows the waveforms of the carrier signal, the PWM signal, and the inter-coil voltage. A carrier period is the duration of one cycle of the carrier signal. Specifically, the left side of FIG. 6 shows the waveform when the inter-coil voltage command Vcmd is smaller than the dead band voltage Vdead, and the right side of FIG. 6 shows the waveform when the inter-coil voltage command Vcmd is larger than the dead band voltage Vdead. The inter-coil voltage command Vcmd can be expressed by the following equation (2):

[0062] Vcmd=Vcmd_AB-Vcmd_CD …(2)

[0063] In the above equation (2), Vcmd_AB is a first voltage command applied to coil end AB, which is one end of the coil 20, and is referred to herein as the "coil end AB voltage command." Also, Vcmd_CD is a second voltage command applied to coil end CD, which is the other end of the coil 20, and is referred to herein as the "coil end CD voltage command."

[0064] The dead band voltage Vdead is the voltage value at which no voltage is applied to the coil 20 due to the dead time period when the absolute value of the inter-coil voltage command Vcmd is reduced, and is determined by the carrier period, the dead time period, and the bus voltage, which is the voltage of the DC power supply bus 15. If the carrier period is represented as "Tcarrier," the bus voltage as "Vbus," and the dead time period as "Ttd," the dead band voltage Vdead can be expressed by the following equation (3).

[0065] Vdead = Vbus × Ttd / Tcarrier …(3)

[0066] Next, the operation of the time chart shown in FIG. 6 will be described. Note that FIG. 6 is an example when the coil terminal AB voltage command Vcmd_AB is larger than the coil terminal CD voltage command Vcmd_CD. From the above equation (2), the value of the inter-coil voltage command Vcmd is positive. Therefore, in FIG. 6, the inter-coil voltage command Vcmd is denoted as "Vcmd (positive)".

[0067] First, in the carrier cycle on the left side of FIG. 6, when the carrier signal becomes smaller than the coil terminal AB voltage command Vcmd_AB, the switching element 40B transitions from on to off. At this time, the switching element 40A does not immediately turn on and transitions from off to on after the dead time period elapses. Also, when the carrier signal becomes smaller than the coil terminal CD voltage command Vcmd_CD, the switching element 40D transitions from on to off. At this time, the switching element 40C does not immediately turn on and transitions from off to on after the dead time period elapses.

[0068] The inter-coil voltage occurs during the period when both switching elements 40A and 40D are on or when both switching elements 40B and 40C are on. However, in the example on the left side of FIG. 6, these periods do not exist, so the inter-coil voltage does not occur. The reason the inter-coil voltage does not occur is that there is a relationship of "Vcmd (positive) < Vdead" between the inter-coil voltage command Vcmd (positive) and the dead band voltage Vdead.

[0069] Also, the carrier cycle on the right side of FIG. 6 has a similar operation. The difference from the operation of the carrier cycle on the left side is that there are two periods during which both switching elements 40A and 40D are on. Therefore, in these periods, as shown in the figure, a positive coil-to-coil voltage will occur. The coil-to-coil voltage occurs because there is a relationship of "Vcmd(positive) > Vdead" between the coil-to-coil voltage command Vcmd(positive) and the dead zone voltage Vdead. When a positive coil-to-coil voltage occurs, a closed circuit is formed with the DC power supply bus 15, and current flows through the coil 20.

[0070] What should be noted in the operation of FIG. 6 is that in the carrier cycle on the left side, although no coil-to-coil voltage occurs, the switching elements 40A, 40B, 40C, and 40D are switching. If no coil-to-coil voltage occurs, it is no exaggeration to say that even if the switching of the switching elements 40A, 40B, 40C, and 40D is stopped, it has almost no impact on the current control performance. Therefore, the inverter circuit control unit 50 according to Embodiment 1 stops the switching of the switching elements 40A, 40B, 40C, and 40D during the period when |Vcmd|, which is the absolute value of the coil-to-coil voltage command Vcmd, is less than Vdead. This control can be realized by setting the switching stop voltage command upper limit value Vstopu and the switching stop voltage command lower limit value Vstopl shown in the above formula (1) as in the following formula (4).

[0071] Vstopu = Vdead, Vstopl = -Vdead …(4)

[0072] That is, the switching stop voltage command upper limit value Vstopu is set to the value of the dead zone voltage Vdead, and the switching stop voltage command lower limit value Vstopl is set to the value obtained by multiplying the dead zone voltage Vdead by "-1".

[0073] 7 is a first time chart illustrating the operation of the inverter circuit control unit 50 according to the first embodiment. FIG. 7 shows the operation when the switching of the switching elements 40A, 40B, 40C, and 40D is stopped in the carrier cycle on the left side. As shown in the above formula (4), the switching stop voltage command upper limit value Vstopu is set to "Vdead." Therefore, it is possible to stop the switching of the switching elements 40A, 40B, 40C, and 40D simply by determining whether or not the switching of the switching elements 40A, 40B, 40C, and 40D is possible according to the above formula (1).

[0074] 8 is a second time chart used to explain the operation of the inverter circuit control unit 50 according to the first embodiment. FIG. 8 illustrates an example in which the coil end CD voltage command Vcmd_CD is greater than the coil end AB voltage command Vcmd_AB, and from the above equation (2), the value of the coil-to-coil voltage command Vcmd is negative. For this reason, in FIG. 8, it is written as "Vcmd (negative)."

[0075] 8, as in Fig. 7, in the carrier cycle on the left side, the switching of switching elements 40A, 40B, 40C, and 40D is stopped, and in the carrier cycle on the right side, the switching of switching elements 40A, 40B, 40C, and 40D is not stopped. This operation is performed because, as shown in equation (4) above, the switching stop voltage command lower limit value Vstopl is set to "-Vdead," and therefore, it is possible to stop the switching of switching elements 40A, 40B, 40C, and 40D simply by determining whether or not switching of switching elements 40A, 40B, 40C, and 40D is possible according to equation (1) above.

[0076] In the above-mentioned Patent Document 1, it was only possible to select whether or not to stop switching for the entire conveyance path unit 11, and it was not possible to select the inverter circuit 21 to stop switching. For this reason, the method of Patent Document 1 was not effective in reducing energy loss when the ratio of the length of the conveyance path unit 11 to the length of the carriage 16 was large. Furthermore, in the method of Patent Document 1, switching could not be stopped when the carriage 16 was stopped, so in the case of a conveyance system 1 in which there were many carriages 16 and the carriages 16 stopped frequently, or in the case of a conveyance system 1 in which there were many carriages 16 and the carriages 16 were stuck, the effect of reducing switching loss was insufficient.

[0077] To address this issue, in the first embodiment, the following control is performed on the first conveying path unit in which the carriage 16 is present. The term "first conveying path unit" refers to the conveying path unit 11 in which the carriage 16 is present. When the carriage 16 is present in a portion of the conveying path 10 formed by a first conveying path unit among one or more conveying path units 11, the inverter circuit control unit 50 performs control to forcibly stop the switching of the switching elements 40 in at least one inverter circuit 21 among one or more inverter circuits 21 provided in the first conveying path unit. As described above, the control signal forcibly stopping the switching of the switching elements 40 is a PWM signal generated based on the result of comparison between the inter-coil voltage command Vcmd and the switching stop voltage command upper limit value Vstopu, which is a preset upper limit value, and the result of comparison between the inter-coil voltage command Vcmd and the switching stop voltage command lower limit value Vstopl, which is a preset lower limit value. When a PWM signal serving as a control signal for forcibly stopping the switching of the switching element 40 is output to the inverter circuit 21, the switching of at least one switching element 40 in the inverter circuit 21 is forcibly stopped.

[0078] In the method of the first embodiment, since the inverter circuit 21 can be selected to stop switching, it is possible to obtain a sufficient effect of reducing energy loss even if the ratio of the length of the transport path unit 11 to the length of the carriage 16 is large. Furthermore, in the method of the first embodiment, it is possible to stop switching even when the carriage 16 is stopped. Therefore, even in the case of a transport system 1 in which the number of carriages 16 is large and the carriages 16 stop frequently, or in the case of a transport system 1 in which the number of carriages 16 is large and the carriages 16 are stuck, it is possible to enhance the effect of reducing switching loss.

[0079] The inverter circuit control unit 50 may include a switching stop function control unit that can enable or disable the stop of switching. Fig. 9 is a block diagram showing another configuration example of the inverter circuit control unit 50 according to the first embodiment. The inverter circuit control unit 50 of Fig. 9 includes a switching stop function control unit 90 in addition to the current controller 24 and the PWM signal generator 29. Like the current controller 24 and the PWM signal generator 29, the switching stop function control unit 90 can be realized by an FPGA, a microprocessor, or the like.

[0080] In the conveyance system 1, there are conveyance path units 11 with various roles. For example, a conveyance path unit 11 that is mainly responsible for sudden stops and sudden accelerations of the carriage 16 is a conveyance path unit 11 for which it is desirable not to degrade the control performance of the carriage 16, i.e., the current control performance of the coil 20. Also, for example, a conveyance path unit 11 that is mainly responsible for running the carriage 16 at a constant speed is a conveyance path unit 11 for which it is okay to degrade the control performance of the carriage 16, i.e., the current control performance of the coil 20. Therefore, if the switching stop function control unit 90 is configured so that the switching stop function can be enabled or disabled depending on the role of the conveyance path unit 11, the usefulness of the conveyance system 1 can be improved.

[0081] For example, it is conceivable to disable the switching stop function in the transport path unit 11 that is mainly responsible for sudden stops and sudden accelerations of the carriages 16, and enable the switching stop function in the transport path unit 11 that is mainly responsible for running the carriages 16 at a constant speed. By setting in this way, it is possible to increase the effect of reducing switching loss in the entire transport system 1 while suppressing a decrease in the current control performance in some of the transport path units 11.

[0082] 1, for example, a configuration is conceivable in which the linear transport path units 11A, 11B, 11E, and 11F are assigned as transport path units 11 mainly responsible for sudden stops and sudden accelerations of the carriages 16, and the curved transport path units 11C, 11D, 11G, and 11H are assigned as transport path units 11 mainly responsible for running the carriages 16 at a constant speed. In this configuration, the switching stop function is set to disabled in the linear transport path units 11A, 11B, 11E, and 11F, and the switching stop function is set to enabled in the curved transport path units 11C, 11D, 11G, and 11H. Alternatively, in contrast to this configuration, a configuration is conceivable in which the linear transport path units 11A, 11B, 11E, and 11F are assigned as transport path units 11 mainly responsible for running the carriages 16 at a constant speed, and the curved transport path units 11C, 11D, 11G, and 11H are assigned as transport path units 11 mainly responsible for sudden stops and sudden accelerations of the carriages 16. In this configuration, the switching stop function is enabled in the linear transport path units 11A, 11B, 11E, and 11F, and the switching stop function is disabled in the curved transport path units 11C, 11D, 11G, and 11H. In either configuration, it is possible to enhance the effect of reducing switching loss in the entire transport system 1 while suppressing deterioration in the current control performance in some of the transport path units 11.

[0083] Any means or method may be used to enable or disable the switching stop function in the inverter circuit control unit 50. For example, it is conceivable that a control signal for disabling the switching stop function is sent from the switching stop function control unit 90 to the PWM signal generator 29, and the PWM signal generator 29, upon receiving the control signal, generates a PWM signal without referring to the switching stop voltage command upper limit value Vstopu and the switching stop voltage command lower limit value Vstopl.

[0084] 9 illustrates a configuration in which the switching stop function control unit 90 is provided in the inverter circuit control unit 50, but the present invention is not limited to this example. The switching stop function control unit 90 may be provided in the control device 12. The control device 12 may transmit a control signal for disabling the switching stop function to each of the inverter circuit control units 50 provided in the plurality of conveying path units 11 via the data communication line 14.

[0085] Furthermore, the enabling and disabling of the switching stop function may be controlled based on the load factor of the transport path unit 11. For example, it is conceivable to enable the switching stop function when the load factor of the transport path unit 11 increases, and disable the switching stop function when the load factor of the transport path unit 11 decreases. The load factor of the transport path unit 11 may be calculated from the detection value of a current detector 22 that detects the current flowing through each coil 20, or may be calculated by a temperature detector (not shown) provided within the transport path unit 11. Generally, the inverter circuit 21 is provided with a temperature detector by default, so the detection value of this temperature detector may be used.

[0086] At the end of the first embodiment, a hardware configuration for realizing the functions of the control device 12 described above will be described with reference to Fig. 10 and Fig. 11. Fig. 10 is a diagram showing an example of a hardware configuration for realizing the functions of the control device 12 according to the first embodiment. Fig. 11 is a diagram showing another example of a hardware configuration for realizing the functions of the control device 12 according to the first embodiment.

[0087] When the functions of the control device 12 according to the first embodiment described above are realized by software, the control device 12 can be configured to include an input unit 81, a processor 82, a memory 83, and an output unit 84. The input unit 81 is an interface circuit that receives data input from outside the control device 12 and provides the data to the processor 82. The output unit 84 is an interface circuit that sends data from the processor 82 or the memory 83 to outside the control device 12.

[0088] The processor 82 is an example of a computing means. The processor 82 may be a computing means called a microprocessor, a microcomputer, a CPU, or a DSP. Examples of the memory 83 include non-volatile or volatile semiconductor memories such as RAM (Random Access Memory), ROM (Read Only Memory), flash memory, EPROM (Erasable Programmable ROM), and EEPROM (registered trademark) (Electrically EPROM), as well as magnetic disks, optical disks, compact disks, minidisks, and DVDs (Digital Versatile Discs).

[0089] The memory 83 stores a program that executes the functions of the control device 12 according to the first embodiment. The program is software, firmware, or a combination of software and firmware, and describes the processing procedures and methods in the control device 12. It can also be said that these programs cause a computer to execute the procedures and methods of the control device 12.

[0090] The processor 82 can perform the above-mentioned processing by receiving necessary information via the input unit 81, executing a program stored in the memory 83, and referring to a table stored in the memory 83. The calculation results by the processor 82 can be stored in the memory 83.

[0091] Furthermore, when realizing the functions of the control device 12 according to the first embodiment, a processing circuit 86 shown in Fig. 11 can be used. In Fig. 11, the processing circuit 86 is provided instead of the processor 82 and memory 83 in Fig. 10.

[0092] The processing circuit 86 may be a single circuit, a composite circuit, a programmed processor, a parallel programmed processor, an ASIC (Application Specific Integrated Circuit), an FPGA, or a combination thereof. Information to be input to the processing circuit 86 is received via an input unit 81, and information to be output from the processing circuit 86 can be sent via an output unit 84.

[0093] It is also possible that some of the processing in the control device 12 is performed by the processing circuit 86, and the processing that is not performed by the processing circuit 86 is performed by the processor 82 and the memory 83.

[0094] Embodiment 2 In the first embodiment, a switching stopping method for forcibly stopping the switching of the switching element 40 in the inverter circuit 21 has been described. In the second embodiment, a method different from that in the first embodiment will be described for control for forcibly stopping the switching of the switching element 40. However, in the second embodiment, a switching method for the inverter circuit 21 different from that in the first embodiment is used. Note that the configuration of the inverter circuit 21, which is a premise of the second embodiment, is a single-phase full-bridge inverter circuit as shown in FIG.

[0095] 6, in the first embodiment, the inter-coil voltage to be applied to the coil 20 is generated by turning on and off all of the switching elements 40A, 40B, 40C, and 40D at least once per cycle of the carrier signal. That is, the modulation method used in the first embodiment is a method of adjusting the voltage to be applied to the coil 20 by switching on and off the switching elements 40A, 40B, 40C, and 40D in two half bridges 49AB and 49CD connected to one end and the other end of the coil 20. This modulation method is generally called a "two-phase modulation method."

[0096] In contrast to this, in the second embodiment, a modulation method called "single phase modulation method" is used. Fig. 12 is a time chart for explaining the single phase modulation method used in the second embodiment. The types of waveforms shown in the time chart of Fig. 12 are the same as those in Fig. 6.

[0097] When a positive voltage is applied to the coil 20 using the one-phase modulation method, the switching element 40C of the upper arm of the half bridge 49CD is fixed in an open state, and the switching element 40D of the lower arm of the half bridge 49CD is fixed in an energized state, and then the switching element 40A of the upper arm of the half bridge 49AB and the switching element 40B of the lower arm of the half bridge 49AB are switched, as shown in the carrier cycle on the left side of Fig. 12. When a negative voltage is applied to the coil 20 using the one-phase modulation method, the switching element 40A of the upper arm of the half bridge 49AB is fixed in an open state, and the switching element 40B of the lower arm of the half bridge 49AB is fixed in an energized state, and then the switching element 40C of the upper arm of the half bridge 49CD and the switching element 40D of the lower arm of the half bridge 49CD are switched, as shown in the carrier cycle on the right side of Fig. 12.

[0098] As described above, the one-phase modulation method is a method in which the switching element 40 of one half bridge 49 connected to the coil 20 is fixed in a conducting state or an open state, and the switching element 40 of the other half bridge 49 is switched to adjust the voltage applied to the coil 20.

[0099] Fig. 13 is a time chart illustrating the operation of the inverter circuit control unit 50 according to embodiment 2. In Fig. 13, the carrier cycle on the left side shows the operation when switching of the switching elements 40A and 40B is stopped, and the carrier cycle on the right side shows the operation when switching of the switching elements 40C and 40D is stopped.

[0100] In the one-phase modulation method, when the inter-coil voltage command Vcmd is positive, i.e., when Vcmd=Vcmd_AB, the switching of switching elements 40A, 40B is controlled by the inter-coil voltage command Vcmd to half bridge 49AB. Also, when the inter-coil voltage command Vcmd is negative, i.e., when Vcmd=-Vcmd_CD, the switching of switching elements 40C, 40D is controlled by the inter-coil voltage command Vcmd to half bridge 49CD. The purpose of providing a dead time period is the same as in the first embodiment.

[0101] In the second embodiment, information on the switching stop voltage command upper limit value Vstopu is held in the PWM signal generator 29. The PWM signal generator 29 operates to stop the switching of the inverter circuit 21 when the absolute value |Vcmd| of the inter-coil voltage command Vcmd satisfies the following equation (5):

[0102] |Vcmd| <Vstopu …(5)

[0103] Here, the switching stop voltage command upper limit value Vstopu is set to a value smaller than the dead band voltage Vdead.

[0104] The PWM signal generator 29 can stop the switching of the switching elements 40A, 40B, 40C, and 40D only by determining whether or not to switch the switching elements 40A, 40B, 40C, and 40D according to the above equation (5).

[0105] In a section where |Vcmd| < Vdead, even if the comparison between the coil voltage command Vcmd and the carrier signal is performed, no coil voltage is generated. Therefore, it is no exaggeration to say that even if the switching of the switching elements 40A, 40B, 40C, and 40D is stopped, there is almost no influence on the current control performance.

[0106] As described above, in the second embodiment, in the inverter circuit 21 which is a single-phase full-bridge inverter circuit, the control signal for controlling the switching of the switching element 40 is generated based on the coil voltage command Vcmd applied to one end side of the coil 20 with the other end side of the coil 20 at a fixed potential, or the coil voltage command Vcmd applied to the other end side of the coil 20 with one end side of the coil 20 at a fixed potential. And the control signal for forcibly stopping the switching of the switching element 40 is generated based on the comparison result between the preset upper limit value, the switching stop voltage command upper limit value Vstopu, and the absolute value |Vcmd| of the coil voltage command Vcmd. At this time, when the absolute value |Vcmd| of the coil voltage command Vcmd is lower than the switching stop voltage command upper limit value Vstopu, as shown in FIG. 13, all the switching of the switching elements 40A, 40B, 40C, and 40D is stopped.

[0107] In the technique of the second embodiment, the absolute value |Vcmd| of the coil-to-coil voltage command Vcmd is used to determine the switching duty width when the switch states of one pair of switching elements 40 of the upper and lower arms are fixed and the other pair of switching elements 40 of the upper and lower arms that are not fixed are switched. A fixed potential is applied to one end or the other end of the coil 20 connected to the pair of switching elements 40 whose switch states are fixed. In the examples of FIGS. 12 and 13 , the fixed potential is the potential of the negative wiring of the DC power bus 15. The positive or negative value of the coil-to-coil voltage command Vcmd changes depending on whether one end of the coil 20 is set to a fixed potential or the other end of the coil 20 is set to a fixed potential. However, by using the absolute value |Vcmd| of the coil-to-coil voltage command Vcmd, it is not necessary to set a lower limit value as in the first embodiment, and it is possible to perform control to forcibly stop the switching of the switching elements 40 based on the comparison result between the absolute value |Vcmd| of the coil-to-coil voltage command Vcmd and the upper limit value, i.e., the switching stop voltage command upper limit value Vstopu.

[0108] 12 and 13 show an example in which one end or the other end of the coil 20 is fixed to the potential of the negative wiring of the DC power bus 15, but an example in which one end or the other end of the coil 20 is fixed to the potential of the positive wiring of the DC power bus 15 may also be used. In this example, in the carrier cycle on the left side of the time charts in FIGS. 12 and 13, the switching element 40C of the upper arm of the half bridge 49CD is fixed in a conducting state, and the switching element 40D of the lower arm is fixed in an open state. Similarly, in the carrier cycle on the right side, the switching element 40A of the upper arm of the half bridge 49AB is fixed in a conducting state, and the switching element 40B of the lower arm is fixed in an open state.

[0109] In the method of the second embodiment, since the inverter circuit 21 can be selected to stop switching, it is possible to obtain a sufficient effect of reducing energy loss even if the ratio of the length of the transport path unit 11 to the length of the carriage 16 is large. Furthermore, in the method of the second embodiment, it is also possible to stop switching when the carriage 16 is stopped. Therefore, even in the case of a transport system 1 in which there are many carriages 16 and the carriages 16 stop frequently, or in the case of a transport system 1 in which there are many carriages 16 and the carriages 16 are stuck, it is possible to enhance the effect of reducing switching loss.

[0110] Furthermore, similar to the first embodiment, the inverter circuit control unit 50 in the second embodiment may include a switching stop function control unit 90 that can enable or disable the stopping of switching. If the switching stop function control unit 90 is configured to enable or disable the switching stop function depending on the role of the transport path unit 11, the usefulness of the transport system 1 can be improved, and the effect of reducing switching loss in the entire transport system 1 can be enhanced while suppressing a decrease in current control performance in some of the transport path units 11. Furthermore, the switching stop function control unit 90 in the second embodiment may be configured to enable or disable the switching stop function based on a detection value of the current detector 22, or may be configured to enable or disable the switching stop function based on a detection value of a temperature detector.

[0111] It is generally said that the control performance of the single-phase modulation method is inferior to that of the two-phase modulation method when the inter-coil voltage command Vcmd is near 0. However, in the conveyance system 1 that conveys objects using the cart 16, a voltage command near 0 is not used even when the cart 16 starts moving due to the influence of friction between the cart 16 and the guide rail, so there is no problem. Therefore, there are almost no disadvantages to applying the single-phase modulation method to the conveyance system 1 that conveys objects using the cart 16, and applying the single-phase modulation method makes it possible to reduce switching loss.

[0112] Embodiment 3 In Embodiment 2, a switching stop method when the switching method for the inverter circuit 21 is a single-phase modulation method was described. In Embodiment 3, a simpler switching stop method will be described while using the same single-phase modulation method.

[0113] As also described in Embodiment 2, in the single-phase modulation method, when applying a positive voltage to the coil 20, the switching element 40C of the upper arm of the half bridge 49CD is fixed in the open state, and the switching element 40D of the lower arm is fixed in the energized state, and then, the switching element 40A of the upper arm of the half bridge 49AB and the switching element 40B of the lower arm are switched. However, when the absolute value |Vcmd| of the voltage command satisfies |Vcmd| < Vdead, due to the existence of the dead time period, the switching of the switching element 40A will not be performed even once in one cycle of the carrier signal.

[0114] Also, in the single-phase modulation method, when applying a negative voltage to the coil 20, the switching element 40A of the upper arm of the half bridge 49AB is fixed in the open state, and the switching element 40B of the lower arm is fixed in the energized state, and then, the switching element 40C of the upper arm of the half bridge 49CD and the switching element 40D of the lower arm are switched. However, when the absolute value |Vcmd| of the voltage command satisfies |Vcmd| < Vdead, due to the existence of the dead time period, the switching of the switching element 40C will not be performed even once in one cycle of the carrier signal. This means that the switching of the switching elements 40A and 40C can be forcibly stopped without comparing the inter-coil voltage command Vcmd with the switching stop voltage command upper limit value Vstopu. This point is the difference from Embodiment 2.

[0115] FIG. 14 is a time chart illustrating the operation of the inverter circuit control unit 50 according to the third embodiment. The amplitude and slope of the carrier signal, the value of the inter-coil voltage command Vcmd, the value of the dead time period, and the like are the same as those in FIG. 13. Compared to FIG. 13, FIG. 14 differs in that switching element 40B switches during the carrier cycle on the left and switching element 40D switches during the carrier cycle on the right. That is, with the technique of the third embodiment, one lower-side switching element (40B or 40D) among the four switching elements 40A, 40B, 40C, and 40D switches during each carrier cycle of the PWM signal. However, because no inter-coil voltage is applied to this one lower-side switching element (40B or 40D), even if switching occurs, switching loss is extremely small, and it is possible to reduce switching loss.

[0116] In the third embodiment, in the inverter circuit 21, which is a single-phase full-bridge inverter circuit, the control signal for controlling the switching of the switching elements 40 is generated based on a coil-to-coil voltage command Vcmd that is applied to one end of the coil 20 while the other end of the coil 20 is held at a fixed potential, or a coil-to-coil voltage command Vcmd that is applied to the other end of the coil 20 while the other end of the coil 20 is held at a fixed potential. The coil-to-coil voltage command Vcmd stops switching of the switching elements 40 of one pair of switching elements 40A and 40B or the pair of switching elements 40C and 40D so that the upper and lower arms have different conductive and open states, and switches the other pair of switching elements 40 so that the upper and lower arms have different conductive and open states. Furthermore, when the switching elements 40A, 40B, 40C, and 40D are switched, the switching elements that transition from the open state to the conductive state become conductive with a certain delay, or the switching elements that transition from the open state to the conductive state become open with a certain advance.

[0117] Furthermore, in the third embodiment, when forcibly stopping the switching of the switching element 40, the inverter circuit control unit 50 controls the switching element 40 as follows, depending on the polarity of the voltage applied to the coil 20. When a positive voltage is applied to the coil 20, the inverter circuit control unit 50 switches the switching elements 40A and 40B, the switching element 40C is in an open state and stops switching, and the switching element 40D is in a conductive state and stops switching. When a negative voltage is applied to the coil 20, the inverter circuit control unit 50 switches the switching elements 40C and 40D, the switching element 40A is in an open state and stops switching, and the switching element 40B is in a conductive state and stops switching.

[0118] In the method of the third embodiment, since the inverter circuit 21 can be selected to stop switching, it is possible to obtain a sufficient effect of reducing energy loss even if the ratio of the length of the transport path unit 11 to the length of the carriage 16 is large. Furthermore, in the method of the third embodiment, it is also possible to stop switching when the carriage 16 is stopped. Therefore, even in the case of a transport system 1 in which the number of carriages 16 is large and the carriages 16 stop frequently, or in the case of a transport system 1 in which the number of carriages 16 is large and the carriages 16 are stuck, it is possible to enhance the effect of reducing switching loss.

[0119] Furthermore, similar to the first and second embodiments, the inverter circuit control unit 50 in the third embodiment may include a switching stop function control unit 90 that can enable or disable the stopping of switching. If the switching stop function control unit 90 is configured to enable or disable the switching stop function depending on the role of the transport path unit 11, the usefulness of the transport system 1 can be improved, and the effect of reducing switching loss can be enhanced throughout the transport system 1 while suppressing a decrease in current control performance in some of the transport path units 11. Furthermore, the switching stop function control unit 90 in the third embodiment may be configured to enable or disable the switching stop function based on a detection value of the current detector 22, or may be configured to enable or disable the switching stop function based on a detection value of a temperature detector.

[0120] In this paper, the dead time provision method has been described as delaying the timing at which the switching element 40 transitions from an open state (off) to a conducting state (on). For example, when switching element 40A transitions from an open state to a conducting state and switching element 40B transitions from a conducting state to an open state, switching element 40A transitioning from the open state to the conducting state is delayed by a certain dead time period before transitioning to the conducting state. FIGS. 6 to 8 and 12 to 14 are all time charts illustrating a method for delaying the timing at which the switching element 40 transitions from the open state to the conducting state. On the other hand, when using the method of the third embodiment, a method for advancing the timing at which the switching element 40 transitions from the open state (off) to the conducting state (on) may also be used. For example, when switching element 40A transitions from the open state to the conducting state and switching element 40B transitions from the conducting state to the open state, switching element 40A transitioning from the open state to the conducting state may be controlled to transition to the conducting state by a certain dead time period before transitioning to the conducting state. In either case, the effect of reducing switching loss can be obtained.

[0121] Furthermore, in the case of the method of embodiment 2 in which the inter-coil voltage command Vcmd is compared with the switching stop voltage command upper limit value Vstopu, it is assumed that switching will not be stopped if the inter-coil voltage command Vcmd is changed within the carrier cycle. In contrast, in the case of the method of embodiment 3, since the inter-coil voltage command Vcmd is not compared with the switching stop voltage command upper limit value Vstopu, there is an advantage in that switching can be reliably stopped even if the inter-coil voltage command Vcmd is changed within the carrier cycle.

[0122] The configurations shown in the above embodiments are merely examples, and may be combined with other known technologies, or different embodiments may be combined with each other. It is also possible to omit or modify parts of the configurations as long as they do not deviate from the gist of the invention. [Explanation of symbols]

[0123] 1 conveying system, 10 conveying path, 11, 11A, 11B, 11C, 11D, 11E, 11F, 11G, 11H conveying path unit, 12 control device, 13 DC power supply, 14 data communication line, 15 DC power bus, 16, 16A, 16B, 16C cart, 17A, 17B, 48 arrow, 20, 20A, 20B, 20C, 20D, 20E, 20F, 20G, 20H, 20I coil, 21 inverter circuit, 22 current detector, 23, 54 capacitor, 24 current controller, 25 linear scale, 26 position sensor, 27, 82 processor, 28 communication slave station, 29 PWM signal generator, 30 permanent magnet, 31 scale magnet, 40, 40A, 40B, 40C, 40D Switching element, 41A, 41B, 41C, 41D isolated gate drivers, 42A, 42C bootstrap circuits, 44 secondary power supply, 45 positive wiring, 46 negative wiring, 47 signal line, 49, 49AB, 49CD half bridge, 50 inverter circuit control unit, 51, 52 connection terminal, 81 input unit, 83 memory, 84 output unit, 86 processing circuit, 90 switching stop function control unit.

Claims

1. a plurality of conveyance path units that form a conveyance path along which one or more conveyance bodies move and that apply power to the conveyance bodies to move the conveyance bodies; Each of the transport path units includes: One or more drive units that generate the power; one or more inverter circuits provided corresponding to each of the drive units and applying a voltage to the drive units; an inverter circuit control unit that controls switching of a plurality of switching elements provided in the inverter circuit, When the transport body is present in a portion of the transport path formed by a first transport path unit among one or more of the transport path units, The switching of at least one switching element of at least one inverter circuit among the one or more inverter circuits provided in the first transport path unit is forcibly stopped. A transport system characterized by:

2. the drive unit includes a coil that generates an electromagnetic force as the power by receiving power from the inverter circuit, The carrier is provided with a permanent magnet.

2. The transport system according to claim 1.

3. a control signal for controlling the switching of the switching element is generated based on a coil-to-coil voltage command that is a difference between a first voltage command to be applied to one end of the coil and a second voltage command to be applied to the other end of the coil; The control signal for forcibly stopping the switching of the switching element is generated based on a comparison result between a preset upper limit value and the inter-coil voltage command, and a comparison result between a preset lower limit value and the inter-coil voltage command.

3. The transport system according to claim 2.

4. The inverter circuit an upper arm switching element that is the switching element connected between a positive electrode of a power supply connected to the inverter circuit and the drive unit; a lower arm switching element, which is the switching element connected between the negative electrode of the power supply and the drive unit; The control signal is provided with a dead time period during which the upper arm switching element and the lower arm switching element are both in an open state so that the upper arm switching element and the lower arm switching element are not simultaneously in an energized state.

4. The transport system according to claim 3.

5. the control signal is a pulse width modulation signal that controls on / off of the switching element based on a comparison result between a carrier signal and the inter-coil voltage command, the upper limit value and the lower limit value are determined by a dead band voltage, which is a voltage value when no voltage is applied to the coil due to the dead time period; the upper limit is set to the value of the dead band voltage, The lower limit is set to a value obtained by multiplying the dead band voltage by −1.

5. The transport system according to claim 4.

6. The inverter circuit control unit includes a switching stop function control unit that can set the switching stop function to be enabled or disabled.

2. The transport system according to claim 1.

7. The switching stop function control unit is configured to be able to set the switching stop function to be enabled or disabled depending on the role of the transport path unit.

7. The transport system according to claim 6.

8. the transport path unit includes a current detector that detects a current flowing in the drive unit; The switching stop function control unit is configured to be able to set the switching stop function to be enabled or disabled based on the detection value of the current detector.

7. The transport system according to claim 6.

9. the transport path unit includes a temperature detector; The switching stop function control unit is configured to be able to set the switching stop function to be enabled or disabled based on the detected value of the temperature detector.

7. The transport system according to claim 6.

10. The transport path units include a linear transport path unit that forms a linear path and a curved transport path unit that forms a curved path, The conveying path is formed by combining the linear conveying path unit and the curved conveying path unit.

2. The transport system according to claim 1.

11. In the linear transport path unit, the switching stop function is set to be disabled, and in the curved transport path unit, the switching stop function is set to be enabled, or The switching stop function is set to be valid in the linear transport path unit, and the switching stop function is set to be invalid in the curved transport path unit.

11. The transport system according to claim 10.

12. the drive unit includes a coil that generates an electromagnetic force as the power by receiving power from the inverter circuit, each of the inverter circuits is a single-phase full-bridge inverter circuit, The single-phase full-bridge inverter circuit includes: a first switching element that is an upper arm switching element connected between a positive electrode of a power supply connected to the single-phase full-bridge inverter circuit and one end of the drive unit; a second switching element that is a lower arm switching element connected between the negative electrode of the power supply and one end of the drive unit; a third switching element which is an upper arm switching element connected between the positive electrode of the power supply and the other end of the drive unit; a fourth switching element which is a lower arm switching element connected between the negative electrode of the power supply and the other end of the drive unit, A control signal for controlling the switching of the first to fourth switching elements is generated based on a coil-to-coil voltage command that is applied to one end side of the coil with the other end side of the coil at a fixed potential, or a coil-to-coil voltage command that is applied to the other end side of the coil with the one end side of the coil at a fixed potential, a control signal for forcibly stopping the switching of the first to fourth switching elements is generated based on a comparison result between a preset upper limit value and an absolute value of the inter-coil voltage command, When the absolute value of the inter-coil voltage command falls below the upper limit value, switching of all of the first to fourth switching elements is stopped.

2. The transport system according to claim 1.

13. The control signal includes: a dead time period during which both the first switching element and the second switching element are in an open state is provided so that the first switching element and the second switching element are not simultaneously in a conducting state; A dead time period is provided during which both the third switching element and the fourth switching element are in an open state so that the third switching element and the fourth switching element are not simultaneously in a conducting state.

13. The transport system according to claim 12.

14. the control signal is a pulse width modulation signal that controls the on / off of the first to fourth switching elements based on a comparison result between a carrier signal and the inter-coil voltage command, the upper limit value is determined by a dead band voltage, which is a voltage value when no voltage is applied to the coil due to the dead time period, The upper limit is set to a value smaller than the dead band voltage.

14. The transport system according to claim 13.

15. the drive unit includes a coil that generates an electromagnetic force as the power by receiving power from the inverter circuit, each of the inverter circuits is a single-phase full-bridge inverter circuit, The single-phase full-bridge inverter circuit includes: a first switching element that is an upper arm switching element connected between a positive electrode of a power supply connected to the single-phase full-bridge inverter circuit and one end of the drive unit; a second switching element that is a lower arm switching element connected between the negative electrode of the power supply and one end of the drive unit; a third switching element which is an upper arm switching element connected between the positive electrode of the power supply and the other end of the drive unit; a fourth switching element which is a lower arm switching element connected between the negative electrode of the power supply and the other end of the drive unit, A control signal for controlling the switching of the first to fourth switching elements is generated based on a coil-to-coil voltage command that is applied to one end side of the coil with the other end side of the coil at a fixed potential, or a coil-to-coil voltage command that is applied to the other end side of the coil with the one end side of the coil at a fixed potential, The coil voltage command switching is stopped so that the conductive state and the open state of the switching elements of one of the first and second switching element sets or the third and fourth switching element set differ between the upper and lower arms, and switching is performed so that the conductive state and the open state of the switching elements of the other set differ between the upper and lower arms; When the first to fourth switching elements are switched, the switching element that transitions from an open state to a conducting state becomes conducting with a certain period of delay, or the switching element that transitions from a conducting state to an open state becomes opening with a certain period of advance.

2. The transport system according to claim 1.

16. When a positive voltage is applied to the coil, the first and second switching elements are switched, the third switching element is in an open state and stops switching, and the fourth switching element is in a conducting state and stops switching; When a negative voltage is applied to the coil, The third and fourth switching elements are switched, the first switching element is in an open state and stops switching, and the second switching element is in a conducting state and stops switching.

13. The transport system according to claim 12.

17. The inverter circuit a switching driver circuit that drives the switching element of the upper arm; a bootstrap type power supply circuit that drives the switching driver circuit.

17. A transport system according to any one of claims 1 to 16.

18. When switching is to be stopped, the switching element of the upper arm is in an open state and switching is stopped; When the switching element of the lower arm is to be stopped from switching, the switching element is in a conducting state and the switching is stopped.

17. A transport system according to any one of claims 1 to 16.

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