Hoist control device and method for controlling same
Patent Information
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- KITO CORP
- Filing Date
- 2026-01-28
- Publication Date
- 2026-08-06
Smart Images
Figure JP2026002866_06082026_PF_FP_ABST
Abstract
Description
Control Device and Control Method for Hoisting Machine
[0001] The present invention relates to a control device and a control method for a hoisting machine that performs hoisting and lowering provided in an electric chain block, an electric rope hoist, or the like.
[0002] In a hoisting machine that drives a three-phase induction motor with an inverter control device, in order to reduce the size of the braking resistor and take energy-saving measures, etc., a technique has been proposed to return the regenerative power generated during high-speed lowering operation to the commercial AC power supply side (Patent Document 1).
[0003] Japanese Patent No. 5145059
[0004] However, in the technique described in Patent Document 1, in order to make the voltage difference at the time of short circuit below a predetermined amount, when the phase of the inverter output and the commercial AC power supply is synchronized, the power supply of the motor is switched from the inverter to the commercial AC power supply. Therefore, a phase synchronization circuit is required, which hinders miniaturization. Also, depending on the phase synchronization confirmation, the switching may take time.
[0005] An object of the present invention is to provide a hoisting machine suitable for high speed.
[0006] A control device for a hoisting machine according to one aspect of the present invention includes a motor for hoisting and lowering, an inverter connected to a system power supply and capable of variably controlling the driving power supplied to the motor, a driving circuit connected to the system power supply and supplying driving power to the motor without passing through the inverter, and in the lowering operation, at a predetermined speed corresponding to the AC frequency of the system power supply, causing the driving circuit to supply driving power to the motor, and at speeds other than the predetermined speed, causing the inverter to supply driving power to the motor, and a control unit that performs control. The control unit stops the driving power from the driving circuit to the motor when decelerating from the predetermined speed, and outputs the driving power of the motor corresponding to the rotational speed of the motor from the inverter.
[0007] One aspect of the present invention relates to a control method for a hoisting machine, comprising: an electric motor for raising and lowering; an inverter connected to a grid power supply and supplying drive power to the motor in a variable-speed control manner; a drive circuit connected to a grid power supply and supplying drive power to the motor without going through the inverter; and a control unit that, in lowering operation, supplies drive power from the drive circuit to the motor at a predetermined speed corresponding to the AC frequency of the grid power supply, and supplies drive power from the inverter to the motor at speeds other than the predetermined speed, wherein when the control unit decelerates from the predetermined speed, it stops the drive power from the drive circuit to the motor and outputs drive power from the inverter to the motor according to the rotational speed of the motor.
[0008] According to the present invention, it is possible to improve the speed of the hoisting machine.
[0009] Figure 1 is a block diagram showing the configuration of the hoisting machine. Figure 2 is a flowchart explaining the unwinding process. Figure 3 is a flowchart explaining the switching from grid power drive to inverter drive. Figure 4 is a time chart for the unwinding process. Figure 5 is a flowchart explaining the unwinding process with an additional light-load function. Figure 6 is a time chart for the unwinding process with an additional light-load function. Figure 7 is a block diagram of a hoisting machine with an additional light-load function and temperature detection function. Figure 8 is a flowchart explaining the unwinding process with an additional light-load function and temperature detection function. Figure 9 is a time chart for the unwinding process with an additional light-load function and temperature detection function.
[0010] [First Embodiment] A hoisting machine according to the first embodiment of the present invention will be described below with reference to the drawings. This hoisting machine 1 is an example of an electric chain hoist, but it may also be an electric rope hoist or other electric hoisting machine, and is not limited to an electric chain hoist.
[0011] (Equipment Configuration) Figure 1 is a block diagram showing the configuration of the hoisting machine 1. The hoisting machine 1 comprises an operation box 11, a control unit 12, an electromagnetic switch 13, an electric motor 14, an inverter 15, and a braking resistor 16. Furthermore, the hoisting machine 1 is equipped with a hoisting mechanism for winding up and unwinding a load chain (not shown) and an electromagnetic brake. The hoisting mechanism winds up and unwinds the load chain in accordance with the rotation of the electric motor 14, and the electromagnetic brake is configured to brake the rotation of the electric motor 14.
[0012] Three-phase (R, S, T) AC power from a grid power source 2, such as a commercial power supply, is supplied to the inverter 15 and the electromagnetic switch 13. In this example, the grid power source 2 is a 50Hz or 60Hz commercial power supply. The motor 14 is a three-phase induction motor. The motor 14 is electrically connected to the output sections of the electromagnetic switch 13 and the inverter 15, and receives three-phase AC power as driving power from both.
[0013] The control box 11 is equipped with a hoisting push-button switch 21, a hoisting push-button switch 22, and an emergency push-button switch 23. The hoisting push-button switch 21 and the hoisting push-button switch 22 are two-stage push-button switches. When the hoisting push-button switch 21, the hoisting push-button switch 22, and the emergency push-button switch 23 are operated, an operation signal corresponding to that operation is output to the control unit 12.
[0014] When the control unit 12 receives an operation signal from the operation box 11, it controls the inverter 15 and the electromagnetic switch 13 based on the operation signal to supply three-phase (U, V, W) AC power from the inverter 15 to the motor 14 to drive the motor 14 at an arbitrary rotational speed (hereinafter referred to as inverter drive), or to supply three-phase (R, S, T) AC power from the grid power supply 2 to the motor 14 to drive the motor 14 (hereinafter referred to as grid power supply drive as appropriate).
[0015] The electromagnetic switch 13 is an electromagnetic switch having a main contact capable of switching between supplying and interrupting power to the motor 14. One side (input) of the electromagnetic switch 13 is electrically connected to the grid power supply 2, and the other side (output) is electrically connected to the motor 14. A command to turn the contact OFF (coil current OFF) from the control unit 12 opens the contact with the grid power supply 2 (setting it to the OFF state). In this state, the power supply from the grid power supply 2 to the motor 14 is interrupted. The electromagnetic switch 13 also closes the contact with the grid power supply 2 (setting it to the ON state) when a command to turn the contact ON (coil current ON) from the control unit 12. In this state, drive power is supplied from the grid power supply 2 to the motor 14. The drive power supplied from the electromagnetic switch 13 to the motor 14 is electrically connected to be in phase with the downwinding (reverse rotation) drive power supplied to the motor 14 by the inverter 15.
[0016] The braking resistor 16 is connected to the inverter 15 and converts regenerative power into heat.
[0017] In this embodiment of the present invention, the inverter 15 is configured to include an inverter circuit (not shown) (composed of an AC-DC converter and a DC-AC converter) and an inverter control unit that controls the same circuit. The DC-AC converter of the inverter circuit (not shown) has six three-phase bridge-connected switching elements and a drive means for driving the switching elements. In the hoisting machine 1 of Figure 1, the control unit 12 and the inverter 15 are shown in separate blocks, but the control unit 12 may also be the inverter control unit within the inverter 15, and the output of the operation box 11 may be input to the inverter 15, and the inverter 15 may output a control signal (coil current) to the electromagnetic switch 13.
[0018] (Hoisting Process) The operation during hoisting will now be explained. When the hoisting push-button switch 21 is pressed to the first position, the control unit 12 recognizes this and outputs a hoisting command signal, which is a forward rotation command signal, to the inverter 15. In the following, the hoisting command signal will also be referred to as the low-speed hoisting command signal as appropriate. When the inverter 15 receives the low-speed hoisting command signal, it supplies power at a frequency that results in a predetermined acceleration to the motor 14 until it reaches the speed for low-speed hoisting operation (hereinafter referred to as the low-speed hoisting speed), and continues to supply drive power at a frequency corresponding to the low-speed hoisting speed while the low-speed hoisting command signal is being received. As a result, the motor 14 is accelerated to a predetermined acceleration and reaches the low-speed hoisting speed. If the hoisting push-button switch 21 is kept pressed to the first position, the motor 14 will rotate in the hoisting direction at this speed after reaching the low-speed hoisting speed.
[0019] When the second position of the hoisting push-button switch 21 is pressed, the control unit 12 recognizes this and outputs a high-speed command signal to the inverter 15 in addition to the hoisting command signal. When it is not necessary to distinguish between the hoisting command signal and the high-speed command signal output to the inverter 15 when the second position of the hoisting push-button switch 21 is pressed, the latter will be referred to as the high-speed hoisting command signal. When the inverter 15 receives the high-speed hoisting command signal, it supplies power at a frequency that results in a predetermined acceleration to the motor 14 until the speed for high-speed hoisting operation (hereinafter referred to as the high-speed hoisting speed) is reached, and continues to supply drive power at a frequency corresponding to the high-speed hoisting speed while the high-speed hoisting command signal is still being received. As a result, the motor 14 is accelerated to a predetermined acceleration and reaches the high-speed hoisting speed. If the hoisting push-button switch 21 is kept pressed to the second position, the motor 14 will rotate in the hoisting direction at this speed after reaching the high-speed hoisting speed. During this time, the control unit 12 continues to output a command to the electromagnetic switch 13 to turn the contact OFF (turn off the coil current).
[0020] (Unwinding process) When the unwinding push button switch 22 is pressed, the control unit 12 performs an unwinding operation. During the unwinding operation, if the control unit 12 can drive the motor 14 at the output frequency of the grid power supply 2 (hereinafter referred to as the grid power frequency), it drives the motor 14 with the output from the grid power supply 2, and at other speeds, it drives the motor 14 with the output from the inverter 15. When the control unit 12 drives the motor 14 at a speed other than the grid power frequency, it cuts off the drive power from the electromagnetic switch 13 to the motor 14 and outputs drive power for the motor 14 from the inverter 15 according to the rotational speed of the motor 14.
[0021] To explain this winding process, we will first describe the flow by referring to the flowcharts in Figures 2 and 3, and then explain a specific example by referring to the time chart in Figure 4.
[0022] The unwinding process is performed as long as the unwinding push-button switch 22 is pressed to the first or second position and the control unit 12 recognizes this. The control unit 12 also separately determines the state of the unwinding push-button switch 22, and terminates the unwinding process if the unwinding push-button switch 22 is not pressed. In step S11 of the unwinding process, the control unit 12 determines the state of the inverter 15.
[0023] In step S11, if the base block is in the OFF state and the control unit 12 determines that the output frequency of the inverter 15 is smaller than the frequency corresponding to the rotational speed of the motor 14 during low-speed unwinding operation (hereinafter referred to as the low-speed unwinding speed) (output frequency < low-speed unwinding speed), the control unit 12 executes the first unwinding acceleration process in step S12. The base block will be described later. Specifically, when the unwinding push button switch 22 is pressed, the control unit 12 outputs an unwinding command signal, which is a reverse command signal, to the inverter 15. Hereafter, the unwinding command signal will also be referred to as the low-speed unwinding command signal as appropriate. When the inverter 15 receives the low-speed unwinding command signal, it supplies power to the motor 14 at a frequency that results in a predetermined acceleration, with the low-speed unwinding speed as the target speed. As a result, the motor 14 is accelerated to the low-speed unwinding speed at a predetermined acceleration, and the motor 14 reaches the low-speed unwinding speed.
[0024] The process in step S12 when the output frequency of the inverter 15 is less than the low-speed unwinding speed is referred to as the first control process D1.
[0025] In step S11, if the base block is in the OFF state and the output frequency of the inverter 15 is determined to be equal to or greater than the low-speed unwinding speed and less than the grid power frequency of the grid power supply 2 (low-speed unwinding speed ≤ output frequency < grid power frequency), the control unit 12 determines in step S13 whether or not it has received an operation signal indicating that the unwinding push button switch 22 has been pressed up to the second position, that is, whether or not high-speed unwinding has been commanded.
[0026] If, in step S13, it is determined that high-speed unwinding has not been commanded, that is, if the unwinding push-button switch 22 is pressed to the first position, the control unit 12 performs a second unwinding deceleration process in step S14. Specifically, if the unwinding push-button switch 22 is pressed to the first position, the control unit 12 outputs a low-speed unwinding command signal to the inverter 15. When the inverter 15 receives the low-speed unwinding command signal, it sets the low-speed unwinding speed as the target speed and supplies drive power to the motor 14 at a frequency that results in a predetermined acceleration. Thereafter, if the unwinding push-button switch 22 is pressed to the first position, it continues to output an output at a frequency corresponding to the low-speed unwinding speed. As a result, the motor 14 is decelerated to the low-speed unwinding speed at a predetermined acceleration, and after reaching the low-speed unwinding speed, it continues to rotate in the downward direction at this speed.
[0027] If, in step S13, it is determined that high-speed unwinding is commanded, that is, if the unwinding push-button switch 22 is pressed to the second position, the control unit 12 executes a second unwinding acceleration process in step S15. Specifically, if the unwinding push-button switch 22 is pressed to the second position, the control unit 12 outputs a high-speed command signal to the inverter 15 in addition to the unwinding command signal (low-speed unwinding command signal). Note that when it is not necessary to distinguish between the unwinding command signal and the high-speed command signal output to the inverter 15 due to the unwinding push-button switch 22 being pressed to the second position, the high-speed unwinding command signal is referred to as the high-speed unwinding command signal. When the inverter 15 receives the high-speed unwinding command signal, it supplies drive power to the motor 14 at a frequency that results in a predetermined acceleration, with a target speed of a frequency equivalent to the system frequency (50 Hz or 60 Hz), that is, a frequency corresponding to the rotational speed of the motor 14 during high-speed unwinding operation (hereinafter referred to as the high-speed unwinding speed). As a result, the electric motor 14 is accelerated at a predetermined acceleration until it reaches a high-speed unwinding speed.
[0028] The process described above, in steps S13 to S15 when the output frequency of the inverter 15 is equal to or greater than the low-speed unwinding speed and less than the grid power frequency, is referred to as the second control process D2.
[0029] If, in step S11, the base block is in the OFF state and the output frequency of the inverter 15 is equal to or greater than the grid power frequency (grid power frequency ≤ output frequency), the control unit 12 determines in step S16 whether or not high-speed unwinding has been commanded. If, in step S16, it is determined that high-speed unwinding has not been commanded, that is, the unwinding push-button switch 22 is pressed to the first position, the control unit 12 executes a second unwinding deceleration process in step S17, similar to the case in step S14, with a low-speed unwinding speed as the target speed. If, even after decelerating to a speed less than the high-speed unwinding speed through this process, high-speed unwinding is still not commanded, the second unwinding deceleration process in step S14 is executed via steps S11 and S13.
[0030] If, in step S16, it is determined that high-speed unwinding is commanded, that is, if the unwinding push-button switch 22 is pressed to the second position, the control unit 12 outputs a command to the inverter 15 in step S18 to turn on the base block (hereinafter referred to as the base block command). Specifically, if the inverter 15 is outputting drive power at the same frequency as or higher than the grid power supply 2, and the unwinding push-button switch 22 is pressed to the second position, the control unit 12 outputs the base block command to the inverter 15. When the inverter 15 receives the base block command, it blocks the output of gate drive signals to the six switching elements in the built-in inverter circuit DC-AC converter (not shown), and turns on the base block. As a result, the output of drive power from the inverter 15 to the motor 14 stops. The inverter 15 continues to turn on the base block until the base block command from the control unit 12 is released.
[0031] The base block function, which stops the output of the secondary power of the inverter 15, is used in the hoisting machine 1 to stop the supply of drive power from the inverter 15 to the motor 14 in the event of an error or emergency stop (when the emergency push-button switch 23 is operated). In this embodiment, however, this base block function is also used in the power switching process.
[0032] Next, in step S19, the control unit 12 outputs a command to the electromagnetic switch 13 to turn on the contacts, and the electromagnetic switch 13 receives the command and closes the main contacts to the grid power supply 2 (becoming ON). As a result, the supply of drive power from the grid power supply 2 to the motor 14 begins without going through the inverter 15. At this time, even if the output terminals U, V, W of the inverter 15 and the motor 14 are electrically connected, the function of the base block prevents current from flowing from the output terminals U, V, W of the inverter 15 into the inverter circuit.
[0033] Furthermore, after the power supply from the inverter 15 to the motor 14 is stopped in step S18, the motor 14 will temporarily be in a free-running state until the power supply from the grid power source 2 to the motor 14 is started in step S19.
[0034] In other words, through the processing in steps S18 and S19, the power supply for the motor 14 is switched from the output of the inverter 15 to the grid power supply 2, resulting in grid power drive.
[0035] The process described above, from step S16 to step S19 when the output frequency of the inverter 15 is equal to or greater than the grid power frequency, is referred to as the third control process D3.
[0036] If, in step S11, the control unit 12 determines that the base block is in the ON state, that is, the motor 14 is either powered by the grid or in a free-run state without going through the inverter 15, then in step S20, the control unit 12 determines whether or not high-speed unwinding has been commanded. If, in step S20, the control unit 12 determines that high-speed unwinding has not been commanded, that is, the unwinding push-button switch 22 is pressed to the first position, then in step S21, the control unit 12 executes a process to switch the power of the motor 14 from the grid power supply 2 to the output of the inverter 15 (hereinafter referred to as inverter switching process as appropriate). If, in step S20, the control unit 12 determines that high-speed unwinding has been commanded, that is, the unwinding push-button switch 22 is pressed to the second position, then the control unit 12 executes control to continue powered by the grid.
[0037] (Process to switch the power supply of the motor 14 from grid power supply 2 to the output of inverter 15) The details of the inverter switching process in step S21 will be explained with reference to the flowchart in Figure 3. The inverter switching process is executed when there is a request for inverter switching.
[0038] In step S41, the control unit 12 refers to the value of the built-in timer, and if the timer value is zero, i.e., if step S41 is executed for the first time with the base block ON, in step S42, it outputs a contact OFF command to the electromagnetic switch 13. Then, in step S43, the control unit 12 starts the timer and begins measuring time. The electromagnetic switch 13 receives the contact OFF command output from the control unit 12 in step S42 and opens its main contact. As a result, the power supply from the grid power supply 2 to the motor 14 is stopped.
[0039] In step S41, if the timer value is greater than zero and less than 50 ms, the control unit 12 does not output a command to the inverter 15 to release the base block (hereinafter referred to as the base block OFF command). That is, the inverter 15 continues to have the base block ON. When the timer value reaches 50 ms, in step S44, the control unit 12 outputs a command to the inverter 15 to release the base block ON state (base block OFF command), and in step S45, the timer is stopped and the value is reset to zero. Then, in step S46, the control unit 12 commands the inverter 15 to perform a speed search for the motor 14. Based on the base block OFF command and the speed search command, the inverter 15 releases the base block ON state and starts detecting the rotational speed of the motor 14, and adjusts the output voltage and frequency of the drive power to match the detected state of the motor 14. When the inverter 15 starts outputting drive power to the motor 14 based on the speed search result, it outputs a speed search completion signal to the control unit 12, the control unit 12 completes the inverter switching process, and returns to step S11.
[0040] Speed search is a function that determines the rotational speed of the motor 14 by applying voltage from the inverter 15 to the motor 14, which is in a free-running state. In step S18 (third control process D3) in Figure 2, the base block is turned ON, and the power supply from the inverter 15 to the motor 14 is stopped. In step S42, the power supply from the grid power supply 2 to the motor 14 is also stopped, causing the motor 14 to enter a free-running state. As a result, the lowering speed of the motor 14 is accelerated by the suspended load. The search function of the inverter 15 then detects the rotational speed of the motor 14, and adjusts the output frequency to a frequency higher than the grid power frequency, for example, to start outputting drive power from the inverter 15 to the motor 14 so as not to cause shocks.
[0041] When step S46 is executed and the switching of the motor 14 to inverter drive is completed, the control unit 12 ends the inverter switching process, checks the state of the inverter in step S11 of the unwinding process, and based on the check result, executes the first control process D1, the second control process D2, or the third control process D3.
[0042] Through the processes of steps S41 to S46 in this way, the driving power of the motor 14 is switched from the electromagnetic switch 13 to the output of the inverter 15 to become inverter drive.
[0043] In the inverter switching process, after the power supply from the electromagnetic switch 13 to the motor 14 stops (step S42), it waits for 50 ms to elapse, and then the power supply from the inverter 15 to the motor 14 is started (step S44). This is to protect the inverter circuit of the inverter 15 by waiting for 50 ms, which is longer than the worst-case time of 26 ms, the total time of the return time of 18 ms of the electromagnetic switch 13 and the arc time (the time considering protection against contact discharge), and then switching the electromagnetic switch 13.
[0044] The processes of steps S20 and S21 when the base block is in the ON state, described above, are referred to as the fourth control process D4.
[0045] In the actual unwinding process of the hoist 1, in addition to the processes shown in FIGS. 2 and 3, an unwinding reverse process, an unwinding start process, and a stop process involving the operation of an electromagnetic brake (not shown) are also performed. However, since they are the same as the processes of the conventional electric chain block, the description of these processes is omitted here.
[0046] (Specific Example) The above-described process will be described with a specific example by referring to the time chart of FIG. 4. Between times t1 and t5, the unwind push button switch 22 is pushed in, the first-stage switch is ON, and the control unit 12 outputs a low-speed unwind command signal (unwind command signal) to the inverter 15. Between times t2 and t4, the unwind push button switch 22 is pushed in up to the second stage and the second-stage switch is also ON, and the control unit 12 further outputs a high-speed command signal to the inverter 15. That is, the control unit 12 outputs a high-speed unwind command signal between times t2 and t4.
[0047] At time t1, when a low-speed lowering command signal is output, since the output frequency of the inverter 15 is lower than the low-speed lowering speed, the first control process D1 is executed. That is, the lowering first acceleration process (step S12 in FIG. 2) is executed and accelerated at a predetermined acceleration. Since the low-speed lowering command signal continues to be output, the output frequency of the inverter 15 reaches the low-speed lowering speed. That is, the output frequency = the low-speed lowering speed.
[0048] Even after the low-speed lowering speed = the output frequency, since the low-speed lowering command signal continues to be output, the second control process D2 is executed via step S11. In the second control process D2, in a state where high-speed lowering is not commanded and no high-speed lowering command signal is output, the low-speed lowering operation is continued by the lowering second deceleration process (step S14). When a high-speed lowering command signal is output from time t2, the lowering second acceleration process (step S15) is executed. While the high-speed lowering command signal is being output, it is accelerated at a predetermined acceleration. As a result, at time t3, the output frequency of the inverter 15 reaches the high-speed lowering speed. That is, the output frequency = the system power supply frequency.
[0049] At time t and when the output frequency = the system power supply frequency, the third control process D3 is executed via step S11. At time t3, since the high-speed lowering command signal continues to be output, the base block of the inverter 15 becomes ON (step S18), and the output from the inverter 15 stops. Then, the main contact of the electromagnetic switch 13 becomes ON (step S19). As a result, the electric motor 14 is switched from inverter drive to system power supply drive.
[0050] When the base block is turned ON, the fourth control process D4 is executed via step S11, and grid power drive continues while the high-speed unwinding command signal is output. When the output of the high-speed unwinding command signal stops at time t4, the drive power of the motor 14 switches from grid power drive to inverter drive (step S21). That is, the main contacts of the electromagnetic switch 13 turn OFF (steps S41, S42), and the timer is started (step S43). Even though the main contacts of the electromagnetic switch 13 are OFF, the base block is ON in the inverter 15, so the motor 14 rotates without power supply and is in a free-run state.
[0051] Subsequently, 50 ms after time t4, the ON state of the base block of the inverter 15 is released (turned OFF) (steps S41, S44), and the timer stops and resets (step S45). Then a speed search is performed, and based on the result, the output voltage and frequency of the drive power are adjusted (step S46). Through this process, the motor 14 is smoothly switched from grid power drive to inverter drive. At this time, the rotational speed of the motor 14 is accelerated by the suspended load during free run to a rotational speed corresponding to the grid power frequency, but the output of drive power from the inverter 15 starts at a frequency that matches the rotational speed detected by the speed search. Since no high-speed unwinding command signal is output, the motor 14 decelerates at a predetermined acceleration due to the inverter drive.
[0052] Once the inverter switching process is complete, the base block is in the OFF state, so the third control process D3 or the second control process D2 is executed via step S11, and since no high-speed unwinding command signal has been output since time t4, the second unwinding deceleration process is executed. That is, deceleration of the motor 14 is started with the low-speed unwinding speed as the target speed.
[0053] At time t5, when the first stage of the unwinding push-button switch 22 is released and the output of the unwinding command signal stops, the inverter 15 supplies drive power to the motor 14 at a frequency that reduces the speed by a predetermined rate, thereby slowing it down. As a result, at time t6, the power supply stops and the motor 14 stops. The inverter 15 can also output a brake activation signal that activates an electromagnetic brake (not shown) when the electromagnetic brake activation frequency is reached.
[0054] [Second Embodiment: Lowering Process with Further Light-Load High-Speed Function] In the first embodiment described above, when high-speed lowering is commanded, the motor 14 is switched from inverter drive to grid power drive. However, for example, as long as the braking resistor 16 does not consume regenerative power and is within the capacity of the braking resistor 16, it is possible to drive at a frequency higher than the grid power frequency. For example, if the weight of the suspended load is a light load for the motor 14, it may be possible to drive at a frequency higher than the grid power frequency.
[0055] In the second embodiment, when the weight of the suspended load is a light load for the motor 14, even when high-speed lowering is commanded, the system does not switch to grid power drive, and inverter drive continues at a frequency higher than the grid power frequency.
[0056] (Unwinding Process) First, the flow of this unwinding process will be explained by referring to the flowchart in Figure 5, and then a specific example will be explained by referring to the time chart in Figure 6.
[0057] The first control process D1, the second control process D2, and the fourth control process D4 perform the same processes as the first control process D1, the second control process D2, and the fourth control process D4 in Figure 2, so their explanation will be omitted.
[0058] The unwinding process is performed while the unwinding push-button switch 22 is pressed to the first or second position and the control unit 12 recognizes this. Similar to the first embodiment, the control unit 12 separately determines the state of the unwinding push-button switch 22, and terminates the unwinding process when the unwinding push-button switch 22 is not pressed. In step S51, the control unit 12 determines the state of the inverter 15.
[0059] In step S51, if the base block is in the OFF state and the output frequency of the inverter 15 is equal to or greater than the grid power frequency (grid power frequency ≤ output frequency), the control unit 12 determines in step S52 whether or not high-speed unwinding has been commanded. If it is determined in step S52 that high-speed unwinding has not been commanded, the control unit 12 performs a second unwinding deceleration process in step S53, similar to step S17 (Figure 2) of the third control process D3, with a low-speed unwinding speed as the target speed. If, even after decelerating to a speed less than the high-speed unwinding speed through this process, high-speed unwinding is still not commanded, the second unwinding deceleration process of the second control process D2 is executed via step S51.
[0060] If the control unit 12 determines in step S52 that high-speed lowering is commanded, in step S54, it determines whether the motor 14 can be driven at a frequency higher than the grid power frequency, and in this example, whether the lowering load is a light load. This determination is made at the grid power frequency after it has been set. Whether the weight of the suspended load is a light load for the motor 14 can be determined by the load signal output by the inverter 15. Note that the determination of whether it is a light load or not may be made in advance at a frequency lower than or equal to the grid power frequency and stored in a memory (not shown).
[0061] If it is determined in step S54 that the load is light, the control unit 12 performs a third unwinding acceleration process in step S55. Specifically, the control unit 12 outputs a light-load high-speed unwinding command signal to the inverter 15, and the inverter 15 supplies drive power to the motor 14 at a frequency higher than the grid power frequency until it reaches a frequency corresponding to a predetermined speed faster than the high-speed unwinding speed (hereinafter referred to as the light-load high-speed unwinding speed). As a result, the motor 14 is accelerated at a predetermined acceleration to the light-load high-speed unwinding speed, and reaches the light-load high-speed unwinding speed. Furthermore, as long as the unwinding push-button switch 22 is pressed to the second position and it is determined in step S54 that the load is light, the motor 14 rotates in the unwinding direction at the light-load high-speed unwinding speed.
[0062] If, in step S54, the control unit 12 determines that the load is not light, in step S56, the base block of the inverter 15 is turned ON, and in step S57, the main contact of the electromagnetic switch 13 to the grid power supply 2 is turned ON, similar to steps S18 and S19 of the first embodiment. As a result, the motor 14 is switched from inverter drive to grid power drive.
[0063] The process described above, from step S52 to step S57 when the output frequency of the inverter 15 is equal to or greater than the grid power frequency, is referred to as the third control process D3'.
[0064] (Specific Example) The above process will be explained with reference to the time chart in Figure 6. Between time t1 and time t7, the first stage of the unwinding push button switch 22 is pressed, and the control unit 12 outputs a low-speed unwinding command signal (unwinding command signal) to the inverter 15. Between time t2 and time t5, the second stage of the unwinding push button switch 22 is pressed, and the control unit 12 further outputs a high-speed command signal to the inverter 15. That is, the control unit 12 outputs a high-speed unwinding command signal between time t2 and time t5. Throughout the entire period, the load determination signal outputs Low. In other words, the load being unwound by the hoisting machine 1 is a light load.
[0065] At time t1, when the low-speed unwinding command signal is output, the output frequency of the inverter 15 is lower than the low-speed unwinding speed, so the first control process D1, similar to that of the first embodiment, is executed. That is, the first unwinding acceleration process (similar to step S12 in Figure 2) is executed, and the load is accelerated at a predetermined acceleration. Subsequently, the low-speed unwinding command signal is output, so the output frequency of the inverter 15 reaches the low-speed unwinding speed. That is, output frequency = low-speed unwinding speed.
[0066] Even after the low-speed unwinding speed equals the output frequency, the low-speed unwinding command signal continues to be output, so the second control process D2, similar to that of the first embodiment, is executed via step S51. In the second control process D2, if high-speed unwinding is not commanded and no high-speed unwinding command signal is output, the low-speed unwinding operation is continued by the second unwinding deceleration process (similar to step S14 in Figure 2). When a high-speed unwinding command signal is output from time t2, the second unwinding acceleration process (similar to step S15 in Figure 2) is executed. While the high-speed unwinding command signal is output, acceleration is performed at a predetermined acceleration. As a result, at time t3, the output frequency of the inverter 15 reaches the high-speed unwinding speed. That is, the output frequency equals the grid power frequency.
[0067] At time t3, when the output frequency equals the grid power frequency, the third control process D3' is executed via step S51. At time t3, since the high-speed unwinding command signal is still being output, it is determined whether or not there is a light load. At time t4, the control unit 12 confirms that the load determination is Low and determines that there is a light load (Yes in steps S52 and S54), and executes the third unwinding acceleration process (step S55). As a result, the unwinding is accelerated at a predetermined acceleration, and since the high-speed unwinding command signal is still being output, the output frequency of the inverter 15 reaches the light-load high-speed unwinding speed.
[0068] Subsequently, at time t5, when the output of the high-speed unwinding command signal stops, the control unit 12 executes the second unwinding deceleration process (step S53). Since high-speed unwinding is not commanded and the high-speed unwinding command signal is not output, the output frequency of the inverter 15 is reduced at a predetermined acceleration until it falls below the grid power frequency. Furthermore, since the high-speed unwinding command signal is not output even after it falls below the grid power frequency, the second unwinding deceleration process in the second control process D2 continues to be executed. At time t6, even after the unwinding speed has decreased to a low speed, the first stage of the unwinding push button switch 22 remains pressed and the low-speed unwinding command signal is output, so the motor 14 rotates in the unwinding direction at a low unwinding speed.
[0069] Then, at time t7, the first stage of the unwinding push-button switch 22 is released, and the output of the unwinding command signal stops. The inverter 15 then supplies power to the motor 14 at a frequency that reduces the speed by a predetermined rate, causing it to decelerate. As a result, the power supply stops at time t8, and the motor 14 stops.
[0070] In the event of a stop, it is preferable to apply braking by outputting a brake signal within a predetermined frequency range before reaching the lowest frequency output by the inverter 15.
[0071] Thus, when the suspended load is light, the inverter drive is performed at a frequency higher than the output frequency of power grid 2.
[0072] In summary, it is possible to determine whether the suspended load is light or not, and if it is light, lowering control may be performed without switching to grid power, or the lowering process may be changed based on the load of the suspended load, which is the object being worked on. Instead of determining whether the suspended load is light or not, in the lowering operation of an electric chain hoist, it may be possible to determine whether lowering operation is possible at a frequency higher than the grid power frequency based on the presence or magnitude of regenerative power. This enables high-speed processing, is suitable for increasing the speed of hoisting machines with long lifting heights, and can improve work efficiency.
[0073] [Third Embodiment: Unwinding Process with Further Temperature Detection Function] In the second embodiment, the braking resistor 16 was driven at a frequency higher than the grid power frequency, within a range where regenerative power is not consumed by the braking resistor 16 and within the capacity in which the braking resistor 16 can process regenerative power, depending on the unwinding load. However, it is also possible to drive the braking resistor 16 at a frequency higher than the grid power frequency depending on the temperature of the braking resistor 16. Figure 7 is a block diagram showing an example of the configuration of a hoisting machine 1 according to the third embodiment having this function. This hoisting machine 1 is further provided with a temperature detection unit 31 compared to the configuration in Figure 1. The temperature detection unit 31 detects the temperature of the braking resistor 16 and supplies the detection result to the control unit 12. The temperature detection unit 31 conceptually includes a temperature estimation unit that monitors the current flowing through the braking resistor 16 to estimate the temperature.
[0074] (Unwinding Process) The unwinding process of the hoisting machine 1 according to the third embodiment will first be explained with reference to the flowchart in Figure 8, and then a specific example will be explained with reference to the time chart in Figure 9.
[0075] The first control process D1, the second control process D2, and the fourth control process D4 perform the same processes as the first control process D1, the second control process D2, and the fourth control process D4 in Figure 2, so their explanation will be omitted.
[0076] The unwinding process is performed while the unwinding push-button switch 22 is pressed to the first or second position and the control unit 12 recognizes this. Similar to the first and second embodiments, the control unit 12 separately determines the state of the unwinding push-button switch 22, and terminates the unwinding process when the unwinding push-button switch 22 is not pressed. In step S71, the control unit 12 determines the state of the inverter 15.
[0077] If, in step S71, the control unit 12 determines that the base block is in the OFF state and the output frequency of the inverter 15 is equal to or greater than the grid power frequency (grid power frequency ≤ output frequency), then in step S72, the control unit 12 determines whether or not high-speed unwinding has been commanded. If, in step S72, it determines that high-speed unwinding has not been commanded, then in step S73, the control unit 12 performs a second unwinding deceleration process with a low unwinding speed as the target speed, similar to step S17 (Figure 2) of the third control process D3 of the first embodiment. If, even after decelerating to a speed less than the high-speed unwinding speed through this process, high-speed unwinding is still not commanded, then the second unwinding deceleration process of the second control process D2 is executed via step S71.
[0078] If the control unit 12 determines in step S72 that high-speed unwinding has been commanded, in step S74, it determines whether the unwinding load is a light load or not, similar to the case in step S54 in Figure 5.
[0079] If it is determined in step S74 that the load is light, the control unit 12 determines in step S75 whether the temperature of the braking resistor 16 is within an acceptable range based on the detection result of the temperature detection unit 31. Specifically, it is determined whether the temperature of the braking resistor 16 is above a predetermined limit temperature, or whether it is predicted to exceed the limit temperature.
[0080] If, in step S75, the control unit 12 determines that the temperature of the braking resistor 16 is within an acceptable range, in step S76, the control unit 12 performs the third winding acceleration process, similar to the case of step S55 (Figure 5) in the second embodiment.
[0081] If, in step S75, the control unit 12 determines that the temperature of the braking resistor 16 is outside the acceptable range, then in step S77, the control unit 12 determines whether the output frequency of the inverter 15 is equal to the grid power frequency.
[0082] If, in step S77, the control unit 12 determines that the output frequency is not equal to the grid power frequency, then in step S78, the control unit 12 executes a third winding reduction process. Specifically, a process is executed to reduce the winding speed to a target speed equal to the grid power frequency.
[0083] If, in step S77, the control unit 12 determines that the output frequency is equal to the grid power frequency, then, similar to steps S18 and S19 of the first embodiment, in step S79, the base block of the inverter 15 is turned ON, and in step S80, the main contact of the electromagnetic switch 13 with respect to the grid power 2 is turned ON. As a result, the motor 14 is switched from inverter drive to grid power drive.
[0084] If the control unit 12 determines in step S74 that the load is not light, it turns on the base block of the inverter 15 in step S81, and turns on the main contact of the electromagnetic switch 13 to the grid power supply 2 in step S82, similar to steps S18 and S19 of the first embodiment. As a result, the motor 14 is switched from inverter drive to grid power drive.
[0085] (Specific Example) The above process will be explained with reference to the time chart in Figure 9. Between time t1 and time t8, the first stage of the unwinding push-button switch 22 is pressed, and the control unit 12 outputs a low-speed unwinding command signal (unwinding command signal) to the inverter 15. Between time t2 and time t7, the second stage of the unwinding push-button switch 22 is pressed, and the control unit 12 further outputs a high-speed command signal to the inverter 15. That is, the control unit 12 outputs a high-speed unwinding command signal between time t2 and time t7. Throughout the entire period, the load determination signal is output as Low. In other words, the load being unwound by the hoisting machine 1 is a light load. At time t5, the temperature detection unit 31 detects that the temperature of the braking resistor 16 has exceeded a predetermined temperature, and starts outputting a resistor temperature determination signal High.
[0086] At time t1, when the low-speed unwinding command signal is output, the output frequency of the inverter 15 is lower than the low-speed unwinding speed, so the first control process D1, similar to that of the first embodiment, is executed. That is, the first unwinding acceleration process (similar to step S12 in Figure 2) is executed, and the load is accelerated at a predetermined acceleration. Subsequently, the low-speed unwinding command signal is output, so the output frequency of the inverter 15 reaches the low-speed unwinding speed. That is, output frequency = low-speed unwinding speed.
[0087] Even after the low-speed unwinding speed equals the output frequency, the second control process D2, similar to that of the first embodiment, is executed via step S71. In the second control process D2, if high-speed unwinding is not commanded and no high-speed unwinding command signal is output, the low-speed unwinding operation is continued by the second unwinding deceleration process (similar to step S14 in Figure 2). When a high-speed unwinding command signal is output from time t2, the second unwinding acceleration process (similar to step S15 in Figure 2) is executed. While the high-speed unwinding command signal is output, acceleration is performed at a predetermined acceleration. As a result, at time t3, the output frequency of the inverter 15 reaches the high-speed unwinding speed. That is, the output frequency equals the grid power frequency.
[0088] At time t3, when the output frequency equals the grid power frequency, the third control process D3'' is executed via step S71. At time t3, since the high-speed unwinding command signal is still being output, it is determined whether or not there is a light load. At time t4, the control unit 12 confirms that the load determination is Low and determines that there is a light load (Yes in steps S72 and S74), and then determines whether or not the temperature of the braking resistor 16 is within the acceptable range (step S75). At this timing, the temperature of the braking resistor 16 is within the acceptable range (resistor temperature determination is Low) (Yes in step S75), so the third unwinding acceleration process is executed at time t4 (step S76), and the motor is accelerated at a predetermined acceleration. Since the load determination is Low and the resistor temperature determination is Low and the high-speed unwinding command signal is still being output, the output frequency of the inverter 15 reaches the light-load high-speed unwinding speed, and thereafter the motor 14 continues to rotate in the unwinding direction at the light-load high-speed unwinding speed.
[0089] Subsequently, at time t5, if the temperature of the braking resistor 16 of the inverter 15 exceeds the limit temperature and it is determined that the temperature of the braking resistor 16 is outside the acceptable range (step S75: No), it is determined whether the output frequency of the inverter 15 is equal to the grid power frequency (step S77). At this timing, the output frequency is not equal to the grid power frequency (step S77: No), so the third winding reduction process is executed (step S78).
[0090] The third winding reduction process reduces the output frequency to the grid power frequency, and when it is determined that the output frequency is equal to the grid power frequency at time t6 (Yes in step S77), the base block turns ON (step S79), and the main contacts of the electromagnetic switch 13 with respect to the grid power 2 turn ON (step S80). As a result, the motor 14 is switched from inverter drive to grid power drive.
[0091] As the base block is turned ON, the fourth control process D4 is executed via step S71. That is, while the high-speed unwinding command signal is output, drive power is supplied from the grid power supply 2 to the motor 14 via the electromagnetic switch 13. Then, at time t7, when the output of the high-speed unwinding command signal stops, the same process as in step S21 is executed, and 50 ms have elapsed since the grid power supply 2 was shut off (same process as step S41 in Figure 3), the base block is turned OFF (same process as in step S44), the speed of the motor 14 is searched, and the output voltage and frequency of the inverter 15 are adjusted according to the result. Then, the second unwinding deceleration process (same process as step S17 of the third control process D3 in Figure 2) is executed as in the first embodiment.
[0092] At time t8, during the second deceleration process for unwinding, the first stage of the unwinding push-button switch 22 is released, and the output of the unwinding command signal stops. The inverter 15 then supplies power to the motor 14 at a frequency that reduces the speed by a predetermined rate, causing it to decelerate. Subsequently, at time 9, the power supply stops and the motor 14 stops.
[0093] In the event of a stop, it is preferable to apply braking by outputting a brake signal within a predetermined frequency range before reaching the lowest frequency output by the inverter 15.
[0094] As described above, when the temperature of the braking resistor 16 is within the permissible range, the light-load high-speed function enables high-speed lowering, allowing for higher speeds when the hoisting machine 1 is used for long lifting heights, increasing the range in which high-speed operation according to the load is possible, and meeting the demand for high-speed lowering operation.
[0095] [Note] The contents described in some of the embodiments above can be understood as follows, for example: (1) Control device for the hoisting machine The hoisting machine 1 described above comprises: an electric motor 14 for hoisting up and down; an inverter 15 connected to a grid power supply 2 and supplying drive power to the electric motor 14 in a variable speed control manner; an electromagnetic switch 13 connected to a grid power supply 2 and supplying drive power to the electric motor 14 without going through the inverter 15; and a control unit 12 that, in the lowering operation, supplies drive power to the electric motor 14 from the electromagnetic switch 13 at a predetermined speed corresponding to the AC frequency of the grid power supply, and supplies drive power to the electric motor 14 from the inverter 15 at speeds other than the predetermined speed, wherein the control unit 12, when decelerating from a predetermined speed (step S21), stops the drive power from the electromagnetic switch 13 to the electric motor 14 (step S42), and outputs drive power for the electric motor 14 from the inverter 15 according to the rotational speed of the electric motor 14 (step S43).
[0096] With this configuration, when the speed is at the grid power frequency, the motor 14 is driven by the output from the electromagnetic switch 13, meaning that the power supply for the motor 14 is switched from the output of the inverter 15 to the grid power 2. As a result, the regenerative power generated by the motor 14 is returned to the grid power 2, saving energy, and the regenerative power that is converted into heat by the braking resistor 16 can be suppressed. If the regenerative power that is converted into heat by the braking resistor 16 can be suppressed, the capacity of the braking resistor 16 can be reduced (it can be made smaller), and a fan or the like to cool the braking resistor 16 becomes unnecessary. Furthermore, there is no need to reduce the winding speed to prevent overheating.
[0097] Furthermore, when switching the motor from grid power drive to inverter drive, phase synchronization is not performed as in the technology described in Patent Document 1 in order to output the drive power of the motor 14 from the inverter 15 according to the rotational speed of the motor. Therefore, the power supply of the motor 14 can be switched more quickly from the output of the inverter 15 to the grid power 2.
[0098] (2) When the motor 14 is being driven by the output of the inverter 15 during the lowering operation, the light-load high-speed function control unit 12 determines whether it is possible to drive at a frequency higher than the AC frequency of the grid power supply 2 (50 Hz or 60 Hz) (step S54 in Figure 5). If it is determined that it is possible to drive at a frequency higher than the AC frequency of the grid power supply 2 (step S54: YES), the inverter 15 outputs drive power at a frequency higher than the AC frequency of the grid power supply 2 (step S55, light-load high-speed lowering speed in Figure 5).
[0099] Thus, in lowering operations, when the motor 14 is driven by the output from the inverter 15, for example, in lowering operations where the suspended load is light and the motor 14 is in powered operation, or when regenerative power is generated but within the range of power that can be handled by the braking resistor 16, it is determined whether it is possible to drive at a frequency higher than the AC frequency of the grid power supply 2. If it is possible to drive at a frequency higher than the AC frequency of the grid power supply 2, high-speed operation becomes possible. As a result, the efficiency of the work is improved.
[0100] (3) In the case of high-temperature heat dissipation for light-load high-speed function, the control unit 12 may, when it is possible to output drive power from the inverter 15 at a frequency higher than the AC frequency of the grid power supply 2, when the temperature of the braking resistor 16 that converts the regenerative power of the inverter 15 into heat reaches a predetermined temperature or is predicted to reach a predetermined temperature or higher (NO in step S75 in Figure 8, t4 in Figure 9), lower the output frequency of the inverter 15 to the AC frequency of the grid power supply 2 (steps S77, S78, t6 in Figure 9), and then switch to the output from the electromagnetic switch 13 (steps S77, S79, S80).
[0101] With this configuration, high-speed operation is possible within the allowable temperature range of the braking resistor 16.
[0102] (4) When the speed search time control unit 12 stops the output from the electromagnetic switch 13 to the motor 14 and outputs the drive power for the motor 14 from the inverter according to the rotational speed of the motor 14, after stopping the output from the electromagnetic switch 13 to the motor 14, it can output the drive power for the motor 14 according to the rotational speed of the motor 14 from the inverter 15 after a predetermined time has elapsed, and the predetermined time can be made longer than the reset time of the electromagnetic switch 13 and the protection time against arc generation during switching.
[0103] This configuration makes it possible to prevent the occurrence of faults such as short circuits.
[0104] 1 Hoisting machine 2 Power supply system 11 Control box 12 Control unit 13 Electromagnetic switch 14 Motor 15 Inverter 16 Braking resistor 21 Hoisting push button switch 22 Unwinding push button switch 23 Emergency push button switch 31 Temperature detection unit
Claims
1. A control device for a hoisting machine, comprising: an electric motor for hoisting and lowering; an inverter connected to a grid power supply and supplying drive power to the motor in a variable-speed control manner; a drive circuit connected to the grid power supply and supplying drive power to the motor without going through the inverter; and a control unit that performs control during lowering operation, such that at a predetermined speed corresponding to the AC frequency of the grid power supply, the drive circuit supplies drive power to the motor, and at speeds other than the predetermined speed, the inverter supplies drive power to the motor, wherein when the speed is reduced from the predetermined speed, the control unit stops the drive power from the drive circuit to the motor and outputs drive power to the motor from the inverter according to the rotational speed of the motor.
2. A control device for a hoisting machine according to claim 1, wherein the control unit determines whether it is possible to drive the motor at a frequency higher than the AC frequency of the grid power supply when the motor is being driven by the output of the inverter, and when it is determined that it is possible to drive at a frequency higher than the AC frequency of the grid power supply, it causes the inverter to output drive power at a frequency higher than the AC frequency of the grid power supply.
3. A control device for a hoisting machine according to claim 2, wherein the control unit, when outputting drive power at a frequency higher than the AC frequency of the grid power supply from the inverter, when the temperature of the braking resistor that converts the regenerative power of the inverter into heat reaches a predetermined temperature or is expected to reach a predetermined temperature or is expected to reach a predetermined temperature, lowers the output frequency of the inverter to the AC frequency of the grid power supply, and then switches the drive power of the motor to the drive power from the drive circuit.
4. A control method for a hoisting machine comprising: an electric motor for raising and lowering; an inverter connected to a grid power supply and supplying drive power to the electric motor in a variable-speed control manner; a drive circuit connected to the grid power supply and supplying drive power to the electric motor without going through the inverter; and a control unit that, in hoisting operation, supplies drive power to the electric motor from the drive circuit at a predetermined speed corresponding to the AC frequency of the grid power supply, and supplies drive power to the electric motor from the inverter at speeds other than the predetermined speed, wherein when the control unit decelerates from the predetermined speed, it stops supplying drive power to the electric motor from the drive circuit and outputs drive power to the electric motor from the inverter according to the rotational speed of the electric motor.