Single-phase induction motor control method, control device, and electric chain block

Abstract

Provided are a single-phase induction motor control method, a control device, and an electric chain block that make it possible to properly determine a motor overload, even in a state where the single-phase induction motor is repeatedly feeding electrical power to an auxiliary coil.　The single-phase induction motor comprises a main coil ML, an auxiliary coil AL, a capacitor C, and an SSR power circuit 121, and in the single-phase induction motor control method, an electrical current is fed to the main coil ML via the SSR power circuit 121 from a single-phase alternating current power source 200, and the electrical current is fed to the auxiliary coil AL if the load is large. An overload is determined in accordance with the proportion of an energization time during which the electrical current is fed to the auxiliary coil AL during a prescribed time period.

Description

[Technical Field]

[0001] The present invention relates to a control method and control device for a single-phase induction motor, which is widely used in the drive unit of a load-moving device such as an electric chain hoist that moves loads of different weights, and to an electric chain hoist. [Background technology]

[0002] Single-phase induction motors are widely used in small load hoisting devices, such as electric chain hoists, that move loads vertically. There are various types of single-phase induction motors, and FIG. 1 shows a schematic circuit diagram of a single-phase induction motor used in this invention. A single-phase induction motor unit 120 includes a main coil ML with U and V terminals at both ends within a stator S, and an auxiliary coil AL with X and Y terminals at both ends. At startup, AC current is applied from a single-phase AC power source 200 to the main coil ML via an SSR (solid-state relay) power circuit 121. At the same time, AC current is also applied to the auxiliary coil AL via the SSR power circuit 121 and a capacitor C. This generates a rotating magnetic field within the stator S, causing a rotor (not shown), which is rotatably supported opposite the main coil ML and auxiliary coil AL, to begin rotating, starting the single-phase induction motor.

[0003] Figure 2 shows the torque change from start to start of a single-phase induction motor. Curve A shows the torque change when the rotor is rotated with the main coil ML and auxiliary coil AL energized, while curve B shows the torque change when the main coil ML is energized and the auxiliary coil AL is de-energized. The vertical axis represents torque, and the horizontal axis represents rotational speed. Operation of a single-phase induction motor with both the main coil ML and auxiliary coil AL energized is referred to as "capacitor run" (see Figure 3), while operation of a single-phase induction motor with the main coil ML energized and the auxiliary coil AL de-energized is referred to as "pure single-phase run" (see Figure 4). This single-phase induction motor is classified as a capacitor-start type, not a capacitor-run type, which operates with the auxiliary coil AL energized at all times.

[0004] First, a single-phase induction motor starts with zero rotational speed and operates in capacitor run mode (point I on curve A in Figure 2). The torque of the single-phase induction motor then increases (increases) with the rotational speed until it reaches a peak, from which point it rapidly decreases (decreases). At point II, a predetermined distance past the peak, the motor switches (transitions) to pure single-phase run mode by turning off the power to the auxiliary coil AL (switching contact 121e of current path 121b OFF), as shown in Figure 4. The rotational speed then increases until it reaches a point III where it is balanced with the load torque C, resulting in steady-state operation. The SSR power circuit 121 determines whether to switch from capacitor run mode (curve A) to pure single-phase run mode (curve B) based on the current flowing through the main coil ML. Furthermore, as shown in Figure 2, the output torque of a single-phase induction motor is determined by the rotational speed, and there is a correlation between the output torque and the current value of the single-phase induction motor. Therefore, the conventional overload limiter OLL (hereinafter simply referred to as "OLL") judges the output torque of the single-phase induction motor based on the value of the current flowing through the main coil ML to determine whether an overload has occurred.

[0005] However, in certain situations, it can be difficult to determine whether a single-phase induction motor has excessive output torque, or an overload, based on the current value. For example, this applies when a load hoisting device such as an electric chain hoist hoists a load of its rated load at the minimum guaranteed operating voltage, or in high or low temperature conditions. When a low voltage is applied or the motor is operating at high temperatures, the output torque of the single-phase induction motor itself decreases. Furthermore, at low temperatures, mechanical loss increases, increasing the load torque applied to the motor, making it difficult to determine whether the load is overloaded.

[0006] Figure 5 shows how a single-phase induction motor accelerates under these harsh conditions. At startup, it starts with capacitor run (curve A) (point I), just like normal operation. The rotation speed then increases steadily, and when the current in the main coil ML falls below a predetermined switching threshold (point II in Figure 5), it switches to pure single-phase run (curve B). Up to this point, the process is the same as a normal capacitor start. However, under these harsh conditions, when switching to pure single-phase run, the load torque C may be nearly equal to or even greater than the output torque of the single-phase induction motor. In this state, the single-phase induction motor may decelerate, and when the current in the main coil ML reaches the threshold for switching to capacitor run, it switches back to capacitor run (curve A) (point III). It accelerates with capacitor run (curve A), switches back to pure single-phase run (curve B) at point II, and then decelerates again before switching back to capacitor run (curve A).

[0007] As mentioned above, the output torque of a single-phase induction motor correlates with its rotational speed. However, when the motor alternates between capacitor run and pure single-phase run, it can continue to operate, but the current value is unstable. Therefore, in such a state, the conventional OLL, which determines the motor's current value, cannot accurately determine the motor's condition, limiting the range of use of single-phase induction motors as products. The simplest solution to this problem is to use a single-phase induction motor with sufficient output margin under all conditions, but this creates the problem of having to increase the size of the single-phase induction motor just to prepare for the worst-case scenario. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Utility Model Application Publication No. 56-067894 Summary of the Invention [Problem to be solved by the invention]

[0009] Patent Document 1 discloses technology relating to an overload control device for an electric motor. The technology disclosed therein is similar to the present invention in that it is an overload control device for a capacitor-started single-phase induction motor, but differs from the present invention in the following points.

[0010] The invention of Patent Document 1 is an overload control device for a capacitor-started single-phase induction motor, and uses whether an overload current flows continuously for more than a predetermined time as a criterion for determining an overload. The overload control device for a single-phase induction motor described in Patent Document 1 has the problem of being unable to be used under the severe conditions targeted by the present invention. Even if operation frequently switches from pure single-phase run to capacitor run in a short period of time, it may be determined to be noise and not an overload.

[0011] The invention of Patent Document 1 excludes noise and temporary overloads from the judgment and claims to be able to make judgments without any problems, whereas the present invention does not aim to prevent such problems, but rather to make it possible to make an overload judgment even under conditions that cannot be made using conventional overload judgment methods, thereby expanding the range of overload judgments that can be handled.

[0012] Another object of the present invention is to provide a control method, a control device, and an electric chain hoist for a single-phase induction motor that can properly determine whether the single-phase induction motor is overloaded, whether the single-phase induction motor is capacitor-run or purely single-phase run. [Means for solving the problem]

[0013] In order to solve the above problems, the present invention provides a coil including a main coil, an auxiliary coil, a capacitor, and a drive circuit, wherein a current is supplied to the main coil from a single-phase AC power supply via the drive circuit, and a current is supplied to the auxiliary coil when the load current of the main coil is large. via the drive circuit and Current is supplied from the single-phase AC power supply via the capacitor When the power supplied to the main coil exceeds a predetermined overload determination threshold, an overload is determined. Control method for a single-phase induction motor Used in combination with (A), (1) to the following (3)10. A control method for a single-phase induction motor, characterized by employing one or more of the overload determination methods described above. (1) An overload determination threshold is set for the ratio of the time during which current is passed through the auxiliary coil to the operating time of the single-phase induction motor, and an overload is determined to have occurred when the ratio of the time during which current is passed through the auxiliary coil exceeds the overload determination threshold set for that ratio of the time during which current is passed through the auxiliary coil. (2) An overload determination threshold is set for the proportion of the time that current is passed through the auxiliary coil within a specified time, and an overload is determined to have occurred when the proportion of the time that current is passed through the auxiliary coil within the specified time exceeds the overload determination threshold set for that proportion of the time that current is passed. (3) An overload determination threshold is set for the cumulative value of the time that current is passed through the auxiliary coil within a specified time, and an overload is determined to have occurred when the cumulative value of the time that current is passed through the auxiliary coil within a specified time exceeds the overload determination threshold set for the cumulative value of the time that current is passed through. As mentioned above, (A), (1) to (3) The overload determination method described in may use only one of these overload determination methods, or may use any two or more of these overload determination methods. When using multiple overload determination methods, a final determination of an overload may be made on the condition that any one of the overload determination methods determines an overload, or on the condition that all of the overload determination methods determine an overload. According to the present invention, in a control method for a capacitor-start type single-phase induction motor, it is possible to accurately determine whether or not the single-phase induction motor is overloaded even in a region where the current in the main coil is unstable. In the present invention, a method for determining an overload is provided in which an overload determination threshold is set for the power supplied to the main coil. (A) and an overload determination method in which an overload determination threshold is set for the energization time of the other auxiliary coils. (1) or (2) or (3) By using this in combination, when a load that greatly exceeds the rated load is applied, it is possible to determine whether an overload exists based on the power value supplied to the main coil before determining whether an overload exists based on the current flow time of the auxiliary coil, thereby making it possible to more effectively prevent damage to the equipment.

[0014] The present invention also provides a motor comprising a main coil, an auxiliary coil, a capacitor, and a drive circuit, wherein a current is applied to the main coil from a single-phase AC power supply via the drive circuit, and a current is applied to the auxiliary coil. When the load current of the main coil is large Through the drive circuit and via the capacitor The current is supplied from the single-phase AC power supply. configured to supply and an overload determination means for determining an overload when the power supplied to the main coil exceeds a predetermined overload determination threshold. In the control device for a single-phase induction motor, (1) to the following (3) an overload determination means for determining an overload by one or more of the methods described in moreover It is characterized by having (A), (1) to (3) above As in the case of the control method for a single-phase induction motor, only one of the overload determination means according to the method described above may be used, or a plurality of overload determination means may be used. According to the present invention, in a control device for a capacitor-start type single-phase induction motor, it is possible to accurately determine whether or not the single-phase induction motor is overloaded even in a region where the current in the main coil is unstable.

[0015] The present invention also relates to an electric chain hoist comprising a load sheave with which a load chain engages and a single-phase induction motor that rotates the load sheave, the electric chain hoist comprising a control device for the single-phase induction motor. This electric chain hoist can accurately determine whether a suspended load is overloaded even in areas where it was previously impossible to determine whether an overload exists, and can safely stop the lifting of an overloaded load. [Effects of the Invention]

[0016] According to the present invention, it is possible to determine an overload even under conditions that cannot be determined by conventional overload determination methods, and the range of overload determination that can be performed can be expanded. As a result, it is possible to properly determine an overload in a single-phase induction motor. [Brief explanation of the drawings]

[0017] [Figure 1] 1 is a diagram showing a schematic circuit configuration of a single-phase induction motor according to the present invention; [Figure 2] FIG. 1 is a diagram showing a state of torque change from the start of a single-phase induction motor. [Figure 3] FIG. 1 is a diagram showing a schematic circuit configuration of a single-phase induction motor during capacitor run. [Figure 4] FIG. 1 is a diagram showing a schematic circuit configuration of a single-phase induction motor during pure single-phase running. [Figure 5] FIG. 1 is a diagram showing a state of torque change from the start of a single-phase induction motor. [Figure 6] 6A and 6B are diagrams for explaining overload determination of a single-phase induction motor according to the present invention. [Figure 7] 10A and 10B are diagrams for explaining overload determination of a single-phase induction motor according to the present invention. [Figure 8] FIG. 8 is an enlarged view of a part of FIG. 7. [Figure 9] FIG. 4 is a diagram showing a process flow for determining an overload of a single-phase induction motor according to the present invention. [Figure 10] 1 is a schematic system configuration diagram of an electric chain block using the present invention. [Figure 11] 1 is a diagram showing an electrical connection configuration of an electric chain block according to the present invention. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0018] An embodiment of the present invention will be described in detail below. Fig. 1 is a diagram showing a schematic circuit configuration of a single-phase induction motor for carrying out an overload determination according to the present invention. The single-phase induction motor includes a single-phase induction motor section 120 having a main coil ML with a U terminal and a V terminal at both ends and an auxiliary coil AL with an X terminal and a Y terminal at both ends within a stator S, an SSR power circuit 121, and a capacitor C. The SSR (solid-state relay) power circuit 121 includes three current-carrying paths 121a, 121b, and 121c, and electrical switch contacts 121d, 121e, and 121f are provided at intermediate portions of the current-carrying paths 121a, 121b, and 121c, respectively. By turning on and off the switch contacts 121d, 121e, and 121f, the input side (single-phase AC power supply 200 side) and the output side (single-phase induction motor section 120 side) are electrically connected and disconnected by the current-carrying paths 121a, 121b, and 121c, respectively. For ease of understanding, the contacts 121d, 121e, and 121f are shown here as being mechanically turned on and off, but in reality they are made up of non-contact elements (such as triacs). The forward / reverse rotation circuit of the motor, the current sensor, and the voltage sensor will be described in detail later.

[0019] The input side of current path 121a of SSR power circuit 121 is electrically connected to the input side of current path 121b, the output side end of current path 121a is connected to the U terminal of the main coil ML of single-phase induction motor unit 120, and the output side end of input / output terminal 121b is connected to the X terminal of the auxiliary coil AL of single-phase induction motor unit 120. The output side end of current path 121c is connected to the V terminal of the main coil ML. One end of capacitor C is electrically connected to the input side of current path 121c of SSR power circuit 121, and the other end is connected to the Y terminal of the auxiliary coil AL of single-phase induction motor unit 120. In the state shown in FIG. 1, i.e., all of switch contacts 121d, 121e, and 121f of current paths 121a, 121b, and 121c of SSR power circuit 121 are OFF, and single-phase induction motor unit 120 is stopped.

[0020] 3 shows the state in which the single-phase induction motor has started, with switch contacts 121d, 121e, and 121f of all current-carrying paths 121a to 121c of SSR power circuit 121 turned ON and single-phase power being supplied to single-phase induction motor section 120. Because capacitor C is connected in series with auxiliary coil AL, a rotating magnetic field is generated in stator S from a rotational speed of 0 due to the phase difference between the current flowing through main coil ML and the current flowing through auxiliary coil AL. This causes a rotor (not shown), which is rotatably supported opposite stator S, to rotate, starting single-phase induction motor section 120. This operation of a single-phase induction motor by energizing auxiliary coil AL with capacitor C connected in series in addition to energizing main coil ML, is referred to here as capacitor run, as mentioned above.

[0021] 4 shows the state in which, after the single-phase induction motor has started, the current in the main coil ML is detected to have decreased to a predetermined value, and the power supply to the auxiliary coil AL is stopped, causing the single-phase induction motor to operate with only the power supply to the main coil ML. In other words, after a predetermined time has elapsed since the start of the single-phase induction motor unit 120, the motor rotation speed increases and the current value in the main coil ML falls below the switching threshold, turning off the switch contact 121e of the current path 121b, and the single-phase induction motor operates in pure single-phase run mode as defined above.

[0022] As described above, when a single-phase induction motor is started in capacitor run mode and then switched to pure single-phase run mode after a predetermined time has elapsed, rated load operation under conditions such as low voltage, high temperature, or low temperature requires an output close to the maximum torque possible under pure single-phase run. To address this, the current value of the main coil ML at which the motor switches from pure single-phase run to capacitor run is set to prevent stalling in pure single-phase run mode. The SSR power circuit 121 switches to capacitor run mode by turning on the switch-on contact 121e of the current path 121b. When the motor rotation speed increases and the current in the main coil ML falls below the switching threshold, the switch-on contact 121e is turned off to return to pure single-phase run mode. When the current in the main coil ML exceeds the switching threshold again, the switch-on contact 121e is turned on to return to capacitor run mode. In this way, the single-phase induction motor is operated by frequently switching between capacitor run and pure single-phase run mode. If a single-phase induction motor is operated by frequently switching between capacitor run and pure single-phase run, it can continue to operate, but the current or power value will not be stable, and overload cannot be determined solely from the current value as in the past. In other words, there is a problem that the range in which OLL can be used is limited.

[0023] The problems with the operation of the conventional single-phase induction motor will be explained in more detail with reference to FIGS. 1 through 5. When all of the switching contacts 121d, 121e, and 121f of the current paths 121a, 121b, and 121c of the SSR power circuit 121 shown in FIG. 1 are switched from OFF to ON as shown in FIG. 3, the single-phase induction motor 120 begins operating at point I in FIG. 2, and its output torque increases as the rotational speed increases along the capacitor run of curve A in FIG. 2. Then, at point II, a predetermined distance beyond the peak of curve A of the capacitor run, the switching contact 121e of current path 121b is switched OFF. This causes the single-phase induction motor 120 to enter steady-state operation in pure single-phase run mode.

[0024] When a single-phase induction motor is operated as described above, output torque decreases when the motor is operated at the minimum guaranteed operating voltage or in high-temperature environments. Furthermore, load torque increases when the motor is operated at low temperatures. This issue is illustrated in Figure 5. When operating at rated load under low voltage and high temperature, a load torque C is required that is close to the maximum torque possible under the same conditions as pure single-phase run (curve B). Therefore, switching to pure single-phase run (curve B) at point II on capacitor run (curve A) may result in a torque that cannot be output for stable operation under pure single-phase run. Or, at low temperatures, the load on the motor may exceed the output torque expected under pure single-phase run (curve B). This causes the current in the main coil ML to exceed the switching threshold, necessitating a switch to capacitor run (curve A) at point III on pure single-phase run (curve B). This results in frequent switching between capacitor run and pure single-phase run. This results in unstable rotational speed, current, or power, making it impossible to determine overload based on current or power alone. However, operation at rated load is still possible. In this range, there is a correlation between the load magnitude and the operating time ratio of curve A for capacitor run and curve B for pure single-phase run, and this correlation can be used to determine overload. This makes it possible to determine overload even in operating ranges where overload detection was not possible with conventional OLL.

[0025] Therefore, in this embodiment, a threshold value is set for the power value of the main coil ML of the single-phase induction motor section 120 and a threshold value is set for the current flow time per unit time of the auxiliary coil AL, and when either the power value to the main coil ML exceeds the threshold value or the current flow time per unit time of the auxiliary coil AL exceeds the threshold value, the single-phase induction motor is determined to be overloaded and is controlled to stop.

[0026] 6A and 6B are diagrams illustrating thresholds for determining an overload of the single-phase induction motor unit 120. The auxiliary coil energization time ratio in FIG. 6A shows the voltage (V) supplied to the single-phase induction motor unit 120 on the horizontal axis and the energization time ratio (%) of the auxiliary coil AL on the vertical axis. The figure shows an example of an electric chain hoist compatible with a single-phase AC power supply with a rated voltage of 115V. 1W (250kg) indicates a rated load of 250kg. The energization time ratio (%) of the auxiliary coil AL indicates the ratio of the time that the auxiliary coil AL is energized to the time that the single-phase induction motor unit 120 is energized. Since the main coil ML is always energized when the single-phase induction motor unit 120 is energized, the auxiliary coil energization time ratio (%) (%) can be calculated by (the time that the auxiliary coil AL is energized) / (the time that the main coil ML is energized) × 100.

[0027] Figure 6A shows that when the voltage supplied to single-phase induction motor unit 120 is 110V or higher, it can operate without energizing the auxiliary coil AL, even when lifting a load with a rated load of 250 kg. On the other hand, when the voltage supplied to single-phase induction motor unit 120 is 100V, the auxiliary coil AL needs to be energized 7.5% of the time. The OLL threshold is 27% when the voltage supplied to single-phase induction motor unit 120 is 100V, and 15% when the voltage is 107V or higher. By determining the OLL threshold (overload determination threshold) based on the auxiliary coil energization time ratio for each supply voltage, it is possible to determine overload even in load ranges where capacitor run and pure single-phase run alternate.

[0028] The main coil power values ​​in Figure 6B show the voltage (V) supplied to the single-phase induction motor unit 120 on the horizontal axis and the power (W) of the main coil ML on the vertical axis. This figure shows an example of an electric chain hoist that is compatible with a single-phase AC power supply with a rated voltage of 115V. The main coil power (W) indicates the power consumed by the main coil ML. It is calculated by a microcomputer (not shown) based on the detected values ​​of a current sensor and a voltage sensor (not shown). Figure 6B shows that the single-phase induction motor unit 120 consumes approximately 350 W of power when the voltage supplied to it is between 110V and 120V, 410 W at 100V, and 380 W at 130V. Taking into account variations in power consumption (not shown), the OLL thresholds are set to 520 W at 100V, 470 W at 110V, and 440 W at 130V. It is difficult to accurately determine OLL when the supply voltage exceeds 110V using only the auxiliary coil current flow time ratio, but by defining an overload determination threshold based on the main coil power for each supply voltage, it is possible to accurately determine OLL even in this range.

[0029] Instead of determining an overload determination threshold for main coil power for each supply voltage, an overload determination threshold for main coil current may be determined for each supply voltage, and OLL determination may be performed. In this case, since the current value changes more significantly with each voltage than the power value, it is better to measure more voltages. In Figure 6B, the load power is measured every 5V to 10V to determine the threshold, but the load current may also be measured every 2V to 5V to determine the threshold.

[0030] In an electric chain block, the load sheave that meshes with the load chain is polygonal, which causes the load on the single-phase induction motor unit 120 to pulsate. Therefore, it is preferable to take into account the period of this pulsation and average the power consumption to use in OLL judgment.

[0031] Figure 7 is a schematic diagram illustrating a method for determining OLL based on the percentage of current-carrying time of the auxiliary coil AL. Figure 7(a) shows the current waveform detected by a current sensor in the main coil ML, Figure 7(b) shows the transition of the effective value (RMS) of the AC current, and Figure 7(c) shows the waveform of the current in the auxiliary coil AL detected by the current sensor. Figure 7(d) is a chart illustrating one method for determining OLL based on the percentage of current-carrying time of the auxiliary coil AL, showing a method for integrating the current-carrying time within a specified time and a method for determining OLL from the integrated value. The horizontal axis represents elapsed time, and the vertical axis represents the current-carrying time within the specified time. The current-carrying time percentage (rate) is calculated by dividing the time the auxiliary coil AL is energized by the time the main coil ML is energized. Replacing the current-carrying time percentage with the current-carrying time within a specified time for detection simplifies control. This method is shown in Figure 7. During operation, a single-phase induction motor energizes the main coil ML. On the other hand, the power supply to the auxiliary coil AL is controlled to be turned on and off, as shown in Fig. 7. By detecting whether or not the auxiliary coil AL is energized at short detection intervals and accumulating the number of times that power is detected within a specified time, it is possible to determine whether or not the proportion of power-on time has reached the overload determination threshold.

[0032] Figure 8 shows an expanded version of (c) and (d) from Figure 7, with an explanation of the OLL determination method. Figure 8(a) corresponds to Figure 7(c), and Figure 8(b) corresponds to Figure 7(d). In Figure 8(a), t1, t3, and t5 respectively indicate the times when current supply to the auxiliary coil AL begins, and t2, t4, and t6 respectively indicate the times when current supply stops.

[0033] 7, the chart is simplified and one ON / OFF threshold value for the auxiliary coil AL is used, but it is preferable to provide separate threshold values ​​for switching from OFF to ON and for switching from ON to OFF. Also, considering that the current value of the main coil ML fluctuates greatly immediately after switching, it is preferable to disable switching based on the current value for a short period of time immediately after switching.

[0034] In addition, in this chart, the percentage of the time that current is applied to the auxiliary coil AL is converted into the cumulative value of the time that current is applied to the auxiliary coil AL within a predetermined time period, and an overload (OLL) is determined to have occurred. As shown in FIG. 8, the cumulative time period is set to 0.3 seconds, and an overload (OLL) is determined to have occurred when the cumulative value of the time that current is applied to the auxiliary coil AL is 0.165 seconds or more, which is 55% or more. At time t1, current application to the auxiliary coil AL begins, and 0.09 seconds later, at time t2, current application to the auxiliary coil AL ends. The presence or absence of current application is detected at predetermined detection intervals (for example, one cycle of the AC power supply frequency, which is 0.02 seconds for 50 Hz), and the cumulative current application value increases in increments of this predetermined detection interval (0.02 seconds). Next, from time t3, current is supplied to the auxiliary coil AL, but before time t2, most of the current is outside the accumulated integration time at time t4, so the accumulated value increases by one unit (0.02 seconds), and from time t4 to time t5, the accumulated value decreases by one unit from time t4, and current continues to be supplied to the auxiliary coil AL from time t5 to time t6, and since time t3 is also within the accumulated integration time at time t6, the accumulated value also increases, and at time t6, the accumulated value reaches the overload judgment threshold (OLL judgment threshold), so it is judged to be an overload (OLL), and current supply to the main coil ML and auxiliary coil AL is stopped.

[0035] In this way, an overload (OLL) can be determined by detecting and integrating the presence or absence of current flowing through the auxiliary coil AL, which allows a small, inexpensive current sensor to be used for the auxiliary coil AL. Alternatively, instead of using a current sensor to detect the current through the auxiliary coil AL, it is also possible to make the determination using an internal signal in the control unit that indicates that the electrical open / close contact 121e is ON. The detection time and integration time can be changed as appropriate using parameters, etc.

[0036] The method for determining overload based on the current flow rate is as follows. (Power-on time rate) = (Auxiliary coil AL power-on time - constant) ÷ (Main coil ML power-on time) is calculated and compared with the OLL threshold value for judgment. The constant is a time determined taking into account the time for which power is supplied to the forced auxiliary coil AL at startup, and it is preferable that it can be set as an appropriate parameter. This effect makes it possible to reduce the influence of external noise, etc.

[0037] Another method for determining overload (OLL) is to determine the current-on time rate within a specified time. This method records the current flow to the auxiliary coil after the start-up time has elapsed, calculates the current-on time rate using a moving average, and compares the current-on time rate within a specified time with the OLL threshold to determine overload. This method has the effect of improving the accuracy of determination in the case of loads that pulsate periodically, such as electric chain hoists.

[0038] FIG. 9 shows a flow chart of a process for determining an overload of a single-phase induction motor. First, in step ST1, the single-phase induction motor is started using the capacitor run circuit shown in FIG. 3. After a predetermined time has elapsed, in step ST2, it is determined whether the power value of the main coil ML exceeds a threshold. If the result is YES, the process proceeds to step ST3, where the single-phase induction motor is stopped. If the power value of the main coil ML does not exceed the threshold in step ST2, the process proceeds to step ST4, where it is determined whether the integrated value of the power-on time of the auxiliary coil AL within a predetermined time exceeds the overload determination threshold. If the result is NO, the process proceeds to step ST2, where the above process is repeated. On the other hand, if the integrated value of the power-on time of the auxiliary coil AL exceeds the overload determination threshold (YES) in step ST4, the process proceeds to step ST3, where the single-phase induction motor is stopped. This process is performed by a microcomputer located on the SSR power circuit 121 side.

[0039] Figure 10 is a schematic diagram of an electric chain hoist 1 that uses a control method and control device for a single-phase induction motor according to the present invention. The electric chain hoist 1 is equipped with parts and devices such as a single-phase induction motor 10 for lifting and lowering a load, a friction clutch (clutch with overload prevention means) 11, an electromagnetic brake 27, a reduction gear mechanism 13, an SSR power circuit 121, and a control unit 25, and these parts and devices are adjusted so that each performs its function and are appropriately arranged inside the equipment casing 4. Reference numeral 2 denotes a load sheave (rotating means) arranged inside the equipment casing 4, and a load chain 3 for lifting and lowering a load (not shown) is wound around the load sheave 2.

[0040] In order for the electric chain hoist 1 to hoist and lower (raise and lower) a load, the load sheave 2 must be able to rotate in the hoisting direction (forward rotation) and the lowering direction (reverse rotation). While it is possible to change the configuration of the reduction gear mechanism 13 to rotate the load sheave 2 forward and reverse, in this case the SSR power circuit 121 is equipped with the forward and reverse rotation function.

[0041] FIG. 11 shows the electrical connection configuration of the control unit 25, SSR power circuit 121, electromagnetic brake 27, etc. of the electric chain hoist 1. Here, the SSR power circuit 121 has the function of rotating the single-phase induction motor 10 forward and reverse, and uses non-contact switching elements 21-1 to 21-5 as ON / OFF elements. The SSR power circuit 121 includes a control board 20. Two external wires 61 and 62 are provided on the input side of the control board 20, where the supply terminals Rt, St, and Tt of the control board 20 are located. The external wire 61 is connected to the supply terminals Rt and St, electrically integrating (short-circuiting) them, and one end forms a power supply terminal SP1 connected to the single-phase AC power source 200. The external wire 62 is connected to the supply terminal Tt and the starting capacitor C, electrically integrating (short-circuiting) them, and one end forms a power supply terminal SP2 connected to the single-phase AC power source 200.

[0042] Single-phase induction motor 10 is disposed on the output side of control board 20, where output terminals Ut, Vt, and Wt are disposed. Single-phase induction motor 10 is configured to include a main coil ML and an auxiliary coil AL, and one end U of main coil ML is connected to output terminal Ut of control board 20 via lead wire 66-1, and the other end V is electrically connected to the cathode of rectifier element D2 and the anode of rectifier element D4 of full-wave rectifier circuit 26 via lead wire 66-2. Furthermore, the cathodes of rectifier element D3 and rectifier element D4 of full-wave rectifier circuit 26 are electrically connected to one end of excitation coil 27a of electromagnetic brake 27, and the other end of excitation coil 27a is electrically connected to the anodes of rectifier element D1 and rectifier element D2 of full-wave rectifier circuit 26. Furthermore, the cathode of rectifier element D1 and the anode of rectifier element D3 of full-wave rectifier circuit 26 are connected to output terminal Wt of control board 20 via lead wire 67. One end Y of auxiliary coil AL is connected to output terminal Vt of control board 20 via lead wire 66-3, and the other end X is connected to one end of starting capacitor C. Non-contact switching element 21-1 controls ON / OFF the electrical connections between supply terminal Rt and output terminal Ut, non-contact switching element 21-2 controls ON / OFF the electrical connections between supply terminal St and output terminal Vt, non-contact switching element 21-3 controls ON / OFF the electrical connections between supply terminal Tt and output terminal Wt, non-contact switching element 21-4 controls ON / OFF the electrical connections between supply terminal Rt and output terminal Wt, and non-contact switching element 21-5 controls ON / OFF the electrical connections between supply terminal Tt and output terminal Ut.

[0043] Control board 20 is equipped with a main current sensor 28T that detects the main current flowing through main coil ML of single-phase induction motor 10, an auxiliary current sensor 28S that detects the auxiliary current flowing through auxiliary coil AL, and other sensors. A microcomputer 23 is mounted in control circuit block 25, which includes control power supply circuit 24. Operation signals SU and SD from operation unit 19, a main current detection signal IT detected by main current sensor 28T, and an auxiliary current detection signal IS detected by auxiliary current sensor 28S are input to control power supply circuit 24. Single-phase AC power is input to control power supply circuit 24 from single-phase AC power supply 200 via wiring 22-6 and 22-7. A voltage sensor (not shown) is also provided to detect the power supply voltage or the voltage output to main coil ML, and a voltage detection signal VT detected by this sensor is input to microcomputer 23.

[0044] When the winding push button switch 19a of the operation unit 19 is pressed, a winding signal SU is output to the microcomputer 23, and the microcomputer 23 processes the non-contact switching elements 21-1 and 21-3 to turn them ON (at this time, the non-contact switching elements 21-4 and 21-5 remain OFF), and at the same time, the non-contact switching element 21-2 is also controlled to turn ON for a certain period at start-up. Thereafter, the supply of current to the auxiliary coil AL is controlled by turning ON / OFF the non-contact switching element 21-2 based on the main current detection signal IT, and winding operation continues. Immediately after the supply of current to the auxiliary coil AL is switched, the current flowing through the main coil ML becomes unstable, so a time is provided during which the ON / OFF switching of the auxiliary coil AL by the main current detection signal IT is disabled. When the hoist pushbutton switch 19a is released and the hoist signal SU stops, the non-contact switching elements 21-1, 21-2, and 21-3 are controlled to OFF, the power supply to the electromagnetic brake 27 is also cut off, and the brake 27, which was open during hoisting operation, is activated. When the lowering pushbutton switch 19b is pressed, the lowering signal SD is output, and the non-contact switching elements 21-4 and 21-5 are controlled to ON through processing by the microcomputer 23 (at this time, the non-contact switching elements 21-1 and 21-3 remain OFF). At the same time, the non-contact switching element 21-2 is also controlled to ON for a certain period at startup. Thereafter, the energization of the auxiliary coil AL is controlled by turning ON / OFF the non-contact switching element 21-2 based on the main current detection signal IT, and the lowering operation continues. Immediately after the energization of the auxiliary coil AL is switched on, the current flowing through the main coil ML becomes unstable, so a time is provided during which the ON / OFF switching of the auxiliary coil AL by the main current detection signal IT is disabled. When the lowering push button switch 19b is released and the lowering signal SD stops, the non-contact switching elements 21-2, 21-4, 21-5 are controlled to be turned OFF and the power supply to the electromagnetic brake 27 is also cut off, so that the brake 27, which was released during the lowering operation, is activated.

[0045] During hoisting operation, the voltage signal VT and current detection signals IT and IS are monitored and hoisting control is performed based on the overload determination process flow in Figure 9 to prevent the lifting of an overload.

[0046] When control unit 25 detects winding signal SU, single-phase power is simultaneously supplied to the main coil ML and auxiliary coil AL of single-phase induction motor 10, causing single-phase induction motor 10 to begin forward rotation. One second after start-up, the main coil power is compared to determine whether it exceeds a power overload threshold. If so, power supply to single-phase induction motor 10 is stopped. If not, the auxiliary coil current duration is compared to determine whether it exceeds an overload threshold. If so, power supply to single-phase induction motor 10 is stopped. If not, the main coil power is compared to determine whether it exceeds the power overload threshold. This control is repeated as long as winding signal SU is detected. When winding signal SU disappears, power supply to single-phase induction motor 10 is stopped. As shown in Figures 6A and 6B, the power overload threshold and the current duration ratio overload threshold are predetermined for each voltage applied to the main coil ML.

[0047] Although an embodiment of the present invention has been described above, the present invention is not limited to the above embodiment, and various modifications are possible within the scope of the claims and the technical ideas described in the specification and drawings. [Explanation of symbols]

[0048] 1 Electric chain hoist 2 Load sheave 3 Load Chain 4. Device casing 6 Hooks 10 Single-phase induction motor 11 Friction clutch 13 Reduction gear mechanism 19 Control section 20 Control board 21-1, 21-2, 21-3, 21-4, 21-5 Non-contact switching elements 27 Electromagnetic Brake 120 Single-phase induction motor section ML main coil AL Auxiliary coil 121 SSR (Solid State Relay) Power Circuit 121a,121b,121c Current carrying path 121d, 121e, 121f Switching contacts 200 Single-phase AC power supply (commercial power supply) C capacitor

Claims

1. A control method for a single-phase induction motor, comprising: a main coil, an auxiliary coil, a capacitor, and a drive circuit; current is supplied to the main coil from a single-phase AC power supply via the drive circuit; and current is supplied to the auxiliary coil from the single-phase AC power supply via the drive circuit and the capacitor when the load current of the main coil is large; and the control method is characterized by employing one or more of the overload determination methods set forth in (1) to (3) below in combination with control method (A) for a single-phase induction motor, the control method determining an overload when the power supplied to the main coil exceeds a predetermined overload determination threshold. (1) An overload determination threshold is set for the ratio of the time during which current is passed through the auxiliary coil to the operating time of the single-phase induction motor, and an overload is determined to have occurred when the ratio of the time during which current is passed through the auxiliary coil exceeds the overload determination threshold set for the ratio of the time during which current is passed through the auxiliary coil. (2) An overload determination threshold is set for the proportion of the time during which current is passed through the auxiliary coil within a specified time, and an overload is determined to have occurred when the proportion of the time during which current is passed through the auxiliary coil within a specified time exceeds the overload determination threshold set for the proportion of the time during which current is passed through the auxiliary coil. (3) An overload determination threshold is set for the cumulative value of the time during which current is passed through the auxiliary coil within a predetermined time, and an overload is determined to have occurred when the cumulative value of the time during which current is passed through the auxiliary coil within a predetermined time exceeds the overload determination threshold set for the cumulative value of the time during which current is passed through the auxiliary coil.

2. A control device for a single-phase induction motor, comprising a main coil, an auxiliary coil, a capacitor, and a drive circuit, configured to supply current from a single-phase AC power supply to the main coil via the drive circuit, and to supply current from the single-phase AC power supply to the auxiliary coil via the drive circuit and the capacitor when a load current of the main coil is large, and further comprising overload determination means for determining an overload when power supplied to the main coil exceeds a predetermined overload determination threshold, A control device for a single-phase induction motor, further comprising an overload determination means for determining an overload by any one or more of the methods set forth in (1) to (3) below. (1) An overload determination threshold is set for the ratio of the time during which current is passed through the auxiliary coil to the operating time of the single-phase induction motor, and an overload is determined to have occurred when the ratio of the time during which current is passed through the auxiliary coil exceeds the overload determination threshold set for the ratio of the time during which current is passed through the auxiliary coil. (2) An overload determination threshold is set for the proportion of the time during which current is passed through the auxiliary coil within a specified time, and an overload is determined to have occurred when the proportion of the time during which current is passed through the auxiliary coil within a specified time exceeds the overload determination threshold set for the proportion of the time during which current is passed through the auxiliary coil. (3) An overload determination threshold is set for the cumulative value of the time during which current is passed through the auxiliary coil within a predetermined time, and an overload is determined to have occurred when the cumulative value of the time during which current is passed through the auxiliary coil within a predetermined time exceeds the overload determination threshold set for the cumulative value of the time during which current is passed through the auxiliary coil.

3. An electric chain hoist comprising a load sheave with which a load chain engages and a single-phase induction motor that rotates the load sheave, An electric chain block comprising the control device for a single-phase induction motor according to claim 2.

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