JP2001151464A - Motor starting control system for traversing inverter driven hoist - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve a problem that a case where a motor is not started due to insufficiency of starting torque is considered when a traversing device of an inverter hoist is used on a curved path of an extremely small diameter, for instance, when load is larger than estimated load when the traversing device of the inverter hoist by a conventional technique is considered, and a failure to be an extremely bad efficient using method occurs because required current or more is supplied to the motor also when load torque is small like a straight path when an inverter control is set on the assumption that the device is used on the curved path of the extremely small diameter. SOLUTION: An operating state of a motor is detected by an encoder mounted on a traversing motor. When the motor is not started, although voltage is impressed on the motor, an increase in an output frequency of an inverter is stopped and output voltage is automatically and gradually increased till the motor is started.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for controlling the output voltage of an inverter at the time of starting a traversing motor in a hoist using the inverter.

[0002]

2. Description of the Related Art When a traverse motor of a hoist is controlled by an inverter, the operation is started at a low speed in order to perform a cushion start, and the output frequency of the inverter is increased to a set rotation speed of the traverse motor at a certain constant increase rate. This accelerates the traversing motor at a constant rate. At this time, the relationship between the output frequency and the output voltage of the inverter is set such that the output voltage increases as the frequency increases, as shown in FIG. This is to perform V / f constant control so that the exciting current of the induction motor is always constant regardless of the output frequency. At low frequencies, the voltage is reduced because the impedance ωL of the stator winding of the induction motor becomes small. Theoretically, the relationship between the output frequency and the output frequency is proportional as shown by the dotted line in Fig. 2. However, the effect of the motor's primary voltage drop can be ignored in the low frequency range near the motor operation start frequency (starting frequency). Therefore, the output voltage is corrected as shown by the solid line in FIG. 1 in the low frequency range. The output frequency and output voltage pattern (V / f
Pattern) is determined from the characteristics of the motor and the load characteristics. Since the output torque of the motor is substantially proportional to the applied voltage, a higher output voltage can be obtained by setting the output voltage higher even in a low frequency range. However, if the voltage is set too high and the excitation current is increased, the stator core is magnetically saturated, resulting in an overexcitation state, which makes it impossible to obtain an increase in output torque as compared with an increase in current consumption, resulting in poor efficiency. Therefore, the V / f pattern is set so that the motor is operated in an optimum state in consideration of the characteristics of the motor, the required output torque and the efficiency.

[0003]

According to the prior art, the V / f pattern of the inverter is uniquely set in consideration of the load characteristics assumed for the motor efficiency. Therefore, when considering the hoist traversing device, when the load is larger than the assumed load, for example, when used on a curved road with an extremely small diameter, the starting torque of the motor may be insufficient and the motor may not start. At this time, the inverter will increase the output frequency and output voltage at a constant acceleration even if the motor does not start, so eventually the energization will stop due to overcurrent detection, the hoist will stop, and in the middle of the curved road Get stuck. On the other hand, if the V / f pattern is set in advance on the premise that the motor will be used on a curved road with an extremely small diameter, an excessive current will be supplied to the motor even when the load torque is small such as a straight road. This causes a problem that the usage is extremely inefficient.

An object of the present invention is to change the output torque of a traversing motor in a hoist traversing device according to a required starting torque on a curved road, a straight road, or the like.
An object of the present invention is to provide an efficient hoist traversing device capable of always obtaining a stable starting characteristic.

[0005]

In order to achieve the object of the present invention, an operation state of the motor is detected by an encoder attached to the traversing motor, and the motor is started even though voltage is applied to the motor. In such a case, the output frequency of the inverter is stopped from increasing and the output voltage is automatically gradually increased until the motor starts.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 3 is a block diagram showing a configuration of a traversing portion of an inverter drive hoist according to an embodiment of the present invention, and FIG. 4 shows a processing flow of a program for automatically increasing the output voltage of an inverter.

The operating state of the traversing motor 3 is monitored by the control unit 5 based on an encoder signal. The control unit 6 determines an operation state and gives a drive command (a drive command based on an output frequency and an output voltage) to the power unit 2, and the power unit 2 performs switching based on the drive command on the voltage converted into DC by the converter unit 1. By performing the operation (PWM control), the output frequency and the output voltage commanded by the control unit 5 are applied to the traversing motor 3.

The control unit 5 generates an output frequency and an output voltage command by a microcomputer operation according to the processing flow shown in FIG. After the energization of the traversing motor 3 is started, first, the input of the encoder signal is confirmed by the decision branching process of S1. When there is no input of the encoder signal, it means that the motor cannot be started due to insufficient starting torque of the motor although the motor is energized. In this case, the V / f pattern is changed to stop the increase in the output frequency of the inverter and output a voltage higher than the voltage currently output by the processing of S3 and S4. For example, when the operation is performed in the V / f pattern 1 in FIG. 1 but the traversing motor 3 cannot be started, a process of switching the voltage command to the V / f pattern 2 is performed. The V / f pattern switching process, that is, the processes of S2 and S3 in FIG. 4 are repeated until the traversing motor 3 starts (until an encoder signal input is detected).

After the start of the motor is detected,
Based on the V / f pattern, the process of S2 for restarting the process of increasing the output frequency of the inverter (the process of accelerating the motor) is executed. This series of processing is executed every time the traversing motor is started. As a result, the voltage applied to the traversing motor
The V / f pattern shown in FIG. 1 depends on the magnitude of the load torque.
Pattern 1 is automatically selected from V / f pattern n, and it is possible to select the minimum applied voltage command necessary for starting the traversing motor. Therefore, the minimum voltage required for starting is always applied to the traversing motor according to the state of the load, and an efficient starting operation can be obtained without consuming unnecessary current.

It should be noted that increasing the voltage command indefinitely in a state where the start of the motor is not detected leads to overcurrent destruction of the apparatus. Therefore, it is necessary to monitor the current by the current detection unit 6 in FIG. 3 and provide overcurrent protection. Protects against abnormalities such as motor lock.

[0011]

According to the present invention, in the traversing device of the inverter hoist, it is possible to automatically change the applied voltage to the traversing motor in accordance with the required starting torque, and to change the output torque. Efficient hoist traversing operation that can always obtain stable starting characteristics can be realized.

Particularly, in a hoist system in which a straight path and a curved path in a traverse track are mixed, an efficient start-up operation of the traverse motor can always be realized.

[Brief description of the drawings]

FIG. 1 is a diagram showing an output frequency and an output voltage (V / f pattern) of a traversing motor inverter according to the present invention.

FIG. 2 is a diagram showing an output frequency and an output voltage (V / f pattern) of a conventional traversing motor inverter.

FIG. 3 is a block diagram showing a control configuration of a traversing motor according to the present invention.

FIG. 4 is a processing flowchart of generating a voltage command (V / f pattern) according to the present invention.

[Explanation of symbols]

1 ... converter part, 2 ... power part, 3 ... traversing motor,
4 encoder, 5 control unit, 6 current detection unit.

Claims (1)

[Claims] An inverter-driven hoist comprising a traversing motor having an encoder for detecting a position or a speed, wherein a rotation of the motor is detected by an encoder when starting the traversing operation of the hoist, and a starting torque of the motor is obtained. An inverter-driven hoist characterized by automatically increasing the output voltage of the inverter to increase the starting torque of the motor and start the motor when starting is impossible due to insufficient power.