JPH0421379A - Inverter provided with positioning function - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention provides, when an AC motor whose speed is to be controlled, a pulse encoder which is interlocked with the AC motor, integration and comparison calculations of feedback pulse signals from the encoder and the motor The present invention relates to an inverter that has a simple positioning function for a mechanical load that does not require strict positioning accuracy, such as a truck driven by the electric motor, by using DC braking for the motor.

[Conventional technology]

Conventional positioning using this type of inverter is known as shown in the operational waveform diagram of FIG.

LS and L S z shown in Fig. 2 are the first and second stage limit switches, respectively, and are used to control the mechanical load driven by the AC motor whose speed is controlled by the inverter during the transition to a predetermined stop position. The distance of each switch setting position from the predetermined stop position is determined according to the deceleration and braking characteristics of the overall motor rotation system including the load. Regarding the rotational speed N of the electric motor, N is the steady operating speed, and NCI is the low speed setting speed (creeping speed) for the first stage deceleration at the start of positioning control.
, N=z is speed Nc+ and the load is limit switch L
S - This is the specified speed at the braking start point for the electric motor, which is obtained during the second stage deceleration at the predetermined deceleration rate, which is started upon reaching the Sz position.

Now, if it is assumed that the load reaches the position of the limit switch LS at time tI after the stop positioning command for the load is issued, then between time t and the following time t2, the inverter The output frequency is reduced to reduce the speed N of the motor to the above N or Ncl, and then, while operating at the speed N C+, the load is switched to the limit switch L.
When the position of Sz is reached at time t3, the speed is decelerated again at a predetermined temporal deceleration rate, and the speed is reduced to the speed Nc at time t4.
2, the operation of the inverter is stopped after that time to try to bring the load to a natural stop, or the inverter applies DC braking to the motor to try to stop the load. In addition, the equivalent C of the motor rotation system as a whole
Regarding D'', the deceleration characteristic shown by the solid line from time t4 to t5 is smaller than that corresponding to the deceleration characteristic shown by the dotted line from time t4 to t6.

[Problem to be solved by the invention]

However, depending on the positioning control using the conventional inverter as described above, there is a difference in the required stopping time and the stop position of the load according to GD2 of the overall rotating system including the load of the AC motor driven by the inverter. In this case, it was inevitable that the cart stopping positions would be considerably uneven due to the weight and weight of the loaded items. Furthermore, regarding the detection of the speed No. 2 that determines the braking start time t4 for the electric motor, since the speed is in an extremely low speed range, the occurrence of detection errors is unavoidable, which is one of the causes of the unevenness of the stop positions. In view of this, the present invention replaces the detection of the speed Nc2 with the detection of the transition distance from the limit switch LS, and makes the transition distance setting variable, thereby improving positioning accuracy and facilitating operation. The purpose of this invention is to provide an inverter with a positioning function.

[Means for Solving the Problems] In order to achieve the above object, the inverter with a positioning function of the present invention uses a pulse signal from a pulse encoder interlocked with the AC motor to be driven to control the speed of the AC motor to be driven. In the inverter, there is provided a pulse integrating means for inputting the pulse signal and integrating the number of input pulses thereof, a pulse number setting means, and an integrated pulse number outputted by the pulse integrating means that exceeds the number of pulses set by the pulse setting means. pulse number comparing means for performing a comparison calculation between the number of pulses so as to generate an output when the mechanical load driven by the electric motor is in the process of moving to a predetermined stop position, and when the mechanical load driven by the electric motor separately setting a calculation start command position located at a distance determined in accordance with the set number of pulses from , and decelerating the electric motor to a predetermined low speed according to the load stop positioning command to shift the load to a low speed;
When the load reaches the calculation start command position, the electric motor is decelerated again at a predetermined deceleration rate, and the pulse integration means, pulse number setting means, and pulse number comparison means are operated, and from then on, the pulse number as described above is The output signal of the pulse number comparison means, which is output when the integrated number of pulses exceeds the set number of pulses, starts direct current braking of the motor via the inverter to stop the load at a predetermined position. Further, in the course of decelerating the electric motor to a predetermined low speed via the inverter in response to a front rudder load positioning command, the electric motor including the load whose characteristics vary due to the temporal follow-up characteristic of the motor speed in response to the deceleration command of the inverter. A deceleration characteristic calculation means for sampling and calculating the deceleration characteristic of the overall rotating system within a predetermined short time is provided, and a predetermined number of pulses is determined by the pulse number setting means in accordance with the deceleration characteristic of the overall motor rotation system calculated and estimated by the calculation means. Automatic increase/decrease correction shall be performed.

[Effect]

In positioning control of a mechanical load such as a cart driven by an electric motor, CD2 of the entire electric motor rotation system including the load, and the rotation of the electric motor at the time when electrical input to the electric motor is cut off and braking control is started. The speed N is important, and the transition distance Lb from the braking start position of the load to its stop position is the speed N due to the braking of the electric motor.

It is defined as the distance required for complete consumption of the rotational energy corresponding to the above-mentioned GD". In other words, the above-mentioned CD"
, Nb, Lb, and braking method are closely related to each other, and in general, the required L
The speed Nb is set to follow in accordance with speed b.

On the other hand, as in the conventional method described above, if the speed N,
If the speed Nc2 is predetermined and fixed, for example, if the load is a truck, the GD will be the same when the vehicle is empty and when it is fully loaded.
Therefore, regardless of the braking method used, there will inevitably be a large difference in the distance. Furthermore, the speed Nb should originally be as small as possible, and in its detection, a relatively large error is unavoidable in relation to positioning accuracy, and this detection error also depends on the load stop position. This becomes a cause of the difference.

Now, as shown in FIG. 2, when deceleration is performed at a constant deceleration rate over time from the preset limit switch LS position, the deceleration characteristic starts from the speed N Cl + time t3 position shown in the figure. The speed Nc2 is obtained as a value after the elapse of time t4-t3 on the line.

Therefore, as long as the speed N C++ NCR and deceleration rate are specified, the sum of the rotation angles of the electric motor between the time t4 and the time La tx, and therefore the migration distance of the load corresponding to the sum of the rotation angles, can be uniquely determined. be done.

According to the above, the present invention starts integrating the number of output pulses of the pulse encoder interlocked with the electric motor from the time t3, and the cumulative number of pulses obtained by the integration is determined by the number of pulses that the electric motor should obtain during constant rate deceleration from the speed Ncl to Ne2 as described above. The time when the number of pulses corresponding to the total rotation angle is reached is regarded as the time t4, and at that time the motor speed is assumed to have been reduced to the Nc2, and DC braking to the motor via the inverter is started. That is, in determining the braking start timing, instead of directly detecting the rotation speed of the electric motor, calculation of the sum of the motor rotation angles by integrating pulse encoder output pulses is used.

Furthermore, the present invention provides a deceleration characteristic calculation value of the motor based on a deceleration command to the motor by the inverter and a calculation of the pulse encoder output pulse during a suitable short period during the deceleration period of the motor from speed N1 to Ncl. The GD2 is sampled and estimated from the difference between the GD2 and GD2, and the set pulse number corresponding to the total motor rotation angle is automatically increased or decreased according to the estimation result, and the braking start timing is automatically corrected in accordance with changes in the load condition. The purpose is to improve the positioning accuracy of the load.

Note that it is possible to perform various calculations such as the above-mentioned pulse calculation in a microprocessor that is shared with various calculations for controlling the inverter itself.

〔Example〕

Embodiments of the present invention will be described below according to the circuit diagram of FIG.
This will be explained with reference to the figures.

In FIG. 1, 1 is an AC motor that drives a mechanical load such as a truck, 2 is a pulse encoder linked to the motor, and 3 is an inverter that controls the speed of the motor and performs DC braking, and rectifies the AC power source. Section 31 and smoothing capacitor C7
It consists of an inverse converter 32 that converts direct current into the required alternating current, a positioning control circuit 33, and a speed control circuit (not shown).

Here, the positioning control circuit 33 controls a switch CI that is closed by a braking preparation signal Sbl that is illuminated after the load reaches the limit switch LS shown in FIG.
The switch C2 is opened in the same way as the switch CI, and the pulse number signal S output from the pulse encoder 2 is connected to the switch CI.
an integrating section 33a which receives and integrates the integrated pulse number signal P via the switch C2 and resets the integrated result by a reset signal Sr received via the switch C2; A comparison calculation is made with the pulse number signal P, and in the state of P≧Ps, the braking start signal Sb2 is generated.
and a comparison section 33b that emits the . The signal Sb2 is input to the speed control circuit (not shown) and instructs DC braking to the electric motor 1 via the circuit.

In addition, a set pulse number signal P that determines the braking start timing mentioned above.
6 is modified in accordance with a change in the deceleration characteristic of the motor rotating system as a whole due to a change in the load state, for example, the set pulse number corresponding to the rated load state is increased as the load is reduced;
The braking start timing is optimized.

The deceleration characteristic of the motor rotating system as a whole is calculated by a deceleration characteristic calculation circuit (not shown). The arithmetic circuit calculates the temporal change pattern of the motor rotation speed corresponding to, for example, a linear reduction command of the inverter output frequency by calculating the integrated value of the number of output pulses of the pulse encoder during a suitable short period of time while the reduction command continues. , calculate the time delay of the integrated value with respect to the reduction command, calculate the deviation from the value corresponding to the reference load state with respect to the time delay that varies depending on the load state of the load, and respond to the deviation. Then, the correction number ΔP8 for the pulse number signal P, including its polarity, is calculated and output.

Therefore, the pulse number signal P8 is generated by a reference pulse number setting section (not shown) that manually sets the reference pulse number Pso and a pulse number addition/subtraction calculation section (also not shown).
P,=P, using the correction signal ΔP. It is created as +ΔPS.

Furthermore, the various calculation sections and the calculation circuit can be integrally configured in a microprocessor together with the speed control circuit.

[Effects of the Invention] According to the present invention, in stop positioning control of a mechanical load such as a cart driven by an AC motor, the motor is controlled by an inverter that performs speed control using output pulses of a pulse encoder interlocked with the motor. In relation to determining when to start DC braking after deceleration control for a motor, instead of detecting when the motor reaches a predetermined low speed state, detecting the position of the load that should naturally be reached in the low speed state, and furthermore, Detection is performed by comparing the sum of rotation angles of the electric motor obtained by integrating the number of output pulses of the pulse encoder,
In addition, by automatically correcting the reference value for the comparison calculation according to the deceleration characteristics of the overall motor rotation system including the load, the load positioning can be adjusted without readjusting the position of the control limit switch in response to changes in the load. Further accuracy can be achieved.

Furthermore, by sharing the microprocessor provided for the speed control circuit of the inverter to perform various calculations related to the positioning, the inverter becomes larger and more expensive due to the addition of the above-mentioned simple positioning function. can be avoided.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, and FIG. 2 is an operation waveform diagram corresponding to positioning control according to the prior art.

Claims (1)

[Claims] 1) In an inverter that uses a pulse signal from a pulse encoder linked to the AC motor to control the speed of the AC motor to be driven, a pulse integration that receives the pulse signal as input and integrates the number of input pulses. means, a pulse number setting means, and a pulse number for performing a comparison operation between the pulse numbers so that the output is generated when the cumulative number of pulses output by the pulse integrating means exceeds the number of pulses set by the pulse setting means. and a comparison means, further comprising a computation start when the mechanical load driven by the electric motor is in the middle of transition to a predetermined stop position and is located at a distance determined according to the set pulse number from the predetermined stop position. A command position is separately set, and the motor is decelerated to a predetermined low speed according to the stop positioning command of the load to shift the load to a low speed, and when the load reaches the calculation start command position, the motor is reduced to a predetermined deceleration rate. Then, the pulse accumulating means, the pulse number setting means, and the pulse number comparing means are operated, and thereafter, when the pulse number integrated value becomes equal to or greater than the set pulse number, the pulse number comparison is outputted. An inverter with a positioning function, characterized in that DC braking of the electric motor via the inverter is started in response to an output signal of the means, and the load is stopped at a predetermined position. 2) In the inverter with a positioning function according to claim 1, in the course of decelerating the electric motor to a predetermined low speed via the inverter due to the stop positioning command of the load, from the temporal follow-up characteristic of the motor speed with respect to the deceleration command of the inverter. A deceleration characteristic calculation means is provided for sampling and calculating the deceleration characteristic of the motor rotation system as a whole including the load whose characteristics vary, within a predetermined short time, and according to the deceleration characteristic of the motor rotation system as a whole calculated and estimated by the calculation means. An inverter with a positioning function, characterized in that the pulse number setting means performs a predetermined automatic increase/decrease correction on the set pulse number.