Electricity: motive power systems – Positional servo systems – Multiple mode systems
Reexamination Certificate
2003-05-08
2004-09-14
Ip, Paul (Department: 2837)
Electricity: motive power systems
Positional servo systems
Multiple mode systems
C318S594000, C318S590000, C318S611000, C318S603000
Reexamination Certificate
active
06791293
ABSTRACT:
TECHNICAL FIELD
This invention relates to a sensorless controller of a synchronous motor which performs positioning operation by utilization of a limit switch.
BACKGROUND ART
Many automatic warehouses, transfer machines, and machine tools are constructed so as to position a predetermined object at a predetermined position while a motor is used as a power source. Generally, two limit switches are used for positioning and are arranged in a specific manner; namely, a desired rotational speed is switched to a low rotational speed (e.g., a creep speed) in accordance with a signal output from a first limit switch provided at a deceleration start position, thus decelerating the motor. While the motor is in this decelerated state, the object is transported to a predetermined position. When the object has reached a predetermined position, the rotation of the motor is stopped in accordance with a signal output from the second limit switch provided at a stop operation start position.
FIG. 11
is a view showing various waveforms produced in conjunction with a simplified positioning method utilizing a limit switch in a deceleration circuit of a related-art motor described in, e.g., JP-A-60-223486.
FIG. 11A
is a waveform of a target speed;
FIG. 11B
is a waveform of a voltage output from a charge-and-discharge circuit;
FIG. 11C
is a waveform of a deceleration timing signal; and
FIG. 11D
is a waveform of a speed instruction.
In the drawings, reference symbol “a” designates a first limit switch provided at a deceleration start position; “b” designates a second limit switch provided at a stop operation start position; “v
1
” designates a voltage signal used for determining a deceleration timing; and “t” designates a time which lapses from input of a deceleration instruction until switching of a target rotational speed to a low speed.
Simplified positioning operation utilizing a limit switch provided in a deceleration circuit of a related-art motor will now be described by reference to FIG.
11
.
When an object has passed by the first limit switch “a” provided at the deceleration start position while being transported at high speed (or medium speed), the charge-and-discharge circuit performs sequential electrical discharge of an output voltage in accordance with a signal output from the limit switch “a” and with a voltage signal corresponding to a desired rotational speed. When the voltage output from the charge-and-discharge circuit has dropped to a voltage signal v
1
(FIG.
11
B), a deceleration timing signal changes from H to L (FIG.
11
C), thereby switching a target speed from high speed (or medium speed) to low speed (FIG.
11
A).
Deceleration operation is started in accordance with a speed instruction at the switching timing of the target speed. When the object has passed by the second limit switch “b” provided at the stop operation start position while being transported at low speed after having completed deceleration, the speed instruction is set to 0, thus halting rotation of the motor (FIG.
11
D).
A sensorless controller which controls an induction motor whose actual position information is unknown for reasons of “slippage” of the motor generally performs the above-described simplified positioning operation involving usage of the limit switch.
In contrast, a permanent magnet synchronous motor—which is more efficient, smaller, and easier to control than an induction motor and has become prevalent in the industry—requires current control corresponding to the position of a rotor for controlling torque. Since a position sensor, such as an encoder or resolver, is usually used, positioning of the synchronous motor is usually controlled by use of the position sensor.
If the position sensor can be removed, realization of a more compact, lighter-weight, and less-expensive motor and improvements in environment resistance and reliability can be achieved. Hence, research on various sensorless control of position is pursued.
JP-T-8-505996 describes a method for controlling an observer base of a permanent magnet synchronous motor as an example of related-art position-sensor-less control operation. Under this method, the position and speed of a rotor of a multi-phase brushless permanent magnet synchronous motor are controlled with high resolution. The values of position and speed of the rotor estimated by use of a measured stator phase current are used for desired adjustment of the position or speed of the rotor. Alternatively, the amount of voltage to be applied to respective stator phases is determined for issuing an instruction to the rotor such that the rotor follows a desired trace of position or speed.
Estimation of a position of the rotor to be performed in the case of sensorless control of the synchronous motor is for detecting the position of the motor within a cycle of electrical angle; that is, the position of a magnetic pole. Since the mechanical position of a shaft of the motor (i.e., a mechanical angle of the motor) is unknown (e.g., an electrical angle of a four-pole motor rotates twice within one cycle of the motor; that is, one cycle of a mechanical angle), controlling a mechanical position requires use of a contrivance. Moreover, when a synchronous motor is subjected to sensorless control, positions of magnetic poles are estimated by means of an electrical current flowing through the motor. Hence, when flow of an electric current is interrupted by stopping operation of a drive circuit when the motor is nonoperational, positions of magnetic poles cannot be estimated. If the shaft of the motor is rotated in this situation, there will arise a problem of positions of the magnetic poles being lost.
As mentioned above, sensorless positional control of the synchronous motor is difficult, and driving of a sensorless synchronous motor is usually employed for controlling a speed.
[Problems that the Invention is to Solve]
As mentioned above, the simplified positioning that is commonly employed by an induction motor and uses a limit switch requires two limit switches; that is, a limit switch to be used for starting deceleration operation, and another limit switch to be used for stopping operation. Moreover, the simplified positioning also presents a problem of complicated operation, such as positional adjustment of limit switches.
When a synchronous motor is to perform positioning control operation, the motor must be equipped with position sensors, thus adding to cost.
The invention has been conceived to solve such a problem, and a first object of the invention is to obtain a sensorless controller of a synchronous motor which positions a synchronous motor at a desired location without use of a sensor.
A second object of the invention is to obtain a sensorless controller of a synchronous motor which enables a reduction in the number of limit switches to be provided and facilitates adjustment of setting of the limit switches.
DISCLOSURE OF THE INVENTION
A synchronous motor sensorless controller of the invention includes a current sensor for detecting an electric current of a synchronous motor, a position-and-speed estimation device for computing an estimated speed of the synchronous motor and an estimated position of a magnetic pole through use of the current output from the current sensor, and a speed controller for controlling speed of the synchronous motor through use of a speed instruction and the estimated speed; and drives the synchronous motor without use of a rotational position sensor. The controller comprises reference position signal output means for outputting a reference position signal serving as a standard for positioning counting operation; a relative position counter which acquires an estimated position of a magnetic pole from the position-and-speed estimation device as a reference position simultaneously with resetting a summated value to zero when the reference position signal is input and which starts summation operation; and a speed instruction generator having a position controller which performs position control operation on the basis of a deviation be
Ip Paul
Mitsubishi Denki & Kabushiki Kaisha
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