Electricity: motive power systems – Synchronous motor systems
Reexamination Certificate
2000-02-23
2001-08-14
Masih, Karen (Department: 2837)
Electricity: motive power systems
Synchronous motor systems
C318S567000, C318S569000, C318S600000, C318S717000, C318S723000
Reexamination Certificate
active
06274997
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a synchronous control device for electric motors and machine axes driven by electric motors in a conveying device.
2. Description of the Related Art
When synchronizing a plurality of electric motors or machine axes driven by electric motors to keep the electrical phases thereof in the same relation to each other, a common rotational frequency reference is set, and correction of the synchronous control is made by using a deviation between the frequency signal corresponding to the rotational frequency reference and the frequency signal of a rotary encoder of the electric motor.
In the prior art, the signal formation and detecting method of the main control loop for the rotational frequency reference is independent from the correction loop for frequency deviation, so that a time lag between them occurs and highly accurate synchronous control is very difficult.
FIG. 7
shows a conventional synchronous control device for a plurality of electric motors, for example, two electric motors.
In
FIG. 7
, Cm is a concentrated control device of a master section. In the concentrated control device Cm, Sm is a rotational frequency setting device, Tm is an communication interface which sends out the rotational frequency setting signals from the rotational frequency setting device. The rotational frequency setting signals are sent to a slave section through a communication line
1
.
Fm is a frequency signal generator which inputs the rotational frequency setting signals output from the rotational frequency setting device Sm and which generates frequency signals proportional to the rotational frequency setting input. The output from Fm is sent to the slave section through a signal line
2
. Now, in the following explanation, a line which transmits signals transformed to the serial signals from the digital signals is called a communication line, and a line which sends pulse signals as they are is called a signal line.
Further, Cs
1
and Cs
2
are slave section control devices, As
1
and As
2
are driving devices of electric motors of the slave section, Ds
1
and Ds
2
are electric motors in the slave section, Rs
1
and Rs
2
are rotary encoders added to the electric motors, Gs
1
and Gs
2
are transmission devices, Ks
1
, Ks
2
are machine axes driven by electric motors of the slave section.
The slave section control device Cs
1
and Cs
2
are composed of the same components, so that, in the following explanation, only the slave section control device Cs
1
is explained, but the components of the slave section control device Cs
2
are similarly numbered.
In
FIG. 7
,
11
is a communication interface, which receives the rotational frequency setting signals output from the communication interface Tm in the master section, and stores them into the rotational frequency reference storing means
12
as the master rotational frequency setting signals.
15
is a rotational frequency feedback detector, which detects feedback rotational frequency from the frequency signals output from the rotary encoder Rs
1
in the slave.
13
is a frequency deviation counter, which up-counts the frequency signals from the frequency generator Fm in the master section, and detects the deviation by down-counting the frequency signals from the rotary encoder Rs
1
in the slave section.
These outputs of the frequency deviation counter
13
are added or substituted to the master rotational frequency setting signals output from the rotational frequency reference storing means
12
through a proportional integration amplifier
14
(in the following, referred to PI) as correction signals, further calculated with the rotational frequency feedback signals output from the rotational frequency feedback detector
15
and sent to the driving device As
1
.
That is, the master rotational frequency setting signals are corrected based on the output of the frequency deviation counter
13
(frequency deviation), and rotational frequency and phase of the electric motor Ds
1
, Ds
2
in the slave section Cs
1
, Cs
2
are controlled based on the deviation between said corrected rotational frequency setting signals and rotational frequency feedback signals.
In the conventional method, the signal formation and the detecting method of the main control loop of the rotational frequency reference and the correction loop of the frequency deviation in the slave section are different, so that the time lag is inevitable and a highly accurate synchronous control is very difficult.
These are explained in
FIG. 8
further.
In
FIG. 8
,
1
is a reference signal which is output from the communication interface Tm in the concentrated control device of the master section Cm in
FIG. 7
, received and detected in the communication interface
11
set in the rotational frequency slave section control device, and stored in the rotational frequency reference storing means
12
. Further in
FIG. 8
,
2
is a frequency signal which is sent from the frequency generator Fm in the master section Cm in
FIG. 7
, and input to the frequency deviation counter
13
set in the slave section.
As shown in
FIG. 8
, the reference signal
1
and the frequency signal
2
are different in the signal form and the detecting method is also different, so that the time lag occurs although they should be overlapped in essence.
Moreover, in
FIG. 8
, times t
1
, t
2
, t
3
. . . show timings to implement synchronous control processing in the slave section. At time t
2
, corresponding to a point A of the reference signal
1
, the frequency signal
2
should agree with A′. However, the frequency signal
2
is controlled by using the value at B point, because of the time lag caused by the difference of a generated method and a transmission path between reference signal
1
and frequency signal
2
. That is, &Dgr;F in
FIG. 8
is occurred in the synchronous loop as an error in the synchronous control, so that a highly accurate synchronous control is difficult.
SUMMARY OF THE INVENTION
This invention is developed for resolving the problem. The present invention provides an accurate synchronous control without causing the time lag by detecting the rotational frequency and phase simultaneously and perpetually with the same signals in the synchronous control of a plurality of electric motors.
A master section outputs phase signals or frequency signals based on rotational frequency reference. A slave section detects master rotational frequency setting signals and master phase setting signals simultaneously and perpetually by using the phase signals or frequency signals from the master section, and detects rotational frequency feedback signals and phase feedback signals simultaneously and perpetually based on output of a rotary encoder attached to an electric motor or connected to an machine axis driven by the electric motor, then detects phase deviation perpetually out of the master phase setting signals and the phase feedback signals.
The electric motor of the slave section or the machine axis driven thereby is synchronously controlled based on the phase deviation, said master rotational frequency setting signals and said rotational frequency feedback signals.
Also, the master section may provide a control device for controlling the electric motor, and a means for sending frequency signals outputted from a rotary encoder attached to the electric motor or a rotary encoder connected to an machine axis driven by the electric motor to the slave section, according to the present invention.
The feature and advantage of the present invention will be apparent from the following mode for implementing the invention with following accompanying drawings.
REFERENCES:
patent: 3974428 (1976-08-01), Hafle
patent: 5541781 (1996-07-01), Barr et al.
patent: 56-081093 (1981-07-01), None
patent: 62-122987 (1987-06-01), None
patent: 03245790 (1991-11-01), None
patent: 09248978 (1997-09-01), None
Kotani Ikuo
Shiba Noriyuki
Bierman, Muserlian and Lucas
Kabushiki Kaisha Tokyo Kikai Seisakusho
Masih Karen
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