Electricity: motive power systems – Plural – diverse or diversely controlled electric motors – Synchronizing or phasing control
Reexamination Certificate
1999-12-16
2001-12-04
Ro, Bentsu (Department: 2837)
Electricity: motive power systems
Plural, diverse or diversely controlled electric motors
Synchronizing or phasing control
C318S041000
Reexamination Certificate
active
06326747
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a device and a method for controlling synchronization where machine shafts are electrically-driven and in phased synchronism by plural, mutually accurate, electric motors. Such shafts may be found in conveyor systems, processing systems for resins and metals, and rotary presses.
2. Background of the Invention
When synchronization control is effected by electrically keeping mutual phases of plural electric motors (or mechanical shafts driven by those electric motors) unchanged, it is necessary to first match the “origins” (or starting points or reference points) of those electric motors or mechanical shafts, and then effect synchronization control.
For matching origins, a conventional method uses an origin detector provided on each electric motor or each rotating machine shaft to detect a machine origin. The electric motor is then interrupted, and the origins of all other electric motors are then detected. When detection of all origins for all motors is complete, synchronous operation is begun. In this way, a time of 30 to 50 seconds is required until the matching has been completed. This lengthens waiting time, causing poor working efficiency.
To solve such a difficulty, a recently proposed method matches the origins of plural electric motors in an improved manner, i.e., the matching of origins is achieved without once interrupting the electric motors during low rotational frequency operation.
FIG. 6
illustrates a prior art example in which matching of origins is effected during low rotational frequency operation of electric motors. In
FIG. 6
, two electric motors are exemplarily used in the matching of origins of plural electric motors for brevity of the description.
In
FIG. 6
, Mm, Ms
1
are electric motors in a master section and a slave section, Pm, Ps
1
are incremental encoders each coupled with the machine shafts driven by the electric motors, and Rm, Rs
1
are the rotating machine shafts driven by the electric motors. Machine origins Gm, Gs
1
are mounted on the machine shafts Rm, Rs
1
, which origins are detected by detectors Km, Ks
1
. The aforementioned master and slave electric motors Mm, Ms
1
are driven respectively by drivers Dm, Ds
1
and controllers Am, As
1
.
The aforesaid controller Am drives the electric motor Mm through the driver Dm following a rotational frequency instruction provided from a concentrated controller C by obtaining a rotational frequency signal through a rotational frequency detector Fm from a continuous pulse signal outputted by the aforementioned incremental encoder Pm, and feeding the rotational frequency signal back.
In the following discussion, the arrangement of the aforementioned controller As
1
of the slave section in
FIG. 6
will be described.
In the controller As
1
a rotational frequency instruction is detected by the rotational frequency detector Ss
1
from the pulse signal obtained from the aforementioned incremental encoder Pm of the master section. Further, a feedback rotational frequency of the slave section is detected from the incremental encoder Ps
1
and the rotational frequency detector Fs
1
of the slave section.
Herein, a cumulative counter Cs
1
is cleared when the aforesaid detector Km of the master section detects the machine origin, and counts a pulse train of the aforesaid incremental encoder Ps
1
of the slave section.
The counted value of the cumulative counter Cs
1
is stored in a Z correlation distance memory area Zs
1
with the aid of a switch RYs
1
, actuated when the detector Ks
1
of the slave section detects the machine origin. More specifically, the stored value in the Z correlation distance memory part Zs
1
indicates a Z correlation distance &Dgr;&thgr; obtained by measuring the phase difference of the mechanical origins of the master and the slave with the number of pulses of the aforesaid Ps
1
of the slave section.
When the origins are matched, two electric motors are actuated and run at a low rotational frequency with a rotational frequency instruction of the aforesaid centralized controller C. In the slave section, the z correlation distance &Dgr;&thgr; is read out from the z correlation Zs
1
in the operation at the low rotational frequency, and &Dgr;&thgr;/&Dgr;T is calculated in order to adjust the time &Dgr;T and a correction value of the &Dgr;&thgr;/&Dgr;T is subtracted from the rotational frequency instruction by the aforesaid rotational frequency detector Ss
1
of the slave section. The correction is executed for the time &Dgr;T with the switch RYs
2
.
Two electric motors are matched in origins thereof by adjusting the rotational frequency of the slave section as described above, and are changed over to synchronization control and then accelerated into ordinary rotational frequency operation.
The prior art method and apparatus however suffer from difficulties that even when the origin matching is effected while operating the electric motors, the Z correlation distance &Dgr;&thgr; is detected by allowing the electric motors of the master and slave to rotate by one revolution or more, so that much time is required for the detection, and it takes 20 to 40 seconds until the origin matching is completed.
Further, in order to detect the Z correlation distance &Dgr;&thgr; it is needed that the rotational frequency of the master and slave electric motors are stabilized and they are operated at the same rotational frequency to the utmost, so that the origin matching must be done at a low rotational frequency, which causes a complicated adjustment.
Furthermore, when there are electric motors under operation and electric motors under interruption and the electric motors under interruption are started for synchronization control, the electric motors already in operation must be operated once at a low rotational frequency for the origin matching, and hence an operation procedure is complicated and much time is required.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a synchronization control device and a synchronization control method in which it is capable of achieving origin matching in a short time continuously in operation of the electric motors without once interrupting the electric motors whether they are operated at low rotational frequency or normal rotational frequency and is capable of shifting the operation to ordinary synchronization operation, and in which it is capable of, even when synchronization operations for electric motors are performed in ordinary operation and for stopped electric motors, starting the stopped electric motors to achieve origin matching in the operation of the electric motors to continuously shift the operation to ordinary synchronization operation without bringing the electric motors in operation into a low rotational frequency.
According to the present invention, for synchronization control of machine shafts driven by electric motors, one electric motor is disposed in a master section and the other one or plural electric motors is or are disposed in a slave section. A rotary encoder composed of an absolute encoder or an incremental encoder with a Z phase pulse is provided on the electric motors of the master section and the slave section or on machine shafts driven by the electric motors to output a signal in response to rotation of the electric motor or the machine shaft. For the aforesaid rotary encoder there may be employed one attached to each electric motor (rotary encoder mounted on the electric motor for detecting rotation of the electric motor), and the rotary encoder may be coupled with a machine shaft connected with a rotary shaft of each electric motor or coupled with a machine shaft connect through a gear and the like.
The electric motor of the master section is driven by ordinary rotational frequency control. A controller of the electric motor of the slave section detects at all times both a rotational frequency and a rotation phase of the aforesaid electric motor or the machine shaft based upon a signal from the rotary encoder o
Fukushima Keiichi
Kotani Ikuo
Mitsuhashi Takeshi
Shiba Noriyuki
Bierman, Muserlian and Lucas
Kabushiki Kaisya Tokyo Kikai Seisakusho
Ro Bentsu
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