Electricity: motive power systems – Positional servo systems – Program- or pattern-controlled systems
Reexamination Certificate
2002-09-04
2004-09-21
Masih, Karen (Department: 2837)
Electricity: motive power systems
Positional servo systems
Program- or pattern-controlled systems
C318S560000, C318S569000
Reexamination Certificate
active
06794842
ABSTRACT:
TECHNICAL FIELD
This invention relates to a servomotor drive control system for performing high-speed and high-accuracy synchronous operation between drive control units by optimized communications and inputting sensor information and performing high-response and high-accuracy machine control.
BACKGROUND OF THE INVENTION
FIG. 14
is a block diagram of a numerical control system in a related art, a kind of servomotor drive control system, for controlling drive control units by a numerical control unit of a command unit. Assuming that the numerical control unit is an upward unit and the drive control units are downward units, numerical control unit
10
and drive control units
12
and
13
are connected by a pair of communication lines made up of a downward communication line
1
and an upward communication line
2
. An acceleration sensor
112
and limit switches
113
and
114
are attached to a controlled machine, and machine information of error information, sequence information, etc., is sent to the numerical control unit
10
. The numerical control system configured as shown in
FIG. 14
synchronously operates the two drive control units
12
and
13
by one numerical control unit
10
and acquires machine information by a sensor and performs sequence control and emergency control. Data transmitted from a transmission section
20
of the numerical control unit
10
is communicated over the downward communication line
1
and is received at reception sections
22
and
23
of the drive control units
12
and
13
. Over the downward communication line
1
, control commands of position, speed, electric current, etc., servo parameters required for the drive control units to perform control, and warning and alarm signals given to the drive control units are communicated from the numerical control unit
10
to the drive control units
12
and
13
. Data transmitted from transmission sections
42
and
43
of the drive control units
12
and
13
is communicated over the upward communication line
2
and is received at a reception section
40
of the numerical control unit
10
. Over the upward communication line
2
, detection data of the drive control units such as position, speed, and electric current, the current state of each of the drive control units, and data of warning and alarm signals, etc., are communicated from the drive control units
12
and
13
to the numerical control unit
10
. The transmission data from the numerical control unit
10
is transmitted in synchronization with the control period of the numerical control unit
10
. The transmission timing of data from each of the drive control units
12
and
13
is kept in synchronization based on the data from the numerical control unit
10
and is scheduled based thereon, an example of which is shown in FIG.
15
. In
FIG. 15
, numeral
1000
denotes communication period of the numerical control unit
10
, numeral
1001
denotes data transmitted from the numerical control unit
10
, and numeral
1003
denotes data transmitted from the drive control units
12
and
13
.
The drive control unit
12
inputs a control command from the numerical control unit
10
, detection data of an encoder
101
attached to a motor shaft end, and detection data of a scale encoder
110
attached to the machine and performs servo control of a servomotor
100
. The drive control unit
13
inputs a control command from the numerical control unit
10
, detection data of an encoder
104
attached to a motor shaft end, and detection data of a scale encoder
111
attached to the machine and performs servo control of a servomotor
103
. As the numerical control unit
10
synchronously operates the drive control units
12
and
13
, the servomotors
100
and
103
drive ball screws
102
and
105
for moving a table
106
on which a workpiece
107
is placed, on the ball screws
102
and
105
.
After detecting data of the acceleration sensor
112
, the numerical control unit
10
transmits data to the downward communication line
1
and gives commands of position, speed, electric current, etc., to the drive control units
12
and
13
so as to prevent the machine from producing machine vibration and reduce overshoot at the machine position for improving the positioning accuracy.
When detecting some anomaly occurring in the system, the table
106
exceeding the moving range, and the limit switch
113
,
114
being turned on, immediately the numerical control unit
10
transmits emergency stop information to the drive control units
12
and
13
via the downward communication line
1
for stopping the drive control units
12
and
13
of the servomotors
102
and
103
.
By the way, to synchronously operate two axes or more in the numerical control system, if the numerical control unit
10
gives a control command to each of the drive control units
12
and
13
in an open loop, when a disturbance is applied to one axis in synchronous operation, a large synchronization error appears. Thus, the numerical control unit
10
in the related art calculates a command in synchronization based on the detection data of position, speed, electric current, etc., transmitted from the drive control units
12
and
13
and then transmits the command to the drive control units
12
and
13
, as described above.
However, if the numerical control unit
10
itself thus generates an error correction command, the preparation of the error correction command imposes a calculation load on the numerical control unit
10
and further the prepared command is a command delayed by one control period and for a disturbance like an impulse, a large synchronization error appears as a command is given in an open loop.
Thus, to prevent a disturbance like an impulse from causing a synchronization error to occur, as shown in
FIG. 16
, the drive control unit
12
is provided with a reception section
51
connected to the upward communication line
2
and receives at the reception section
51
the detection data of position, speed, electric current, etc., of the drive control unit
13
transmitted in accordance with the control period of the numerical control unit
10
and compares the received detection data with the detection data of the drive control unit
12
, thereby correcting the synchronization error before the next control period of the numerical control unit
10
. The system shown in
FIG. 16
is disclosed in JP-A-9-34520.
However, if the drive control unit
12
corrects the synchronization error as described above, the data of the drive control units
12
and
13
is transmitted in accordance with the control period of the numerical control unit
10
and therefore the period in which the drive control unit
12
can correct the synchronization error depends on the control period of the numerical control unit
10
and thus there is a limit to correcting of the synchronization error with good accuracy by the drive control unit
12
. To improve the control performance of the drive control unit, it is possible to shorten the control period of the numerical control unit; however, to provide the numerical control unit with high performance, complicated coordinate computation and control processing need to be performed for a larger number of control axes and it is not easy to shorten the control period.
For the drive control unit to perform control based on a plurality of pieces of sensor information, the drive control unit requires a large number of connectors, etc., for receiving detection data, but it is substantially impossible to provide the drive control unit with connectors, etc., for receiving detection data corresponding to sensors. Therefore, the numerical control unit
10
in place of the drive control unit inputs the detection data of the acceleration sensor
112
and generates a command. Thus, the command is delayed by one control period as in the synchronous operation described above and if machine information is acquired by the sensor, the control performance is not much improved and there is a problem of increasing the calculation load on the numerical control u
Masih Karen
Mitsubishi Denki & Kabushiki Kaisha
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