Electricity: motive power systems – Positional servo systems – Program- or pattern-controlled systems
Reexamination Certificate
2001-12-05
2004-04-20
Salata, Jonathan (Department: 2837)
Electricity: motive power systems
Positional servo systems
Program- or pattern-controlled systems
C318S560000, C318S567000
Reexamination Certificate
active
06724167
ABSTRACT:
TECHNICAL FIELD
This invention relates to a numerical control drive system and in particular to a numerical control drive system having a servo drive unit for driving a motor, a drive unit such as a spindle drive unit, a numerical control unit for outputting a control command for driving the motor to the two or more drive units, and a motor drive power converter for converting AC power into DC power and supplying the DC power to the two or more drive units.
BACKGROUND OF THE INVENTION
FIG. 16
is a drawing to show the configuration of a numerical control (NC) drive system in a related art. In the Figure, numeral
41
denotes an AC power supply, numeral
42
denotes an AC reactor, numeral
43
denotes a motor drive power converter, numeral
44
denotes a spindle drive unit, numeral
45
denotes a spindle motor driven by the spindle drive unit
44
, numeral
46
denotes a servo drive unit, numeral
47
denotes a servo motor driven by the servo drive unit
46
, numeral
48
denotes an NC unit, and numeral
49
denotes a bus line. Numeral
50
denotes an AC-DC conversion circuit, numeral
51
denotes a diode, numeral
52
denotes a power module, and numeral
53
denotes a smoothing capacitor.
The motor drive power converter
43
rectifies AC power (L
1
, L
2
, L
3
) input via the AC reactor
42
from the AC power supply
41
to direct current through the diode
51
, further smoothes the direct current through the smoothing capacitor
53
to produce DC power supply voltage VP, VN, to the spindle drive unit
44
and the servo drive unit
46
. The spindle drive unit
44
and the servo drive unit
46
input the DC power supply voltage VP, VN and drive the spindle motor
45
and the servomotor
47
based on a position command from the NC unit
48
.
When the servomotor
47
or the spindle motor
45
performs power running at the acceleration time, the AC-DC conversion circuit
50
rectifies alternating current to direct current and through the diode
51
supplies power. When the servomotor
47
or the spindle motor
45
runs in a regenerative mode at the deceleration time, the power module
52
switches so as to return the power to the AC power supply
41
.
In recent years, with productivity improvement of a tool machine and development of technologies, shortening of the acceleration/deceleration time constant in a rapid feed mode and shortening of the cycle time have been demanded and further a larger torque (electric current) has been demanded at the acceleration/deceleration time and a servo drive unit and a spindle drive unit have been put into a high gain.
The demands for providing a high torque and a high gain described above have resulted in severe operating conditions of thermal stress of excessive current and power cycle in the motor drive power converter for supplying power to the servo drive unit and the spindle drive unit, and the capacity of the motor drive power converter has been increased as measures against heat of a diode and a power module and thus there are problems of upsizing and an increase in costs.
FIG. 17
is a block diagram of a variable-speed controller of an AC motor in a related art described in Japanese Patent Laid-Open No.85085/1986. In the Figure, numeral
61
denotes a motor for driving load of a fan, a pump, etc., numeral
62
denotes a position sensor being attached to the motor
61
for detecting the number of revolutions of the motor
61
, and numeral
63
denotes an AC variable-speed drive for operating the motor
61
at variable speeds, an AC power supply being connected to the primary side of the AC variable-speed drive via a current transformer
64
. Numeral
65
denotes is an overcurrent relay being connected to the secondary side of the current transformer
64
for stopping the operation of the AC variable-speed drive
63
to protect the motor if the motor is operated or accelerated in such a manner that the primary current value of the operation of the AC variable-speed drive
63
exceeds a rated value, and numeral
66
denotes a speed reference controller for setting speed reference. Numeral
67
denotes a current comparison controller for comparing the input current with a preset current limit value based on the input current supplied via the current transformer
64
to the AC variable-speed drive
63
and the number of revolutions of the motor input from the position sensor
62
, and sends a control signal to the speed reference controller
66
.
In a self-cooled motor with the cooling effect changing in response to the number of revolutions, the cooling effect changes in response to the number of revolutions and the current value limited from the heat resistance amount of the motor changes. A variable-speed controller of an AC motor in a related art is adapted to operate the motor within predetermined current limit values without stopping the motor by presetting the current limit value at the rated operation time and the current limit value at the acceleration time in all variable-speed area from the relationship between the cooling effect responsive to the number of revolutions and the heat resistance amount and when the input current reaches the current limitvalue at the related operation time in the rated operation mode, decreasing the number of revolutions of the motor for lowering the input current or when the input current reaches the current limit value at the related operation time in the acceleration operation mode, limiting an increase in the input current for temporarily stopping the acceleration.
In the variable-speed controller of an AC motor in the related art described above, if the input current of the AC variable-speed drive exceeds the rated value, the operation thereof is stopped by means of the overcurrent relay for protecting the motor or when the input current of the AC variable-speed drive is compared with the preset current limit value and the input current reaches the current limit value, the input current is lowered or an increase in the input current is limited, whereby protection against overheating is conducted without stopping the motor, namely, protection of the variable-speed controller is accomplished singly. In the whole NC drive system made up of the spindle drive unit
44
for driving the spindle motor
45
, the servo drive unit
46
for driving the servomotor
47
, etc., as shown in
FIG. 16
, if the spindle drive unit
44
or the servo drive unit
46
is equal to or less than the allowable current, whether or not an overcurrent occurs as the whole NC drive system cannot be determined; this is a problem.
The invention is intended for solving the problems as described above and it is an object of the invention to provide an NC drive system capable of performing stable motor control without increasing the capacity of a background motor drive power converter even in high-speed, high-acceleration drive.
DISCLOSURE OF THE INVENTION
According to the invention, there is provided a numerical control drive system having two or more drive units consisting of a servo drive unit for driving a motor, a spindle drive unit, etc., a numerical control unit for outputting a control command for driving the motor to the two or more drive units, and a motor drive power converter for converting AC power into DC power and supplying the DC power to the two or more drive units, wherein
the motor drive power converter comprises input current detection means for finding an input current, input current determination means for comparing the input current found by the input current detection means with an allowable current value with respect to less-than, equal-to, or greater-than relation, and control signal output means for outputting a control signal to the drive unit based on the determination result of the input current determination means, wherein the drive unit comprises control signal execution means for changing the control command from the numerical control unit based on the control signal output from the control signal output means, and wherein
if the input current determination means determines that the input current is
McCloud Renata
Mitsubishi Denki & Kabushiki Kaisha
Salata Jonathan
Sughrue & Mion, PLLC
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