Electricity: motive power systems – Positional servo systems
Reexamination Certificate
2000-01-10
2001-06-26
Nappi, Robert E. (Department: 2837)
Electricity: motive power systems
Positional servo systems
C318S700000, C318S713000, C318S807000, C318S809000, C318S801000
Reexamination Certificate
active
06252367
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a servo controller for controlling an AC servo motor and an AC spindle motor used as a driving source for a machine tool, an industrial machine, a robot and the like which are controlled by a numerical control (NC) device.
2. Description of the Related Art
A machine tool sometimes uses a synchronous motor for a feed axis for positioning and an induction motor for a spindle in combination. Further, in a vertical-type lathe, when a particular table-feed axis is to be driven in a machining mode putting emphasis on power and also in a positioning mode putting emphasis on efficiency, a synchronous motor and an induction motor are sometimes used by being changed over for each mode.
Generally, in driving the synchronous motor, position of the magnetic pole is determined by using an optical absolute position sensor. In driving the induction motor, the absolute position sensor required for the synchronous motor is unnecessary and an incremental position senor for detecting a relative position can sufficiently carry out the control.
As described above, in order to servo-control the motors which require to be driven in different control modes, such as the synchronous motor and the induction motor, it is necessary to use a servo controller dedicated to each motor and a sensor associated with the motor.
For this reason, when providing servo controllers for maintenance and replacement for a machine having both of the synchronous motor and the induction motor, servo controllers each dedicated to the synchronous motor or the induction motor have to be made ready, which raises problems in terms of maintenance management and cost.
When the synchronous motor and the induction motor are used by being changed over, a servo controller has to be provided for each motor, which increases the number of axes controlled by an NC device and causes problems of an increase in installation area and cost.
FIG. 11
is a block diagram showing an arrangement in which a plurality of motors to be driven in a different control mode are controlled by individual servo controllers. In
FIG. 11
, a first motor (synchronous motor) Ma is controlled by a servo controller
1
a
for the first motor, and a second motor (induction motor) Mb is controlled by a servo controller
1
b
for the second motor. The servo controller
1
a
for the first motor and the servo controller
1
b
for the second motor each carry out position control and/or velocity control by using signals fed back from the first motor Ma and the second motor Mb, respectively. In this servo control, the induction motor does not require absolute position information in the feedback signals, so that a relative position sensor suffices for the installed sensor. In contrast, the synchronous motor requires absolute position information in the feedback signals, so that an absolute position sensor is needed.
As the absolute position sensor is constituted by optical mechanisms using a glass plate or the like, it has a problem of being easily affected by the operation environment such as vibration and dust. In contrast, as the relative position sensor which generates incremental signals may be a gear-type sensor or the like, it has an advantage of high reliability against vibrations at the time of high-velocity rotation. Also, a through hole is sometimes formed at the center of the motor for cooling etc. In such a case, a through hole can be formed easily at the center of the gear-type sensor.
The servo controller
1
a
for the first motor and the servo controller
1
b
for the second motor are supplied with a position command and/or a velocity command from a CNC
2
. Also, a PC (programmable controller)
3
operates by a control signal from the CNC
2
for controlling electric circuits
4
for peripheral equipments.
As described above, when servo-controlling the motors having different control modes, such as the synchronous motor and the induction motor by the conventional servo controller, each motor requires a dedicated servo controller to raise problems in terms of maintenance, increase in size and installation area of the devices, cost, load on the CNC, etc.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a servo controller capable of controlling motors of different type which requires different control modes, such as a synchronous motor and an induction motor.
Another object of the present invention is to provide a servo controller capable of carrying out servo control on the motors of different type by using incremental feedback signals.
The servo controller of the present invention includes a control section common to individual motors and control sections dedicated to the individual motors, and the common control section is always used, while the dedicated control section is selectively used in accordance with the motor to be driven, to thereby enable control of the motors having different control modes by a servo controller of one type.
The use of a servo controller of one type can reduce maintenance management and load on a CNC. Also, the provision of the control section common to individual motors can restrain enlargement of size of the device and increase in installation area and cost.
The servo controller of the present invention comprises a common control section for carrying out control common to a plurality of types of motors requiring different control modes, dedicated control sections each for carrying out control dedicated to each type of motors, and a selecting section for selecting a dedicated control section and driving parameters in accordance with the motor to be driven.
The common control section is for carrying out control common to the plurality of types of motors requiring different control modes and always used. Only one common control section is provided for the plurality of types of motors. Each of the dedicated control sections is for carrying out control dedicated to each type of motors and is selectively used as necessary. The dedicated control sections are provided respectively to correspond to each type of motor.
The selecting section selectively connects a power line to the motor to be driven and selects the dedicated control section dedicated to the selected motor to connect the selected dedicated control section to the common control section. Thereby, the common control section and the dedicated control section cooperatively constitute one servo controller suitable for control of the selected motor.
For driving another type of motor, the selecting section switches the power line, selects the dedicated control section and connects the selected dedicated control section to the common control section, thereby constituting another servo controller suitable for control of the newly selected motor.
Thereupon, the plurality of types of motors requiring different control modes can be controlled by one servo controller.
In the servo controller of the present invention, the common control section carries out position control and/or velocity control, and the selecting section may selectively switch the position control and the velocity control in the common control section.
The plurality of types of motors may consist of an induction motor and a synchronous motor, and a first dedicated control section for the induction motor may comprise a magnetic flux current command generator and a slip command generator, and a second dedicated control section for the synchronous motor may comprise a d-axis current command generator to command a d-axis current of zero.
According to the present invention, a sensor for outputting incremental signals may be associated with each of the induction motors and the synchronous motors, and the common control section and the dedicated control section can perform the control using incremental feedback signals from each sensor.
For achieving this function, the dedicated control section is provided with magnetic pole position determining means for moving the magnetic pole position of the synchronous motor
Sakamoto Keiji
Takahashi Kenji
Toyosawa Yukio
Fanuc Ltd.
Nappi Robert E.
Smith Tyrone
Staas & Halsey , LLP
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