Electricity: motive power systems – Constant motor current – load and/or torque control
Reexamination Certificate
2001-03-29
2003-02-25
Nappi, Robert E. (Department: 2837)
Electricity: motive power systems
Constant motor current, load and/or torque control
C318S434000, C053S317000, C053S331500, C053S490000
Reexamination Certificate
active
06525498
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the field of electric motor control, in particular the field of calibrating an energy conversion device.
The present invention can be applied in fields where an electric motor must apply a precise torque to an object, for example in the field of screwing, in particular of screwcaps.
2. Description of the Prior Art
The document EP 0 524 196 discloses a screwing device including a stopper cone, a motor for driving rotation of the stopper cone, a switching device and a power supply. A control device includes a torque sensor adapted to measure an instantaneous drive torque, a comparator for comparing the instantaneous torque with a predetermined closure torque, and a sensor responsive to the angle of rotation of the cap receiving member adapted to be activated only if the instantaneous torque reaches the predetermined value. Thus a drive torque is applied to a cap to screw it onto a container, the instantaneous torque applied to the cap is measured and compared with a closure torque of predetermined value, and the rotation angle of the cap is measured only if the instantaneous torque reaches the predetermined value.
However, the presence of a torque sensor and an angle sensor makes the device somewhat complicated without guaranteeing very reliable and convenient closure of the containers by the caps.
The present invention proposes, in particular, an improved control device and method enabling a very precise torque to be applied.
The present invention proposes, in particular, an economical calibration method reducing the duration of the maintenance calibration operations carried out at regular intervals during the life of an electric motor.
SUMMARY OF THE INVENTION
The device in accordance with one aspect of the invention is for controlling an electric motor and includes means for measuring the current I
m
drawn by the motor, means for measuring the torque C
m
supplied by the motor, power supply means for the motor, and an initialization unit capable of generating a torque set point C
c
and of receiving and processing information relating to the current I
m
and the torque C
m
to deduce therefrom a relationship between the set point C
c
, the torque C
m
and the current I
m
in order to be able to determine the torque C
m
from the set point C
c
and the current I
m
.
The means for measuring the torque C
m
supplied by the motor are advantageously removable. They can be removed after calibration, the torque C
m
being controlled in accordance with the set point C
c
and verified by means of the current I
m
.
In one embodiment of the invention the device includes a calculation unit associated with memory means and a user interface, a first data bus between the initialization unit and the power supply means of the motor, and a second data bus between the initialization unit and the calculation unit.
In one embodiment of the invention the means for measuring the torque C
m
are provided with a removable calibrator for calibrating the torque measuring means.
The device can be used to control a plurality of motors and can include a corresponding number of current measuring means and motor power supply means.
The invention also relates to an electromechanical system including a device as defined hereinabove. The system can be a machine for applying a particular torque to an object, for example a screwing, drilling, tapping, capping, etc. machine.
The method according to one aspect of the invention is for controlling an electric motor. An initialization unit generates a torque set point C
c
addressed to power supply means of the motor. Current measuring means measure the current I
m
drawn by the motor. Torque measuring means measure the torque C
m
supplied by the motor. The initialization unit receives and processes information relating to the current I
m
and the torque C
m
to deduce therefrom a relationship between the set point C
c
, the torque C
m
and the current I
m
in order to be able to determine the torque C
m
from the set point C
c
and the current I
m
.
The torque measuring means are preferably installed beforehand and then removed after measuring at least one value of the torque C
m
. The same torque measuring means can be used for several electric motors.
In one embodiment of the invention the initialization unit generates three torque set point values C
c
, the current measuring means measure n values of the current I
m
drawn by the motor, where n is greater than 2, the torque measuring means measure n values of the torque C
m
supplied by the motor, and the initialization unit receives and processes n values relating to the current I
m
and the torque C
m
to deduce therefrom a relationship between the set point C
c
, the torque C
m
and the current I
m
in order to be able to determine the torque C
m
from only the set point C
c
and the current I
m
.
In one embodiment of the invention the initialization unit calculates three coefficients a, b, c of a second order equation relating to the set point C
c
and the torque C
m
and three coefficients a′, b′, c′ of a second order equation relating the current I
m
and the torque C
m
. Using a second order equation is very suitable when using electric motors operating over a particular range outside their area of linear operation. A higher order equation or any other type of mathematical equation can be used for operation over a very wide range.
The computer program in accordance with one aspect of the invention includes program code means for implementing the steps of the method defined hereinabove.
The medium in accordance with one aspect of the invention can be read by a device for reading program code means stored therein and which are adapted to implement the steps of the method defined hereinabove.
One particular embodiment of the invention is shown in the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1
is a diagrammatic view of a motor, a torque measuring system and a calibrator.
FIG. 2
is a diagrammatic view of a motor control device and its environment.
FIG. 3
is a functional block diagram of a motor control device.
FIG. 4
is a process step flowchart.
FIG. 5
is a block diagram of a torque measuring system.
REFERENCES:
patent: 4803640 (1989-02-01), Mitomi et al.
patent: 4934844 (1990-06-01), Orii
patent: 5075870 (1991-12-01), Kojyo et al.
patent: 5321935 (1994-06-01), Spatz et al.
patent: 5400564 (1995-03-01), Humphries et al.
patent: 5419094 (1995-05-01), Vander Bush, Jr. et al.
patent: 5587762 (1996-12-01), Watanabe
patent: 5718097 (1998-02-01), Kinoshita et al.
patent: 5881326 (1999-03-01), Sakamoto
patent: 6105343 (2000-08-01), Grove et al.
patent: 37 15935 (1988-11-01), None
patent: 0 524 196 (1993-01-01), None
patent: 0 618 168 (1994-10-01), None
Matthys Philippe
Ostrowski Laurent
Zalkin Daniel
Duda Rina I.
Etablissements Andre Zalkin
Nappi Robert E.
Smith , Gambrell & Russell, LLP
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