GB2105882A - Microprocessor-based electric motor speed control system - Google Patents
Microprocessor-based electric motor speed control system Download PDFInfo
- Publication number
- GB2105882A GB2105882A GB08127535A GB8127535A GB2105882A GB 2105882 A GB2105882 A GB 2105882A GB 08127535 A GB08127535 A GB 08127535A GB 8127535 A GB8127535 A GB 8127535A GB 2105882 A GB2105882 A GB 2105882A
- Authority
- GB
- United Kingdom
- Prior art keywords
- motor
- microprocessor
- control
- speed
- electric motor
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Withdrawn
Links
Classifications
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02P—CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
- H02P23/00—Arrangements or methods for the control of AC motors characterised by a control method other than vector control
- H02P23/0077—Characterised by the use of a particular software algorithm
-
- G—PHYSICS
- G05—CONTROLLING; REGULATING
- G05B—CONTROL OR REGULATING SYSTEMS IN GENERAL; FUNCTIONAL ELEMENTS OF SUCH SYSTEMS; MONITORING OR TESTING ARRANGEMENTS FOR SUCH SYSTEMS OR ELEMENTS
- G05B19/00—Programme-control systems
- G05B19/02—Programme-control systems electric
- G05B19/18—Numerical control [NC], i.e. automatically operating machines, in particular machine tools, e.g. in a manufacturing environment, so as to execute positioning, movement or co-ordinated operations by means of programme data in numerical form
- G05B19/19—Numerical control [NC], i.e. automatically operating machines, in particular machine tools, e.g. in a manufacturing environment, so as to execute positioning, movement or co-ordinated operations by means of programme data in numerical form characterised by positioning or contouring control systems, e.g. to control position from one programmed point to another or to control movement along a programmed continuous path
- G05B19/27—Numerical control [NC], i.e. automatically operating machines, in particular machine tools, e.g. in a manufacturing environment, so as to execute positioning, movement or co-ordinated operations by means of programme data in numerical form characterised by positioning or contouring control systems, e.g. to control position from one programmed point to another or to control movement along a programmed continuous path using an absolute digital measuring device
- G05B19/29—Numerical control [NC], i.e. automatically operating machines, in particular machine tools, e.g. in a manufacturing environment, so as to execute positioning, movement or co-ordinated operations by means of programme data in numerical form characterised by positioning or contouring control systems, e.g. to control position from one programmed point to another or to control movement along a programmed continuous path using an absolute digital measuring device for point-to-point control
- G05B19/291—Numerical control [NC], i.e. automatically operating machines, in particular machine tools, e.g. in a manufacturing environment, so as to execute positioning, movement or co-ordinated operations by means of programme data in numerical form characterised by positioning or contouring control systems, e.g. to control position from one programmed point to another or to control movement along a programmed continuous path using an absolute digital measuring device for point-to-point control the positional error is used to control continuously the servomotor according to its magnitude
- G05B19/293—Numerical control [NC], i.e. automatically operating machines, in particular machine tools, e.g. in a manufacturing environment, so as to execute positioning, movement or co-ordinated operations by means of programme data in numerical form characterised by positioning or contouring control systems, e.g. to control position from one programmed point to another or to control movement along a programmed continuous path using an absolute digital measuring device for point-to-point control the positional error is used to control continuously the servomotor according to its magnitude with speed feedback only
Abstract
An electric motor 15 is controlled by a thyristor control 17 and main contactor 16 which are in turn controlled by a microprocessor 2 in accordance with operator controls and data prestored in EPROM 1, together with motor speed and direction signals from tachometer 7. In a preferred embodiment the microprocessor 2 and EPROM 1 are used to control the various motors of an electric crane. The EPROM 1 can be loaded with different control programs for the different motions of the crane. <IMAGE>
Description
SPECIFICATION
Microprocessor-based infinitely variable electric motor speed control system.
The present invention relates to a microprocessor-based infinitely variable speed control system for electric motors and particularly, but not exclusively, for electric motors used with travelling cranes and hoists.
On standard control systems creep speeds are obtained by the use of additional motors, clutches and controls which increase the cost and complexity of such systems. In addition, the control acceleration is difficult and may lead to operating problems. This means that the operating efficiency of the crane with this control system may be reduced. Similarly braking is difficult to control completely which is a disadvantage in certain circumstances.
This may also reduce the reliability of operation which is a further disadvantage of these systems.
There has also been proposed a control system for travelling cranes and hoists in which the speed of all motions of the crane is controlled i.e. long travel, cross travel and hoist. In this control system a desired speed for a particular motion is set by setting a reference voltage by means of a controller. A d.c. tachometer which is coupled to the driver motor shaft provides a voltage signal for the actual speed of the motion. The actual and desired signals are summed and amplified, and the magnitude of the amplifier output voltage is fed to a thyristor conduction unit, which controls the conduction angle of a 3 phase thryistor/diode stack and hence the effective voltage applied to the motor. The direction of the motor was also determined by the polarity of the amplifier output voltage via a reversing contactor control unit.With this system, control of acceleration is limited and providing greater control would require considerably more hardware and expense.
An object of the present invention is to obviate or mitigate the abovesaid disadvantages.
According to the present invention there is provided a speed control system for an electric motor comprising storage means for storing information relating to the movement of an electric motor, generating means for generating a signal representative of the actual speed and direction of the motor, microprocessor means connected to the storage means and to the generating means, said storage means providing a signal to the microprocessor representative of a desired speed and direction of the meter, the miccroprocessor processing the signals from the storage means and from the generating means and providing an output speed and direction control signal to the motor.
Preferably the movement of the electric
motor is acceleration or deceleration.
Preferably also, the output speed and direc
tion control signal is fed to the motor via solid
state switches which control the effective vol tage applied to the motor and via contractors
which control the direction of rotation of the
motor.
Preferably also, said storage means is an
erasable programmable-read-only memory (E
PROM) and a random-access memory (RAM).
Preferably also, said means for generating a
signal representative of the actual speed and
direction is a tachogenerator.
Preferably also, there are a plurality of mo tions connected to, and controllable by, the
microprocessor.
Alternatively, a single microprocessor may
be used to control each motion.
The microprocessor-based infinitely variable
speed control system has been developed
primarily for application to the electrical motor
drives of cranes although it has application in
any field where accurate control of electric
motors is required. It can be utilised to control
the speed of all motions of the crane, that is,
long travel cross travel, hoist and lower.
An embodiment of the present ivention will
now be described by way of example with
reference to the accompanying drawings in which Figure 1 is a block diagram of a control
system according to the present invention;
Figure 2 is a block diagram of the power
supply to the crane drive;
Figure 3 is a flow diagram of control of
acceleration of the crane drive; and
Figure 4 is a schematic diagram of position
control achieved by the apparatus according
to the present invention.
Referring now to the drawings, an erasable
programmable read only memory (EPROM) 1
contains a program for controlling the direc
tion and accleration of electric motors for
travelling crane drives. The EPROM 1 is con
nected to a microprocessor (MPU) 2 which is
connected via PIA'S (3a, 3b, and 3cto) speed
and direction detecting means 4 to motor
driving and control means 6 and to position
detecting means 5. respectively. It will be
understood that in the interest of clarity the
embodiment relates to the control of one
electric motor, although several electric mo
tors may be controllable by the same MPU.
The speed and direction detecting means is a a tachogenerator 7 of speed detection and polarity detection. A speed and direction refer
ence is provided by a control potentiometer 8.
The tachogenerator 7 and the control poten
tiometer 8 are connected to the same pulse
amplifier 3a via analogue to digital convertors
9, 10.
The position detecting means 5 comprises a
position sensor 11 and a position reference 1 2 which are connected to the same PIA 3c.
The motor control and driving means 6 com prises fault indicators 6a, direction contactors 6band 6c, a rotor resistance 6d, braking means 6e and thyristors 6f. The outputs of the direction contactors 6b, so the rotor resistance 6d and the brake Se are connected to the reversing contractors control unit 13, the output of which is in turn, connected to the reversing contactors 1 4. The outputs of the thyristors 6f are also connected to the reversing contactor 14. The reversing contactors are in turn connected to the electric motor 1 5 which may be of the squirrel cage or slip-ring type.
The 3-phase supply (Fig. 2) is fed to a main contactor 1 6 the output of which is connected to a 3-phase thyristor/diode stack 1 7. The output of the stack 1 7 is connected to contactors 6b. 6 c which control the direction of rotation of the motor 1 5.
in use, speed is selected by means of a potentiometer on the pendant of the crane, and in response to a control signal, which is provided by setting a reference voltage by the potentiometer and or resistance chain and selector switch to the MPU2, the MPU2 accesses the EPROM 1 and reads the section of the program contained therein which is required to be executed for the particular motion desired.
The MPU 2 then compares the desired speed and direction of the motor program in the EPROM 1 with the actual speed and direction signals from the tachogenerator 7 respectively. In accordance with the result of the comparisons the MPU 2 sends an output signal via the PlA's 3a, 3b, and 3cto the motor control and driving means 6 respectively.
The magnitude of the error determines, by means of the thyristors firing unit Sf, the conduction angle of the 3-phase thyristor/diode stack 1 7 which controls the voltage applied to the motor 1 5.
The sign of the error determines, by means of 3-phase changeover contactors, the phase sequence, and hence the direction of developed torque, of the voltage applied to the motor 1 5. If the speed drops below the selected value then this produces an increase in the mangitude of the error which in turn increases the conduction angle and hence the voltage applied to the motor. This causes the motor speed to return to the selected value. If the speed rises above the selected value then the sign of the error changes causing the changeover contactors to operate hence producing a controlled braking torque i.e. torque developed in the opposite direction until the speed returns to the selected value.
Therefore the motor 1 5 drives from one position to another in accordance with a predetermined program. For example, the motor controlling long travel will be driven either in the forward or reverse direction to accelerate the long travel motion over a given time up to a predetermined velocity, and the feedback control system maintains this velocity constant independent of load until a deceleration signal is supplied from the MPU 2. During periods of acceleration (or deceleration) the magnitude of the acceleration (or deceleration) is limited to a predetermined value by controlling the voltage ramp to the motor by means of the program. Prior to a contactor opening the thyristors are switched off to eliminate arcing.
After a contactor has closed the thyristor conduction angle is increased gradually to provide a "soft-start" for the motor.
With reference to Fig. 3 of the drawings the program read by the MPU2 firstly compares the difference to the desired and actual speed signals and increases or decreases the voltage of the thyristor stack in accordance with the acceleration values falling within a predetermined range. If the resultant error is positive (1 6a 1 7a) the voltage is increased (forward, hoisting motion) and if the resultant error is negative (1 Sb, 1 7b) the voltage is decreased (reverse, lowering motion).
The order of control of the motor control and drive is as follows for the hoist motion; the direction 1 and motor resistance controls are selected and actuated.
Power is applied to the hoist motor via the thyristors and then the brake is released. Once the brake is released the motor then starts to drive. In a slip-ring motor however, there is always resistance in the circuit; in the hoist motion there is one resistance for hoist and another resistance for lower. The resistance varies the current to the motor to suit different running conditions.
Referring now to Figs. 1 and 4. These are a plurality of positions detecting means disposed along the long travel axis of a travelling crane.
There are metal strips 1 8 disposed along the gantry for determination of zones 19.
Within the zones 1 9 there are position strips 20 within the zone for determining the position of the crane 21 therein. In the example shown readings from five sensors located on the crane are required to determine its position; 4 zone sensors and 1 position sensor.
Binary coding is used for example if the crane was at position 5 the corresponding coding would read (0101) and if it was desired to move the crane to position 11 the new coding required to be entered would be 1011. The direction of travel of the crane is determined by the sign of the zone error (positive in the above example), and the speed of travel is determined by the magnitude of the zone error. An alternative technique would be to use 4 position on/off switches on the crane and operating pins on the gantry whereby as the crane travelled along is long-travel direction the operating pins on the gantry would trip the switches on the crane, the combination of the switches tripped depending on the particular zone the crane was in; the coding being the same as the aforementioned.
This microprocessor-based infinitely variable speed control system has particular advantage in the field of computer aided warehousing.
The microprocessor can easily be interfaced to a computer which would then facilitate control of the storage movement of articles, for example, containers in a container park. The computer would permit the injection removal storage and collation of information, and the software may be modified to suit different applications.
Without departing from the scope of the invention a battery powered random-accessmemory (RAM) 22 may be connected to the microprocessor 2. This would enable fault diagnosis of the control system to be carried out even if there was a power shut-down. In addition, the potentiometer for speed selection may be sited in cabin of the crane, or at any other control station for the crane.
Advantages of the present invention are:
the system includes safety checks in order to close-down if a fault occurs i.e. main failure, loss of control signal, loss of radio-signal where radio telemetry control of the crane is present, overspeeding, motor overheating, loss of tachogenerator signal; all pulses which operate the thyristors and contactors are generated by the software then any supply or component failure which causes the program to stop running results in close-down of the system;
a totally variable choice of speed over the full range up to the maximum for the particular motor is provided,
acceleration and deceleration of any motion is controlled by the program chosen for the particular duty irrespective of the speed of movement of its controller.Controlled dynamic braking is an inherent feature of the system in that retardation of a motor involves application of torque opposed to the direction of motion. This is of course advantageous.Therefore the brake wear is minimal as there are no mechanical brakes involved in braking, except when the controller is on the offposition, which provides an automatic parking brake feature.
In practice the operator will simply move a joystick controller to a position in its arc between neutral and maximum, and the microprocessor will set the speed for that position. The acceleration of deceleration values are set by the microprocessor, and this imposes maximum values. Thus the acclerataion is controlled effectively without limiting torque, as is required at present. It will also be understood that the system hereinbefore described has application in any other field where control of a.c. motor drives is required e.g. for a.c. motors and stepper motors in disc drives, line printers and the like.
In summary, the microprocessor-based travelling crane control system disclosed herein utilises standard electrical motors to provide superior speed control than previous systems.
Claims (8)
1. A speed control system for an electric motor comprising storage means for storing information relating to the movement of an electric motor, generating means for generating a signal representative of the actual speed and direction of the motor, microprocessor means connected to the storage means and to the generating means, said storage means providing a signal to the microprocessor means representative of a desired speed and direction of the motor, the microprocessor means processing the signals from the storage means and from the generating means and providing an output speed and direction control signal to the motor.
2. The system of claim 1, in which the movement of the electric motor is acceleration or deceleration.
3. The system of claim 1 or claim 2, in which the output speed and direction control signal is fed to the motor via solid state switches which control the effective voltage applied to the motor and via contactors which control the direction of rotation of the motor.
4. The system of any preceding claim, in which said storage means is an erasable programmable-read-only memory (EPROM) and a random-access memory (RAM).
5. The system of any preceding claim, in which said means for generating a signal representative of the actual speed and direction is a tachogenerator.
6. The system of any preceding claim, in which there are a plurality of motions connected to, and controllable by, a common microprocessor.
7. The system of any of claims 1 to 5, in which each of a plurality of motions is controlled by a respective microprocessor.
8. A speed control system for an electric motor, substantially as herein described with reference to the drawings.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB08127535A GB2105882A (en) | 1981-09-11 | 1981-09-11 | Microprocessor-based electric motor speed control system |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB08127535A GB2105882A (en) | 1981-09-11 | 1981-09-11 | Microprocessor-based electric motor speed control system |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| GB2105882A true GB2105882A (en) | 1983-03-30 |
Family
ID=10524451
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB08127535A Withdrawn GB2105882A (en) | 1981-09-11 | 1981-09-11 | Microprocessor-based electric motor speed control system |
Country Status (1)
| Country | Link |
|---|---|
| GB (1) | GB2105882A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN112740535A (en) * | 2018-09-26 | 2021-04-30 | 西门子股份公司 | Method for regulating the rotational speed of a permanently excited three-phase electric machine having a soft starter by means of a regulator cascade and three-phase electric machine |
-
1981
- 1981-09-11 GB GB08127535A patent/GB2105882A/en not_active Withdrawn
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN112740535A (en) * | 2018-09-26 | 2021-04-30 | 西门子股份公司 | Method for regulating the rotational speed of a permanently excited three-phase electric machine having a soft starter by means of a regulator cascade and three-phase electric machine |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| WAP | Application withdrawn, taken to be withdrawn or refused ** after publication under section 16(1) |