Harvesters – Motorized harvester – Having fluid-pressure or stored-energy motor
Reexamination Certificate
1997-04-25
2001-01-09
Will, Thomas B. (Department: 3671)
Harvesters
Motorized harvester
Having fluid-pressure or stored-energy motor
C056S01020R, C318S434000
Reexamination Certificate
active
06170241
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to motor controllers and in particular to solid state motor controllers for electric motors adapted for use with portable power equipment, such as lawn and garden equipment.
2. Related Art
Motor controllers are designed to interrupt power to a motor in the event of a fault in the motor. A fault in the motor can cause excessive current to flow through the motor windings and thereby overheat the windings and damage the motor.
To provide overcurrent protection, motor controllers on small motors typically use a relay approach. In the relay approach, when an overcurrent condition is sensed, a circuit breaker connected in series with the motor trips open to interrupt current flow to the motor and halt the motor.
However, circuit breakers do not limit current, they merely interrupt the current path when a particular current threshold has been exceeded for a certain period of time. A problem with using mechanical devices such as circuit breakers to interrupt the current path is that there can be a significant delay between the time the high current condition occurs and the time the circuit breaker trips open. Due to the time delay, high current can flow to the motor as well as to other components of the system before the circuit breaker opens, thereby causing damage to the system. This can be a particular problem with small motors which may be easily damaged by rapid power surges and for which the aprroach may be ineffective.
Another problem with the relay approach is that the circuit breaker is either shut or tripped open. If the current is below a threshold, the circuit breaker remains shut, but if the current exceeds the threshold, the circuit breaker trips open to interrupt the current path. Such an approach is susceptible to spurious trips from transients. If the circuit breaker opens during momentary transients, the operator is forced to reset the circuit breaker before the motor can be restarted thereby causing unnecessary delay and inconvenience.
Also, circuit breaker based protection systems do not readily lend themselves to the addition of auxiliary control features, for example, thermal protection and battery monitoring, in a compact, integrated package.
Therefore, what is needed is a motor controller which can quickly and reliably limit motor current flow and thereby prevent excessively high current through the motor and the system, even for sharp power surges.
What is also needed is a motor controller which can automatically shut down the motor if current limiting is required for a predetermined period of time.
What is also needed is a motor controller which is capable of quickly stopping the motor after an automatic shutdown condition occurs.
What is also needed is a motor controller which provides the flexibility to easily add additional control features for operator interface.
What is also needed is a motor controller which includes the above-cited feature and is adapted for use with portable power equipment, such as lawn and garden equipment.
SUMMARY OF THE INVENTION
The motor controller of the present invention is a solid state based motor controller which includes a microprocessing unit to provide a number of advantages over motor controllers using a relay approach, particularly in portable equipment applications. The microprocessing unit comprises any IC device capable of accepting input signals comparing the input signals with predetermined thresholds and providing output signals based on the input signals, the comparison or any programmed manipulation of the input signals. A solid state design that uses a microprocessor is better from a reliability standpoint because the current can be easily limited to any chosen level. A solid state design is also advantageous because many other features can easily be added, for example, a battery level indicator or a load level gauge, to the overall control package.
In the present motor controller, the microprocessor senses the current through the motor, compares the sensed motor current with a first current threshold level and provides a warning if the sensed motor current exceeds the first current threshold level. The microprocessor also compares the sensed motor current with a second current threshold level and actuates a current limiting device if the sensed motor current exceeds the second current threshold level. If the current limiting condition, namely the sensed current exceeding the second current threshold level, exists for a predetermined period of time, the microprocessor shuts down the motor.
In one form thereof, the motor controller includes first and second solid state switches, connected to the microprocessor through a driver unit, for limiting the current through the motor and for shutting down the motor. The current limiting feature is implemented by rapidly switching the first solid state switch, which is connected in series with the motor and the power source, between an ON and an OFF state. The rapid switching prevents the current through the motor from rising above a predetermined level. The motor is shut down by placing the first solid state switch in the OFF state and rapidly switching the second solid state switch, which is connected in parallel with the motor, between an ON and an OFF state to quickly dissipate the energy in the motor windings and stop the motor.
In applications where the motor is driven by a battery, particularly portable lawn and garden equipment, the microprocessor also senses the battery voltage level and actuates a warning if the battery voltage falls below a first voltage threshold level, and shuts down the motor if the battery voltage falls below a second voltage threshold level. The microprocessor also senses the temperature around a selected component and shuts down the motor if the sensed temperature exceeds a predetermined temperature threshold level. The motor shutdown is rapidly achieved using the method described above.
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“Industrial Control Applications”, Motorola Inc., First Edition DL412/D Rev. 1, 1994.
Farr James B.
Pfaff Joseph L.
Shibilski John
Baker & Daniels
Pezzuto Robert
Tecumseh Products Company
Will Thomas B.
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