Electricity: motive power systems – Automatic and/or with time-delay means – Movement – position – or limit-of-travel
Reexamination Certificate
2000-03-16
2001-02-06
Ip, Paul (Department: 2837)
Electricity: motive power systems
Automatic and/or with time-delay means
Movement, position, or limit-of-travel
C318S266000, C318S286000, C318S445000
Reexamination Certificate
active
06184641
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a controller for controlling a commercial door operator or barrier operator, and more particularly to a controller for controlling the motor, interface, safety systems and other functions of a commercial door or barrier operator.
Commercial door operators, depending on the voltage requirements necessitated by the size and weight of the door or barrier to be moved, use single phase and three phase induction motors to move the door. Some door operator applications require use of a DC motor, which is somewhat easier to start. Creating enough starting torque and being able to select the direction of rotation of an induction motor is an important function of a door operator.
In a single phase induction motor, the rotor is of the squirrel cage type. The stator has a main winding which produces a pulsating field. At standstill, the pulsating field cannot produce rotor currents that will act on the air-gap flux to produce rotor torque. However, once the rotor is turning, it produces a cross flux at right angles with the main field and produces a rotating field comparable to that produced by the stator of a two-phase motor.
To start a single phase motor, a starting coil is used. In a capacitive motor, the starting winding is connected to the supply through a capacitor. This results in the starting winding current leading the applied voltage. The motor then has winding currents at standstill that are nearly 90 degrees apart in time and space, thus producing high starting torque and high power factor.
A three phase motor has three coils, so applying current to each coil always produces a current which leads the applied voltage, resulting in sufficient starting torque to start the motor.
Traditionally, because of the high current required for operating the motor used to drive a commercial door, commercial door operators employed an electromechanical control package. The electromechanical control package typically used relays for logic functions and contactors for motor control. Contactors are essentially relays that can switch large currents. While electromechanical control packages are considered reliable in the field and cost effective, they have limited versatility. Their logic functions are hard wired at the factory and not field programmable, so customers cannot change the configuration of their door operators after acquiring them. Also, electromechanical control packages do not readily accommodate additional features, although additional features, such as delay on reverse and start coil control can be provided via costly add-on modules. Other features, such as an RS-232 interface, RPM system and maximum run timer, are not possible at all.
To overcome some of the limitations of the electromechanical control packages, some commercial door operators employ a solid state controller. The solid state controller includes microelectronics for controlling some of the logic functions and power control electronics for controlling the motor. The controller, or logic control device, is typically built onto a printed circuit board which is usually located within the electronic control box at the head of the operator. Specialized programmable functions, such as storing and responding to transmitter codes (if the operator has a radio control feature) and failsafe operation features (such as for a fire door), are usually handled on a separate programmable logic board, which also sits in the electronic control box. The solid state logic control device includes DIP switches for selecting control options, such as the B2, C2, D1 and E2 options described below. Other functions may be provided by software programs in an onboard nonvolatile memory and run by an onboard microprocessor.
One particular prior art solid state logic control device employs five triacs in lieu of contactors for controlling the motor. Four of the triacs are used in an H-bridge circuit to steer current in order to control the direction of rotation (the motor start coil of a single phase motor), one pair for the forward direction and the other pair for the reverse direction; the fifth triac is used to control the motor main coil. Since a triac is a solid state device and, in theory, should have no maximum useful switch cycles, a triac should be more reliable than a contactor. A contactor, or relay, will fail eventually due to mechanical fatigue or erosion of the electrical contacts or some other mechanical part anywhere from 50,000 to 500,000 cycles. While the five triac solution provides cost reductions over the contactors and relays used in the electromechanical control package, the triacs have proven to be less reliable than the contactors.
Triacs, while solid state, are susceptible to voltage spikes across the power line, or local dV/dt tolerance. In the prior art motor control in which the two pairs of triacs were joined together on either side of the motor start coil, one triac of each pair was connected to AC neutral, the other side of the triac pair was connected to AC hot. This enabled the triacs to reverse the polarity of the motor start coil, thus reversing the rotational direction of the motor. However, power line spikes, high dV/dt, can cause the triacs to switch on, when they should not. If a pair of triacs turns on simultaneously, this causes a dead short between AC neutral and AC hot through the triac pair, burning out the triacs or the printed circuit board traces.
In addition to the effect of power line spikes on the triacs, the motor itself can sometimes produce enough noise to turn on the triacs in the H-bridge circuit. Many of the traditional techniques for minimizing the effect of power line spikes have been tried: capacitors across the triacs, MOVs and snubber networks. Unfortunately, none of the traditional techniques have worked.
Many commercial door operators are equipped with single phase capacitor start motors, which include a start coil and a main coil. The motor is activated by supplying AC current to the start coil and the main coil. As described above, the start coil is used to give the motor its initial rotational direction (forward or reverse) and high starting torque characteristics. During operation, the motor accelerates to approximately eighty percent of its synchronous speed, at which point a mechanical governor opens the start coil circuit by opening an inline switch. After the motor reaches eighty percent (or such other manufacturer specified percentage of the motor's maximum rated speed), the start coil is no longer needed. Indeed, if the start coil is left energized, copper losses would cause the motor to overheat.
The mechanical governors used in the single phase motors generally consist of a centrifugal governor and switch assembly. While relatively inexpensive, they are unreliable. The most common malfunctions of the centrifugal governor and switch assembly are seizing of the governor and switch contact failure. Once the mechanical governor fails, the start coil cannot be activated on start up, resulting in no motor rotation.
Some motor manufacturers (and third party suppliers) offer built-in or add-on electronic modules for shutting off the start coil. These electronic packages are more expensive than the mechanical governors. For example, some motor controllers rely on a set time delay and no RPM measurement. In such systems, the start coil is energized for a predetermined time, say half a second, and then released. This approximation works as long as the motor will start and continue to rotate in the desired direction given temperature variations, load variations, starting torque requirements for the application. Commercial door applications generally require RPM measurements to adequately control the start coil.
To assist in the maintenance of the commercial door operator, many include a cycle counter. A cycle counter increments a mechanical odometer type counter every time the commercial door cycles open or closed. The odometer is then read, for example, during routine servicing of the operator and the door. If the odometer
Crimmins Terence E.
Gioia William G.
Fitch Even Tabin & Flannery
Ip Paul
The Chamberlain Group, Inc.
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