Electricity: motive power systems – Motor-reversing
Reexamination Certificate
1999-11-24
2001-01-23
Masih, Karen (Department: 2837)
Electricity: motive power systems
Motor-reversing
C318S468000, C318S466000, C318S467000, C318S280000, C318S445000
Reexamination Certificate
active
06177771
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a process and device for automatically controlling the opening and closing of a door, and in particular to pivoting doors weighing in excess of 20,000 pounds at a relatively high frequency of usage, such as the lead doors for linear accelerator rooms used for the treatment of cancer patients.
BACKGROUND OF THE INVENTION
A door operator is known from the U.S. Pat. No. 5,018,304 and offers a variable torque clutch as a method of controlling operating torque and free egress. In many applications, especially linear accelerator doors, it is desirable, and some times mandated, that the door be movable by an external force below a predetermined magnitude. This is done, so that in an emergency situation such as during a power failure, it is still possible to open and close the door. In the patent to Longoria, an electromagnetic clutch is used which is supposed to slip at a predetermined value. This design has been found to be less than optimal with respect to when the clutch should and should not slip in actual field conditions. Research into presently available electromagnetic clutches, finds that present manufacturers do not recommend using electromagnetic clutches in slip clutch applications, and the electromagnetic clutches are preferably only to be used as an on/off clutch. In particular the potentiometer voltage control of these clutches is only for adjusting the start-up and running modes, and not meant to control slippage.
Automatic door operators are known for standard commercial doors, such as those seen in department stores. These swinging doors are mostly only powered in one direction and have a spring return for the other direction. Spring returns are known to have difficulty operating the movement of a door if particular problems such as out of plum or misalignment of the frame, or a pressure differential exists in a particular installation. The standard commercial door operators, because of their design, are usually limited to applications where the door weighs less than 4,500 pounds. When the weight of the door exceeds this amount, the standard controlling and driving devices experience problems.
One of the problems, such as in applications similar to U.S. Pat. No. 5,453,736 to Noren, is that the position of the door is measured using an encoder with a counter. Movement of the door generates a series of pulses, which are then counted to determine how much the door has moved. When power is interrupted, when electrical noise is present, and/or an automated door operator needs to be reset, encoder/counter systems need to move the door to a start or home position and then reset the counting. If the door operator of Noren was used on a linear accelerator door during a power failure, during electrical noise or reset, a door weighing up to 20,000 pounds is being moved without any microprocessor control, until the door is returned to its start or home position. This can be a dangerous situation.
Also the motor and drive train used for relatively light weight doors, are not significantly effected by the weight of the door. Braking or slowing of the door is therefore not a significant consideration. With doors weighing up to tens of thousands of pounds, the driving of the extra weight of the door is accomplished by using a much more powerful motor and drive train, however, such factors such as slowing, braking and the door overrunning the motor now become significant problems, as is the importance of power operation in both the forward and reverse directions.
SUMMARY AND OBJECTS OF THE INVENTION
It is a primary object of the present invention to provide an automatic door operator for very massive doors, which overcomes the above problems, and is simple and convenient to manufacture, install and operate.
The present invention accomplishes this by having a motor connectable to a door for moving the door between an open and closed position, and to a plurality of positions in between. An absolute position transducer is provided for measuring an absolute position of the door. A control means senses an external input signal indicating one of an open state and a closed state of the door, and any one of the plurality of in between positions. The control means compares the absolute position of the door with the position or state indicated by the external signal and the control means generates a drive signal to the motor for driving the motor until the absolute position is substantially identical to the position indicated by the external signal. The in between positions are preferably preset by the operator at the time of installation and can be modified at any time. The preset in between positions can also be used to indicate where the speed of the door should be changed.
The absolute position transducer measures the absolute position of the door independently of previous positions of the door. By absolute position, it is intended that the measuring of the position does not depend on the direction or movement of the door. The present invention is able to determine the position of the door without movement of the door and without needing knowledge of the previous positions of the door.
The control means of the present invention is preferably a digital Programmable Logic Control (PLC), and the absolute position transducer is an analogue device such as a rotary potentiometer which is continuously able to report position regardless of whether the door is moving or not. An analogue/digital convertor is then used to convert the analogue voltage signal from the potentiometer into a digital signal which can then be read by the digital PLC.
The motor of the present invention is a full wave four quadrant regenerative drive which is designed to be operatable in all four combinations of driving torque and motor rotation. The most common combination, is when the electrical current applied to the motor produces a torque that is in the same direction as the present rotation of the rotor of the motor. Many motor drives for swinging doors are only one directional, and electrical driving torque to the motor can only be in one direction. Some motor drives are bidirectional, where the torque and the direction, while always having to be in the same direction, can both either be forward or backwards. A full wave four quadrant regenerative drive can have the electrical driving torque in either direction to the rotation of the motor, and does not require that the electrical driving torque be in the same direction as the present rotation of the motor. This allows a four quadrant regenerative drive to actively brake the rotor, control an overrunning motor, and even quickly reverse the rotation of a motor without contractors, switches, brake resistors and inhibit plugs. All the braking, slowing, reversing and controlling of overrunning, is done by controlling the direction and magnitude of the energy being supplied to the regenerative drive. The control means of the present invention actively controls the movement of the door by electrically driving the regenerative drive in directions opposite to the actual and present rotation of the regenerative drive. The control means generates the energy of the motor back into the AC source thus providing motor torque opposite of motor rotation of the regenerative drive.
In the field of linear accelerator doors, it is important that the door be closed before the linear accelerator can operate. The linear accelerator therefore usually has limit switches which are separate from the door operator to determine when the door is closed and the linear accelerator will not operate until these limit switches indicate that the door is closed. Aging of the door, the surrounding frame, and even of the entire building, can cause alignment of the door to deviate from an optimal state. Misalignment can also be caused by warping, settling, or even the initial installation being out of tolerance. This misalignment can bias the door away from its fully closed state. Also with the forced air ventilation in modem buildings, a significant
Kinzer Karl P.
Leblanc Richard J.
Miller Gary J.
Simo-Kinzer Christopher M.
Brookfield Industries, Inc.
Masih Karen
McGlew and Tuttle , P.C.
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