Patent GB-1273301-A (GB)
Title: Digital pattern generator for motor speed control
IPC: B66B1/30
Filed: 1970-04-29
Abstract: 1,273,301. Lift control systems. WESTING- HOUSE ELECTRIC CORP. 29 April, 1970 [7 May, 1969], No. 20546/70. Heading B8L. [Also in Division G3] A reference signal for a lift speed control is generated by a non-linear digital-to-analogue converter B5 as a function of the accumulated count in a first reversible digital counter B2, which, during acceleration and deceleration only, counts pulses from a generator B3 representative of increments of displacement between the car and the hatchway, the accumulated count being limited at B6 to a number corresponding to a desired maximum speed. A second reversible counter B1 maintains a running count representing the actual position of the car, and, as shown, the counts in the two counters are totalized to indicate an advance car position. When this total corresponds to a desired stopping-point indicated at B10, as determined by a bit-by-bit comparator B9, deceleration is initiated by causing subsequent pulses to reduce the count in the first counter B2. Alternatively, the advance car position is indicated directly by the second counter by directing pulses to this counter at twice the normal rate while pulses are being accumulated in the first counter, and then at the normal rate during the constant speed phase when no pulses are being accumulated in the first counter, Fig. 3 (not shown). In this arrangement, no pulses are directed to the second counter during deceleration while pulses are being subtracted in the first counter. A bias signal is applied to the digital-toanalogue converter to give a starting impetus to the system, a maximum indicator on the counter being operative, when the car has travelled a distance corresponding to maximum speed, to discontinue the introduction of pulses into this counter. The output of the digital-toanalogue converter then remains constant and a steady speed is maintained. The incremental count representing the advance position of the car is transformed by a decoder into a floorposition signal which serves as an input to a supervisory system. The closest floor at which the car is to stop is indicated by an incremental count which is continuously compared with the advance car position. When the two are equal, decleration is initiated. In one embodiment, no further pulses are applied to the advance car position counter once deceleration is initiated, so that, when the car comes to a stop, the count in this counter reflects the actual car position. When the car is at rest and a call is registered the position of the call and the position of the car are compared for starting in the appropriate direction. If the coded position of the call exceeds that of the car, the second counter begins to count in the up-direction, and, in the first embodiment, an adder-subtractor is prepared to add the counts. If the coded position of the call is less than that of the car, the second counter counts in the down direction, and the counts are subtracted. Detectors are connected to the first counter from which the speed reference signal is derived, for generating signals when the car is at a predetermined distance from the floor at which it is to stop. The signals are used for pre-opening the car-doors, and for transferring control to a transducer system for precise landing.