Electricity: motive power systems – Positional servo systems – With stabilizing features
Patent
1989-10-20
1991-11-05
Shoop, Jr., William M.
Electricity: motive power systems
Positional servo systems
With stabilizing features
318266, 318466, 187103, B66B 1308
Patent
active
050633376
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a method of regulating the rotational speed of an AC electric motor, particularly an asynchronous motor, supplied at a frequency varying according to a reference between two endmost adjustable angular positions of the rotor spaced apart by an adjustable number of rotor revolutions and in which positions the speed is zero.
The invention also relates to the means for implementing this method as well as to the motors equipped with such means.
More particularly, but not exclusively, the field of application of such a method is in the equipment for opening and closing linearly moving doors such as those equipping passenger lifts or goods lifts, even the entrances to buildings.
In this field, the motor is associated with transmission members driving at least one leaf of a door between two positions in which the door is either opened or closed which, depending on the transmission ratio, corresponds to a certain number of revolutions of the rotor between the two said endmost positions adjusted in particular on installation as a function of the width of the door.
So as to prevent doors from having sudden movements, prejudicial to the mechanical strength, the doors must have a movement which is accelerated from their zero starting speed up to a level speed then a movement slowing down to the zero speed on arrival.
For this, using a cranked link system it is known to transform the uniform circular movement generated by the shaft of the motor into a substantial reciprocating movement whose speed is a sinusoidal function.
These transmission members are however cumbersome, costly and limited to doors of similar size.
Particularly for lift doors, and for obvious safety reasons, the standards in force fix a maximum closing energy and so a maximum closing speed.
Except with doors of a type such that, when fully open, they would present risks of squeezing, these standards and reasons practically do not exist on opening of the doors which may then generally take place at a speed substantially greater than that for closing, if only for accelerating evacuation of the cabin.
To avoid at least the drawback of cumbersomeness, doors are known whose transmission members form a screw-nut system in which the screw, driven in rotation by the motor, may have a variable pitch, by means of which the doors, during their opening or closing movements, are driven with a movement which, in a final phase, is accelerated then uniform and finally decelerated.
Of course this system is of relatively simple design and is only adaptable to a door of given width.
In order to adapt to doors of variable width within wide limits, it is known to control the opening and closing of doors having at least one leaf and with linear movement by means of an endless belt on which is fixed a member for connection with the leaf.
In order to regulate the speed of such a leaf, not only for opening but also for closing and particularly for slowing it down in the vicinity of its ends of travel, it is of course possible to act at the level of the motor instead of acting at the level of the transmission members.
In a closely related application, a method is in fact known (DE-A-2 625 397) and means for regulating the rotational speed of an AC electric motor, particularly an asynchronous motor, fed at a frequency varying in accordance with a reference between two endmost angular positions of the rotor, spaced apart by an adjustable number of rotor revolutions and in which endmost positions the speed is zero.
Associated with the transmission member such as screw or belt, the motor then receives, under the control of an adequate device such as a microprocessor, a power supply which varies depending on a reference as a function of the state of the signals representing the position of the leaf during its travel so as to identify the part of the reference which applies.
The opening and closing of the doors may thus take place at optimum speed.
Although such an assembly, which is relatively simple, makes it possible to regulate at will the closing speed
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Ip Paul
Shoop Jr. William M.
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