US2506805A - Load limit control - Google Patents

Description

May 9, 1950 L. M. MATTHEWS LOAD LIMIT CONTROL Original Filed Feb. 2l, 1946 Patentecl May 9, 1950 LOAD LEMIT CONTROL Leigh M. Matthews, Moline, Ill., assigner to Montgomery Elevator Company, a corporation of illinois Continuation of application Serial No. 649,249, This application May 2, i946, Serial No. 666,553

February 21, 1946.

9 Claims.

This invention relates to improvements in load limit controls in elevating systems, and more particularly to means for preventing the control from being operative due to acceleration or brain ing loads when the static load is within the predetermined safe limits.

One feature of this invention is that it pron vides an improved load limit control system; another feature of this invention is that it provides a load limit control system which is direct and positive in action; another feature of this invention is that it provdes a load limit control system which can be installed in elevating systems already huilt and in use; another feature of this invention is that it provides a load limit control system which prevents starting oi the elevating system if overload occurs; another feature of this invention is that it provides an inA dication upon overload, thereby enabling the op erator to correct the overload condition before attempting to operate the elevating system; and still another feature of this invention is that it provides a means whereby, when the elevating system is not overloaded, apparent overload caused by inertia effects upon starting is prevented from operating the load limit control system. Other features and advantages ci this invention will be apparent from the following specification and the drawing, which is a schematic representation of one embodiment of my invention.

'I'he problem of load limit control in elevator systems has been, in the past, perplexing to elevator manufacturers and operators. In ordinary passenger elevators such as are found in stores and office buildings, the problem, it is true, is not serious because the load capacity and the square foot area of the platform are functions of each other, and the elevator may be designed and built so that it cannot be overloaded with more than its rated capacity so long as it carries human beings. However, in the case of freight elevators, the capacity and the square foot area of the platform are not functions of each other, and the problem of overload becomes serious. Since such elevators are often of large platform area so they may accommodate light, bulky materials, they are susceptible to being overloaded by placing on them loads of small volume, but of great weight, such as iron bars, rails, or sheets, etc. A converse aspect of the problem is seen in the case of hospital elevators, which must necessarily he of large platform area, but which are not heavily loaded in operation. Because of the large plataform area, code requirements force manufacturers to build these elevator systems with a large load capacity, such as 3,500 pounds, including large machine units and unnecessarily heavy equipment, for in operation these elevators are seldom loaded in excess of 1,000 or 1,200 pounds.

One difculty with many existing load limit control systems is that ii the load on the elevating system approaches, but does not exceed, overload, inertia of the load upon starting causes the load limit control system to operate causing apparent overload, and citen cutting out the power to the system and resulting in a false start.

This application for a patent is a continuation of my application for Load limit control, led February 21, 1946, as Serial No. 649,249, now abandoned.

I have devised and am disclosing and claiming a load limit control system which, upon overload of the elevating system wherein it is installed, will forestall operation by cutting out the power to the drive means, thereby making it impossible to operate the elevating system, by providing an indication of overload to the operator so he may remove some of the load before attempting to start, or both; but which, if the load approaches, but does not exceed overload, will act to prevent inertia effects from operating the load limit control system, and will thereby do away with apparent overload upon starting, and false starts.

Referring now to the drawing, l0 represents a conventional three phase reversible elevator motor including windings Ica, lsb and lilo, power for said motor being supplied from three wires I l, l2 and I3, which lead to a conventional source of power (not shown) through fuses Ill, E5 and I6, respectvely, which fuses are of high amperage, and may each be in the order of one hundred amperes, Relay l'l controls the operation of the motor, and includes a coil I'la and three pairs of contact points Ilb, llc and lid, each of said pairs of contact points including a stationary and a movable element, which elements are referred to herein as together constituting a contact, and each contact being open when relay coil Ila is not energized. Relay coil lla is connected at its upper end (on the drawing) to wire i3 through lead i8, and is connected at its lower end as hereafter explained. Wir-e i3 is also connected to one element of contact l'lb through lead I9; wire l2 is connected to one element of contact llc; and wire Il is connected to one element of contact Hd by lead 20, the other element of contact Hd being connected to winding lila of the motor by lead 2l.

Two relays are shown at 22 and 23 for conditioning the motor for up or down operation as desired. Relay 22 includes relay coil 22a and two contacts, 22h. and 22e, which contacts are open when relay coil 22a is not energized; and relay 23 includes relay coil 23a and two contacts 23h and 23o, which contacts are open when relay coil 23a is not energized. The upper end of each of relay coils 22a and 23a is connected to. wire I3 by leads 24 and 25 as shown, the lower end of each of said relay coils being connected as hereafter described. One element of each of contacts 22h and 23e is connected to winding Ilb of the motor by leads 26 and 21, respectively, and one element of each of contacts 22e and 23h is connected to winding Illc of the motor by leads 28 and 29. The other element of contact 22h is connected'to the other element of contact 23h by leads 38 and 3I, and both of said contacts are connected to the other element of relay contact I1c by lead 32, and in a similar manner the other element of contact 22e is connected to the other element of contact 23e by leads 33 and 34, and both of said contacts are connected to the other element of relay contact I1b by lead 35.

It will be seen that if relay 22 is energized, contacts 22h and 22e will be closed, connecting winding Ib of the motor to the stationary element of relay contact I1c, and connecting winding IIJc of the motor to the stationary element of relay contact I 1b, and thus conditioning the motor for operation in one direction upon energization of the motor control relay I1, while if conditioning relay 23 is energized instead of relay 22, contacts 23h and 23e will be closed, connecting winding I b to the stationary element of relay contact |117, and connecting winding I llc to the stationary element of relay contact I1c, and thus conditioning the motor rfor operation in the oppocontroller if the weight load on the elevator does not exceed a predetermined maximum. Relay 4I, including relay coil 4Ia and two contacts, Ib and 4Ic, which are both open when coil 4Ia is deenergized, is so connected that when the main controller is moved from its neutral position as shown in the drawing to its up position (the elevator not being overloaded), relay coil 4Ia is energized by a ow of current from line wire I3 site direction upon energization of the control l relay I1.

Inserted in wires Il and I3, respectively, are fuses 36 and 31, which are of lower amperage than fuses I4, I5 and I6, and may be each in the order of 10 amperes. Fuses 35 and 31 are so inserted in each of wires I I and I3 that the heretofore described. connections from said wires to the motor and its associated control circuits are between fuses I4 and 36 speaking with reference to wire I I, and are between fuses I6 and 31 speaking with reference to wire I3.

In wire II on the opposite side of fuse 36 from the heretofore described connections, is a switch 38, which is movable between two positions in accordance with the load on the elevating system, which switch may be of the type shown in the co-pending application of Joseph F. Green for ya. Load limit control, Serial No. 649,283, filed February 21, 1946, now abandoned. The switch is normally in the position shown in the drawing, and moves to its abnormal or overload position if the load exceeds a predetermined maximum. A main controller, 33, which is shown in the drawing as being manually movable between an f up or down and a neutral position, but which may consist of a lever, a push-button, a

knife switch, or any other type of operators control device, is connected to wire I3v by lead 40,

and normally controls the operation of the ele' through lead 40, through main controller 39 and lead 43 connecting the up contact of the main controller to the lower end of coil 4 Ia and through coil 4Ia, and lead 44 `connecting the upper end of coil 4Ia to wire II at a point below (on the drawing) the switch 38. Similarly, relay 42, including relay coil 42a and two contacts 42h and 42e, which contacts are both open when coil 42a is deenergized is so connected by means of leads 45 and 46 that relay coil 42a is energized when the main controller is moved to its down position.

One element of contact 4Ic is connected to the lower end of relay coil. 22a by lead 41, and the other element of the Contact is connected to wire II at a point between fuses I4 and 36 by lead 48. Likewise, one element of contact 42e is connected to the lower end of relay coil 23a by lead 49, and the other element of the contact is connected to Wire II by lead 50. Lead 5I connects the lower end of coil 4 Ia to one element of contact 4 Ib, lead 52 connects the lower end of coil 42a to one element of contact 42D, and the other elements of each of contacts 4Ib and 42h are connected by leads 53 and 54, respectively, to the upper end of the coil 55a of another relay 55. Relay 55 includes two contacts 55h and 55e which are open when the relay coil 55a is deenergized, and athird contact 55d which is closed when said coil is deenergized. The lower end of relay coil 55a is connected to wire II at a point below switch 38 'by lead 56.

One element of contact 55h is connected to wire II at a point between fuses I4 and 36 by lead 51, and the other element of contact 55h is connected to the lower end of relay coil I1a by lead 58. One element of contact 55e is connected to wire II at a point below switch 33 by lead 59, and the other element of contact 55e is connected to wire II at a point above switch 38 by lead in such manner as to form a short circuit across switch 38 when contact 55c is closed. Lead 6I connects the abnormal or overload position contact of switch 38 with one element of contact 55d, said lead incorporating an indicating device therein. Such indicating device is shown as a lamp at 62, but it will be understood that various indicating devices other than the lamp shown at 62 may be employed. The other element of contact 55d is connected to wire I3 at a position, current will flow through relay coil 4 Ici,

and it will become energized, closing contacts 4Ib and 4Ic. flow through relay coil 22a, energizing said coil and closing contacts 22h and 22c, and this will close a circuit connecting motor windings IUb and Ic with relay contacts I1c and I'Ib as hereltofore explained, thus conditioning the motor!l When contact 4Ic closes, current will' accesos to run in one direction. When contact lib closes, relay 55 will also be energired, closing contacts 55h and 55o and opening contact 55d. Closure of contact 55h results in actuating relay I l, which controls the current to the motor. Since the motor has already been conditioned to operate in the desired direction, when the contacts of relay Il close the motor will start to run in the desired direction.

It often happens that upon starting, the inertia of the load causes an apparent overload and the switch 38 will move to its abnormal or overload position while acceleration of the elevator is taking place. Ordinarily this would mean that the circuit to the motor would be opened so the motor would stop, and the indicator lamp 62 would light. However, when contact 55o closes it places a short circuit consisting of leads 59 and 60 around the switch 38, and said switch is rendered ineiective to forestall operation of the motor. Further, the opening of contact 55d upon actuation of relay 55 opens the circuit to the indicator lamp 62 so that no false indication of overload will be given as the elevator starts.

If the main controller be moved to down position, relay 42 will be actuated, and will in turn actuate relay 23 which will condition the motor for operation in the opposite direction. Relay 55 will also be actuated, and the motor will be energized as above described.

Should the elevator be loaded beyond the predetermined maximum weight before the main com troller is moved from its neutral position, however, the switch 38 will move to its abnormal or overload position, thus forestalling operation un der the dangerous overloaded conditions. rI'his forestalling operation of the switch results in breaking the lead H and making it impossible to start the motor and complete a circuit through indicator 52, so that an indication of overload will be given, thus giving the operator an opportunity to relieve the overload condition before attempting to start.

While I have shown and described a certain embodiment of my invention, it is to be understood that it is capable of many modications. Changes, i

therefore, in the construction and arrangement may be made without departing from the spirit and scope of the invention as disclosed in the appended claims.

I claim:

1. In an elevating system including a hoisting device and drive means therefor, an operating circuit including: conditioning means for determining the direction of operation of said drive means; separate control means for normally determining the operation of the drive means switch means movable between two positions in accordance with the load on the hoisting device, said switch means being so connected as to forestall operation of said drive means upon overload of the hoisting device; and means operated by said control means for rendering said switch means ineiective to forestall operation of said drive means.

2. In an elevating system including va hoisting device and drive means therefor, an operating circuit including: control means for normally determining the operation of the drive means, such control means including a main controller, and a pair of separate switch devices selectively actuated thereby according to the desired direction of operation; switch means movable between two positions in accordance with the load on the hoisting device, said switch means being so connected as to forestall operation. o'f said drive means upon overload of the hoisting device; and

a circuit separate from said drive means and im cluding a relay operated by said control means for rendering said switch means ineffective to forestall operation of said drive means.

3. In an elevating system including a hoisting device and drive means therefor, an operating circuit including: control means for normally determining the operation of the drive means, such control means including a main controller, and a plurality ci separate switch devices selectively actuated thereby according to the desired direction of operation; switch means movable between two positions in accordance with the load on the hoisting device, said switch means being so connected as to forestall operation of said drive means upon overload of the hoisting device; and a circuit separate from said drive means and including a relay operated by Said control means, said relay including a plurality 0f contacts, one of said contacts determining the operation of said drive means upon operation of the relay, and another of said contacts being in'- cluded in a circuit adapted to bridge said switch means upon operation oi the relay, rendering said Vswitch means ineffective to forestall operation of said drive means.

4. In an elevator system including a cage and a high current circuit including drive means therefor, a low current operating circuit including: conditioning means for determining the direction of operation of said drive means; control means for normally determining the operation of the drive means, such control means including a main controller, a 'first relay normally actuated by operation of the main controller in one direction, and a second relay normally actuated by operation of the main controller in the other direction, each of said relays including a plurality of contacts, one of said contacts on each of said relays determining the operation of said conditioning means; switch means movable between two positions in accordance with load on the cage, said switch means being so connected as to positively prevent operation of said drive means upon overload of the cage; and a third relay, operation of which is determined by another contact on each of said rst and second relays, said third relay including a plurality of contacts, one of said contacts being connected in said high current circuit and determining the operation of said drive means upon operation of said third relay, and another of said contacts being included in the low current circuit adapted to bridge said switch means upon operation of said third relay, rendering said switch means ineffective to prevent operation of said drive means.

5. In an elevator system including a cage and a high current circuit including drive means therefor, a low current operating circuit including: control means for normally determining the operation of the drive means, such control means including a main controller, and means selectively actuated thereby according to the desired direction of operation; switch means movable between two positions in accordance with the load on the cage, said switch means being so connected as to forestall operation of said drive means upon overload of the cage; indicating means actuated by said switch means upon overload of the cage for indicating such condition; and a circuit separate from said drive means and including a relay operated by said control means, said relay having a plurality of contacts, one of said contacts determining the operation of said drive means, and another of said contacts being adapted to render said indicating means inoperable upon operation of the relay to effect operation of the drive means.

6. In an elevating system including a hoisting device and a high current circuit including drive means therefor, a low current operating circuit including: control means for normally determining the operation of the drive means, switch means movable between two positions in accordance with the load on the hoisting device, said switch means being so connected in said low current circuit as to positively prevent operation of said drive means upon overload of the hoisting device; indicating means in the low current circuit actuated by said switch means upon overload of the hoisting device for indicating such condition; and a. relay in a circuit separate from saiddrive means, said relay being operated by said control'means, and including a plurality of contacts, one of said contacts being connected in the high current circuit and determining the operation of said drive means upon operation of the relay, another of said contacts being included in the low current circuit and being adapted to bridge said switch means upon operation of the relay, rendering said switch means ineffective to prevent operation of said drive means, and another of said contacts being connected in the low current circuit and being adapted to render said indicating means inoperable upon operation of the relay.

7. In an elevating system, including a hoisting device and a high current circuit including drive means therefor, a low current operating circuit including; control means for normally determining the operation of the elevating system, such control means including a manually operated control, and a plurality of devices selectively actuated thereby; switch m'eans movable between two positions in accordance with the load on the hoisting device, said switch means being so connected as to forestall overloaded operation of said elevating system; and a relay in the low current circuit operated by said control means for rendering said switch means ineffective to forestall operation of said elevating system.

8. In an elevator system including a cage and drive means therefor, an operating circuit including: control means for normally determining the operation of the elevator system, such control means including main control means and a pair of switch devices selectively actuated thereby according to the desired direction of operation; switch means movable between two positions in accordance with the load on the cage, said switch means being so connected as to forestall overloaded operation of the elevator system; and a relay'operated by said control means, said relay being in a series circuit with said control means but in a separate circuit from said drive means, said relay including a plurality of contacts, one of said contacts determining the operation of said elevator system uponv operation of the relay, and another of said contacts being included in a circuit adaptedY to bridge said switch means upon operation of the relay,frendering said switch means ineffective to forestall operation of said elevator system.

9.' In an elevator system including a cage and drive means therefor, an operating circuit including: control means for normally determining the operation of the elevator system, such control means including main control means and two separate relays selectively actuated thereby according to the desired direction of operation; switch means movable between two positions in accordance with the load on the cage, said switch means being so connected as to forestall overloaded operation of said elevator system; indi' cating means actuated by said switch means upon overload of the cage for indicating such condition; and a third relay, operated by said control means, said relay being in a series circuit with said control means butin a separate circuit from said drive means, said relay including a plurality of contacts, one of said contacts determining the operation of the elevator system and another oi said contacts being adapted to render said indicating means inoperable upon operation of the relay to effect operation of the elevator system.

LEIGI-I M. MATTHEWS.

REFERENCES CITED The yfollowing references are of record in the le of this patent:

UNITED STATES PA'I'EN'IS Number Name Date 1,613,216 Albersheim et al Jan. 4, 1927 1,730,747 Schienfeld Oct. 8, 1929 2,298,174 Santini Oct. 6, 1942

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