US3908939A

US3908939A - Crane trolley speed limiter

Info

Publication number: US3908939A
Application number: US444428A
Authority: US
Inventors: Ralph W Sheffler
Original assignee: United States Steel Corp
Current assignee: United States Steel Corp
Priority date: 1974-02-21
Filing date: 1974-02-21
Publication date: 1975-09-30
Anticipated expiration: 1992-09-30

Abstract

Apparatus for limiting the speed of a crane trolley along a runway has a sectionalized control rail providing maximum allowable speed reference voltages. A pilot generator driven by the trolley drive motor provides an actual speed voltage. When the actual speed voltage reaches the reference voltage level at any trolley location a dynamic braking circuit is activated.

Description

Elite States atet 1 Sheffler [451 Sept. 30, 1975 CRANE TROLLEY SPEED LIMITER [75] Inventor: Ralph W. Sheffler, Ewing Twp., NJ.

[73] Assignee: United States Steel Corporation, Pittsburgh, Pa.

[22] Filed: Feb. 21, 1974 [21] Appl. No: 444,428

[52] U.S. Cl 246/182 R; 104/153; 246/187 R 511 int. cl. B61L 3/18 [58] Field of Search 246/167 R, 182 R, 182 A,

246/182 B, 182 C, 187 B, 63 A, 49, 47,187 R; 104/153, 152, 149

[56] References Cited UNITED STATES PATENTS 3,397,309 8/1968 Stone 246/182' R Burke 246/167 R Cocciu 246/182 R Primary E.\'aminerM. Henson Wood, Jr. Assistant Examiner-Reinhard J. Eisenzopf Attorney, Agent, or Firnz'Rea C. Helm 7 1 ABSTRACT 3 Claims, 2 Drawing Figures Rwk EMU MGR QR .QQ QMQSSQ Sept. 30,1975

US. Patent mounted on the runway and trolley structures together; with speed switches mounted on the trolley motor.shaft extension. The moving trolley trips a limit switch as it approaches the end of the runwayand if the motor speed switch indicates a desired'speed has been exceeded, an undervoltage circuit in the trolley motor control opens to slow down the trolley'by dynamic braking and to apply the brakes. A pair of limit switches near each end of the runway provides a twostep or two-level control of the speed reduction. However, this system is not reliable because the deflection of the trolley when loaded sometimes causes the limit switch to miss the tripping arm. This system is not readily adapted to accommodate varying conditions of operation and hampers the operators in achieving high unloading rates.

In accordance with my invention a sectionalized control rail provides a position reference voltage throughout the length of the runway. A speed voltage is provided by a pilot generator connected to the trolley drive and whenever the speed voltage equals or exceeds the position reference voltage a control relay acts to stop the trolley.

It is therefore an object of my invention to provide a system for limiting the speed of a crane trolley in the crane runway end zones.

Another object of my invention is to provide such a system that is readily adaptable to varying operating conditions.

These and other objects will become more apparent after referring to the following specification and drawings in which FIG. 1 is a schematic diagram of the essential features of my invention and FIG. 2 is a chart of characteristic curves which explain the operation of my invention.

Referring now to FIG. 1, reference numeral 2 indicates a control rail which is divided into sections. Control rail 2 runs along the length of a crane trolley runway (not shown) in a convenient location for contact by a trolley mounted collector shoe 4 as the trolley (not shown) moves on the runway. A variable resistor 6 is connected between each pair of adjacent rail sections. A variable resistor 8 is connected between each end. section of control rail 2 and the negative terminal of a source of direct current 10. The positive terminal of source 10 is connected to the section of control rail 2 located at the center of the runway through a variable resistor 12. Collector shoe 4 is connected to the nega-.

tive terminal of source 10 through a disconnect switch 14, a voltage relay 16, a diode l8 and a variable resistor 20. Relay 16 has normally open contacts 22 connected to a conventional trolley drive motor controller 24 which controls a trolley drive motor 26. Controller 24 includes a conventional undervoltage circuit 28, to which contacts 22 are connected, for establishing dynamic braking loops to stop the trolley by connecting the-trolleydrive motors as generators and dissipating the energy in dynamic braking resistors. Motor 26 also drives a pilot generator 30. The output of pilot generator.30 is connected .through a diode bridge 32 between the negative terminal of source 10 and the connection between variable resistor 20 and diode l8.

A- position voltage reference, illustrated by the curve marked position" in FIG. 2 is established by adjusting

resistors

6, 8 and 12. Resistors 8 and 12 are set to pro vide the desired voltage levels on each half of the control rail 2. Resistors 6 are set to provide the desired voltage drop in the control rail sections between the center and the ends. The curve in FIG. 2 represents a typical desired speed control characteristic as a voltage representative of the maximum allowable speed for any positionbetween the center and one end of the runway. The curve is shown as a smooth curve for illustrative purposes only, obviously the curve is a series of steps, one for each section of the'control rail. The number and length of the control sections is determined by the desired level of control. The desired position voltage reference is not necessarily the same for both ends of the crane runway.

In operation switch 14 is closed and resistor 20 is set to establish a minimum current drain through relay 16. Assuming that the trolley is in the middle of the runway so that collector shoe 4 contacts the middle section of rail 2, the voltage across relay 16 will be at a maximum, closing contacts 22. As the trolley moves towards one end of the runway, collector shoe 4 moves towards the corresponding end of control rail 2 step by step reducing the voltage across relay 16 in accordance with the position curve of FIG. 2. At any position of the trolley along the runway, pilot generator 30 generates a voltage representative of the speed of the trolley and opposing the voltage across relay 16. A typical curve plotting this voltage is indicated by the curve marked speed in FIG. 2. If at any point on the runway the speed voltage equals the position voltage, the voltage across relay 16 will be zero and contacts 22 will open. This will activate undervoltage circuit 28 in controller 24 to brake the trolley movement.

Diode bridge 32 provides a unidirectional voltage from pilot generator 30 regardless of the direction of travel of the trolley. Diode 18 prevents current flow through relay 16 in the reverse direction in the event that generator 30 provides a voltage in excess of the position voltage picked up by shoe 4. If diode 18 was not in the circuit, relay 16 would close contacts 22 when the voltage from generator 30 was greater than the position voltage reference picked up by shoe 4 and thus nullify the speed control.

While contacts 22 have been shown as connected to initiate plugging of the trolley motor 26 for braking by use of undervoltage circuit 28, contacts 22 could also be used for other types of braking if desired.

This control system has the advantage of being easily adaptable to a wide variety of operating conditions. For example, the position voltage reference curve may be very flat, providing minimal speed control, or very steep to provide a high degree of control. The position voltage reference characteristics can readily be changed by adjusting the variable resistors 6 to any desired characteristic within the limits of the control rail section lengths. The control system has the added advantages of applying the control only as long as a desired safe speed is exceeded and at any location along the crane runway.

While one embodiment of my invention has been shown and described, it will be apparent that other modifications and adaptions may be made.

I claim:

1. Apparatus for limiting the speed of a crane trolley along a crane runway comprising a sectionalized control rail running the length of the crane runway,

a resistor connected between each pair of adjacent control rail sections,

a source of direct current power connected to energize the control rail thereby providing a reference voltage representative of a desired maximum al lowable trolley speed for each control rail section,

a collector shoe mounted on said trolley and adapted to contact the control rail and transfer the reference voltage as the trolley moves along the length of the runway,

means for providing a voltage representative of the actual speed of the trolley and means mounted on said trolley and connected to said collector shoe and said means for providing a voltage representative of the actual speed of the trolley and responsive to the voltage representative of the actual speed increasing to the level of the reference voltage for reducing the speed of the trolley.

2. Apparatus according to claim 1 in which said means for providing a voltage representative of the actual speed of the trolley includes a pilot generator drive by the trolley drive motor and a diode bridge driven to the output of the pilot generator thereby providing a unidirectional speed voltage for both directions of trolley travel.

3. Apparatus according to claim 2 in which the means for reducing the speed of the trolley includes a dynamic braking circuit mounted on the trolley,

a voltage relay connected between the collector shoe and the source of direct current power,

said relay having contacts connected to activate the dynamic braking circuit and means connecting said diode bridge to said direct current source and said relay whereby the voltage from the diode bridge is in opposing relation to the reference voltage at the collector shoe.

Claims

1. Apparatus for limiting the speed of a crane trolley along a crane runway comprising a sectionalized control rail running the length of the crane runway, a resistor connected between each pair of adjacent control rail sections, a source of direct current power connected to energize the control rail thereby providing a reference voltage representative of a desired maximum allowable trolley speed for each control rail section, a collector shoe mounted on said trolley and adapted to contact the control rail and transfer the reference voltage as the trolley moves along the length of the runway, means for providing a voltage representative of the actual speed of the trolley and means mounted on said trolley and connected to said collector shoe and said means for providing a voltage representative of the actual speed of the trolley and responsive to the voltage representative of the actual speed increasing to the level of the reference voltage for reducing the speed of the trolley.

3. Apparatus according to claim 2 in which the means for reducing the speed of the trolley includes a dynamic braking circuit mounted on the trolley, a voltage relay connected between the collector shoe and the source of direct current power, said relay having contacts connected to activate the dynamic braking circuit and means connecting said diode bridge to said direct current source and said relay whereby the voltage from the diode bridge is in opposing relation to the reference voltage at the collector shoe.