US 4,395,706 AGranted

Boom limit safety control circuit

AssigneeJLG Industries, Inc.

InventorEugene L. Garber

Life of this patent

Estimating the term…

Loading patent…

Abstract

A safety circuit for a lifting device extensible boom is presented wherein the boom angle of elevation and boom length are each converted into a parallel coded word. The two coded words, one representing boom angle and the other boom length, are processed in a digital logic network which provides inhibit functions that prevent boom extension or boom lowering when either of the two boom actions will place the boom in a position which will damage the boom or topple the machine. A plurality of switches are associated with the boom to generate and apply the boom length code word to a monitoring circuit, which responds thereto to provide a switch malfunction signal when one of the switches is defective, whereby boom extension or lowering are inhibited.

Claims13

Dependent claims

An extensible boom safety control circuit comprising:

a. means for generating a coded boom angle word representing the boom angle of elevation comprising a voltage divider network including a pendulum potentiometer having a plurality of sequential swept contacts for providing discrete voltage levels representing boom angles;
and electrical contact means for contacting said swept contacts of said pendulum potentiometer;
an electrical bus connected to said electrical contact means;
a plurality of voltage comparators connected in parallel to said electrical bus for producing a parallel, coded word representing boom angle;
and a plurality of voltage dividers for providing reference potentials for said plurality of comparators;
b. means for generating a coded boom length word representing boom length, comprising a plurality of microswitches connected in parallel and means responsive to boom length for actuating said microswitches in a mutually exclusive fashion;
c. boom angle logic means responsive to said boom angle word and said boom length word for generating a boom extension control signal, wherein said boom angle logic means comprises a plurality of 3-input NAND gates each of which includes a first input electrically connected to one of said comparators, a second input electrically connected via an inverter to a different one of said comparators, and a third input electrically connected to one of said microswitches, and an inhibit function NAND gate including an input for each of said 3-input NAND gates, said 3-input NAND gates each connected to one of said inputs;
and
d. boom length logic means responsive to said boom length word and said boom angle word for generating a boom lowering control signal;
e. boom extension inhibit means responsive to said boom extension control signal for preventing boom extension;
and
f. boom down inhibit means responsive to said boom lowering control signal for preventing boom lowering.

9 more elements

A safety control circuit for a variable length boom extensible in a rectilinear direction along its axis and pivotable between a down position and an up position, said safety control circuit comprising:

first means for generating a first coded word indicative of the angle of elevation of the boom from its down position;
second means for generating a second coded word indicative of the length of the boom;
boom extension control means disposable to a first state for permitting boom extension and to a second state for preventing boom extension;
boom lowering control means disposable to a first state for permitting boom lowering toward its down position and to a second state for preventing boom lowering to its down position;
first control logic responsive to the first and second coded words as indicative of an unstable boom condition for disposing said boom extension control means to its second state;
and second control logic responsive to the first and second coded words as indicative of an unstable boom condition for disposing said boom lowering control means to its second state;
monitoring means responsive to said second coded word for providing an inhibit signal if said second means is malfunctioning, and said boom lowering control means responsive to said inhibit signal to be disposed to its second state.

4 more elements

Dependencies are inferred from the claim text.