Lift vehicle with fail-safe overload protective system

Details Lift vehicle with fail-safe overload protective system Lift vehicle with fail-safe overload protective system

1975-04-03

1978-01-17

Spar, Robert J.

Communications: electrical

Land vehicle alarms or indicators

Internal alarm or indicator responsive to a condition of the...

340267C, 212 39MS, 177 45, 177210R, B65E 4700, G08B 2100

Patent

active

040687732

ABSTRACT:
An overload protective system continuously monitors the forward overturning moment on a counterbalanced lift truck and prevents further raising of the carriage or further forward tilting of the mast when the overturning moment is excessive. Resistance strain gage sensors mounted on a load carrying tilt jack pin which resists the overturning moment are connected in an electrical bridge which may be inherently unbalanced due to the weight of the unloaded carriage and derives a strain signal proportional to the mechanical strain in the load carrying anchor pin when the carriage supports a load; a high gain differential amplifier raises the level of the strain signal output from the bridge and unbalance compensating adjustment means permit selective variation of the potential difference between the inputs to the differential amplifier until its output voltage is substantially zero to thereby compensate for unbalance in the bridge when the carriage is unloaded; a visual indicator is lighted when the differential amplifier output voltage is substantially zero to thereby indicate that bridge unbalance is compensated for; a comparator derives a trip signal when the differential amplifier output voltage reaches a predetermined magnitude when the carriage supports a load; a shift register receiving clock pulses from an oscillator as a time reference records the history of the comparator output and a decoder analyzes the shift register output and sets a latch when the trip signal comparator output has been present for a predetermined interval of time; and disabling means responsive to setting of the latch de-energize operating coils for blocking valves which inhibit further raising of the carriage or further forward tilting of the mast.

REFERENCES:
patent: 2723844 (1955-11-01), Thurston
patent: 3777828 (1973-12-01), Dietemeyer
patent: 3819922 (1974-06-01), Horn et al.
patent: 3866200 (1975-02-01), Paredes et al.
patent: 3888321 (1975-06-01), Wiiki et al.
patent: 3913081 (1975-10-01), Hamilton
patent: 3971008 (1976-07-01), Nishizaki et al.

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