Patent ID: 6385870
Filing Date: 2002-05-14
Classification: E02F

Abstract:
A thumb control for a thumb on an excavator, said thumb adapted to engage a workpiece against a bucket, said thumb control comprising:a thumb close switch; a thumb close latch adapted to be set by said thumb close switch; a thumb close valve adapted to provide pilot pressure fluid at an output when activated by a set signal from said latch; a thumb control valve adapted to connect a source of high pressure hydraulic fluid to a thumb cylinder piston extend line and connect a reservoir of low pressure hydraulic fluid to a thumb cylinder piston retract line when activated by said thumb close valve; a pressure limiter limiting pressure in said thumb cylinder piston extend line to a selected thumb cylinder close pressure limit; a thumb open switch adapted to reset said thumb close latch: a thumb open valve adapted to provide pilot pressure fluid at an output when activated by said thumb open switch; and, said thumb control valve further adapted to connect said source of high pressure hydraulic fluid to said thumb cylinder piston retract line and connect a reservoir of low pressure hydraulic fluid to said thumb cylinder piston extend line when activated by said thumb open valve.