Control system for an excavator thumb and a method of controlling an excavator thumb

A thumb control for a thumb on an excavator, said thumb being positioned by a thumb cylinder said thumb adapted to engage and retain 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 fluid at an output when activated by a set signal from said latch;
• a hydraulically operated thumb control valve adapted to connect a source of high pressure hydraulic fluid to a thumb cylinder piston extend line when activated by said thumb close valve;
• a pressure limiter limiting pressure in said thumb cylinder piston extend line to a selected thumb close pressure limit;
• a thumb open switch adapted to reset said thumb close latch;
• a thumb open valve adapted to provide 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 a thumb cylinder piston retract line when activated by said thumb open valve.

A thumb control for a thumb on an excavator having a hydraulic system with a maximum system pressure, said thumb being positioned by a thumb cylinder having an extend port and a retract port, said thumb being adapted to engage a workpiece against a bucket, said thumb control comprising:

• an operator actuable actuator means;
• a close means directing hydraulic fluid to said extend port at a preselected thumb close pressure less than said maximum system pressure and maintaining said thumb close pressure;
• an open means stopping the flow of hydraulic fluid to said extend port and directing hydraulic fluid to said retract port;
• and,
• said actuator means controlling said close means and said open means.

A method of controlling a thumb on an excavator, said thumb being movably opposed to a movable implement, said implement being positioned by an implement cylinder, said thumb being positioned by a thumb cylinder having a piston fixed to said thumb, a piston extend port and a piston retract port comprising the following steps:

• providing a thumb close latched manual control;
• providing a thumb open manual control;
• providing a source of hydraulic fluid at a high pressure;
• providing a drain to low pressure hydraulic fluid;
• providing a connection to hydraulic fluid at a selected pressure less than said high pressure to said thumb cylinder piston extend port and providing a connection to said drain to low pressure hydraulic fluid when said thumb close latched manual control is actuated;
• maintaining said selected pressure at said piston extend port and said connection to said drain to low pressure hydraulic fluid regardless of thumb position while said thumb close latched manual control is latched;
• and,
• upon actuation of said thumb open manual control, unlatching said thumb close latched manual control, connecting said thumb cylinder piston extend port to said drain to low pressure, connecting said thumb cylinder retract port to said source of hydraulic fluid at high pressure.