ROLLER-GEAR DRIVE FOR ROBOTIC MANIPULATORS

MULTIROLLER PLANETARY TRACTION DRIVES (FIGURE 1) OFFER A UNIQUE COMBINATION OF COMPACTNESS, HIGH EFFICIENCY AND HIGH TORSIONAL STIFFNESS IN HIGH RATIO DRIVES. THEY HAVE THE ADDED ADVANTAGES OF BACK-LASH FREE OPERATION, LOW NOISE AND VIBRATION, NO GEAR COGGING AND SMOOTH TORQUE TRANSFER IN BIDIRECTIONAL OPERATION. PRESENTLY USED PLANETARY GEAR SYSTEMS SUFFER FROM EITHER BACK-LASH OR LOSS OF EFFICIENCY, WHILE HARMONIC DRIVES COG IN REVERSE. FURTHER BENEFITS IN COMPACTNESS (HIGH TORQUE CAPABILITY) WITHOUT SACRIFICE OF THE INHERENT ADVANTAGES CAN BE ACHIEVEDBY COMBINING TRACTION ROLLERS AND GEARS. A TYPICAL DRIVE (FIGURE 2) EMPLOYS A PLANETARY ARRANGEMENT OF GEARS AND ROLLERS CONSISTING OF A SUN ROLLER GEAR, TWO CONCENTRIC CLUSTERS OF STATIONARY ROLLER GEAR PLANETS AND A RING GEAR. THE LOW TORQUE, HIGH SPEED INPUT IS SUPPLIED TO THE SUN, AND THE HIGH TORQUE, LOW SPEED OUTPUT IS TAKEN FROM THERING GEAR. ROLLER DIAMETERS ARE NOMINALLY EQUAL TO GEAR PITCH DIAMETERS WITH A PRELOAD AT ASSEMBLY WHICH SLIGHTLY EXCEEDS THE GEAR SEPARATING FORCE. THIS INSURES THAT THE ROLLERS WILL NOT SEPARATE AND CAUSE BACKLASH OR CHATTER. THE GEAR TEETH TRANSMIT PURELY TANGENTIAL FORCES. A SPECIFIC DRIVE RATIO, TORQUE REQUIREMENT AND SPEED WILL BE CHOSEN FOR STUDY. FINAL DESIGNS WILL BE WORKED OUT FOR TWO DRIVES OF HIGH MODULUS STEEL, ONE WITH DRY FILM AND ONE WITH GREASE LUBRICATION. DRIVE KINEMATICS, SIZE, LIFE AND EXPECTED PERFORMANCE WILL BE FULLY DEFINED.