HARMONIC DRIVES

OVERVIEWHarmonic DriveWrist end mechanism

HARMONIC DRIVESHarmonic Drive is a strain wave gear which improve certain characteristics compared to traditional gearing systems. It is trademarked by Harmonic Drive AG Company and was invented in 1957 by C.W.Musser.They are typically used in industrial motion control, machine tool, printing machine, robotics and aerospace.

Application in Aerospace: They are used in satellite for proper orientation of solar panels towards Sun. It was first used in space during Apollo 15 mission.Application in Robotics and Automation: They are used for handling of tasks particularly pick and place .Application in Defence: They are used in Remote Weapon Station (RWS). RWS is a remotely operated weapon station for light and medium weapons, which is mounted on a vehicle.

Strain Wave Gearing is a special type of mechanical gear system whose theory is based on elastic dynamics and utilizes flexibility of metals.The three basic components:Wave Generator (Input)Flex Spline (Output)Circular SplineWave Generator is made of two separate parts:Elliptical disk called wave generator plugOuter ball bearing

Flex Spline Flex Spline is like shallow cup. The sides of the spline are very thin but the bottom is thick and rigid. Teeth are positioned radially around the outside of the flex spline. The flex spline fits tightly over the wave generator, so that when the wave generator plug is rotated, the flex spline deforms to the shape of a rotating ellipse.Circular SplineThe circular spline is a rigid circular ring with teeth on the inside. The flex spline and wave generator are placed inside the circular spline, meshing the teeth of the flex spline and the circular spline. Because the flex spline has an elliptical shape, its teeth only actually mesh with the teeth of the circular spline in two regions on opposite sides of the flex spline, along the major axis of the ellipse.

WorkingAssume that the wave generator is the input rotation. As the wave generator plug rotates, the flex spline teeth which are meshed with those of the circular spline change. The major axis of the flex spline actually rotates with wave generator, so the points where the teeth mesh revolve around the centre point at the same rate as the wave generator. The key to the design of the strain wave gear is that there are fewer teeth (for example two fewer) on the flex spline than there are on the circular spline. This means that for every full rotation of the wave generator, the flex spline would be required to rotate a slight amount (two teeth, for example) backward relative to the circular spline. Thus the rotation action of the wave generator results in a much slower rotation of the flex splinein the opposite direction.

ROBOT WRIST MECHANISMWrist mechanism relates to the linkages connecting the robot arm and the end effector.Desirable characteristics of a wrist are:CompactnessLight weightStiffness and Dexterity

The wrist has three degrees of freedom: pitch, roll, yaw.A pitch is defined as rotation about horizontal axis and it is with this pitch motion, an aircraft is able to move its nose up and down.Yaw is a rotational movement about the vertical axis and this motion moves the nose of the aircraft to left or right.Roll is rotation about its own axis.

Pitch roll wrist

PITCH:- M1 and M2 simultaneous in same directionwith same speed.ROLL:- M1 and M2 simultaneous in opposite directionwith same speed.Uses three sets of bevel gears (M,N and P).The shafts M and P are driven by two separate stepper motors.Holding a tool in a welding robot.

ROLLMNPActuator 1Actuator 2

Pitch roll Yaw wrist

ROLLYAWPITCH1234ROLL:- Motor 4

YAW:- Motor 1

PITCH:- Motor 2,4 (opposite direction)

Uses 5 sets of bevel gears.Holding gripper in assembly and handling operations.