Design of Compact Variable Gravity Compensator (CVGC) Based on Cam and Variable Pivot of a Lever Mechanism In this paper, we propose a new compact variable gravity compensation mechanism (CVGC). The CVGC can be used to generate gravity compensation torque by using the cam and lever mechanism and can also amplify the target gravity compensation torque by varying the pivot point of the lever. The feature of variable gravity compensation is very useful to the mobile platform, which needs to handle unstandardized tasks with a high variation of the workpiece weight. The proposed CVGC has many advantages. Most importantly, it is designed as a compact, independent onepiece structure and is lightweight, meaning it can easily be used as a mobile platform with a simple modification. The CVGC can also have a full range of compensation angle (360circ), so it does not restrict any of the original workspaces of the target platform when it is installed. First, the mechanism concept and details are explained. Next, the mechanics of the prototype for force analysis are presented. Based on these mechanics and cam theory, the methodology of the cam profile design is presented. Finally, the performance of variable gravity compensation is verified through experiments that compare the designed and measured gravity compensation torque. The verification test shows adequate performance, as we had hoped, which shows potential for the development of the CVGC.

WallMounted Robot Arm Equipped with 3DOF RollPitchPitch Counterbalance Mechanism The use of highcapacity motors and harmonic drives increases the manufacturing cost and the energy consumption of the robot. It is well known that most motor torques are used to support the robot mass and payload. To deal with this problem, we propose a wallmounted 3DOF rollpitchpitch counterbalance mechanism (CBM). Unlike previous CBMs used for floormounted industrial robot arms, the proposed CBM can be applied to wallmounted robots in which the first three joints are all coupled and affected by gravity. This mechanism is composed of pure mechanical components such as coil springs, differential gear structure, and beltpulley system. A 6DOF robot arm equipped with the proposed CBM was fabricated to verify the performance of gravity compensation. It is shown that the proposed 3DOF CBM can effectively compensate for gravitational torques, thus drastically reducing the motor torques required to operate the robot.