Abstract
Home service robots need to have compact size to work in the house and also have wide reachable range of their hands. An extendable arm which reach to both ceiling and floor while working and can be shrunk out of working is proposed and developed. Using two motors separately for rotation and extension of each joint increases arm weight and it is not efficient. Therefore, two motors with half of the power needed for joint rotation are used and they cooperatively drive both joint rotation and extension via planetary gears. Two stages of screw mechanism are also arranged to enlarge the rate of joint extension.
