Generally, a hybrid control is realized by sensor signal feedback of position and force. However, some robot manipulators do not have a force sensor due to the environment of robot manipulator. Moreover, a precise force sensor is very expensive. In order to overcome these problems, this paper proposes the estimation system of reaction force without using a force sensor. This force estimation system consists of the torque observer and the inverse dynamics calculation. Using both this force estimation system and H∞
acceleration controller, this paper realizes the hybrid control of position and force without force sensor. H∞
acceleration controller is based on H∞
control theory, and it takes account of the frequency characteristics of both sensor noise effect and disturbance rejection. The experimental results in this paper illustrate the fine hybrid control of the tested three-degrees-of-freedom DD robot manipulator without force sensor.