Abstract
A new type of telescopic double ball bar is presented in this thesis for the Hexapod type six-DOFs motion measurement device (MMD). This double ball bar has a symmetrical geometry design to avoid the effect of self-rotation due to the mass center offset. Besides, this double ball bar uses low thermal expansion material INVAR for the linear scale so that it is non-sensitive to temperature variation. These two design improvements greatly increase the precision of the MMD. In addition to the design of the new double ball bar, this thesis also presents a new concept of machining in a single reference coordinate system, which uses the MMD to close the serial kinematic chain between the tool and the work piece. The MMD, serving as a direct measurement device, can measure the relative position and orientation between the cutting tool and the work piece in real-time. Variations caused by the changing room temperature or the internal heat sources of the machine tool such as the main spindle and motors can be measured by the MMD. The MMD is used to close the serial kinematic chain and serves as direct feedback device for the real-time position control of the machine tool. Because the relationship between the cutting tool and the work piece is measured directly, the machine tool will not be influenced by its geometric and thermal errors resulted from changing room temperature, main spindle or other heat sources. This feature is testified by real cutting tests of work pieces