Although the possibility of a 6 degrees of freedom adjustment based on a single body pulled onto on six adjustable supports follows directly from the kinematic theory, such mechanisms are seldom used in actual products. Two major drawbacks for the use of this solution are:
1. Due to the sliding contact between the body and the supports, friction will occur and may inhibit movement.
2. Coupling between the adjusted axes cannot be avoided, this may interfere with the necessity of an adjustment procedure with a limited number of iterations
This paper presents a matrix calculation method that offers a prediction whether the body will move as required, depending on the position of the supports and on the magnitude of the friction. This method enables to check the functionality of a design. This method has been used in the design of several adjustment mechanisms consisting of a body pulled onto six supports.
The matrix calculation method also allows predicting the movement of the adjusted body due to adjustment of the separate supports. Using this it is relatively simple to simulate the movements that an operator will observe, and in this way check whether an operator is capable to handle the couplings present in the adjustment. Using the simulation the adjustment procedure can be optimized.
Modern mirror optics often consists of a limited number of elements, in which many aberrations may be attacked by adjusting only one element in five degrees of freedom, i.e. all degrees of freedom except the rotation around the optical axis. When the adjustment has to be reusable and mass and stiffness are of importance, a hexapod mechanism is 'the mechanism of choice' for this function. This choice holds even though the hexapod controls six degrees of freedom, while control of only five degrees of freedom is required, simply because there was no known configuration that does only control the required five degrees of freedom while maintaining the superior mass and stiffness properties of the hexapod.
In this paper a mechanical configuration is presented that offers a worthwhile alternative for the simultaneous adjustment of five degrees of freedom (one rotation constrained), in the sense that:
1. The rotation around one axis is constrained by the mechanical configuration, meaning that only the required five degrees of freedom have to be controlled. This means only five instead of six actuators are needed, which results in an increase in reliability.
2. The mass and stiffness of the mechanism are comparable with the hexapod.
3. From a mechanical and control point of view the configuration is less complex than the hexapod.