Two Axis Rate Table
Each axis of a two axis system has the design problems of a single axis table, but with the additional difficulties:
- Alignment of the inner axis support trunnions
- Alignment of the outer axis bores
- Achieving low orthogonality errors
- Achieving good servo response of the outer axis which includes the total inertia of the inner axis (often carrying an environmental chamber)
Traditionally, the first three of these problems is overcome by precision machining of the major components This adds significantly to the cost of manufacture of the critical components and tolerance build up can result in system, errors that are even more costly to correct upon assembly. Cranfield Precision’s two axis systems use a novel and much lower cost approach.
The main support yoke is a polymer concrete moulding providing a highly stiff, stable and damped base structure.
Polymer concrete is a cold moulding process, enabling two tubular housings to be moulded into the tines of the yoke structure to take two sub-spindle assemblies. Great accuracy is not required in the moulding since the interface between the spindle assembly and its housing is adjustable.
The tubular housings have an array of adjusting screws that contact with location features machined into the sub-spindle bodies. It is then possible to align the two sub-spindle axes relative to each other using the two sets of adjusting screws.
This adjustability does not detract from system performance because once set during manufacture, the sub-assemblies are cast into their housings using more polymer concrete mix. The results is that great accuracy of alignment and orthogonality can be achieved at significantly lower cost than by traditional means and in a highly damped structure.
Two axis rate table specifications:
- Azimuth axis torque range: 34Nm to 110Nm
- Tilt axis torque range: 68Nm to 220Nm
- Rate accuracy: 0.01% set rate
- Max rate azimuth: 1000°/s
- Max rate tilt: 500 °/s
- Rate resolution: 0.0001 °/s
- Payload mass: 70kg (Balanced)
- Payload dimensions: Up to 850mm diameter x 450mm high
- Axial error motion (max): 0.0005mm
- Radial error motion (max): 0.0025mm
- Wobble (max): 2 arc sec
- Orthogonality (max): 1 arc sec