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Twin Turret Generator

Cranfield Precision's Twin Turret Generator is a completely new machine tool concept. The machine concept is covered by granted UK and European patents with patents pending worldwide.

                TTG Precision Optical Generator

There are many applications that require the controlled motion of points relative to each other in both position and angle over a swept area or volume. It is highly desirable to minimize the number of axes required to achieve the control of these motions. It is also desirable to maintain a very tight and constant stiffness loop between the points of interest as the position and angle are controlled.

Taper Grinding

The Twin Turret Optical Grinder's unique design uses two vertical rotary axes and one in-feed axis (linear or rotary) in order to produce relative motion (position and angle) between two points in space over a swept area. The design eliminates the need for the stacked orthogonal linear axes typically used in conventional machines. This in turn reduces the machine's thermal and stiffness loops, resulting in a highly stiff, thermally insensitive machine tool.

Key design advantages with the TTG

Eliminates many problems associated with conventional stacked linear axis machines

Conventionally, machines that enable relative motion between two points (eg tool and workpiece) employ orthogonally stacked linear axes. If the two points are also to be controlled relative to each other in angle, a rotary axis is conventionally stacked upon the stack of orthogonal linear axes. This array of stacked axes typically results in a compliant stiffness loop between the two points.

Additionally, it is often the case that linear axes are most compliant in the direction that is orthogonal to the direction of motion, resulting in machine compliance characteristics that are directionally dependent and variable over the machine's working area.

Rotary axes such as those used by the TTG, can have very large thrust bearings (typically hydrostatic or aerostatic) mounted directly upon the machine base to provide highly stiff, damped axes with an excellent bearing ratio in all directions resulting in axisymmetric stiffness characteristics. This results in more predictable stiffness loop and often a higher stiffness which in turn gives a higher level of precision and repeatability throughout the machine's working volume.

2. Eliminates the requirement for orthogonal axes alignment.

The use of orthogonal linear axes often requires time consuming (and expensive) alignment to maintain orthogonality between axes and the pitch yaw and roll errors for each axis.

With the TTG, the use of the two rotary axes and one infeed axis enables software error correction to maintain position and angular motion control between the tool component. Thus no linear bearing orthogonality alignment is required.

During machine build, it is possible to measure the precision of the interpolated motion between the tool and the component and make software compensations to produce very low and repeatable errors (typically to sub-micron) over the machine's full working area

3. Eliminates disturbance forces from slideway covers

In harsh machining environments, conventional machines that have long linear axes require telescopic covers that are expensive, introduce friction, often fail and can influence the precision of linear motion (eg, straightness, positioning precision and repeatability).

With the TTG, the two rotary axes have solid, non contacting covers/labyrinths. These have no friction joints and do not influence the motion of the precision machine axes.

4. Reduced machine footprint

The Twin Turret Generator unique configuration means that for a given component size, the machine footprint is significantly smaller (typically 40%) than would be the case with conventional machines.

Potential applications

Machining, inspection or positioning of complex components that require high precision control of position and angle over a swept area or volume.

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