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Fast Tool Servo Module for Diamond
Turning Lathes Offers The Ultimate Precision
Kinetic Ceramics Fast Tool Servos (Models FTS-400, FTS-600) have been an enromous benefit to the contact lens manufacturing industry. Currently these units are working worldwide manufacturing contact lenses providing outstanding surface form and finish with high-throughput. These Precision Fast Tool Servo Modules incorporate the latest piezoelectric positioning technology to achieve optical quality machining performance. Our Fast Tool Servos can also be found working in the production of contoured automotive pistons and many other high precision automotive and aerospace products.
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Square Profile Cut While Spindle Rotates at High Speed |
Piezo FTS Tool Head |
Turnkey Piezo Fast Tool
Servo System |
System Description
When used with a single point diamond turning lathe, these Fast Tool Servos routinely achieve 12 nanometer RMS surface finishes on ashperes, toric off-axis spheres and other "free form" optical surfaces with superior dynamic range, speed and reliability. The cutting tool is driven by a fully temperature compensated and backlash free piezoelectric mechanism allowing surface features to be cut in a part turning at upwards of 6,000 rpm. This fast Z axis lathe accessory is rapidly gaining acceptance.
The servo can be fitted to any lathe including high precision diamond turning machines, forming a supplementary fast 'Z' axis. Typical axis bandwidths for such lathes are less than10Hz, but the FTS provides a bandwidth of up to 1000Hz, allowing the machining of complex shapes on a range of materials at high spindle speeds. Although the technology was developed for direct machining of contact lenses and casting molds, parts that have been successfully machined range from optically clear lens molds to contoured automotive pistons. Better than 12 nm rms. surface finish can be routinely produced and cut depths to 400 microns (.016 inches) are possible.
Extremely fast response coupled with substantial output force and high rigidity were principal requirements for the actuation system. The fast tool servo utilizes state of the art piezoelectric technology, along with a patented mechanical amplification mechanism to achieve these goals. The marriage of mechanical amplifier and piezoelectric actuators has permitted a heretofore laboratory technology to break out into mainstream usage in industry.
Thermal expansion effects in metal structures can be of the same order as the output motion from a piezoelectric actuator, potentially causing tool offset. In the Fast Tool Servo T-lever amplifier, thermal changes cause equal expansion and contraction in both support paths, resulting in no net output displacement.
Feedback control
A double feedback loop is used to linearize the output motion with respect to the control signal over a broad frequency range. A high bandwidth inner loop does most of the work by monitoring the amount of electrical charge stored in each PZ actuator and generating an error signal that is summed with the control signal. The charge loop requires no special stability compensation since it is first order and hence unconditionally stable. A position loop is constructed around the charge loop, with its position sensor mounted on the tool beam. For further information on this product please click here: Precision Fast Tool Servo (PDF - 109KB) or call and speak with an application engineer at (510) 264-2140.
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