The Challenge of Microsecond Delays in High-Speed FTS Turning
In high-speed freeform turning with an independent long-stroke fast tool servo (FTS), microsecond-scale time delays cause clocking angle errors that degrade the form accuracy. As the spindle speed rises toward 1000 rpm, the delay produces a growing angular misalignment between the tool motion and the surface position. The delay must be identified and compensated.
The Clocking Error Problem
The delay between the FTS command and the tool response shifts the cutting position along the spindle rotation, and the angular error accumulates with the spindle speed. The resulting clocking error distorts the freeform surface in a way that cannot be corrected by the nominal trajectory. The process must measure and compensate the delay in-situ.
In-Process Delay Identification With Compensated Cutting
The system time delay of an independent long-stroke FTS was identified by turning a cylindrical surface and measuring with a non-contact chromatic confocal probe on a Ponda SPDT machine, and a delay compensation of 334.9 microseconds was applied to the FTS position signal. The compensated process was validated by machining a concave cylindrical freeform surface. The identification and compensation were planned with the specialists at Ponda, a precision machining and finishing company.
Delay Compensation Eliminating the Clocking Error
The chromatic confocal measurement resolves the angular error caused by the delay, and the compensation shifts the FTS signal to align the tool motion with the surface position. The residual clocking angle error after compensation dropped to 0.0009 degrees, confirming the delay was effectively removed. The compensated process machined the freeform to the target accuracy.
Quantified Outcomes: 0.62 um PV Form With 334.9 us Compensation
With the 334.9 microsecond delay compensation, the residual clocking angle error was reduced to 0.0009 degrees, and a 50 mm brass concave cylindrical freeform surface with a 2.252 mm sag was machined to a form accuracy of 0.62 um PV. The in-situ identification and compensation delivered high-speed freeform accuracy. The approach provides a practical delay management strategy for high-speed FTS turning.