Tolerancing of single point diamond turned diffractive optical elements and optical surfaces

Abstract

Single point diamond turning is now gaining increasing importance with the production of the surfaces for different optical systems such as infrared systems, the prototype production of camera phones or head mounted displays featuring plastic lenses, or master manufacturing for the injection moulding of plastic lenses for mass products. Tolerances which occur during single point diamond turning of aspheric surfaces and diffractive elements or during polar coordinate laser plotting of computer-generated holograms will be examined. In both cases we expect similar tolerances, because the work piece is rotated in both diamond turning and laser plotting. The objective is to understand the typical tolerances and to simulate their influence on the aberrations in the optical system.

Form error in diamond turning

“…It is very important to know what may cause the spindle star form error since each machine may operate at different spindle speeds. However, both these articles [9] and [11] addressed the source of such error as coming from the spindle axial motion due to the imbalance in the air-bearing spindle system.…”

“…Bittner [9] simulated all possible sources of error while diamond turning diffractive optical elements. His simulations covered not only physical errors from decentering of the tool with respect to the center of rotation and tilting of the machine slide relative to the spindle, but also periodic errors like variable shift between tool and spindle, periodic structures formed due to thermal effects, and tool wear and vibration of the axis of rotation which produces a spindle star pattern on the part.…”

Parametric Mid-Spatial Frequency Surface Error Synthesis

“…Specifically, the error can be caused by spindle movement during the turning process. This is referred to in the literature as "spindle star error" [21,22]. It is typically observed for on-axis fabrication in close proximity to the rotation axis.…”

Influencing Factors and Theoretical Models for the Surface Topography in Diamond Turning Process: A Review

“…Their theoretical results prove that the slide straightness and angular errors result in the oscillating and tilting surface profile, while the vibrations can cause the segments on the machined surface as demonstrated in Figure 8. Bittner et al and Wu et al considered the tilt error between the moving direction of the diamond tool and the spindle axis, and pointed out this error can lead to a conical profile error on the machined surface topography [95,96].…”