Absolute position encoder scale having layers in a stacked configuration

摘要

An absolute position encoder scale includes first and second layers in a stacked configuration. A read head moves relative to spatial modulation patterns of first (top) and second (lower) signal layers along a measuring axis, and a sensing portion produces one or more scale sensing fields to sense the signal layers. A higher frequency scale sensing field may provide a first limited sensing depth to sense position relative to the top signal layer pattern, and a lower frequency field may provide a second deeper sensing depth to sense position relative to the lower signal layer pattern. In some embodiments, an isolation layer between the first and second layers may include a spatial modulation pattern that complements the first layer pattern, to nullify its signal effects when sensing position relative to the second layer pattern using the second sensing depth.

主权项

1. A position sensing device usable to measure a position of a first member with respect to a second member along a measuring axis, the position sensing device comprising:
a scale comprising first and second layers that extend along the measuring axis and that are stacked on one another along a depth direction that is approximately normal to the scale layers, the first layer comprising material forming a first spatial modulation pattern along the measuring axis, and the second layer comprising material forming a second spatial modulation pattern along the measuring axis that is different than the first spatial modulation pattern over an absolute range along the measuring axis; and a read head for being moved relative to the scale along a direction of the measuring axis, the read head comprising a sensing portion arranged along the depth direction relative to the scale and configured to produce at least one scale sensing field that may be modulated by the first and second spatial modulation patterns of the first and second layers and provide first and second position signal components based on using first and second circuit configurations to provide a first smaller signal-sensing depth and a second smaller signal-sensing depth for the at least one scale sensing field; and configured wherein: the first layer is closer to the read head along the depth direction than the second layer, and the first spatial modulation pattern of the first layer provides a dominant first position signal component sensed using the first circuit configuration; the second spatial modulation pattern of the second layer provides a significant second position signal component sensed using the second circuit configuration and a less significant second position signal component when using the first circuit configuration; and the first and second spatial modulation patterns are configured such that the second position signal component includes a signal characteristic that provides a plurality of unique values relative to the first position signal component at corresponding positions along the absolute range.