Combination optical and capacitive absolute position apparatus and method

An absolute position determination system, comprising:

• a scale portion having an optical pattern and a capacitive pattern interleaved into a single integrated scale pattern for interaction with a light interrogating signal and a voltage interrogating signal, respectively;
• a transceiver portion having optical and capacitive transmission means for transmitting the optical and voltage interrogating signals to the integrated scale pattern, and also having optical and capacitive receiving means for receiving the interrogating signals after interaction with the scale;
• support means for moveably supporting the scale and transceiver portions relative to each other;
• signal generating means, connected to the transceiver portion for generating the optical and voltage interrogating signals;
• and
• signal processing means electronically coupled to the optical and capacitive receiving means, for processing the interrogating signals after interaction with the scale to absolutely determine the relative positions of the scale and transceiver portions within a predetermined error margin.

A method for determining the absolute relative position of a scale portion and transceiver portion, comprising the steps of:

• capacitively determining the relative position of the scale and transceiver portions to within a first error margin;
• storing the capacitively determined position as position data in a first memory;
• optically determining the relative position of the scale and transceiver portions to within a second error margin, wherein the second error margin is smaller than the first error margin but wherein the optically determined position can contain an ambiguity regarding gross position data;
• storing the optically determined position as position data in a second memory;
• comparing the position data stored in the second memory with the position data stored in the first memory;
• generating a correction factor which is an integer number of the optical wavelength present on the scale if the position data stored in the first and second memory are not in agreement and applying the correction factor to the position data stored in the second memory;
• and
• reading out the position data stored in the second memory.

An absolute positioning determination system, comprising:

• a scale portion having a first regular pattern and a second regular pattern interleaved with said first pattern so that said first and second patterns are combined into a single integrated scale pattern, the first and second patterns interacting with first and second interrogating signals of qualitatively different types;
• a transducer portion having first and second sensing means for sensing the position in a defined measurement direction relative to the first and second pattern on the scale portion via scale interaction with the first and second interrogating signals;
• support means for supporting the scale and transceiver portions relative to each other in a way that makes them moveable relative to each other in the defined measurement direction;
• signal generating means, connected to the transceiver portion for generating the first and second interrogating signals;
• and
• signal processing means electronically coupled to the first and second sensing means, for processing the interrogating signals after interaction with the scale to allow determination of the absolute relative position of the scale and transceiver portions within a predetermined error margin.

An absolute position determining system, comprising:

• a scale portion having a optical diffraction pattern and an electrode pattern;
• a transceiver portion;
• capacitive interrogating means having electrical transmission means for transmitting an electrical interrogation signal from the transceiver portion to the electrode pattern on the scale portion, said capacitive interrogating means further including receiver means for receiving the electrical interrogation signal after interaction with the electrode pattern on the scale portion as a function of the relative position between the scale portion and the transceiver portion over a first range and within a first margin or error;
• optical interrogating means for transmitting an optical interrogation signal from the transceiver portion to the optical diffraction pattern on the scale portion, the optical interrogating mans further including receiver means for receiving the optical interrogation signal after interaction with the diffraction pattern on the scale portion, the interaction being a function of the relative position between the scale portion and the transceiver portion over a second range that is substantially smaller than the first range and within a second margin of error that is substantially smaller than the first margin of error;
• support means for moveably supporting the scale and transceiver portions relative to each other;
• and
• signal processing means electrically coupled to the capacitive interrogating means and the optical interrogating means for determining the absolute position of the scale portion relative to the transceiver portion over a range determined by the range of the capacitive interrogating means and with an accuracy determined by the accuracy of the optical interrogating means.

A method of determining the absolute position between a scale portion and a reference portion, comprising:

• capacitively determining the relative position between the scale portion and the reference portion over a first range and within a first margin of error;
• optically determining the relative position between the scale portion and the reference portion over a second range that is substantially smaller than the first range and within a second margin of error that is substantially smaller than the first margin of error;
• and
• using the capacitive position determination and the optical position determination to determine the absolute position of the scale portion relative to the reference portion over a range corresponding to the range of the capacitive position determination and with an accuracy determined by the accuracy of the optical position determination.