Absolute encoder for linear or angular position measurements

A encoder of the absolute position type, comprising

• a code plate having a first grid pattern wherein items of information, represented by 1 and 0, are disposed periodically, and a second grid pattern wherein items of information, represented by 1 and 0, are disposed periodically at a pitch slightly different from that of the disposition of said first grid pattern;
• a first and a second sensor array, each comprising a plurality of detecting elements, for respectively detecting said first and second grid patterns and moved in relation to said code plate;
• driving means for driving said first and second sensory arrays, said driving means comprising
• first and second switching circuits, each comprising a plurality of switches connected to said plurality of detecting elements of said first and second sensory arrays,
• a timing circuit for generating clock pulses and an alternating reference signal, and
• drive circuit means responsive to said clock pulses for turning ON and OFF said plurality of switches of said first and second switching circuits in a sequence according to a predetermined cycle thereby to transmit signals from said detecting elements;
• signal processing means for obtaining alternating output signals from said first and second sensory arrays as switched by said first and second switching circuits in response to operation of said driving means;
• phase measuring means responsive to said alternating output signals and said alternating reference signal for measuring difference between phase angles of said alternating output signals and difference between phase angles of said alternating output signals and said reference alternating signal, said phase measuring means comprising a first interval counter for counting said clock pulses in response to a signal from said second switch circuit and for stopping the counting in response to a signal from said first switch circuit, and a second interval counter for counting said clock pulses in response to a signal from said first switch circuit and for stopping the counting in response to a signal from said second switching circuit thereby to enable measurement of the differences of phase angles;
• and
• computation means responsive to said difference of phase angles between said alternating output signals and said difference of phase angles between said alternating output signals and said reference signal for calculating the position using said differences of phase angles.