Apparatus for measuring displacement between two relatively movable members

Claim 1

In combination with a measuring apparatus for determining the extent and sense of the movement between first and second relatively moving members, the apparatus being of the general type wherein relative movement of a vernier grating and an optical grating, each having spaced lines thereon and one superimposed over the other, produce a cyclic pattern in response to the relative movement of the gratings, and wherein a transducer provides a signal in response to the cyclic pattern formed, the improvement which comprises: an elongated housing having a channel defined therein; an elongated optical grating mounted within said housing along the base of said channel; means fixedly securing one end of said grating adjacent one end of said housing; tension securing means operatively connected with said optical grating at the other end to support said optical grating in floating fashion above the channel base of said housing, said tension securing means permitting length calibration of said optical grating depending on the tension force applied thereto wherein the tension force maintains said optical grating taut whereby expansion and contraction of said housing due to temperature fluctuations do not effect the length calibration of said optical grating; a support carriage slidably carried in said housing channel for relative movement therealong, said carriage having the transducer and vernier grating mounted thereon, said vernier grating being supported in continuous spaced relationship adjacent said elongated optical grating; housing adjustment means adapted to mount said housing to said first relatively moving member, said adjustment means providing for limited axial and transverse movement of said housing relative to said first member wherein said housing may be precisely positioned for calibration purposes relative to the linear axis of measurement; bracket means projecting outwardly from said housing, said bracket means adapted to secure said bracket means to said second relatively moving member; flexible joint means operatively connecting said bracket means with said support carriage wherein relative movement between said first and second members will cause a relative movement between said housing and said carriage wherein relative movement occurs between the vernier grating and optical grating; and bias means connected to said bracket and acting against said flexible joint means to impart a preload force against said joint means thereby preventing miscounts between the vernier and optical grating when the direction of relative motion is changed.