US 7,321,231 B2
Measurement instrument
Shuuji Hayashida, Kawasaki (Japan); Shozaburo Tsuji, Kawasaki (Japan); and Yuji Fujikawa, Kure (Japan)
Assigned to Mitutoyo Corporation, Kawasaki (Japan)
Filed on Jul. 17, 2006, as Appl. No. 11/487,427.
Claims priority of application No. 2005-213298 (JP), filed on Jul. 22, 2005.
Prior Publication US 2007/0018658 A1, Jan. 25, 2007
Int. Cl. G01R 27/26 (2006.01); G01B 3/18 (2006.01)
U.S. Cl. 324—662  [324/66; 33/813] 7 Claims
OG exemplary drawing
 
1. A measuring instrument comprising:
a main body;
a spindle screwed into the main body and advanceable/retreatable in an axial direction in accordance with its rotation;
a phase signal transmitter that transmits a phase signal in accordance with the rotation of the spindle, the phase signal differing corresponding to a rotation angle of the spindle; and
an arithmetic processor that arithmetically processes the phase signal to obtain an absolute position of the spindle,
wherein the phase signal transmitter transmits the phase signal at a predetermined pitch, and
wherein the arithmetic processor further comprises:
a rotation angle calculator that calculates the rotation angle of the spindle based on the phase signal;
a rotation number calculator that counts the rotation number of the spindle based on the rotation angle of the spindle calculated by the rotation angle calculator;
a total rotational phase calculator that calculates a total rotational phase of the spindle based on the rotation number of the spindle counted by the rotation number calculator and the rotation angle of the spindle calculated by the rotation angle calculator; and
a spindle position calculator that calculates the absolute position of the spindle based on the total rotational phase of the spindle calculated by the total rotational phase calculator,
wherein the phase signal transmitter comprises a single rotor that rotates integrally with the spindle and includes a rotating surface perpendicular to the axial direction of the spindle, and a single stator provided on the main body and including a rotation-detecting surface for detecting the rotation of the rotor opposing to the rotor, the stator transmitting the phase signal corresponding to a rotation angle of the rotor,
the stator further comprises two detecting tracks for detecting the rotation of the rotor on the rotation-detecting surface and transmitting signals different from each other, the two tracks being a first track that transmits a first phase signal and a second track that transmits a second phase signal varying at a period different from that of the first phase signal,
phase difference between the first phase signal and the second phase signal differs corresponding to the rotation angle of the rotor, and
the rotation angle calculator calculates the rotation angle of the rotor based on the phase difference.