Modular optical shaft encoder having a slide gap centering mechanism and method of use

An optical modular shaft encoder for mounting on a rotatable shaft and its supporting structure, comprising:

• an encoder housing for connection to the supporting structure of the rotatable shaft so as to be non-rotatably mounted relative to the shaft, said encoder housing having an axial opening through which the shaft extends when connected to the supporting structure, an engagement surface extending at least partially around said axial opening and at least one transverse passage that opens into said axial opening;
• a light source connected to said encoder housing so as to be non-rotatably mounted with the supporting structure relative to the shaft;
• a photodetector axially spaced from said light source and connected to said encoder housing so as to be non-rotatably mounted with the supporting structure relative to the shaft;
• a mask having a mask pattern, said mask positioned axially between said light source and said photodetector and connected to said encoder housing so as to be non-rotatably mounted with the supporting structure relative to the shaft;
• a pattern wheel including a hub having an axial passage for slideably receiving the shaft and for mounting the hub to the shaft to be rotatable therewith and a radially extending surface having an optical pattern thereon, said radially extending surface axially positioned between said light source and said mask, said hub having an engagement surface extending at least partially around said axial passage and positioned to engage with said engagement surface of said encoder housing;
• and
• a linear cam element having a platform portion, said linear cam being movably disposed within said transverse passage of said encoder housing between a first position in which said platform is positioned within said transverse passage but out of said axial opening of said encoder housing so that the engagement surfaces of said hub and said encoder housing can contact one another and a second position in which at least a part of said platform portion extends within said axial opening of said encoder housing for engagement with said hub so as to space the engagement surfaces of said hub and said encoder housing from one another.

A method of mounting and aligning a modular encoder to a rotatable shaft of the type having a supporting structure, the encoder having an encoder housing with an axial opening and a radial alignment sloped surface extending at least partially around the opening, a light source connected to the encoder housing, a photodetector axially spaced from the light source and connected to the encoder housing, a mask having a mask pattern, the mask positioned axially between the light source and the photodetector, and a pattern wheel including a hub having an axial passage and a radially extending surface having an optical pattern thereon, the radially extending surface axially positioned between the light source and the mask, the hub having a radial alignment sloped surface extending at least partially around the axial passage and positioned to engage with the radial alignment surface of the encoder housing, said method comprising the steps of:

• positioning the modular encoder on the rotatable shaft with the shaft extending through the axial opening of the encoder housing and the axial passage of the hub;
• urging the hub and encoder housing toward the supporting structure of the rotatable shaft and engaging the radial alignment surfaces of the encoder housing and the hub with one another and thereby causing radial alignment of the optical pattern of the pattern wheel to the mask pattern of the mask;
• and
• mounting the encoder housing to the supporting structure of the rotatable shaft with the optical pattern of the pattern wheel radially aligned to the mask pattern of the mask.