Rotating laser transmitter
The transmitter has a generally flat, circuit board stator, a rotor including a plurality of magnets mounted in a ring around a central opening, and a bearing, supporting the rotor for rotation about an axis that extends through the central opening, A pentaprism assembly including an optics holder is mounted on the rotor for rotation therewith. The pentaprism assembly receives a beam of laser light through the central opening and redirects at least a portion of the laser light outward in a direction normal to the rotation axis. A laser source, mounted on the stator, provides a beam of laser light through the central opening to the pentaprism assembly. The beam of laser light is aligned with the rotation axis. The laser source includes a collimating lens positioned within the rotor. A shield plate of magnetic material beneath the stator exerts a force on the rotor in conjunction with the magnets, taking play out of the bearing. The transmitter uses Hall effect sensors on the stator to control switching current to coils on the stator. The transmitter also uses the outputs of the Hall effect sensors and a timer output to control dithering of the laser beam.
1. A laser transmitter, comprising:
a generally flat, circuit board stator, including a plurality of motor coils,
a laser source, mounted on said stator, for providing a beam of laser light directed outward from said circuit board stator,
a rotor including a plurality of magnets mounted in a ring around a central opening,
a pentaprism assembly including an optics holder mounted on said rotor for rotation therewith, said pentaprism assembly receiving said beam of laser light through said central opening and redirecting at least a portion of said laser light outward in a direction normal to said rotation axis,
a bearing, supporting said rotor for rotation about a rotation axis that extends through said central opening and that is aligned with said beam of laser light,
said bearing comprising a single ball bearing having a plurality of bearing balls between an outer race secured to said rotor and an inner race, and
a magnetic shield plate on the side of said circuit board stator opposite said rotor for providing for magnetic attraction between said plurality of magnets and said magnetic shield plate, whereby play in said bearing is substantially eliminated.
2. The laser transmitter of claim 1 , in which said plurality of magnets comprises a ring magnet having a plurality of poles arranged in a circle.
3. The laser transmitter of claim 1 in which said laser source comprises a light emitting diode and a generally cylindrical housing mounted on said circuit board stator, said housing surrounding said light emitting diode and permitting the beam from the diode to pass there through, said collimating lens being mounted in said housing such that a collimated beam of laser light is directed to said pentaprism assembly.
4. The laser transmitter of claim 3 in which said bearing has an inner race mounted on said generally cylindrical housing and an outer race secured to said rotor.
5. A laser transmitter, comprising:
a stator,
a laser source, mounted on said stator, for providing a beam of laser light directed outward from said stator,
a rotor including magnets in a ring around a central opening,
a bearing, supporting said rotor for rotation about a rotation axis that extends through said central opening and that is aligned with said beam of laser light,
a pentaprism assembly including an optics holder mounted on said rotor for rotation therewith, said pentaprism assembly receiving said beam of laser light through said central opening and redirecting at least a portion of said laser light outward in a direction normal to said rotation axis, and
a magnetic shield plate on the side of said stator opposite said rotor for applying a force to said rotor in the direction of said axis of rotation such that said rotor applies an axial force to said bearing, whereby magnetic attraction between said plurality of magnets and said magnetic shield plate substantially eliminates any play in said bearing.
6. The laser transmitter of claim 5 , in which said bearing comprises an inner race supported on said laser source, and an outer race engaged by said rotor, and a plurality of balls between said inner race and said outer race.
7. The laser transmitter of claim 5 , in which said laser source includes a cylindrical housing, and in which said inner race is supported on said cylindrical housing of said laser source.
8. The laser transmitter of claim 5 in which said magnetic shield plate on the side of said stator opposite said rotor is annular in shape.
9. The laser transmitter of claim 5 , in which said bearing comprises an outer race supported by said inner race and engaging said rotor.
10. A laser transmitter, comprising:
a stator,
a laser source for providing a beam of laser light,
a rotor including magnets,
a bearing, supporting said rotor for rotation about a rotation axis, said bearing comprising a single inner race and a single outer race with a plurality of bearing balls therebetween,
a pentaprism assembly including an optics holder mounted on said rotor for rotation therewith, said pentaprism assembly receiving said beam of laser light and redirecting at least a portion of said laser light outward in a direction normal to said rotation axis, and
a plate of magnetic material positioned to provide an axial biasing force to said bearing whereby magnetic attraction between said plurality of magnets and said plate substantially eliminates the play in said bearing.
11. The laser transmitter of claim 10 , in which said magnets are arranged in a ring, and in which said plate of magnetic material is annular in shape.
12. A laser transmitter, comprising:
a stator including a plurality of motor coils and a pair of Hall effect sensors,
a rotor including magnets mounted in a ring,
a bearing, supporting said rotor for rotation about a rotation axis,
a laser source for providing a beam of laser light,
a pentaprism assembly including an optics holder mounted on said rotor for rotation therewith, said pentaprism assembly receiving said beam of laser and redirecting at least a portion of said beam outward in a direction normal to said rotation axis, and
a motor drive circuit, responsive to said Hall effect sensor and to a timer, for repeatedly driving the rotor in a first direction and then driving the rotor in a second direction, with the reversal of the direction of rotation being based at least in part on the passage of time after the Hall effect sensor provides an indication of the rotor being in a specific location.
13. The laser transmitter of claim 12 in which said motor drive circuit drives the rotor in a first direction upon receipt of an output from a Hall effect sensor, and reverses the direction of rotation after the passage of a predetermined amount of time.
14. The laser transmitter of claim 12 in which said motor drive circuit drives the rotor in a first direction after a passage of a predetermined time following the receipt of an output from a Hall effect sensor, and drives the rotor in a second direction after a passage of time following the receipt of the next output from the Hall effect sensor.