Abstract:
A laser transmitter has a transmitter housing and a laser source in the housing. A gimbal support arrangement supports the laser source in the housing and includes a gimbal motor arrangement for moving the gimbal support arrangement and said laser source in said housing. A gimbal motor drive circuit actuates the gimbal motor arrangement to cause the gimbal support arrangement to move in said housing. A plurality of optical proximity sensors sense the orientation of said gimbal support arrangement to the interior of said housing. By this arrangement, damage to the transmitter is prevented.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     Not applicable. 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not applicable. 
     BACKGROUND OF THE INVENTION 
     The present invention relates to laser transmitters of the type that are useful for surveying or for spatial positioning at a construction site or elsewhere. Such laser transmitters project a thin beam of laser light or a fan-shaped beam of laser light, and rotate the beam about a rotation axis, have been in use for a number of years at construction sites. Such transmitters can be used with manual surveying systems and also as a part of automated surveying systems. Laser transmitters of this type can also be used in spatial positioning systems that provide for control of earthmoving machines, and the like, to shape a construction site to a desired contour. 
     Laser transmitters of this type typically have self-leveling and automatic orienting capabilities. The laser transmitter is typically positioned at a worksite on a support tripod and then roughly leveled manually. A worker will manually adjust the transmitter housing while watching bubble vials. Fine leveling is then effected automatically by adjusting the orientation of the laser and associated optics inside the transmitter housing. Additionally, if it is desired to project a slightly tilted beam, the orientation of the laser and associated optics will be tilted inside the transmitter housing. In either event, the housing remains stationary and electric motors drive a gimbal mounting arrangement that supports the laser and associated optics to achieve the desired level or tilted orientation automatically. A control arrangement uses electrical level vials that move with the gimbal mounting arrangement, and that provide an electrical indication when the gimbal mounting arrangement has been moved to the desired orientation. 
     A difficulty encountered with such an arrangement is that the level motors could conceivably cause the gimbal arrangement to tilt by too much with respect to the housing, with the result that the laser or other movable internal components could be driven into contact with some portion of the housing or with other parts of the transmitter. Such contact could cause damage to the laser or other parts of the transmitter. In the past, to prevent this damage, a series of mechanical limit switches have been used that are actuated when the laser and associated structures reach the end of their normal range of travel in either direction along either of two orthogonal axes. Such mechanical limit switches are difficult to configure and calibrate, however. Further, mechanical limit switches are closed when the end of travel is reached, but provide no indication as the end of travel is about to be reached. Therefore, the movement of the transmitter internal gimbal supports must necessarily be undesirably slow. 
     Other problems result from using mechanical limit switches to detect the end of travel of the gimbal support arrangement. Because mechanical limit switches must necessarily be relatively close to bosses or other structures on the interior of the transmitter housing so that the switches can be actuated by contact with the bosses or other structures, a transmitter using such switches is not as rugged as might be desired. If the transmitter is inadvertently dropped and one of the switches is relatively close to the interior of the housing, the switch can strike the interior of the housing, resulting in damage. 
     Further, it will be appreciated that if, for example, four switches used in a transmitter to detect the end of travel in either direction along either of two orthogonal axes, it is possible that the gimbal support arrangement may be moved so that the maximum tilt of the laser and components with respect to the housing actually occurs along an axis that is between the axes on which the mechanical switches is situated. To take this into account, the mechanical limit switches must be arranged to be actuated when the gimbal support arrangement is tilted by a lesser amount along an axis on which the switches are positioned. As a consequence, the interior of the housing must be designed in a way that is less than optimum to assure that the gimbal support arrangement and other movable components do not come into contact with the housing. 
     SUMMARY OF THE INVENTION 
     These difficulties are overcome by a laser transmitter according to the present invention that comprises a transmitter housing, a generally flat, circuit board stator, and a rotor defining a central opening. The transmitter further includes a bearing supporting the rotor for rotation about an axis that that is generally perpendicular to the generally flat, circuit board stator, and that is aligned with the center of the central opening. A laser source is mounted on the stator for providing a beam of laser light that is directed outward from the circuit board stator in alignment with the rotation axis. A pentaprism assembly is mounted on the rotor for rotation therewith. The pentaprism assembly receives the 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 gimbal support supports the stator within the transmitter housing. A gimbal motor arrangement orients the gimbal support. A plurality of pairs of light sources and light sensors sense the proximity of the circuit board stator with respect to the interior of the transmitter housing. 
     A plurality of reflectors on the interior of the transmitter reflect light from the light sources to corresponding light sensors in the pairs. The reflectors may be adjustably positioned with respect to the housing. 
     A laser transmitter may comprise a transmitter housing, a laser source in the housing, and a gimbal support arrangement for supporting the laser source in the housing. The gimbal support arrangement further includes a gimbal motor arrangement for moving the gimbal support arrangement and the laser source in the housing. A gimbal motor drive circuit actuates the gimbal motor arrangement to cause the gimbal support arrangement to move in the housing. A plurality of optical proximity sensors sense the orientation of the gimbal support arrangement with respect to the interior of the housing. By this arrangement, damage to the laser transmitter that might otherwise result from movement within the transmitter housing is prevented. 
     The transmitter may include a plurality of reflectors inside the transmitter housing, for reflecting light back to the optical proximity sensors. The reflectors may be adjustably positioned with respect to the housing. 
     There may be four optical proximity sensors for sensing the proximity of the sensors to the interior of the housing, with the four proximity sensors being spaced uniformly around the periphery of the gimbal support arrangement. The outputs of the four optical proximity sensors may be combined to determine the amount of tilt of the gimbal support arrangement in the direction of maximum tilt. 
     A method of positioning a laser source and support structure in the housing of a laser transmitter of the type having a gimbal support for supporting the laser source and support structure, includes the steps of providing a plurality of optical sensors on the support structure, sensing the proximity of the interior of the transmitter housing with each of the optical sensors, and preventing the support structure from being moved into contact with the interior of the transmitter housing. The maximum tilt of the support structure is determined based on outputs from the optical sensors. The maximum tilt is limited to a predetermined maximum such that the support structure is prevented from contacting the interior of the housing. The optical sensors may be positioned around the periphery of the support structure. More particularly, four optical sensors may be equally spaced around the periphery of the support structure. The maximum tilt of the support structure may be determined based on outputs from the four optical sensors, such that the maximum tilt can be determined regardless of the axis along which it occurs. 
     Accordingly, it is an object of the present invention to provide a laser transmitter in which the construction and operation of the transmitter are improved. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a laser transmitter according to the present invention; 
         FIG. 2A  is a sectional view of the laser transmitter taken through the rotatable laser head; 
         FIG. 2B  is a side view of the transmitter with the housing removed, taken from the same direction as  FIG. 2A ; 
         FIG. 2C  is a bottom view of the transmitter with the housing removed; 
         FIG. 3  is a sectional view, similar to  FIG. 2 , of a portion of the transmitter; 
         FIG. 4  is a perspective view of the portion of the transmitter shown in  FIG. 3 , but with some of the parts broken away; 
         FIG. 5  is a diagrammatic representation of a gimbal support and optical sensor arrangement useful in understanding the present invention; 
         FIG. 6  is a graph showing the outputs from the optical sensors of the arrangement of  FIG. 5 ; and 
         FIG. 7  is a schematic diagram showing control circuitry for the transmitter. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIGS. 1 through 4  illustrate a laser transmitter  40  constructed according to the present invention. The laser transmitter  40  has a transmitter housing  42 . The transmitter includes a generally flat, circuit board stator  68 , a rotor  70  including a plurality of magnets  66  mounted in a ring around a central opening in rotor  70 , a bearing  64 , supporting the rotor  70  for rotation about a rotation axis that extends through the central opening, and a pentaprism assembly  50  including an optics holder  71  mounted on the rotor  70  for rotation therewith. If desired, the optics holder  71  may be molded as a unitary upper portion of the rotor  70 , as shown. Also, if desired, the plurality of magnets  66  may be a continuous ring magnet having a plurality of poles arranged therearound. A laser source  44 , including laser diode  52 , collimating lens  56  and generally cylindrical housing  59 , directs a beam of laser light generally upward in alignment with the axis of rotation of the rotor  70 , with respect to the frame of reference illustrated in  FIG. 2A , to pentaprism  53  of the pentaprism assembly  50 . The pentaprism assembly  50  receives the beam of laser light through the central opening in the rotor  70  and redirects at least a portion of the laser light outward through opening  58  in cover  60  in a direction normal to the rotation axis. The path of the laser beam is illustrated by dashed line  61  in  FIGS. 3 and 4 . It will be noted that the laser diode  52  emits a beam that is then collimated by lens  56  positioned within the rotor  70 . Lens  56  is positioned a substantial distance from the circuit board stator  68  and the laser diode  52  to permit the beam to widen to the desired diameter prior to collimation. 
     As shown in  FIG. 2A , the laser transmitter has a non-rotatable portion  46  and a rotatable laser head  48 . Rotatable laser head  48  includes the pentaprism element  53  which redirects a laser beam that is generated by a laser diode  52  and that passes upward through housing  59  and lens  56 . The beam is directed radially outward through an opening  58  in cover  60  by the pentaprism  53 , and is swept around the axis of rotation of the rotor  70 . A portion of the beam may also pass upward through the pentaprism  53 , the upper surface of which may be only partially reflective, through optical wedge  55 , and pass out of the cover  60  through opening  62  in the same direction as the rotation axis of rotor  70 . Optical wedge  55  prevents the beam from being refracted as it passes out of the pentaprism assembly. 
     A flexible bellows seal  74  is provided in the opening  72 , surrounding the laser generating unit and sealing the opening between the housing  42  and the non-rotatable portion  46 . The flexible bellows seal  74 , extends from the edge of the opening  72  to the non-rotatable portion  46  and a plurality of annular accordion pleats which flex when the laser generating unit is tilted with respect to the housing  42 . The flexible bellows seal  74  may be made of an elastomer material, such as a silicone rubber. The bellows seal  74  permits the laser diode  52  and associated optics and other structures to be tilted with respect to housing  42 . 
     The rotor rides on bearing  64  and is driven by the interaction of a ring of magnets  66  and a pair of coils  75  that are included on generally flat, circuit board stator  68 . The bearing  64  has an inner race  95  mounted on the generally cylindrical housing  59  and an outer race  97  secured to the rotor  70 . The bearing  64  includes a plurality of bearing balls  100  that are arranged in a single ring between inner race  95  and outer race  97 . A magnetic shield plate  102 , made of a magnetic material, such as steel, is mounted on the side of the circuit board stator  68  opposite the rotor  70 . Plate  102  provides a magnetic attraction between the plurality of magnets  66  that are arranged in a ring on the rotor  70  and the magnetic shield plate  102 . Plate  102  is preferably annular in shape, although other shapes may be used. The plate  102  applies a downward force to the rotor  70  that reduces or eliminates play in the bearing  64  that may result from manufacturing tolerances or from bearing wear. 
       FIG. 5  is a diagrammatic representation of the end of travel detection arrangement, useful in illustrating the manner in which components of the laser transmitter tilt with respect to the housing, and the way in which the amount of tilt of those components with respect to those components with respect to the housing is detected and limited. The illustrated construction does not correspond precisely to the structure of  FIGS. 1 through 4 , but corresponding structural elements have been given corresponding reference numerals. A gimbal arrangement is diagrammatically represented in two dimensions as a plate  104  that pivots about a stationary pivot  106 . The plate  104  is secured to circuit board  68  by bolts  107 , and pivots about an axis that is perpendicular to the plane of the drawing, as indicated by arrow  110 . The plate  104  is moved by motor  112  and this tilts the circuit board  68 , raising one end while lowering the other end. The present invention monitors the movement of the circuit board  68  and limits the range of movement of the circuit board  68  and the other structure it supports, such as the laser source and optics (not shown in  FIG. 5 ), so that the circuit board  68  and supported structure do not contact the inner surface of the housing  42 . It will be appreciated that such contact could cause significant damage to the moving transmitter components. Additionally, the transmitter accomplishes this in a way that keeps the moving structure far enough from the interior surface of the housing so that the vibration produced by accidentally dropping the transmitter or other rough handling will not cause the moving transmitter components to come into contact with the interior of the housing and be damaged. Finally, the transmitter accomplishes this in a way that maximum tilting of the moving transmitter components along any axis can be determined and limited. 
     The transmitter incorporates optical sensors, such as the XPI-A7 photo-interrupter, sold by SunLED Company Limited, 105 Hewlett Centre, 54 Hoi Yuen Rd., Kwun Tong, Kowloon, Hong Kong. This optical sensor includes a photo diode that provides a source of light, and a photo detector that detects light which is generated by the photo diode and reflected back to the photo detector by a reflective surface. The closer the reflective surface, the greater the amount of light is reflected back to the photo sensor, within certain limits.  FIG. 6  illustrates the voltage outputs of optical sensors  114  and  116  when receiving light from reflectors  118  and  120 , respectively, as the plate  104  is tilted from 6 degrees to the left to 6 degrees to the right. Curve  122  shows the output from optical sensor  114 , while curve  124  shows the output from the sensor  116 . It will be noted that each of the sensors  114  and  116  provides the most useful output information as it is moving further away from its associated reflector. As a sensor moves closer to a corresponding reflector, the curves  122  and  124  show a marked flattening, and therefore a corresponding reduction in accuracy of the output. 
     It will be appreciated that the tilting of the circuit board  68  with respect to the housing  42  shown in  FIGS. 5 and 6  is along a single axis. In the actual transmitter shown in  FIGS. 1 through 4 , however, four optical sensors are mounted on the circuit board  68 , and the circuit board  68  that carries the laser diode  52 , optics  56 , bearing  64 , rotor  70 , and pentaprism  50  is arranged to be tilted in any direction, not just along one axis. As seen in  FIGS. 2B , and  2 C, to effect this tilting, a motor  111  raises and lowers cooperating tab  113  which is part of outer ring gimbal  115  that is supported by pivot structures  117  on opposite sides of the transmitter. In like manner, a second motor  119  tilts an inner gimbal ring  121  about an axis  125  that is parallel to the plane in which  FIGS. 2A and 2B  are taken. By operating both motor  111  and motor  119 , the circuit board can be tilted simultaneously about axes  125  and  127 , resulting in tilting in any desired direction. As a consequence, operating motors  111  and  119  can orient the laser source, support structure, including circuit board  68 , pentaprism  52 , and motor including rotor  70 , in any of a range of tilted positions within the housing  42 . 
     As seen in  FIGS. 3 and 4 , optical sensors  114  and  116  are mounted along a first axis  125 , and optical sensor  126  and another optical sensor  128  (shown in  FIG. 7 ) are mounted along a second axis  127 , normal to axis  125 . As seen in  FIGS. 1 and 3 , the optical sensors  114  and  116  have cooperating reflectors  118  and  120  that are mounted on the ends of bolts  130  and  132 , respectively, which are threaded into openings inside housing  42  so that they can be set at a nominal distance from the optical sensors  114  and  116 , and an adjustment made for manufacturing tolerances. Additional reflectors (not shown) are provided for cooperation with the optical sensors along axis  127 . 
     It will be appreciated that if the sensors along axis  125  indicate a tilt of 5 degrees, and the sensors along axis  127  indicate a tilt of 0 degrees, then the maximum tilt at that time is 5 degrees. However, if the sensors along the axis  125  and the sensors along the axis  127  both indicate a tilt of 5 degrees, then the actual maximum tilt at that time is somewhat greater along an axis at a midpoint between axes  125  and  127 . It is possible, therefore, to determine the maximum tilt experienced by the circuit board at any instant with respect to the housing  42 , regardless of the axis of maximum tilt, and to prevent the circuit board  68  and associated components from tilting beyond a predetermined amount, regardless of the axis of maximum tilt. To accomplish this, transmitter control circuitry  140 , illustrated in  FIG. 7 , simply determines the amount of tilt along axes  125  and  127 , and makes reference to a look up table in circuit  140  in which the maximum tilt angle is provided for each of the combination of measured tilt angles. The control circuit  140  then limits the maximum tilt to no more than a predetermined maximum value, and controls motor drive circuits  142  and  144  to drive motors  111  and  119  accordingly. 
     Other aspects, objects, and advantages of the present invention can be obtained from a study of the drawings, the disclosure, and the appended claims.