Abstract:
A surveying instrument which comprises a rotation unit  7  adapted to direct a distance measuring optical axis to an object to be measured and the rotary drive unit  5  rotates the rotation unit, comprising a rotary motor for rotating an output shaft  6  and a clutch unit for connecting or disconnecting the rotary motor and the output shaft, wherein the rotary motor and the clutch unit are arranged in a series along the output shaft, and the output shaft is fixed to the rotation unit.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a rotary drive unit used in a surveying instrument and to a surveying instrument using the rotary drive unit. 
     A surveying instrument, e.g., a total station has a telescope unit that sights a measurement point. The telescope unit is supported by a frame unit so as to be rotatable in a vertical direction, and the frame unit is supported by a base unit so as to be rotatable in a horizontal direction. Further, the total station is provided with a motor for rotating the telescope unit and a motor for rotating the frame unit. Hereinafter, the telescope unit and the frame unit will be generically referred to as a rotation unit. 
     Conventionally, an adopted motor is an electric motor. An output shaft of the electric motor and a rotary shaft of the rotation unit are connected via a first gear provided to the output shaft and a second gear which is provided to the rotary shaft and meshes with the first gear. Thereby a mechanism is configured so that the rotational force of the electric motor is transmitted to the rotation unit via the first gear and the second gear. Further, a backlash exists in the mesh of the first gear and the second gear. The backlash affects a rotational accuracy and a rotational positioning accuracy, and hence the backlash must be reduced as much as possible. In particular, in surveying instruments, the accuracy of a rotation angle is required in units of seconds. Therefore, highly accurate gears are required, and further, a high accuracy is also required in an assembling accuracy. Thus, the manufacturing cost is high. Furthermore, the backlash increases due to the wear and the like of the gears, and the accuracy decreases over time. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a rotary drive unit of a surveying instrument that has no error caused due to a backlash and others and has a high accuracy and a simple structure and to provide a surveying instrument comprising the rotary drive unit of the surveying instrument. 
     To attain the above object, in the rotary drive unit of a surveying instrument according to the present invention, the surveying instrument comprises a rotation unit adapted to direct a distance measuring optical axis to an object to be measured and the rotary drive unit rotates the rotation unit, comprising a rotary motor for rotating an output shaft and a clutch unit for connecting or disconnecting the rotary motor and the output shaft, wherein the rotary motor and said clutch unit are arranged in a series along the output shaft, and the output shaft is fixed to the rotation unit. 
     Further, in the rotary drive unit of a surveying instrument according to the present invention, the rotary motor rotates a driven body via a friction force, the clutch unit is interposed between the driven body and the rotation unit and configured so as to transmit the rotation of the driven body to the rotation unit via the friction force, and the friction force between the rotary motor and the driven body is set to be larger than the friction force between the driven body and the rotation unit. 
     Further, in the rotary drive unit of a surveying instrument according to the present invention, the driven body has a ring-like shape and the rotary motor comprises a ring-shaped vibration generating unit that provides the driven body with the rotational force, wherein the vibration generating unit generates a flexural wave motion that moves in a circumferential direction by ultrasonic vibration, and the flexural wave motion adapted to rotate the driven body via the friction force between the rotary motor and the driven body. 
     Further, in the rotary drive unit of a surveying instrument according to the present invention, the clutch unit has a structure to enable selecting the friction force between the rotation unit and the driven body. 
     Further, in the rotary drive unit of a surveying instrument according to the present invention, the clutch unit comprises a friction generating member interposed in a rotational force transmission path and a biasing means for allowing the pressing force to act on the friction generating member. 
     Further, in the rotary drive unit of a surveying instrument according to the present invention, the output shaft is provided so as to integrally rotate with the vibration generating unit, and the driven body is provided on a member that supports the rotation unit. 
     Further, a surveying instrument according to the present invention comprises a frame unit as a rotation unit provided on a base unit so as to be rotatable in the horizontal direction, a horizontal rotary drive unit provided on the base unit and drives the frame unit to rotate, a telescope unit as a rotation unit provided on the frame unit so as to be rotatable in a vertical direction, and a vertical rotary drive unit that is provided on the frame unit and drives the telescope unit to rotate, wherein a rotary drive unit is used for at least one of the horizontal rotary drive unit and the vertical rotary drive unit. 
     According to the present invention, in the rotary drive unit of a surveying instrument, the surveying instrument comprises a rotation unit adapted to direct a distance measuring optical axis to an object to be measured and the rotary drive unit rotates the rotation unit, comprising a rotary motor for rotating an output shaft and a clutch unit for connecting or disconnecting the rotary motor and the output shaft, wherein the rotary motor and the clutch unit are arranged in a series along the output shaft, and the output shaft is fixed to the rotation unit. As a result, the rotational force transmission path from the rotary motor to the rotation unit becomes simple and a highly accurate drive becomes possible without an error due to backlashes and the like. 
     Further, according to the present invention, in the rotary drive unit of a surveying instrument, the rotary motor rotates a driven body via a friction force, the clutch unit is interposed between the driven body and the rotation unit and configured so as to transmit the rotation of the driven body to the rotation unit via the friction force, and the friction force between the rotary motor and the driven body is set to be larger than the friction force between the driven body and the rotation unit. As a result, the rotation unit can be rotated manually when the rotary motor is not driven, and in a case where an excessive load acts at the time of the drive, the clutch unit rotates and prevents the rotary motor from being damaged. 
     Further, according to the present invention, in the rotary drive unit of a surveying instrument, the driven body has a ring-like shape and the rotary motor comprises a ring-shaped vibration generating unit that provides the driven body with the rotational force, wherein the vibration generating unit generates a flexural wave motion that moves in a circumferential direction by ultrasonic vibration, and the flexural wave motion adapted to rotate the driven body via the friction force between the rotary motor and the driven body. As a result, the rotation unit becomes a minimum structure of the driven body, the structure is simplified, and a generation state of the ultrasonic vibration of the vibration generation unit need only be controlled, hence the controlling of the rotation unit is easy. 
     Further, according to the present invention, in the rotary drive unit of a surveying instrument, the clutch unit has a structure to enable selecting the friction force between the rotation unit and the driven body. As a result, a rotation output can be changed without changing the basic structure. 
     Further, according to the present invention, in the rotary drive unit of a surveying instrument, the clutch unit comprises a friction generating member interposed in a rotational force transmission path and a biasing means for allowing the pressing force to act on the friction generating member. As a result, by adjusting the material and the pressing force of the friction generating member, a rotation output can be changed without changing the basic structure. 
     Furthermore, according to the present invention, a surveying instrument comprises a frame unit as a rotation unit provided on a base unit so as to be rotatable in the horizontal direction, a horizontal rotary drive unit provided on the base unit and drives the frame unit to rotate, a telescope unit as a rotation unit provided on the frame unit so as to be rotatable in a vertical direction, and a vertical rotary drive unit that is provided on the frame unit and drives the telescope unit to rotate, wherein either of the rotary drive units described above is used for at least one of the horizontal rotary drive unit and the vertical rotary drive unit. As a result, a driving system becomes simple, the number of components that require accuracy is reduced, manufacturing costs are decreased, and a highly accurate drive becomes possible. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematical drawing showing an example of a surveying instrument according to the present invention. 
         FIG. 2  is a schematic cross-sectional view of the surveying instrument according to an embodiment of the present invention. 
         FIG. 3  is a cross-sectional perspective view of an ultrasonic motor used in the embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     An embodiment of the present invention will be described hereinafter by referring to the drawings. 
     A surveying instrument  1  according to the present embodiment will be described with reference to  FIG. 1 . 
     A leveling unit  3  is provided on a tripod  2 , and a base unit  4  is provided on the leveling unit  3 . A horizontal rotary drive unit  5  is accommodated in the base unit  4 . The horizontal rotary drive unit  5  has a horizontal output shaft  6  which is hollow and extend in vertical direction, and a frame unit  7  as a rotation unit is mounted on an upper end of the horizontal output shaft  6 . 
     The frame unit  7  has a concave portion  8 , a telescope unit  9  as a rotation unit is accommodated in the concave portion  8 , and the telescope unit  9  is rotatably supported in the frame unit  7  via a vertical rotary shaft  11 . A sighting telescope  10  with a distance measuring optical axis is provided in the telescope unit  9 , and a distance measuring unit (not shown) is accommodated in the telescope unit  9 . 
     A vertical rotary drive unit  12  is accommodated in the frame unit  7 , and the vertical rotary drive unit  12  is arranged on a shaft center line of the vertical rotary shaft  11 . The vertical rotary drive unit  12  has a vertical output shaft  13  which is concentric with the vertical rotary shaft  11 , and a forward end of the vertical output shaft  13  is fixedly attached to the telescope unit  9 . 
     The horizontal rotary drive unit  5  has a rotary motor  14  and a clutch unit  15 . The rotary motor  14  and the clutch unit  15  have the same shaft center line, and are arranged in series (tandem) along the horizontal output shaft  6  with the horizontal output shaft  6  as the center. When the clutch unit  15  is in a connected state, the rotational force of the rotary motor  14  is directly transmitted to the horizontal output shaft  6 . When the clutch unit  15  is in a disconnected state, the horizontal output shaft  6  is disconnected from the rotary motor  14 , and the horizontal output shaft  6  alone can rotate. Further, when the clutch unit  15  is in the disconnected state, the horizontal output shaft  6  and the rotary motor  14  are connected via the predetermined friction force. 
     Therefore, when the clutch unit  15  is in the disconnected state, the frame unit  7  can relatively rotate with respect to the horizontal rotary drive unit  5 , and a position of the frame unit  7  is maintained by the friction force. 
     The vertical rotary drive unit  12  also has the same structure as that of the horizontal rotary drive unit  5 . 
     The vertical rotary drive unit  12  has a rotary motor  16  and a clutch unit  17 , and the rotary motor  16  and the clutch unit  17  are arranged on the same shaft center line in tandem. When the clutch unit  17  is in the connected state, the rotational force of the rotary motor  16  is directly transmitted to the vertical output shaft  13 . When the clutch unit  17  is in the disconnected state, the vertical output shaft  13  is disconnected from the rotary motor  16 , and the vertical output shaft  13  alone can rotate. Further, when the clutch unit  17  is in the disconnected state, the vertical output shaft  13  and the rotary motor  16  are connected via the predetermined friction force, and is so arranged that the telescope unit  9  is maintained at an arbitrary position even if the clutch unit  17  is in the disconnected state. 
     It is to be noted that, although not shown, a horizontal angle encoder is provided on the horizontal output shaft  6 , and a rotation angle of the horizontal output shaft  6  is detected. A vertical angle encoder is provided on the vertical rotary shaft  11  so that a rotation angle of the vertical output shaft  13  can be detected. 
     By the cooperation of the horizontal rotation of the frame unit  7  and the vertical rotation of the telescope unit  9 , a distance measuring optical axis is directed toward an object to be measured, the distance measuring unit emits a laser beam via the telescope unit  9 , and a distance is measured by receiving the reflected light from the object to be measured. Further, based on the detection results of the horizontal angle encoder and the vertical angle encoder, a horizontal angle and a vertical angle are measured. 
     In the embodiment as described above, since the motor and the clutch unit are arranged on the same shaft center line, the horizontal rotary drive unit  5  and the vertical rotary drive unit  12  has a compact structure. Further, since the motor and the clutch unit are arranged in tandem and the rotational force of the motor is directly transmitted to the output shaft in the clutch connected state, there is no backlash, an error does not occur in the rotation transmission path, and the drive is transmitted highly accurately. Further, the assembling is easy. 
     It is to be noted that in the embodiment as described above, both the horizontal rotary drive unit  5  and the vertical rotary drive unit  12  are said to have a tandem type structure, but any one of these units alone may have a tandem type structure. 
     Next, an example where each of the horizontal rotary drive unit  5  and the vertical rotary drive unit  12  having the tandem type structure, which has an ultrasonic motor, will now be described with reference to  FIG. 2  and  FIG. 3 . 
     It is to be noted that, in  FIG. 2  and  FIG. 3 , the same component as shown in  FIG. 1  is referred by the same symbol, and a description thereof is not given here. 
     In the drawing, reference numeral  21  denotes a horizontal angle detection encoder provided with respect to the horizontal output shaft  6 , reference numeral  22  denotes a vertical angle detection encoder  22  provided with respect to the vertical rotary shaft  11 , and reference numeral  23  denotes a control unit that is provided inside the frame unit  7  and controls the drive of the horizontal rotary drive unit  5  and the vertical rotary drive unit  12 . 
     In  FIG. 3 , the horizontal rotary drive unit  5  and the vertical rotary drive unit  12  will now be described more concretely. It is to be noted that the horizontal rotary drive unit  5  and the vertical rotary drive unit  12  have the same structure, and hence the horizontal rotary drive unit  5  will be described below. 
     A motor case  25  has a structure that a hollow cylindrical body  27  is protruded on a bottom plate  26 . A bottom hole  28  is provided at the bottom plate  26 , a top hole  31  is provided at a top plate  29  of the hollow cylindrical body  27 , and the bottom hole  28  and the top hole  31  are concentrically arranged. 
     A cylindrical bearing member  32  is engaged with the top hole  31  from above. A fixed flange  33  is formed around the bearing member  32 , and the fixed flange  33  is fixed to the top plate  29  by a bolt  34 . Therefore, the bearing member  32  is fixed to the top plate  29  via the fixed flange  33 , and a shaft center line of the bearing member  32  is concentric with the bottom hole  28  and the top hole  31 . 
     The horizontal output shaft  6  rotatably penetrates through the bearing member  32 , and an upper end portion  6   a  and a lower end portion  6   b  of the horizontal output shaft  6  protrude from the bearing member  32 , respectively. 
     A coupling portion  35  is formed at an upper end of the horizontal output shaft  6 , and a shaft portion&#39;s flange  36  is continuously formed at a lower end of the coupling portion  35 . A pattern ring  37  of the horizontal angle detection encoder  21  is fixed to the shaft portion flange  36  (see  FIG. 2 ). The coupling portion  35  is coupled with a bottom surface of the frame unit  7  in a spigot-like fashion and fixed to a bottom surface of the pattern ring  37  by a bolt (not shown) (see  FIG. 2 ). 
     A retaining ring  38  is provided to the lower end portion  6   b , and by engaging the retaining ring  38  with the lower end of the bearing member  32 , a displacement of the horizontal output shaft  6  in a shaft center direction is suppressed. 
     Apart of the lower end portion  6   b , which extends downward from the retaining ring  38 , has a step structure with two steps. A rotating plate  39  as a rotating body is fixed to a first step and a fixing nut  41  is screwed to a second step. The rotating plate  39  has a diameter smaller than the inner diameter of the hollow cylindrical body  27 , and the rotating plate  39  is in a condition separated from the bottom plate  26 . A displacement of the rotating plate  39  in the shaft center line direction is restricted by the fixing nut  41 , and the rotating plate  39  is arranged so as to integrally rotate with the horizontal output shaft  6 . 
     A piezoelectric ceramic (a piezoelectric element)  42  with a thin sheet ring-shape is secured to an upper surface of the rotating plate  39  concentrically with the rotating plate  39 , and a vibrator  43  is fixed to the upper side of the piezoelectric ceramic  42  with intimate contact. The vibrator  43  is made of an elastic material, and the vibrator  43  has a ring shape with a radius (a central radius) R. The slits  44  are formed in the vibrator  43  in a circumferential direction at a predetermined pitch, the slits  44  separate the necessary ranges from the top toward the lower side, and form the comb teeth  45  as arranged in the circumferential direction at predetermined intervals. Further, an aggregate of the comb teeth  45 , which are arranged in the circumferential direction at predetermined intervals, form a circumferential column group. 
     A fixing ring  46  as a stator is fitted in the hollow cylindrical body  27 . The fixing ring  46  can be displaced in the shaft center line direction with respect to the hollow cylindrical body  27  and can freely rotate in the circumferential direction. The fixing ring  46  has the same diameter as the vibrator  43  and is placed on the vibrator  43 , and the vibrator  43  and the fixing ring  46  are mechanically in contact with each other. 
     A necessary space is formed between an upper surface of the fixing ring  46  and a lower surface of the top plate  29 , and a ring-shaped friction sheet  47 , a wave washer  48  as a biasing member, and a friction sheet  49  are accommodated in the space. 
     The friction sheet  47  is fixed on the upper surface of the fixing ring  46  by necessary means such as gluing, and the friction sheet  49  is fixed on the lower surface of the top plate  29  by necessary means such as gluing. The wave washer  48  is interposed between the friction sheet  47  and the friction sheet  49 , and the wave washer  48  biases the friction sheet  47  and the friction sheet  49  in opposite directions. The friction sheet  47  and the friction sheet  49  are interposed in a rotational force transmission path between the fixing ring  46  and the top plate  29 , and function as a friction generating member that generates the necessary friction. 
     Further, the biasing force of the wave washer  48  is transmitted to the fixing ring  46  through the friction sheet  47 , and the wave washer  48  presses the fixing ring  46  against the vibrator  43  with the predetermined force. 
     Due to the biasing force of the wave washer  48 , the friction force F1, which is generated between the wave washer  48  and each of the friction sheet  47  and the friction sheet  49 , acts between the fixing ring  46  and the top plate  29  (i.e., the motor case  25 ), and the friction force F2 according to the pressing force of the wave washer  48  is generated between the fixing ring  46  and the vibrator  43 . 
     By applying a high-frequency wave to the piezoelectric ceramic  42 , an ultrasonic vibration is generated, and flexural vibration is produced in the comb teeth  45 . Further, the circumferential column group, which is an aggregate of the comb teeth  45 , forms a flexural vibration wave (flexural wave motion) that moves in the circumferential direction by the flexural vibration, and the flexural vibration wave relatively rotates the fixing ring  46  via the friction force. Further, by controlling the high-frequency wave applied to the piezoelectric ceramic  42 , it will become possible to be able to control a rotating speed and a rotating direction of the fixing ring  46 . Here, the piezoelectric ceramic  42  and the vibrator  43  make up a vibration generating unit, and the piezoelectric ceramic  42 , the vibrator  43 , and the fixing ring  46  make up an ultrasonic motor  51 . 
     It is to be noted that reference numeral  52  in the drawing denotes a cable, and the cable  52  is electrically connected to the piezoelectric ceramic  42 , inserted into a hollow portion of the horizontal output shaft  6 , and electrically connected to the control unit  23 . 
     Then, the friction force F1 acts between the fixing ring  46  and the top plate  29 , and the top plate  29 , i.e., the motor case  25  relatively rotates with respect to the vibrator  43  via the friction force F1. 
     In the case of this embodiment, since the motor case  25  is fixed to the base unit  4 , the fixing ring  46  is fixed to the motor case  25  by the friction force F1, and the vibrator  43  rotates. 
     The rotation of the vibrator  43  is transmitted to the horizontal output shaft  6  via the rotating plate  39 , and the frame unit  7  rotates via the horizontal output shaft  6  (see  FIG. 2 ). 
     Then, in a state where the high-frequency wave is not applied to the piezoelectric ceramic  42 , i.e., a state where the ultrasonic motor  51  is not driven, the friction force F1 acts between the fixing ring  46  and the top plate  29 , the friction force F2 acts between the vibrator  43  and the fixing ring  46 , and hence the horizontal output shaft  6  (i.e., the frame unit  7 ) is fixed by friction forces F1 and F2. 
     Further, between the friction force F1 and the friction force F2, a relationship of the friction force F1&lt;the friction force F2 exists, and the restricting force acts for the rotation due to the friction torque T1&lt;the friction torque T2. It is to be noted that, in order to realize the friction force F1&lt;the friction force F2, a friction coefficient between each of the friction sheet  47  or the friction sheet  49  and the wave washer  48  and the biasing force of the wave washer  48  are appropriately selected. In addition, as a material of the friction sheet  47  and the friction sheet  49 , there is a polymer compound, e.g., a polymer compound such as a fluororesin, and if conditions are met, there is also a metal or a material obtained by giving a treatment to a surface of the metal or the like. 
     The friction torque T1 is determined according to a friction coefficient between the fixing ring  46  and the top plate  29  and the pressing force of the wave washer  48 . The friction coefficient is selected by changing the material of the friction sheet  47  and the friction sheet  49 , and the pressing force is changed by changing a material, a board thickness, and a shape of the wave washer  48 . Therefore, adjusting the friction coefficient and the pressing force enables selecting the optimum friction torque T1. 
     Here, when the rotational force M&gt;T1 is allowed to act on the horizontal output shaft  6  as an external force, the horizontal output shaft  6  rotates according to the relationship of the friction torque. Further, in a state where the horizontal output shaft  6  is rotating, the rotational force M&lt;T2 is achieved, and the vibrator  43  and the fixing ring  46  are in a fixed state. 
     Therefore, in the surveying instrument  1 , when the rotational force M is manually operated to the frame unit  7  in a non-driving state of the horizontal rotary drive unit  5 , the frame unit  7  rotates with the horizontal output shaft  6  as the center, and the frame unit  7  can be fixed at an arbitrary position. 
     Further, this can be likewise with respect to the telescope unit  9 , and even if the vertical rotary drive unit  12  is set in the non-driving state, the telescope unit  9  can manually rotate, and the telescope unit  9  can be fixed at an arbitrary position. 
     Therefore, the fixing ring  46 , the friction sheet  47 , the friction sheet  49 , and the wave washer  48  make up a clutch mechanism  53 . In the driving state of the ultrasonic motor  51 , the clutch mechanism  53  transmits the rotational force to the horizontal output shaft  6 . Further, in the non-driving state of the ultrasonic motor  51 , the rotation of the horizontal output shaft  6  is allowed in accordance with the external force. 
     Further, the clutch mechanism  53  also functions as a safety device that causes a slip between the motor case  25  and the fixed ring  46  and avoids the damage to the ultrasonic motor  51  in a case where an excess load acted on the horizontal output shaft  6  during the drive of the ultrasonic motor  51 . 
     As described above, in the present embodiment, since an error factor such as a backlash does not exist in a path through which the rotational force from the ultrasonic motor  51  is transmitted to the horizontal output shaft  6  and the rotational force of the ultrasonic motor  51  is directly transmitted to the horizontal output shaft  6 , the highly accurate rotation control can be carried out, further, the number of components is small, and the number of rotating portions (the horizontal output shaft  6  alone in the drawings), is small, and hence the assembling errors are reduced. 
     Further, when the ultrasonic motor  51  is not driven, the rotation unit can be manually rotated. In this case, a slip is not caused between the piezoelectric ceramic  42  and the fixing ring  46  at this moment, so abrasion does not occur. Therefore, the ultrasonic motor  51  can maintain high accuracy for a long time. 
     In a case where distance measurement and angle measurement is carried out by using the surveying instrument  1  provided with the horizontal rotary drive unit  5  and the vertical rotary drive unit  12 , in a state that the horizontal rotary drive unit  5  and the vertical rotary drive unit  12  are not driven, the frame unit  7  is manually rotated in the horizontal direction and the telescope unit  9  is rotated in the vertical direction. The sighting telescope  10  is visually sighted on an object to be measured, the horizontal rotary drive unit  5  and the vertical rotary drive unit  12  are driven when the object to be measured is captured in a viewing field of the sighting telescope  10 , and sighting is performed automatically on the object to be measured. 
     In a state where the object to be measured is sighted, a distance is measured, further, a horizontal angle and a vertical angle in the sighted state are measured by the horizontal angle detection encoder  21  and the vertical angle detection encoder  22 , and the distance measurement and the angle measurement are performed. 
     In the surveying instrument  1 , by using the horizontal rotary drive unit  5  and the vertical rotary drive unit  12 , the structure of the drive system and its periphery is simplified, the number of components is reduced, and the number of components requiring accuracy is reduced, and a manufacturing cost can be lowered. Further, since the number of rotation units is reduced and the frame unit  7  and the telescope unit  9  are directly driven, highly accurate drive becomes possible, and a decrease in accuracy over time can be avoided. 
     It is to be noted that the ultrasonic motors are used for both the horizontal rotary drive unit  5  and the vertical rotary drive unit  12 , in the embodiment given above, but the ultrasonic motor may be used for one of these drive units alone. 
     It is to be noted that the above-described surveying instrument  1  concerns a total station, but as another example of the surveying instrument, there is a laser scanner that emits a distance measurement light via a deflection mirror, further rotates the deflection mirror in a horizontal direction and a vertical direction, irradiates a laser beam in a predetermined range and measures multiple points, and the present embodiment may be applied to the laser scanner.