Abstract:
A spherical orienting device includes a base, first and second actuation shafts, an orientable device, an inner member, a middle member, and an outer member. The first and second actuation shafts are rotatably held by the base for rotary actuation about first and second actuation axes, respectively, which intersect orthogonally at a spherical center of rotation. The orientable device is supported by first and second revolute support joints which are disposed for rotation about an orientation axis of the orientable device and a support axis, respectively. The inner member is fixed to the first actuation shaft and linked to the second support joint. The middle member is inwardly linked to the first support joint and outwardly linked to a middle revolute joint disposed for rotation about a linkage axis. The outer member is fixed to the second actuation shaft and linked to the middle revolute joint.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a spherical orienting device, e.g., a two degree-of-freedom spherical orientation device driven via two actuation shafts, which supports an orientable device having an orientation axis, and the present invention further relates to a method for manufacturing such a spherical orienting device. 
         [0003]    2. Description of Related Art 
         [0004]    Two-dimensional spherical orienting devices, which orient an orientable payload device towards a desired direction in space by rotating it around a fixed point, are used in many fields of technology, for example in inertial sensors such as gyrometers, including in micromechanics, in gyroscopes, in orientable mirrors e.g. in two degree-of-freedom optical scanners, in gyroscopic stabilization of cameras and camera objectives, in water cannons for fire trucks or gaming, in robot wrists, artificial hands and in artillery equipment. Another important field of application is joysticks and similar input devices that sense the spherical orientation of an object rotated by a user, e.g. in user interfaces in automotive or industrial applications, in mobile hydraulic machinery, or in gaming or general computer user interfaces. 
         [0005]    A conventional mechanism for the tilting of an orientable device into two directions is an assembly of two gimbals, i.e. pivoted supports that each allow the rotation of an object about a single axis, wherein one inner gimbal is mounted on an outer gimbal with pivot axes orthogonal or otherwise disposed at a non-collinear angle. However, in order to actuate the inner gimbal, an actuating motor or, in the case of an input device, rotational sensor has to be born by the outer gimbal. This leads to an increase of inertia for the outer gimbal, hindering fast movements, which are required in many applications. 
         [0006]    In another conventional mechanism an orientable device is pressed onto a tip and tilted in two directions. The center of rotation is located at the apex of the tip where a bearing is installed. Due to such presence of material at the center of rotation, the object cannot be freely positioned within the mechanism, which is unsuitable for many applications. For example, in a case of the orientable device being a mirror such as in a mirror scanner application, the mechanism does not allow the mirror to be positioned such that the center of rotation lies in the mirror plane. 
         [0007]    U.S. Pat. No. 5,966,991 discloses a two degree-of-freedom spherical orienting device in which a spherical five-bar mechanism with payload support is actuated by two rotary actuators fixed in position to a base. Payload support means for supporting a payload on an orientation axis include first and second revolute support joints each disposed for rotation about a support axis, wherein the orientation axis and each support axis pass through the spherical center of rotation in mutually orthogonal disposition. An inner sphere arm fixed to the shaft of the first rotary actuator is linked to the first revolute support joint of the payload support, the first actuator axis disposed orthogonal to the first support axis. A middle sphere arm is radially inwardly linked to the second revolute support joint of the payload support and outwardly linked to a middle revolute joint disposed for rotation about a linkage axis passing through the spherical center of rotation, the linkage axis disposed orthogonal to the second support axis. An outer sphere arm is fixed to the shaft of the second rotary actuator and linked to the middle revolute joint, the linkage axis disposed orthogonal to the second actuator axis. 
         [0008]    Although the disclosed orienting device allows the payload to be positioned at the geometric center of rotation, the device requires a large spherical internal free space around the payload, independent of the shape of the payload to be oriented and of its orientation. Since in general applications orientable payload devices such as listed above are typically not spherically shaped, this leads to an undesirable large space requirement, in particular for orientable payload devices considerably deviating from a spherical shape, e.g. flat or elongate pay-loads. Large distances of the inner, outer, and middle sphere arms from the orientable device furthermore unfavorably influence high-speed operation due to an increased moment of inertia and the possibility of parasitic movements. 
         [0009]    It is therefore desirable to provide a spherical orienting device that enables to orient non-spherical payload devices, in particular at high speed, without requiring a large installation space. 
       BRIEF SUMMARY OF THE INVENTION 
       [0010]    In accordance with the present invention, a spherical orienting device is provided which includes a base, first and second actuation shafts, an orientable device, an inner member, a middle member, and an outer member. The first and second actuation shafts are rotatably held by the base for rotary actuation about first and second actuation axes, which intersect orthogonally at a spherical center of rotation. The orientable device is supported by first and second revolute support joints, the first support joint being disposed for rotation about an orientation axis of the orientable device and the second support joint being disposed for rotation about a support axis, which orthogonally intersects the orientation axis at the spherical center of rotation. The inner member is fixed to the first actuation shaft and linked to the second support joint, the first actuation axis being disposed orthogonal to the support axis. The middle member is inwardly linked to the first support joint and outwardly linked to a middle revolute joint disposed for rotation about a linkage axis, which passes through the spherical center of rotation and is disposed orthogonal to the orientation axis. The outer member is fixed to the second actuation shaft and linked to the middle revolute joint, the linkage axis being disposed orthogonal to the second actuation axis. 
         [0011]    Because the first support joint is disposed for rotation about the orientation axis of the orientable device, the rotational movement of the middle member with respect to the orientable device describes a generated surface of rotational symmetry around the orientation axis. This enables the middle member to be formed according to an outer contour of the orientable device even when the orientable device substantially deviates from a spherical shape. In particular in typical cases such as mirrors, lenses, cameras, joysticks, cannons or nozzles, where orientable devices typically are flat, disk-like or elongate, tube-like objects that deviate clearly from spherical symmetry but exhibit at least in portions an approximate rotational symmetry around the orientation axis, the middle member is enabled to be shaped to closely conform to the outer contour of the orientable device with minimal gap. Therefore, little installation space is required, while reliable high-speed operation is enabled through a minimized moment of inertia and prevention of parasitic movements. 
         [0012]    According to an example embodiment, the orientable device is an optical device, the orientation axis being an optical axis of the optical device. Such devices typically are constructed at least in portions from mirrors, lenses, apertures, tubes etc. arranged with rotational symmetry around the optical axis. Thus, the middle member is enabled to be shaped to conform to the outer shape of the optical device or the rotationally symmetric portion thereof with particularly little gap. Preferably, the orientable device is a mirror, wherein the orientation axis perpendicularly intersects a mirror surface of the mirror. This enables to construct e.g. scanners, projectors and similar ray-reflecting devices that are compact and operable at high speed, even for THz applications, where relatively large mirrors are required due to the longer wave-lengths of THz radiation as compared to visible light. Preferably, the orientation axis intersects the mirror surface at the spherical center of rotation. 
         [0013]    According to an example embodiment, the orientable device has a substantially disk-like shape. The middle member comprises a radial leg extending radially along a rear side of the orientable device. This enables the orienting device to be constructed in a particularly compact way, with only minimal material required for the middle member. 
         [0014]    According to an example embodiment, at least one of the first support joint, the second support joint and the middle revolute joint comprises an elastic joint. This enables to reduce manufacturing cost because the number of parts and the number of assembly steps are reduced. 
         [0015]    According to an example embodiment, the orientable device has an outer shape substantially rotationally symmetric around the orientation axis. The middle member comprises a sheath having an inner shape corresponding to the outer shape of the orientable device. The sheath rotatably holds the orientable device. In this way, a small moment of inertia of the middle member and thus of the moving parts of the orienting device is enabled to be achieved even in the case of elongate orientable devices, since the middle member does not have to e.g. extend longitudinally along the length of the orientable device. Furthermore, also orientable devices such as lenses that require both a rear and a front path along the orientation axis to remain unobstructed during operation are enabled to be oriented. 
         [0016]    Preferably, the sheath comprises at least one slit circumferentially extending around the orientation axis, the second support joint being configured to support the orientable device through the slit. In this way, the sheath is enabled to be positioned anywhere along the length of the orientable device. For example, the sheath can be positioned such that the mass center of the orientable device is located within the volume surrounded by the sheath, thus enabling smooth control of the rotation at high speed. 
         [0017]    Under a further aspect, a method for manufacturing the spherical orienting device is provided. The method comprises a step of providing a substrate, and a further step, in which at least two of the base, the inner member, the middle member, and the outer member are formed from the substrate. In this way, the orienting device enabled to be manufactured at low cost and small overall size, e.g. as a micromechanical device. A small overall size in turn enables a small moment of inertia and in consequence particularly high operation speed. Preferably, the substrate is a silicon wafer substrate such that conventional, efficient processes of micromechanical manufacturing can be employed. 
         [0018]    According to an example embodiment, when the orienting device comprises a mirror, the method further comprises forming the mirror from the substrate. This further simplifies the manufacturing process by reducing the number of parts and the number of assembly steps. 
         [0019]    According to an example embodiment, the method further comprises forming at least one of the first support joint, the second support joint and the middle revolute joint as an elastic joint from the substrate. This enables further miniaturization and cost reduction since less precision is required in manufacturing such elastic joints. Furthermore, the elastic joint can be configured to function as a spring e.g. for returning the orienting device into a neutral position, or as an electric connection to the orientable device. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
         [0020]      FIG. 1  shows a front elevation view of a spherical orienting device according to an embodiment of the present invention. 
           [0021]      FIG. 2  shows a front elevation view of the orienting device of  FIG. 1 , in which a first actuation shaft has been rotated 90° as compared to  FIG. 1 . 
           [0022]      FIG. 3  shows a front elevation view of the orienting device of  FIG. 1 , in which the first actuation shaft has been rotated 135° as compared to  FIG. 1 , and a second actuation shaft has been rotated 45° as compared to  FIG. 1 . 
           [0023]      FIG. 4  shows a rear perspective view of a spherical orienting device according to another embodiment of the invention. 
           [0024]      FIG. 5  shows a front perspective view of a spherical orienting device according to another embodiment. 
           [0025]      FIG. 6  shows a perspective view of a spherical orienting device according to a further embodiment. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0026]      FIGS. 1-3  depict a spherical orienting device  100  including a mirror  114  as a payload to be oriented in space, relative to a fixed base  102 . The base  102  is formed as a rectangular frame, which surrounds the mirror  114 . In  FIGS. 1-3 , the rectangular frame of the base  102  lies in the drawing plane. 
         [0027]    The mirror  114  comprises an outer shape substantially conforming to a disk of rotational symmetry around an orientation axis  116 , bounded by a cylindrical peripheral surface  128 .  FIG. 1  shows the mirror  114  arranged in a neutral position in which it is oriented parallel to the drawing plane, i.e. the plane defined by the base frame  102 . The side of the mirror  114  facing the observer comprises a circular reflecting mirror plane  115 . A rim  134  circumscribing the mirror plane  115  is formed on the side of the mirror plane  115  along the periphery of the mirror  114 , such that the mirror plane  115  as a whole is recessed with respect to the mirror&#39;s  114  cylindrical outer shape. In  FIGS. 2 and 3 , the mirror  114  is shown to have been rotated around a spherical center of rotation  112 , into two different exemplary orientations with respect to the base frame  102 . The mirror  112  is positioned such that the spherical center of rotation  112  coincides with the center of its circular mirror plane  115 . 
         [0028]    On the rear surface  200  of the mirror  114 , i.e. the side of the mirror  114  opposed to the mirror plane  115 , a central shaft  400  is formed that projects away from the center of the rear surface  200  with cylindrical symmetry around the orientation axis  116  of the mirror  114 . An L-shaped middle member  122  is provided comprising a radial leg  130 , which radially extends from the central shaft  400  along the rear surface  200  outward until slightly beyond the periphery  128  of the mirror  124 , and a longitudinal leg  131 , which extends perpendicularly from the outer end of the radial leg  130  towards the front side of the mirror  114 . The radial leg  130  of the middle member  122  comprises a bore in which the central shaft  142  is rotatably held, thus forming a first revolute support joint  118  supporting the mirror  114  rotatably on its orientation axis  116 . 
         [0029]    A first rotary actuator  104  and a second rotary actuator  105  are rigidly mounted on adjacent sides of the base frame  102 , each in a position close to the center of the respective frame side. The rotary actuators  104 ,  105  are e.g. configured as electric stepping motors. The first actuator  104  comprises a first actuation shaft  106  arranged along a first actuation axis  108 , while the second actuator  105  comprises a second actuation shaft  107  arranged along a second actuation axis  109 . Each actuation shaft  106 ,  107  is rotatably guided through a respective bore in the base frame  102  from the corresponding actuator  104 ,  105  into the interior space surrounded by the base frame  102 , with both actuation axes  108 ,  109  intersecting perpendicularly at the spherical center of rotation  112 . 
         [0030]    On the interior-facing side of the bore guiding the first actuation shaft  106 , two inner members  120  are fixed to the first actuation shaft  106 , extending perpendicularly therefrom into opposing directions. Each of the inner members  120 , although in the present embodiment formed from piecewise linear portions, follows the general shape of an arc subtending a 90° angle, with an inner radius of the arc that is slightly greater than an outer radius of the cylindrical peripheral surface  128  of the mirror  114 . Together, both inner members form a general shape of a combined arc subtending a 120° angle. 
         [0031]    Each inner member  120  comprises at its end a bore which rotatably holds one of two support shafts  404  radially extending from diametrically opposed positions of the cylindrical peripheral surface  128  of the mirror  114 . Each support shaft  404  together with the corresponding bore forms a first revolute support joint  119 , such that the inner members  120  support the mirror  114  rotatably on a support axis  117  defined by a common symmetry axis of the support shafts  404 . The support axis  117  passes through the spherical center of rotation  112  and is disposed orthogonal to both the first actuation axis  108  and the orientation axis  116  of the mirror  114 . 
         [0032]    On the interior-facing side of the bore guiding the second actuation shaft  107  through the base frame  102 , an outer member  124  is fixed to the second actuation shaft  107 , extending perpendicularly therefrom. The outer member  124 , although in the present embodiment formed from piecewise linear portions, approximately follows the general shape of an arc subtending a 90° angle, with an inner radius of the arc that is slightly greater than an outer radius of the inner members  120 . As can be seen in  FIG. 1 , the outer member  124  is formed such that in a position where the inner members  120  and the mirror  114  are rotated into an orientation coplanar with the plane defined by the base frame  102 , i.e. by the actuation axes  108 ,  109 , and the outer member  124  is rotated into a position coplanar with the plane defined by the base frame  102  and facing away from the side of the first actuator  104 , the outer member  124  does not touch the mirror  114  nor the inner members  120 . 
         [0033]    The outer member  124  comprises at its end a bore which rotatably holds a middle shaft  406  that radially extends outward from the longitudinal leg  131  of the middle member  122 . Together, the middle shaft  406  and corresponding bore form a middle revolute joint  132  configured for rotation around a linkage axis  126  that passes through the spherical center of rotation  112  and is configured orthogonal to the orientation axis  116  of the mirror  114 . 
         [0034]    As demonstrated in  FIGS. 2 and 3 , the mirror  114  is enabled to be rotated into arbitrary spherical orientations over a large angular range by rotary actuation of the actuation shafts  106 ,  107 . In  FIG. 2 , the first actuation shaft  106  has been rotated by 90°—counter-clockwise as seen from the first actuator  104 —from the position shown in  FIG. 1 . In  FIG. 3 , the second actuation shaft  107  has been rotated further into the same direction over a total of 135° C. from its position in  FIG. 1  while the first actuation shaft  109  has been rotated by 45°—clock-wise as seen from the second actuator  105 —from its position in  FIG. 1 . 
         [0035]      FIG. 4  shows an embodiment in which the central shaft  400  and the radial leg  130  of the middle member  122  are connected by a pair of elastic lamellae  402 , thus providing the first support joint  118  as an elastic bearing. In alternative embodiments, additionally or alternatively any of the second support joints  119  and/or the middle revolute joint  132  can be configured as an elastic bearing. 
         [0036]      FIG. 5  shows an embodiment comprising only a single inner member  120  and a single second revolute support joint  119 . In this embodiment, the outer member  124  is identical in shape to the inner member  120 , which has the advantage of reducing the number of distinct parts to be manufactured. Furthermore, due to the similarity in shape the inner  120  and outer  124  sphere members are similar in their mechanical properties such as their respective moment of inertia around the corresponding actuation axis  108 ,  109  as well as their elastic bending properties etc. This enables the orientation device  100  to respond substantially in a similar to actuation from either one of the actuators  104 ,  105 , leading to particularly smooth and precise operation. A spacer ring  500  has been inserted between the inner member  120  and the peripheral surface  128  of the mirror  114 , corresponding in length to the radial thickness of the longitudinal leg  131  of the middle member  122 , thus enabling identically shaped inner  120  and outer  124  sphere members to be used. 
         [0037]      FIG. 6  shows a further embodiment in which the orientable device  614  is of an elongated cylindrical shape, rotationally symmetric around the orientation axis  116 . Examples of the orientable device  614 , which for simplification purposes is shown as a plain cylinder, can include a lens system or camera, robotic arm, joystick, spotlight, water cannon or nozzle. Here, the middle member, L-shaped in the embodiments of  FIGS. 1-5 , is a cylindrical sheath  620  with an inner diameter that is slightly larger than the outer diameter of the cylindrically-shaped orientable device  614 . Within the sheath  620 , the orientable device  614  is held rotatably around the orientation axis  116 . The sheath  620  and the outer shape of the orientable device  614  itself thus form the first support joint  118  in the present embodiment. 
         [0038]    In two diametrically opposed sections of the sheath  620  circumferential slits  690  are formed, each extending over an angle of approximately 90°. The support shafts  404  of the second revolute support joints  119  rotatably connect the orientable device  615  to the inner members  120 , each through a corresponding one of the slits  690 . When the orientable device  614  is rotated around its orientation axis  116 , the support shafts  404  slide along the length of the corresponding slit  690 . Between the inner member  106  and the orientable device  614 , spacer rings  500  have been inserted, which are slightly longer than a difference between outer radii of the orientable device  614  and the sheath  620 , thus preventing friction and enabling identically shaped inner  120  and outer  124  sphere members to be used, with similar advantages as in the embodiment of  FIG. 5 . 
         [0039]    The orienting devices  100  as shown in  FIGS. 1-6  are manufacturable substantially by using micromechanical manufacturing methods. For example, the orienting device of  FIG. 1-3  can be seen in  FIG. 1  in a neutral position where all major structural parts, i.e. the base  102 , the mirror  114 , the inner member  120 , the middle member  122 , and the outer member  124  lie within a flat volume defined by the outer dimensions of the base frame  102 . In an exemplary micromechanical manufacturing process, these parts are shaped from a common substrate, e.g. a conventional silicon wafer comprising a thickness that corresponds to a height of the base frame  102 , perpendicularly to the drawing plane of  FIGS. 1-3 . In a further step, the mirror surface  115  is formed on the mirror  114  e.g. by metal evaporation. 
         [0040]    Moreover, also the orienting devices  100  of  FIGS. 4 and 5 , as well as the orienting device  100  of  FIG. 6  when excluding the orientable device  620 , can be rotated into a neutral position substantially as shown in  FIG. 1  wherein all major structural parts lie within a flat volume defined by the outer dimensions of the respective base frame  102 , thus rendering them suitable in principle for being manufactured by micromechanical processes from a common substrate. Furthermore suited to such processes is the forming of one or more of the revolute joints  118 ,  119 ,  132  as elastic joints, such as the elastic first support joint  118  of the orienting device of  FIG. 4 .