Abstract:
A carriage adapted for carrying a laboratory instrument such as a pipette, electrode, or syringe is driven by a drive shaft in the form of a lead screw. The lead screw is selectively driven by a high speed drive wheel or by a low speed drive wheel. The drive wheels are coaxially mounted around the drive shaft and concentrically and coaxially arranged with respect to one another. The drive shaft and the two drive wheels all rotate in unison in the same rotary direction.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates in general to manually operated precision mechanical drives and in particular to an ergonomic dual gear drive system for use in laboratory equipment such as micromanipulators and stereotaxic systems. 
     2. Description of Prior Developments 
     Various experimental and investigative procedures are commonly performed on live test specimens such as laboratory animals. These animals, which are often rodents such as rats and mice, are typically secured in a rigidly fixed position during these procedures. It is often desirable to accurately position an instrument such as a pipette, potentiometer, electrode, probe, sensor, laser or other tool adjacent, on or within the specimen, in order to accurately induce and/or monitor various reactions and responses to certain stimuli or other inputs. 
     The instruments used in these procedures are typically mounted on mechanical slides which are manually driven along a slideway by a lead screw, rack and pinion or other similar drive. In order to operate the slide so as to move the instrument into position, an operator typically rotates a knob which is connected to a gear drive. The gear drive then drives the movable slide over a fixed slideway and thereby moves an attached instrument into and out of position. 
     In some positioning systems, only a single drive is provided to position an instrument along a slideway. This presents the instrument designer with a choice of using a relatively coarse or high gear ratio drive or a relatively fine or low gear ratio drive. Each type of drive has both advantages and disadvantages. 
     A high ratio drive allows an operator to quickly move an instrument along the slideway with relatively few turns of a drive knob. This is convenient for quickly moving an instrument from a position remote from a test specimen to a position close to the test specimen and vice versa. 
     However, such a coarse adjustment is difficult to manipulate so as to achieve small delicate and precision movements of the instrument once it is positioned close to the test specimen. That is, small movements of the rotary drive knob by an operator result in relatively large movements of the instrument, thereby making fine manual adjustments of the instrument difficult to achieve. 
     If a low ratio drive is provided instead, precision movements and adjustments of the instrument are facilitated, but large movements of the instrument along the slideway are time consuming and inconvenient That is, an operator must complete many turns on the drive knob in order to move the slide and its attached instrument any appreciable distance along the slideway. 
     It is possible to provide two separate drives for driving an instrument into position. One drive can be a coarse, high speed drive and the other a fine, low speed drive. The first drive can be driven by a first manually operated rotary knob which drives a relatively coarse pitch lead screw drive and the second drive can have a separate, remotely positioned manually operated drive knob which turns a relatively fine pitch lead screw drive. 
     With two separate drives, an instrument can be brought into close proximity to a test specimen by the high speed, high gear ratio drive, and then an operator can switch over to manipulating a low speed, low gear ratio drive for achieving accurate, final positioning of the instrument. 
     While a dual drive positioning system of the type noted above can provide both coarse and fine movements of an instrument along a slideway, an operator is somewhat inconvenienced by the required hand movement over some considerable distance from one drive knob to another. That is, the operator&#39;s hand must be moved from one position to another at spaced apart locations on the apparatus to move from one drive knob to another. 
     This can be distracting to the operator as the operator&#39;s attention must often be intensely focused on the position of the instrument relative to the test specimen. This attention can be broken if the operator has to look away from the instrument to find the other drive knob. 
     Accordingly, a need exists for an ergonomic dual drive system for quickly and accurately positioning an instrument relative to a test specimen. 
     A further need exists for such a dual drive system which allows an operator to quickly move an instrument into a desired position with a high speed coarse drive and to subsequently accurately position the instrument into a final position with a low speed fine precision drive. 
     Yet a further need exists for such a dual drive system which allows an operator to manually switch between coarse and fine instrument drives without the necessity of moving the operator&#39;s hand over any significant distance which would otherwise distract the operator from the precision adjustment of the instrument relative to a specimen. 
     Still a further need exists for such a dual drive system which includes a pair of drive knobs ergonomically arranged so as to allow an operator to selectively manipulate each drive knob without the need for moving the operator&#39;s focus from the instrument and specimen to the drive knobs. 
     SUMMARY OF THE INVENTION 
     The present invention has been developed to fulfill the needs noted above, and therefore has as an object the provision of a dual drive system for manipulating positioning apparatus, particularly laboratory apparatus such as precision slides and slideways for moving various instruments and tools into position relative to a workpiece or other specimen such as a laboratory test animal. 
     A further object of the invention is the provision of a dual drive manipulator which includes a high speed coarse drive and a low speed fine drive, each having a drive knob located ergonomically with respect to the other. 
     Yet another object of the invention is the provision of such a dual drive manipulator which has a pair of drive knobs coaxially arranged in close proximity so as to allow an operator to maintain a substantially fixed hand position while switching between coarse and fine drives using small, comfortable finger and thumb movements. 
     Another object of the invention is the provision of a dual drive precision slide for precision instruments which allows an operator to maintain fixed eye focus on the instrument while switching between coarse and fine drives. 
     Still another object of the invention is the provision of a dual drive manipulator having a high speed or coarse adjustment knob and a low speed or fine adjustment knob each geared to the same single drive screw to avoid tolerance build up associated with multiple drive screw manipulators. 
     Another object of the invention is the provision of a precision mechanical manipulator having a pair of coaxially mounted drive knobs arranged coaxially with a single drive shaft or lead screw. 
     A further object of the invention is to provide a manipulator with a dual drive driven by a pair of rotary drive knobs which, when turned in the same direction, (clockwise or counterclockwise) each drives a slide in the same direction (forward or backward). This reduces operator error and potential confusion as to which knob drives the slide in what direction when turned and rotated in a given direction. 
     These and other objects are met in accordance with the present invention which is directed to a dual gear drive system for moving and positioning tools, sensors or other instruments along a slideway of a precision positioning instrument. The dual gear drive has found particular advantage in laboratory equipment such as micro-manipulators and stereotaxic apparatus. 
     An important feature of the invention is the coaxial mounting of a low speed or fine rotary drive knob closely adjacent to a high speed or coarse rotary drive knob. The fine rotary drive knob can be mounted closely axially adjacent to the course rotary drive knob to minimize the distance required to move one&#39;s finger and thumb from one knob to the other. This, in turn, allows an operator to maintain eye focus on an instrument and specimen as the operator moves from one drive knob to the other. No gross hand movements are required. 
     The aforementioned objects, features and advantages of the invention will, in part, be pointed out with particularity, and will, in part, become obvious from the following more detailed description of the invention, taken in conjunction with the accompanying drawings, which form an integral part thereof 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the drawings: 
     FIG. 1 is a schematic perspective view of a portion of a laboratory apparatus fitted with a dual drive positioning system constructed in accordance with the invention; 
     FIG. 2 is a view in axial section taken through a dual drive system of the type shown in FIG. 1; 
     FIG. 3 is a schematic top plan view of the gear arrangement of the dual drive system of FIG. 2; and 
     FIG. 4 is a perspective view of a stereotaxic system provided with a plurality of dual drive positioning systems constructed in accordance with the invention. 
     In the various views of the drawings, like reference numerals designate like or similar parts. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention will now be described in conjunction with the drawings, beginning with FIG. 1 which shows as an example, a precision laboratory positioning apparatus  10 , sometimes referred to as a micromanipulator. Apparatus  10  is used as a precision positioning system for accurately positioning an instrument  12 , such as a syringe, with respect to a specimen such as a laboratory animal. 
     Apparatus  10  includes a fixed weighted base  16  to which a vertical support rod  18  is anchored. A pair of adjustable clamps  20 ,  22  is provided to allow for adjustable sliding movement of clamp bar  24  along the vertical rod  18 . A three axis tool positioning slide assembly  26  is clamped to the free end of bar  24  in a known fashion with an adjustable clamp  28 . The slide assembly  26  includes three individual slides and slideways mutually orthogonally interconnected to allow the instrument  12  to be moved along three mutually perpendicular directions. 
     For the purpose of explanation, a first slide  30  is movably mounted on a first slideway  32  to provide movement to slide assembly  26  along an “x” axis  34 . Lead screw  36 , which extends along the x axis  34 , engages and drives assembly  26  via engagement with a rack of fixed gear teeth on the underside of slideway  32 . Alternatively, the lead screw can be engaged with an intervally threaded drive nut fixed to the underside of slideway  32 . 
     Knob or dial  38  is directly connected to lead screw  36  for a one-to-one drive ratio according to conventional practice. Projections or tongues on the underside of slideway  32  ride in grooves  39  in slide  30 . Instead of a rack of teeth on the bottom of slide  32 , a simple threaded bore can be provided for receiving each screw  36 . 
     A second slide  40  is likewise movably mounted to a second slideway  42  to provide movement to the slide assembly  26  along a “y” axis  44  which is orthogonal to the x axis  34 . The second slideway  42  is substantially the same as the first slideway  32  in that it is provided with a threaded bore or a linear rack of gear teeth which mesh with a lead screw driven directly on a one-to-one ratio by a rotary knob  46 . Slideway  42  is fixed to a mounting block  48  which is in turn fixed in position to the underside of the first movable slide  30 . 
     A third slide  50  is movably mounted to a third slideway  52  such as by a dovetail or tongue and groove to provide movement to the slide assembly  26  along a “z” axis  54  which is orthogonal to both the x and y axes  34 ,  44 . Slideway  52  is modified in accordance with the invention as discussed further below. 
     A dovetailed plate  56  is fixed in position on a mounting block  58  which is in turn fixed in position on the second slide  40 . Slideway  52  is fixed in place on the dovetailed plate  56  along a dovetailed groove which complements the dovetail on plate  56 . As detailed below, a dual drive system  60  is provided for driving the third slide  50  over slideway  52 . Drive system  60  includes a coarse rotary drive knob  62  and a fine rotary drive knob  64  coaxially mounted with the coarse knob around a common drive shaft or lead screw. 
     The third slide  50  has a support plate  66  fixed on one proximal axial end portion and an end cap  68  fixed on the opposite distal axial end portion. A dovetail slideway  70  extends along the top surface of the third slide  50  for guiding and supporting a mounting block  72  having a dovetail groove receiving the dovetail slideway  70 . The mounting block  72  may be fixed in place along slideway  70  with a set screw  74 . 
     A tool clamp  76  is adjustably mounted to the mounting block  72  via mounting bar  78 . Mounting bar  78  is slidably received in a groove or channel  80  in the mounting block and fixed in position with set screw  82 . A tool, probe or instrument  12  is received within the jaws  84  of clamp  76  and held in a fixed position with clamp set screw  85 . In some cases, tool  12  can be directly held in mounting block  72  as shown in FIG.  2 . 
     It can be appreciated that gross adjustments of tool  12  can be made with movement of the clamp bar  24 , up and down rod  18 , and by relatively coarse adjustment along the x and y axes made by turning knobs  38  and  46 , respectively. Additional gross adjustment of the position of tool  12  can be made along the z axis by sliding mounting block  72  along the top of the third slide  50  as well as by sliding mounting bar  78  back and forth within channel  80 . Finally, tool  12  itself can be moved within jaws  84  along the z axis for additional gross adjustment. 
     Tool  12  can be further moved along the z axis by turning the rotary drive knob  62  for a relatively coarse setting. Rotary drive knob  64  can provide a fine precision movement of tool  12  along the z axis. Although only the third slide  50  is provided with a dual drive positioning system  60 , the second and/or first slides  40  and  30  can also be provided with similar dual drive positioning systems, if desired. 
     Details of the dual drive positioning system  60  are shown in FIG.  2 . System  60  may be clamped to the dovetailed plate  56  via slideway  52  as shown in FIG. 1, or alternatively clamped to a manual clamp assembly  86  as shown in FIG.  2 . Clamp assembly  86  includes a dovetail  88  for sliding into the dovetail groove in slideway  52 . A small split bore  90  is provided in clamp block  92  for clamping around small diameter support rods such as clamp bar  24  and a large split bore  94  is likewise provided for clamping around larger diameter support rods such as vertical rod  18 . A winged rotary clamp screw  96  is threaded through the open jaws  98  of the clamp block  92  to provide clamping pressure within the split bores  90 ,  94 . 
     Turning now to the details of the dual drive positioning system  60 , it is seen in FIG. 2 that both the coarse rotary drive wheel or knob  62  and the fine rotary drive wheel or knob  64  are mounted coaxially with one another and coaxially around the axis  99  of a drive member such as a threaded drive shaft or lead screw  100 . Other drive members can include rack and pinion drives and gear and pinion drives including worm gear drives. The fine drive wheel  64  is fixed on one end portion  102  of the drive shaft  100  by a set screw  104 . 
     A fine adjustment calibration ring  106  is fixed around the outer circumference of the fine drive wheel  64  with a set screw  107 . The inner axial end of the calibration ring  106  is concentrically nested with a close rotary clearance fit within a shallow circular recess formed in the outer surface of a stationary annular cover plate  108 . The cover plate  108  is fixed in position by threaded screws  110  which hold the cover plate to the outer ends of three axially-extending anchor posts  112 , two of which are shown in FIG.  2 . 
     The inner ends of the anchor posts  112  are held by press fits within bores formed in a stationary annular bearing housing  114 . The bearing housing is fixed in place against the support plate  66  with screws  118 , and the support plate  66  is fixed to the third slide  50  by screws  120 . 
     In this manner, the cover plate  108 , which may be marked with one or more calibration ticks, is rigidly fixed in position along with the bearing housing  114 , support plate  66  and the third slide  50 . As described below, each of these members moves axially in unison when either of the knobs  62 ,  64  is rotated. 
     An internally fluted or toothed gear ring  122  is fixed within an internal annular step  124  formed on the inner surface of the coarse or high speed rotary drive wheel  62 . Adhesive or set screws can be used to hold the gear ring  122  within drive wheel  62 . A coarse adjustment calibration ring  126  is fixed with a set screw  128  within an annular step  130  formed on the outer surface of this coarse drive wheel  62 . 
     The coarse drive wheel  62  is fixed to the outer race of a ball bearing  132  which has its inner race adhesively bonded or otherwise fixed to an axially extending annular boss or sleeve  134 . 
     Boss  134  is formed on the outer end of the bearing housing  114 . This mounting allows the course drive wheel  62  and its internal gear ring  122  to be smoothly rotated around the bearing housing. A small radial clearance  136  is maintained between the rotary drive wheel  62  and the fixed cover plate  108 . 
     The drive shaft or lead screw  100  is rotatably mounted within bearing housing  114  with a pair of ball bearings  138 ,  140  which are press fit and adhesively bonded within a central bore formed through the bearing housing. The portion of the drive shaft journaled within the bearings  138 , 140  is held axially in place between a flange or collar  144  formed on or pinned to shaft  100 , and a conical nut  146  threaded over the outer axial end of the journaled portion of shaft  100 . 
     Nut  146  applies axial pressure only to the inner race of bearing  138  to preload the bearing assembly. The journaled portion of shaft  100  is press fit into the inner races of bearings  138 , 140 . 
     An axially fluted pinion gear  150  is cut into or otherwise separately mounted on the shaft  100  adjacent its outer end portion  102 . As seen in FIGS. 2 and 3, pinion gear  150  meshes with an intermediary or idler gear  152  which is rotationally mounted on the end of one of the fixed anchor posts  112 . The idler gear is axially restrained between the stationary (non-rotating) anchor post  112  and the stationary (non-rotating) cover plate  108 . 
     The idler gear  152  is also in constant driving meshed engagement with a spur gear  160  which is rotationally mounted on a separate anchor post  112 . Spur gear  160  is axially supported on one face against an axial boss  162  formed on the bearing housing  114  and axially held on anchor post  112  on its other face by the cover plate  108 . The spur gear  160  is further in constant toothed engagement with the ring gear  122 . 
     With the gear drive train described above, any desired gear ratios can be chosen to achieve the relative rotational drive speed of drive shaft  100 . That is, in one embodiment, the pinion gear  150  has  10  teeth or flutes, and the ring gear has  100  teeth or flutes. This will provide a drive reduction of ten to one between the fine drive wheel  64  and the coarse drive wheel  62 . The relative number of teeth on the idler gear  152  and spur gear  160  is not particularly critical or significant, as they will not affect the final gear drive ratio between knobs or wheels  64  and  62 . 
     It should be noted from the directional arrows in FIG. 3 that rotation of either drive wheel  62 ,  64  in one direction rotationally drives the drive shaft in the same direction. This coordinated actuation is provided by the idler gear  152 . This is ergonomically significant as noted above. When either of the drive wheels  62 ,  64  is rotated, they rotationally drive the drive shaft  100  in the same direction within a lead screw drive nut  166  mounted within slideway  52 . 
     Drive nut  166  has an externally threaded end  168  which is threaded into a threaded bore formed through a lead screw or drive shaft mounting plate  170 . The mounting plate  170  is fixed to slideway  52  with fasteners such as screws  172 . A small clearance is maintained between the drive nut  166  and the internal walls of slideway  52  to allow the drive nut to be cantilevered inside the slideway. A spring  173  and nut  175  can be mounted on drive shaft  100  to reduce backlash in a known manner. 
     It can be appreciated that when the lead screw or drive shaft  100  is rotated by either drive wheel, i.e., directly at a 1:1 ratio by wheel  64  or at a higher drive speed ratio by wheel  62 , the drive shaft  100  linearly advances to the left or moves backwards to the right as it rotates within drive nut  166 . As the drive shaft  100  moves linearly, so does the entire third slide  50  along with any tool, instrument, instrumentation, sensor or other device attached to it. 
     It can be appreciated that the provision of ball bearings  132  for mounting the high speed drive wheel  62  on the bearing housing  114  provides extremely smooth rotation of the drive wheel  62 . Moreover, ball bearings  138 ,  140  likewise provide extremely smooth rotation of the drive shaft  100  within the bearing housing  114 . This gives the drive system a precision feel to the operator, which is most desirable. 
     Another example of an application of the dual drive system described above is shown in FIG. 4 wherein a stereotaxic device  200  of generally known construction is provided with dual drive systems  60  of the type described above. The stereotaxic device  200  is designed to hold a laboratory animal in a fixed position with ear bars  202  which engage within the animal&#39;s ears during various laboratory procedures. 
     There has been disclosed heretofore the best embodiment of the invention presently contemplated. However, it is to be understood that the various changes and modifications may be made thereto without departing from the spirit of the invention.