Abstract:
A robotic device for moving at least one object between locations, including a servo motor system having a single servo axis for effecting motion in at least two directions of motion. The robotic device includes a link arm rotationally coupled to said servo motor system for lifting and placing said at least one object, a head assembly having gripper arms for gripping and releasing said at least one object at said locations. The head assembly includes a leveling mechanism for maintaining said at least one object in a desired orientation, and a split ring sensing mechanism, disposed between said gripper arms, for determining the presence of said at least one object.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]    This application claims the benefit of U.S. Application No. 60/330,832, which is hereby incorporated by reference as though fully set forth herein. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    The present invention relates to a method and apparatus for the automated transfer of objects between locations.  
         BACKGROUND OF THE INVENTION  
         [0003]    In medical, chemical and biological laboratories, microtiter plates are commonly used and are filled with various media. The media may either be in a liquid form, or in a more viscous form such as Agar. For efficient productivity of the laboratory, the use of a robotic device to move the microplates between locations is desirable. Such automated machines can produce considerably greater throughput than a technician. To this end there are several automated devices that are currently available to effect such transportation.  
           [0004]    Traditionally, an articulated or cylindrical automated machine with three degrees of motion has been used. Such automated machines are often mounted on a substantially long linear axis and are moved through the entire system to load a plate from one instrument to another. Also, in more complicated systems, conveyors with escapements and slides are used as part of the system to move an object between spaced locations.  
           [0005]    One of the disadvantages of these automated machines is that each requires a minimum of three axes of motion to transfer an object such as a microtiter plate. Typically, such machines require three to six motors to obtain the movement required at the various joints. During movement of an object between locations it is frequently necessary to maintain a fixed orientation for the object, such as maintaining a microtiter plate in a horizontal plane. On traditional machines, plate leveling is accomplished by means of a servomotor controlling an additional joint. This requires additional control functions and mechanical complexity.  
           [0006]    In order to pass signals between the automated machine&#39;s motor and the controller, a flexible wire harness is often used, while another solution involves the use of conductive rings with metal brushes that slide along the rings to replace wire harnesses. A wire harness is susceptible to mechanical fatigue and failure, and takes a certain amount of space in the design. The drawbacks of using brushes and rings are that noise and sparks are generated by the brushes, and the mechanism requires regular maintenance. Typically, the above solutions involve substantially complex systems having a substantial number of parts requiring maintenance.  
           [0007]    It is thus an object of this invention to obviate or mitigate at least one of the above mentioned drawbacks.  
         SUMMARY OF THE INVENTION  
         [0008]    In one aspect, a robotic device comprises a base, an arm rotatable about a first axis relative to the base. A drive motor controls rotation of the arm about the first axis. A head is rotatably mounted on the arm for rotation about an axis parallel to the first axis, and a leveling mechanism operable between the base and the head assembly to maintain the head assembly in a predetermined orientation during rotation of the arm about the first axis.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]    These and other features of the preferred embodiments of the invention will now be described by way of example only in the following detailed description in which reference is made to the appended drawings wherein.  
         [0010]    [0010]FIG. 1 is a perspective view of a robotic device;  
         [0011]    [0011]FIG. 2 is a front elevation of the device shown in FIG. 1;  
         [0012]    [0012]FIG. 3 is a side elevation of the device shown in FIG. 1;  
         [0013]    [0013]FIG. 4 is a rear elevation of the device shown in FIG. 1;  
         [0014]    [0014]FIG. 5 is a perspective view similar to FIG. 1 with the device in an alternative configuration;  
         [0015]    [0015]FIG. 6 is a detailed sectional view on the line  6 - 6  of FIG. 5;  
         [0016]    [0016]FIG. 7 is a schematic representation showing the movement of the robotic device between a pair of locations;  
         [0017]    [0017]FIG. 8 is a set of figures showing a sensor mechanism used in conjunction with the device shown in FIG. 1;  
         [0018]    [0018]FIG. 9 is a view similar to FIG. 8, showing an alternative configuration of sensing mechanism;  
         [0019]    [0019]FIG. 10 is a perspective view of a station assembly used with the device shown in FIG. 1; and  
         [0020]    [0020]FIG. 11 is an exploded perspective view of the station shown in FIG. 10. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0021]    Referring therefore to FIG. 1, a robotic device generally indicated  10  is secured through a base  12  to a workstation  14 . The base  12  includes an upstanding flange  16  that carries a planetary gearbox  18 . The gearbox supports a servo motor  20 , which includes an encoder and associated circuitry to cause rotation of the armature of the motor  20  upon receipt of a control signal.  
         [0022]    As can be seen in further detail in FIG. 6, the output from the motor  12  is transmitted through the gearbox  14  an output shaft  22 . The shaft  22  is connected to a robot arm  24  that projects radially outwardly from the shaft  22 . The arm  24  carries a bearing assembly  26  at the opposite end to the shaft  22  to support a head assembly  28 . The head assembly  28  is supported on a tubular shaft  30  that is rotatable within bearing  32  and so is free to rotate relative to the arm  24 . The head assembly  28  includes a base plate that supports a hand assembly  40 . The hand assembly  40  is rotatably supported on the base plate  36  by a bearing  41  and a servo motor  34  is operable through a drive shaft  38  to rotate the hand assembly relative to the base plate  36 . The bearing  41  is oriented to constrain rotation of the hand assembly about an axis orthogonal to the axis of rotation of the motor  12 . The hand assembly  40  has a pair of fingers  42 ,  44  that can be moved toward or away from one another to engage or release an object. A sensor assembly  46  is incorporated into the hand assembly  40  to indicate the presence or absence of an object as will be described in further detail below. A servo  
         [0023]    A toothed pulley  50  is connected to the shaft  3  for rotation with the shaft and a drive belt  52  is entrained about the pulley  50 . The belt  52  is also entrained about a lower toothed pulley  54  that is secured to a bracket  56  on the base  12 . The lower toothed pulley  54  is secured so as to be stationary relative to the base  12  and is centered on the axis of rotation of the arm  24 .  
         [0024]    The circumferential position of the pulley  54  relative to the base may be adjusted by a clamp bolt  58  (FIG. 5) that is located within a slot  60  in the bracket  56  and so permits limited rotation of the lower pulley  54  relative to the base  12 . The limited adjustment available for the pulley  54  is transmitted through the belt  52  and causes a corresponding rotation of the shaft  30  and head assembly  28 . This permits the orientation of the head assembly  28  to be adjusted into a preferred orientation relative to the base  12  that is maintained during the swinging movement of the arm  24 .  
         [0025]    As may best be seen in FIG. 5, control signals and power to the motor  34  and hand assembly  40  is provided through a wiring harness  70  that passes through the centre of the tubular shaft  30  to the outer edge of the pulley  50 . The harness  70  passes alongside the run of the belt  52  and through an aperture provided in the flange  16  adjacent to bracket  56  to a control box  72 .  
         [0026]    Referring again to FIGS. 1 and 3, the hand assembly  40  includes an actuator  80  to control sliding movement of the fingers  42 ,  44  toward and away from one another. The fingers  42 ,  44  have lower edges with apertures and pins  82  configured to engage standard formations on an object to be conveyed. The fingers  42 ,  44  are slideably mounted on a base plate  84  which in turn is rotatably supported on bearings  41  on the plate  36 . Motor  34  is supported on the base plate  36  on a flexible coupling  88  formed by a double-sided tape such as that sold by 3M under the trademark VHB. The flexible coupling a high shear force to resist torque induced in the motor  34  through the output shaft  38  whilst allowing limited flexibility to accommodate alignment between the components in the head assembly  40 .  
         [0027]    The sensor assembly  46 , shown in more detail in FIGS. 8 and 9, includes a pair of circular segments  90 ,  92 , each secured a respective one of the fingers  42 ,  44 . A proximity sensor  94  is carried on the base plate  36  and is typically an inductive sensor providing a signal indicating the presence or absence of a component. As may be seen in FIG. 8 a , with the fingers  42 ,  44  moved together, the sensors are triggered indicating the presence of the ring  90  over the sensor  94 . This indicates that the actuator has moved to the limit of its travel and no object has been located between the fingers  42 ,  44 . In an alternative position shown in FIG. 8 b , the fingers  42 ,  44  have been moved toward one another, but the sensor  94  remains uncovered, thereby not providing a control signal. The combination of a pressure signal from the actuator  80  and the lack of a sensor signal indicates that the hand is closed but not fully closed so as to be indicative of an object secured between the jaws.  
         [0028]    In the third position shown in FIG. 8 c , the sensor is uncovered but pressure is not applied to the actuator thereby indicating that the jaws are open.  
         [0029]    The provision of the split ring formed by the two segments  90 ,  92  permits similar functionality to be achieved with the hand assembly  40  rotated through 90 degrees by the motor  34 . Thus, as shown in FIG. 9 a , with the fingers fully closed, the gap between the segments  90 ,  92  is closed causing the sensor to be triggered. In the orientation shown in FIG. 9 b , the sensor is uncovered and no signal is received from the sensor.  
         [0030]    In operation, the robot device  10  is located between a pick location indicated in FIG. 7 at A and a place location indicated in FIG. 7 at B. In the pick location the robot arm is operable to be positioned so that the jaws  42 ,  44  overlap the edges of a tray T and, through operation of the actuator  80  grip the sides of the tray T. The capture of the tray T between the fingers  40 ,  42  is signaled through the sensor corresponding to the condition shown in  8 B. The control is then operable to rotate the motor  12  and cause the arm  24  to rotate about the axis of the motor. As the arm rotates, the belt  52  walks about the circumference of the pulley  54  and causes a corresponding rotation of the shaft  30  in the bearing assembly  26 . The orientation of the head  28  is thus maintained as the arm rotates and thereby maintains the tray T in a horizontal disposition. Rotation continues until the tray T is moved to the place location B where the hand assembly may be released and the tray T deposited.  
         [0031]    If during movement of the tray T from the pick location A to the place location B it is necessary to turn the tray T, the motor  34  may be operated to rotate it in a vertical axis and turn it through 90 degrees. During this movement the sensing ring moves from the position shown in FIG. 8 b  to that shown in FIG. 9 b  and maintains the logical control of the hand assembly on the tray.  
         [0032]    To assist in accurate placement of the tray T at either the pick location or the place location, each of those locations may employ an adjustable platten that facilitates accurate placement of the tray T within a desired location. The platten is shown in FIGS. 10 and 11 and includes a support surface  100  supported on three support feet  102 . Each of the support feet  102  is similar and includes a base  110  with a spindle  112  projecting upwardly from the base  110 . The spindle  112  is threaded to receive a nut  114 . The support surface  100  has an aperture  104  to receive each of the spindles  112  with clearance between the spindles  112  and the wall of the aperture  104 . The spindle  112  is formed with flats  116  to receive a washer  118  that is formed with a corresponding slot. The washer  118  is thus unable to rotate on the spindle  112 . A similar washer and nut  120 ,  122  is provided on the upper edge of the plate to secure the plate between the nuts  114 ,  122 .  
         [0033]    The nuts  114 ,  122  permit the height of the support surface  100  to be adjusted at each of the support feet  102  and the limited clearance between the spindle  112  and the aperture  104  permits lateral and longitudinal adjustment of the plate relative to the support feet. Accurate positioning of the surface  100  is thus possible, which can then be secured by tightening of the bolts  122 . The flats  116  and the spindles  112  prevent rotation of the washers  118  and therefore prevent the transmission of a displacement due to rotation of the washers to the plate  100 . The platten thus provides a method of accurate positioning beneath the tray to ensure that the tray is delivered to the correct location.  
         [0034]    The arrangement of the stations A,B at either end of the arc of travel ensures that the placement of a tray or the surface  100  is performed in a substantially vertical manner. Thus, the tray T may be inserted within a rested support or well having vertical sides yet still be removed during initial movement of the arm.  
         [0035]    It will also be noted that during movement of the arm  24  that the harness undergoes a minimal flexure over the range of movement of the arm. Thus stresses induced on the harness are minimized.  
         [0036]    It will also be noted that the head assembly  28  is positioned over the gearbox  18  and motor  20  as the arm functions to move the tray between the locations. This, however, enables a very compact footprint to be obtained for the robot  10  without impeding the operation of the device.  
         [0037]    It will be seen that a compact and simple device is provided that permits the movement of an object between spaced locations. The movement imposed on the object is smooth and continuous with a single acceleration and deceleration phase allowing for controlled movement of the object and its contents. The provision of the leveling mechanism provided by the belt and pulleys obviates the need for additional controls for a separate servo motor and consequently reduces the bulk of the device  10 . It will be appreciated that if rotation of the hand assembly is not required the motor  34  may be omitted and the hand assembly secured directly to the base plate  36 .