Abstract:
A manipulator head for use in a precision assembly unit is disclosed. The manipulator head includes a coarse X-Y stage or movement along the top surface in the X and Y-axis, a fine X stage for fine X-axis movements, a fine Y stage for fine Y-axis movements, and a Z stage for movement in the Z direction. Additionally, a θ stage carried by the manipulator is included. A video camera is coupled to the fine X stage and fine Y stage. The video camera has an optical axis directed substantially in the Z direction. The video camera&#39;s field of view encompassing at least a portion of a part secured by a gripper attached to the manipulator head when the part is in position for processing at the workstation.

Description:
TECHNICAL FIELD OF THE INVENTION  
         [0001]    This invention relates to automated assembly equipment and more particularly to a manipulator/end effector head for robotic assembly.  
         BACKGROUND OF THE INVENTION  
         [0002]    Robotics are commonly used today for the processing and/or assembly of miniature and subminiature assemblies. Robotics are used, amongst other things, to pick up and move parts from a storage area to processing and assembly areas. Robotics can also be used to orient the part and hold it in position for assembly or move the part to an assembly position and help effect assembly of two or more parts to make an assembly. For example, a semi-conductor chip can be taken from a storage area and then placed into a socket on a circuit board after which the chip would be soldered in place on the circuit board. Robotics can move in various directions including X-Y-Z and θ (rotation). As parts to be assembled have become smaller and more complex, the robotics must be more precise in both their ability to pick up and hold a part in a proper position for processing, and also to move the part to a position with greater precision in its placement relative to a processing device or another part to which it is to be joined or otherwise assembled. For many operations, the location accuracy needs to be on the order of about 1 micrometer (μm) (0.00004 inches).  
           [0003]    To achieve higher dimensional or location precision, machine vision systems are used to allow viewing of a part and fiducial points accurately positioned on the part so that the vision system can precisely detect and determine the location of the part and points thereon. In one form of machine vision system controlled robot, the vision system views the part that is held stationary and the robot moves another part to it for assembly therewith. After determining the location of the stationary part, the robot then moves the other part into position and assembles the two parts together. However, such a vision system and associated controller assumes the relative position between the two parts while they are some distance apart which is an acceptable method unless the requirements for placement is very stringent. Such a vision system is typically mounted on the side of a robot and moves therewith. After locating the stationary part, the controller then effects movement of the second part to the first part assuming precise relative positions. Such systems can also be used to move a part to be processed from a pick-up station to processing stations, say for example, for the application of glue or other type of liquid thereto and then to an assembly station for subsequent assembly with a stationary part. Such apparatus with associated vision systems have been effective for lower precision work. However, they have not always been as effective as desired for higher precision work. Thus, there is a need for an improved apparatus and method for processing of parts requiring high precision placement for processing.  
         SUMMARY OF THE INVENTION  
         [0004]    The present invention provides an apparatus for processing miniature and sub-miniature parts using robotics for moving and placing parts. In one aspect of the invention, the apparatus includes an X-Y manipulator for accomplishing the coarse movement of the gripper and the part once gripped. A second device is provided for fine X, Y, Z, and θ movement of the gripper and part carried thereby. A machine vision system is provided that is operable to view the part at a processing station and to provide a signal indicative of the part&#39;s location relative to either another part or a processing device and to help guide the part into the proper location by the continued viewing of the part during the final movement or to provide ongoing information about the location such that any assumption regarding part location when the part is not being viewed will cause minimal error with subsequent part movement. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0005]    For a more complete understanding of the device and advantages thereof, reference is now made to the following descriptions in which like reference numerals represent like parts:  
         [0006]    [0006]FIG. 1 a  is a front elevation view of an apparatus used for robotically moving and assembling parts;  
         [0007]    [0007]FIG. 1 b  is an elevation view of the apparatus of FIG. 1;  
         [0008]    [0008]FIG. 1 c  is a cutaway overhead view of the apparatus;  
         [0009]    [0009]FIG. 2 is a partially cutaway view of a manipulator device;  
         [0010]    [0010]FIG. 3 is a cutaway view of one side of a manipulator device;  
         [0011]    [0011]FIG. 4 is a cutaway view for a second side of the manipulator device; and  
         [0012]    [0012]FIG. 5 is an enlarged view of the gripper. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0013]    [0013]FIG. 1 a  is a front view of an assembly system  100 , FIG. 1 b  is a side view of assembly system  100  and FIG. 1 c  is a cutaway overhead view of the assembly system  100 . Illustrated in these drawings are an assembly system  100 . Assembly system  100  includes a top portion  102  coupled to a base portion  104  using isolation pad  106 . Top portion  102  is preferably manufactured from granite. Top portion includes a top surface  102   a  and a bottom surface  102   b . Base portion  104  is preferably manufactured using a welded structural steel. Isolation pad  106  is manufactured from urethane. Top portion  102 , base portion  104  and isolation pad  106  together form an assembly system that is extremely rigid and vibration free.  
         [0014]    Inside top portion  102  and coupled to a top surface  102   a  is a robot platen  108 . Coupled to robot platen  108  is a manipulator device  110 . Robot platen  108  in one embodiment is a steel plate. Manipulator device  110 , discussed in further detail below, has magnets distributed about the portion that couples to the steel plate and is able to move about the steel plate. This is accomplished by injecting compressed air between the manipulator device  110  and the robot platen  108 . This forms what is commonly known as an air bearing between the manipulator device  110  and robot platen  108 .  
         [0015]    Inside top portion  102  and coupled to a base plate  102   b  are a part processing station  114 , part assembly station  112 , and a part pick up station  116 . Adhesive dispense system  114  is operable to apply an adhesive to a work piece and is discussed in further detail in copending application entitled “ADHESIVE DISPENSING AND VISION SYSTEM FOR AN AUTOMATIC ASSEMBLY SYSTEM”, Ser. No.______ and filed May 25, 2001. The disclosure of the co-pending application is incorporated herein by reference.  
         [0016]    Part assembly station  112  is an area where an object may be assembled with another. Part pickup station  116  is an area where manipulator device  110  can pick up a part.  
         [0017]    Bottom portion  104  provides a rigid support base for top portion  102 . Bottom portion  102  also provides an area to place an AC distribution enclosure as well as mount controls and provide various storage areas.  
         [0018]    A computer  150  including is provided to control the manipulator device  110 , part processing station  114  and other parts of the system  100 . Computer  150  can be any general purpose computer, such as a small office computer running the WINDOWS operating system, as sold by Microsoft, Corp. of Redmond, Wash. Computer  150  will typically include a display screen, keyboard, sensor inputs and other input output connections.  
         [0019]    In operation, under computer control or, optionally under manual control, manipulator device  110  utilizing the air bearing formed between manipulator device  110  and robot platen  108 , will move over to part pickup station  116  where it will get a workpiece. Manipulator device  110  will then move the workpiece to the part assembly station  112  such as an adhesive dispensing system  114 . There, the adhesive dispensing system  114  applies adhesive to the workpiece. The manipulator device  110  will then move the work piece to part assembly station  112  where the manipulator device  110  will place the work piece onto a second workpiece while applying force to connect the two workpieces.  
         [0020]    Referring now to FIGS. 2, 3 and  4 , FIG. 2 is a partially cutaway isometric view of the manipulator device, FIG. 3 is a cutaway view of the side of the manipulator device and FIG. 4 is a second cutaway side view. As seen in those figures, manipulator device  110  includes a coarse stage  202 . In the illustrated structure, the coarse stage  202  utilizes a Normag Dual Axis Linear Stepper Motor Forcer unit (available from NORMAG Corp. of Santa Clarita, Calif.) which is in the form of a planar motor that is magnetically suspended from the robot platen  108 . Compressed air is injected between an upper plate  203  of coarse stage  202  and robot platen  108  to provide what is generally referred to as a frictionless air bearing between the upper plate  203  and the platen  108 . Coarse stage  202  contains the planar motor which is operable to move the manipulator device  110  in X and Y directions as directed by signals from a controller connected thereto. Coarse stage  202  carries and moves the rest of the manipulator device  110  including the various means for fine movements. Coupled to coarse stage  202  are fine X movement stage  204  and fine Y movement stage  206 . The X axis movement is accomplished through the X axis motor  204  while the Y movement is accomplished by the Y axis motor  206 . The motors  204 ,  206  accomplish the fine X-Y movement and encoders can be used with the motors to provide information about the amount of movement and location. The X-Y movement of the fine stage is accomplished through the use of a dual axis positioning system utilizing linear motion motors of high precision such as those available under the name Inchworm from Burleigh Instruments, Inc. of Fishers, N.Y. These motors utilize compact piezoelectric ceramic actuators to achieve ultra-high resolution linear motion positioning.  
         [0021]    The motors  204  and  206  are secured to the coarse stage  202  in any suitable manner. A bracket  205  is secured to the Y motor  206  and suspends therefrom. A linear motion motor  208  is mounted on the bracket  205  and is operable to provide the Z axis movement of a pick up head assembly  214  mounted to housing  209  and, which in turn is carried by a bracket  207  which is mounted for movement to the motor  208 .  
         [0022]    A pick up assembly  214  is carried by the manipulator device  110  and is operable for releasably retaining a workpiece  216 . Pick up head assembly  214  is a variable force vacuum pick up head assembly as are known in the art and is pivotally mounted on the manipulator device  110 . The force applied to the workpiece  216  by the pick up head assembly  214  engaging the part, is exerted by a voice coil motor  212  to prevent the over application of force to the workpiece  216 . Such a pick up head assembly  214  is well known in the art. The workpiece  216  is releasably retained in the pick up head assembly  214  by the application of vacuum to the part and is released from attachment to the pick up device by the release of the vacuum.  
         [0023]    θdirection movement of the pick up head assembly  214  and hence a work piece  216  coupled to a gripper portion  215  of the pick up head assembly  214  is accomplished by a servo motor (not seen in FIG. 2) which connects to a housing  209  via a toothed driving belt  218  (sometimes referred to as a gearbelt or a timing belt) that engages a pulley  303  on the servo motor  302  and pulley  305  mounted on the housing  209 . The θ direction rotation is in the X-Y plane, generally parallel to the top surface of the top portion  102 . Housing  209  is rotatably mounted on a protective shroud  310  via one or more high precision ball bearings  220 . The housing  209  is movable in the Z direction via the Z-axis motor as described above. A machine vision system is provided and includes camera  210  mounted on the manipulator device  110  in the housing  209  for movement in at least the X and Y directions. The position of the camera  210  can be adjusted relative to the opening  224  through which the camera  210  views the workpiece  216  for proper focus of the camera on the part and portions of the processing station  114 , pickup station  116 , and assembly station  112 . Alternatively, the pick up head assembly  214  can be moved out of the field of view of camera  210  for viewing just the processing station  114 , pick up station  116  and assembly station  112 .  
         [0024]    The camera  210  can be any suitable machine vision camera, e.g., a video camera, that has the appropriate focal length, field view, correct working distance and depth of field for viewing the workpiece  216  and portions of the processing stations  114  and/or other components. In operation, the camera  210  simultaneously views the workpiece  216  and some element (including a secondary component or part to make an assembly with) at a processing station  114  to provide information to the computer/controller  150 . The provided information is analyzed (processed) by the computer/controller  150  which in turn provides control signals to control operation of the manipulator device  110  and hence movement of the workpiece  216  relative to some predetermined point or location at the processing station for processing of the workpiece. The signals generated by the computer/controller  150  are sent to the various elements of the manipulator device  110  for controlling movement of the coarse stage  202  and X motor  204 , Y-motor  206  and Z-axis motor  208 .  
         [0025]    The invention will be better understood by a description of the operation thereof. A workpiece  216  is located at the pick-up station  116 . The manipulator device  110  moves the gripper  215  to a location for picking up the workpiece  216 . In the particular form of invention illustrated, vacuum is applied through a vacuum tube  213  to the workpiece  216  that then releasably retains the workpiece  216  on the gripper  215 . The amount of force applied to the workpiece  216  is monitored by the voice coil motor  212  to insure adequate retention while reducing the risk of damage to the part. The computer/controller  150  is programmed with instructions for movement of the workpiece  216  to the locations at the various subsequent processing stations, for example the stations  114 . Coarse (low precision or low resolution) movement of the workpiece  216  is accomplished by the coarse stage  202  of the manipulator under control of the computer/controller  150 . When adjacent to a processing station, the camera  210  is operative to simultaneously view both the workpiece  216  and at least a portion of the processing station  114  such as a glue nozzle to determine the relative position between the workpiece  216  and the processing station  114 . Fiducial points can be provided both on the workpiece  216  and/or secondary part at the processing station for precisely locating the relative position of the workpiece  216  and the processing station  114 . The controller then determines the direction and magnitude of movement required for the workpiece  216  to position it accurately at the processing station  114 . After the part is close to the final position, signals are then sent to the fine stage of the manipulator device  110  for movement of the workpiece  216  to the appropriate position relative to the processing station. X, Y, Z and θ movements may be required to appropriately position the workpiece  216  for one or more operations. A fiber optic light source  308  is provided to camera  210  to provide illumination within the field of vision of camera  210 .  
         [0026]    Preferably the vision system is operable to continuously monitor movement of the workpiece  216  relative to the processing station  114  to ensure proper final location of the workpiece  216 . However, it is to be understood that when the workpiece  216  is close to the desired location, the last portion of the movement of the workpiece  216  need not be continuously monitored by the camera  210 . However, it has been found desirable to continuously monitor the movement of the part  210  relative to the processing station  114  until the precise relative position has been attained. Continuous monitoring may include some interval breaks in the monitoring during movement to the final position and still provide adequate location precision or the continuous monitoring may have no breaks. The above described movement process is also applicable to moving the workpiece  216  relative to a secondary part positioned for such things as forming an assembly.  
         [0027]    An example of an operation that can be performed at the first processing station  20  is the application of one or more spots of adhesive to the part. In this case, the workpiece  216  would be located relative to the adhesive dispensing nozzle at one or more positions on the workpiece for the application of adhesive thereto at predetermined locations on a downwardly facing surface.  
         [0028]    An example of a processing step that could be conducted, e.g., at the assembly station  114 , is the application of a secondary part or subcomponent, such as an electronic component, to the workpiece  216  by moving the workpiece  216  into engagement with the subcomponent for the adhesive securement of the two together.  
         [0029]    [0029]FIG. 5 is a view pick up head assembly  214 . Pick up head assembly  214  includes a gripper portion  215 , which is operable to hold a workpiece via the application of a vacuum via a vacuum line  213 . Voice coil motor  212  applies a force on a workpiece proportional to the current applied to the voice coil motor. A sensor  402  detects very small rotational motion in pick head assembly, which is indicative of the gripper portion  215  contacting a workpiece. A stop  404  limits how far the pick up head assembly can rotate about pivot point  400 .  
         [0030]    In operation, pick head assembly  214  is mounted to the rest of manipulator device  110 . Once it is over a workpiece, it will be lowered in the z-axis. Once the sensor  402  will indicate when the gripper portion contacts the workpiece. Then, if the workpiece is to be moved a vacuum is applied to vacuum line  213  to hold the workpiece. The amount of force exerted on the workpiece is determined by the current applied to the voice coil motor,  
         [0031]    In view of the above, it will be seen that several objects of the invention are achieved and other advantageous results attained.  
         [0032]    As various changes could be made in the above construction without departing from the scope of the invention, it is intended that all matter contained in the above description and shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.