Abstract:
A machine for performing machining operations on a work-piece is disclosed that includes a carriage with a robotic arm mounted thereon. The arm includes a movable head containing a tool for performing the machining operations on the work-piece. A laser position determination system is included for determining the actual spatial relationship position the carriage and the work-piece and providing a first signal representative thereof and further determining the spatial relationship of the head to the work-piece during actual machining operations on the work-piece and providing a second signal representative thereof. A computer having a computer program provides a third signal to the robotic arm for machining the work-piece based on a predetermined spatial relationship between the carriage and the work-piece and for receiving the first and second signals and adjusting the third signal based on the actual spatial relationship between the carriage and the work-piece and the head and the work-piece.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The invention relates to the field of computer controlled and laser guided portable machines for machining parts or work-pieces and, in particular, to a machine that uses a laser position determination system to correct errors in the position of the machining head due to uncontrolled movements of the machine or work-piece.  
           [0003]    2. Description of Related Art  
           [0004]    Computer controlled milling machines and the like are old in art. They generally consist of a very rigid rails to which is mounted a movable carriage containing a head for mounting a cutter or other tool. The work-piece to be machined is mounted on a very rigid platform and the head is moved thereover. Such machines are so rigid that the head and tool can be precisely positioned under the control of a computer.  
           [0005]    Some machines, by the nature of their design, can not position the head and tool to a precise position and thus require supplemental alignment systems. For example, U.S. Pat. No. 5,302,833 “Rotational Orientation Sensor For Laser Alignment Control System” by M. R. Mamar, et al.  
           [0006]    U.S. Pat. No. 5,044,844 “Machining Apparatus” by A. E. Backhouse discloses a machine wherein the machining head is mounted on a carriage located on the end of a boom. The boom pivots in a horizontal plane about an axis on spaced circular rails. A laser alignment system senses any inaccuracies in the level of the rails and adjusts the machining head accordingly. However, this system assumes that the cutting head is always properly positioned. This is because the boom and carriage are robust assemblies and only subject to rail inaccuracies. A somewhat similar system is disclosed in U.S. Pat. No. 5,240,359 “Machining Apparatus” also by A. E. Backhouse.  
           [0007]    U.S. Pat. No. 5,768,137 “Laser Aligned Robotic Machining System For Use In Rebuilding Heavy Machinery” by R. J. Polidoro, et al. discloses a positioning system for resurfacing and repairing rails and guideways of large heavy machinery. A monorail assembly incorporating the milling head is assembled parallel to the rail. The straightness of the rail is determined by a laser measurement system. This information is fed to a computer and is used to align the monorail with the rail. The rail can then be machined to bring it back into tolerance. However, this machine requires a complex set up procedure and is only adapted to machine rails. It could not be used to machine molds and the like.  
           [0008]    None of the above machines are capable of being brought to a remote site and used to machine a work-piece that has been previously setup in a fixed position. All of the prior art machines require precise alignment of the work-piece to the machine. In addition, none of the prior art machines automatically monitor the position of the cutting head and insure that it is in the proper position during machining operations; thus compensating for any movement of the machine or work-piece.  
           [0009]    Thus, it is a primary object of the invention to provide a portable machine for performing machining operations.  
           [0010]    It is another primary object of the invention to provide a portable machine for performing machining operations on a work-piece that does not require precise positioning of the machine prior to commencement of machining operations.  
           [0011]    It is a further object of the invention to provide a portable machine for performing machining operations on a work-piece that automatically compensates for any movement, inadvertent or otherwise, of the machine or work-piece being machined.  
         SUMMARY OF THE INVENTION  
         [0012]    The invention is a machine for performing machining operations on a work-piece. In detail, the invention includes a carriage having a movable robotic arm assembly incorporating a head containing a tool for performing the machining operations on the work-piece. A laser position determination system is included for determining the actual spatial relationship of the carriage and the work-piece and provides a first signal representative thereof. The laser position determination system further determines the spatial relationship of the head to the work-piece during actual machining operations on the work-piece and provides a second signal representative thereof. A computer running computational software provides a third signal to the robotic arm for machining the work-piece based on a predetermined spatial relationship between the carriage and the work-piece. The computer is adapted to receive the first and second signals and the software adjusts the third signal based on the actual spatial relationship between the carriage and the work-piece prior to machining operations and between the head and the work-piece during machining operations.  
           [0013]    In a first embodiment, it is assumed that the work-piece remains in a fixed position, thus it is only the carriage that can move due to vibrations or the like and the robotic arm subject to error in positioning. Thus it is only necessary to initially determine the spatial relationship between the carriage and work-piece and thereafter only monitor the spatial position of the head during machining operations. Therefore, the laser position determination system includes a single laser transceiver assembly and at least one laser target on the carriage, work-piece and head of the robotic arm assembly. The laser transceiver is first used to determine the spatial relationship of the work-piece, then the carriage and then is placed in a tracking mode to track the head during machining operations.  
           [0014]    In the second embodiment, it is assumed that the work-piece may move. For example, the work-piece could be on a conveyor system that passes by the machine. The work-piece could also be stationary, but subject to movements due to vibrations and the like. Preferably, there are three laser transceivers, one to determine the spatial relationship of the work-piece prior and during machining operations, one to determine the spatial relationship of the carriage prior to machining operations and a third to determine the spatial relationship of the head of the robotic arm assembly during machining operations. In this, embodiment, the computer program continuously monitors the spatial relationship of the work-piece during machining operations and adjusts the third signal accordingly.  
           [0015]    The method of increasing the accuracy of a machine for performing machining operations on a work-piece, the machine having a movable head containing a tool for performing the machining operations on the work-piece, the head movable to predetermined positions directed a computer program within a computer, includes the steps of:  
           [0016]    1. Determining the actual spatial relationship between the carriage and work-piece prior to machining operations and providing a first signal representative thereof;  
           [0017]    2. Continuously determining the actual spatial relationship between the head and work-piece during the performance of machining operations and providing a second signal indicative of the actual position; and  
           [0018]    3. Adjusting predetermined spatial relationship of the head during machining operations based on the first and second signals.  
           [0019]    The method of using the second embodiment involves the steps of:  
           [0020]    1. Continuously determining the actual spatial relationship between the carriage and work-piece and providing a second signal representative thereof;  
           [0021]    2. Continuously determining the actual spatial relationship between the head and work-piece during the performance of machining operations and providing a third signal indicative of the actual position;  
           [0022]    3. Continuously determining the actual spatial relationship of the work-piece during machining operations and providing a third signal indicative thereof; and  
           [0023]    4. Adjusting the spatial relationship of the head based on the difference between the first, second and third signals.  
           [0024]    The first embodiment of the machine can be used to perform machining operations on a stationary work-piece while compensating for inadvertent movement of the carriage or positional errors caused by the robotic arm. In the second embodiment inadvertent movement of the carriage, robotic arm errors, as well as unintentional movement of the work-piece can be compensated for. In fact, this latter embodiment could be used with parts on a movable assembly line, because the work-piece position is continuously monitored.  
           [0025]    The novel features which are believed to be characteristic of the invention, both as to its organization and method of operation, together with further objects and advantages thereof, will be better understood from the following description in connection with the accompanying drawings in which the presently preferred embodiments of the invention are illustrated by way of examples. It is to be expressly understood, however, that the drawings are for purposes of illustration and description only and are not intended as a definition of the limits of the invention. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0026]    [0026]FIG. 1 is a side view of the machine and work-piece to be machined.  
         [0027]    [0027]FIG. 2 is a perspective view of the machine and work-piece to be machined.  
         [0028]    [0028]FIG. 3 is a view similar to FIG. 1 illustrating the machine actually performing machining operations on the work-piece.  
         [0029]    [0029]FIG. 4A is a first part of a flow chart of process for controlling the machine.  
         [0030]    [0030]FIG. 4B is a second part of the flow chart illustrated in FIG. 4A.  
         [0031]    [0031]FIG. 5 is a top view of a second embodiment of the machine illustrating the machining of a work-piece in a first position along a moving conveyor.  
         [0032]    [0032]FIG. 6 is a view similar to FIG. 5 illustrating the machine with the conveyor having moved the work-piece to a second position.  
         [0033]    [0033]FIG. 7 is a portion of FIG. 4B illustrating a revised In-Situ Processing Step. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0034]    Referring to FIGS.  1 - 4 , a work-piece or part to be machined, indicated by numeral  10 , is shown secured to the floor  12  by a mounting fitting  14 . As illustrated, the work-piece  10  is rigid foam; however, the work-piece could be a ceramic or metal. The top surface  16  includes three tooling holes  18  in a spaced relationship thereon. The subject machine, generally designated by numeral  19 , includes a laser alignment system  20 , which comprises a laser transceiver assembly  22  mounted in proximity to the work-piece  10 , and three laser targets  24 A,  24 B and  24 C mounted in the tooling holes  18 . A typical laser alignment system is fully discussed in U.S. Pat. No. 4,714,339 “Three to Five axis Laser Tracking Systems” b y K. C. Lau, et al., herein incorporated by reference; although other laser alignment systems can be used.  
         [0035]    In detail, the laser transceiver tracking assembly  22  transmits a laser beam, indicated by numeral  26  to the laser targets  24 A-C mounted on the work-piece  10  and is directed back to the tracking assembly. An interferometer interferes the source beam with the beam that has traveled twice between the laser transceiver assembly  22  and targets in order to measure the separation. By measuring the directions of the beams relative to the to targets, the targets can be located in spatial coordinates and additionally the orientation of the targets can be determined. The measurements are fed to a laser-tracking computer (not shown), which is able to calculate the spatial coordinates of the tool  10 . Systems based on this technology are commercially available. It must be noted that while three laser targets are shown, in some applications a single target may be adequate.  
         [0036]    The machine  19  further includes a portable carriage  28  having a robotic arm assembly  30  mounted on top. The carriage  28  includes wheels  32 , stabilizing jacks  34  and a computer  36 . As illustrated the robotic arm has a tool head  38  in which is mounted a cutter  40 . Robotic arms are commercially available from companies such as Fanuc Robotics, Rochester Hills, Mich. The front face  42  of the carriage  28  includes three laser targets  44 A,  44 B and  44 C in a spaced relationship; although in some applications, a single target can be used. While the targets  44 A-C are shown positioned on the front face  42  other positions are possible such as on the top surface  43 . The carriage  28  is wheeled up to the work-piece  10  and locked in place by the jacks  34 . Preferably, the carriage  28  is positioned in a predetermined optimum position in relationship to the work-piece  10 . This optimum position would be the position of carriage as originally set in the machining program in the computer  36 . However, even if the carriage is set with precise hand measurements, they will not generally be precise enough, such that compensation for positional error must be taken into account.  
         [0037]    Thus the alignment system  20  is used to determine the spatial relationship of carriage  28  to the work-piece  10  using the targets  24 A-C and  44 A-C. Again, it should be noted that in some cases a single target  44 A might suffice. The spatial coordinates of the work-piece  10  and carriage  28  are provided to the computer  36 . Since the relationship between the carriage  28  and robotic arm assembly  30  will be known by the computer  36 , the relationship of the robotic arm to the work-piece can be computed. Thus the computer  36  can calculate the actual offsets to the spatial relationship required to compensate for the actual position of the carriage  28  to the work-piece  10 .  
         [0038]    As previously stated, the carriage  10 , even if locked in place by the jacks  34 , may move and the robotic arm assembly  30  may introduce inaccuracies, and the work-piece  10  is not necessarily on a rigid platform, as in the case of a typical milling machine or the like. Therefore, it is possible that such movement, even if extremely small, could cause inaccuracies in the machining operations. Thus a laser target  46  is mounted on the head  38  of the robotic arm assembly  30 . The laser transceiver assembly  22  uses the target  46  to locate the actual spatial relationship of the head  38  during actual machining operations. This information is provided to the computer  36 , which continuously adjusts the position of the head  38  so that it is in the required spatial relationship to the work-piece  10 .  
         [0039]    In FIG. 4 is a flow chart of the machining process. The flow chart is divided into four sections:  
         [0040]    1. Set up  50 , wherein the work-piece and carriage positions are determined. The carriage  28  is wheeled into position in proximity to the work-piece  10 . Once in position, the jacks  34  are engaged so that all the weight of the carriage  28  is on the jacks. Note, while desirable, the carriage  28  need not be level or in a particular orientation. The laser alignment system  20  is used to determine the position of the work-piece  10  and carriage  28 . The data on the coordinates of both the work-piece and carriage are used to update the computer program within the computer  36  for machining the work-piece.  
         [0041]    2. Pre-Processing  52 , wherein the computer processes the positional information and up-dates the machining program. The position information is stored in the computer  36  and is used to calculate a coordinate transformation matrix that will be applied to adjust the robotic arm assembly  30  to machine the work-piece  10 . This allows the tool  40  to be moved to any position necessary to perform the machining operations on the work-piece.  
         [0042]    3. In-Situ Processing  54 , wherein the work-piece is machined with the laser tracker assembly providing head  38  position information to correct for errors. Prior to machining operations, transceiver assembly  22  will focus on the target  46  on the head  38  of the robotic arm assembly  30  and go into a live feedback tracking mode. The robotic arm assembly  30  will follow the preprogrammed computer program that has been modified by the incorporation of actual positions of the carriage  28  and work-piece  10 . However, the transceiver assembly receives real-time head  38  spatial relationship information. If there is a deviation, the computer program calculates a difference or offset matrix and uses it to “real time” re-position the head  38  to the required position. This process is updated several times a second insuring a smooth machining operation.  
         [0043]    4. Post Processing  56 , wherein the work-piece is inspected. After the machining operation, the robotic arm assembly  30  is used to inspect the work-piece  10 . It will replace the cutter  40  with an inspection target (not shown). The transceiver assembly  22  tracks the inspection targets&#39; position as the now the machined work-piece is probed. In detail, the flow chart is as follows.  
         [0044]    Section 1, Set up  50  involves steps of:  
         [0045]    Step  60 —Set up carriage  28  and alignment system  20  in proximity to the work-piece  10 .  
         [0046]    Step  62 —Determination of positional relationship of work-piece to the robotic arm assembly  30  of the carriage  28  and provides the information to the computer  36 .  
         [0047]    Section 2, Pre Processing  52  involves the steps:  
         [0048]    Step  64 —Store positional information in computer  36 .  
         [0049]    Step  66 —Perform coordinate transformation to generate transformation matrix  
         [0050]    Step  68 —Update machining program using transformation matrix.  
         [0051]    Section 3, In-Situ Processing  54  involves the steps of:  
         [0052]    Step  70 —Transceiver assembley  22  tracks target  46 .  
         [0053]    Step  72 —Machine to preprogrammed path.  
         [0054]    Step  73 —Measure actual position of head  
         [0055]    Step  75 —Determine if head  38  at proper position. Computer program determines deviation between actual head position and desired position. If the head  38  is at the proper position, to Step  76 .  
         [0056]    Step  76 —Determine if machining is complete. If complete then to Step  78  of Post Processing  56  Section. If machining is not complete then Step  80 .  
         [0057]    Step  80 —Generate a delta transformation matrix and calculate offsets. Thereafter return to Step  72   
         [0058]    Section 4, Post Processing  56   
         [0059]    Step  78 —Robotic arm assembly  30  replaces cutter  40  and inserts a spring loaded laser target (not shown)  
         [0060]    Step  82 —Machine work-piece inspected.  
         [0061]    Step  84 —Record measured data  
         [0062]    Step  86 —compare measured data with desired surface contour. If not within tolerance, return to step  80 , if within tolerance then job is complete.  
         [0063]    A second embodiment of the invention is depicted in FIGS. 5 and 6. Here work-pieces  90 A,  90 B and  90 C are shown mounted on a conveyor system  92  and have two slots  94 A and  94 B shown on completed part  90 C, partially machined on work-piece  90 B and in dotted lines on part  90 A. The carriage  28 ′ is identical to carriage  28  except that the laser targets  44 A,  44 B and  44 C are mounted on the top surface  43 . The tool  40  mounted in the head  38  of the robotic arm  30  is shown machining the slot  94 A in the work-piece  90 B. In FIG. 6, the work-piece  90 B, which has moved further down the conveyor system  92  and the machine has machined the slot  94 A and has started to machine slot  94 B. A support column  96  extends up from the floor  12 , which includes a horizontal arm  98  extending over the conveyor system  92  and carriage  28 ′. The arm  98  mounts three laser transceiver assemblies  100 A, for tracking laser targets  44 A- 44 C;  100 B for tracking laser targets  24 A,  24 B and  24 C mounted on the work-piece  90 B; and  100 C for tracking laser target  46  mounted on the head  38 . The spatial relationships of the work-piece  90 B and head  38  can be tracked as the conveyor system  92  moves the work-pieces there along. Note that is not necessary to track the carriage  28 ′ during the machining operations because the head  38  is monitored. Therefore, the laser transceiver  100 C could be used to initially locate the carriage  28 ′ and thereafter used to monitor head  38  position; thus only two laser transceiver assemblies are really necessary.  
         [0064]    Referring to FIG. 7, the process is similar to that disclosed in FIG. 4B except the In-Situ Processing Section, now indicated by numeral  54 ′, includes a “Step  73 A Determination of actual position of work-piece” between “Step  73 —Determine if head is in proper position” and “Step  74 —Is mill at proper position  74 . In Step  73 A, the laser transceiver assembly  100 B tracks the targets  24 A, B and C to determine if the work-piece has moved from its initial position.  
         [0065]    Thus the invention can be used to perform machining operations on a work-piece. In the first embodiment, it can accommodate movement inadvertent movement between the work-piece and carriage. In the second embodiment, the machine can accommodate continuous movement between the carriage and work-piece. Furthermore, while a conveyor system was shown for purposes of illustration, a basically stationary work-piece, subject to small movements, could easily accommodated. Additionally, it should also be noted that while the machining operations discussed were milling, hole drilling or other operations can be performed with the machine.  
         [0066]    While the invention has been described with reference to particular embodiments, it should be understood that the embodiments are merely illustrative, as there are numerous variations and modifications, which may be made by those skilled in the art. Thus, the invention is to be construed as being limited only by the spirit and scope of the appended claims.  
       Industrial Applicability  
       [0067]    The invention has applicability to the machine tool industry.