Abstract:
A method and apparatus for confirming identification of a tool position relative to a workpiece and selecting the tool operating program associated with the position of the tool. A laser location confirmation apparatus is mounted on a tool and measures the distance between the tool or laser source and a surface feature adjacent to the tool, after the tool is engaged with a workpiece joint. When a distance match is made by a laser controller with one of a plurality of prestored reference distances identified with each different work operation or joint, the proper tool operating program is selected and activated.

Description:
BACKGROUND 
       [0001]    The present invention relates, in general, to tools and, more particularly to automatic tools running a stored operating program. 
         [0002]    Tools are used to assemble most machines, vehicles and other apparatus. The common type of tool used in assembly of various apparatus applies or tightens a fastener to join two or more work pieces together. 
         [0003]    One such tool is a nutrunner which executes a control program, when the nutrunner is activated by an operator, programmed robot, or other control apparatus, to tighten a nut on a threaded fastener according to the pre-programmed tightening speed, maximum torque, torque angle or other parameters required for that particular fastener or joint. 
         [0004]    Nutrunners coupled to a controller which is capable of storing and supplying control values to the nutrunner to execute a number of different tightening and torque application programs are used in many assembly operations, and, in particular, vehicle assembly operations. However, in the case of manually operated nutrunners, it is up to the operator to identify the particular joint and then select the appropriate tightening or torque program. This leaves an opportunity for judgment errors on part of the operator which could result in an incomplete torque of the nut or over tightening of the nut, the wrong maximum torque applied to the nut or joint or the torque angle of the nut, stripping of the threads in the nut and bolt, etc. 
         [0005]    In an attempt to address defects caused by operator error, a smart arm apparatus has been designed for use in fixture tools having assist arms which support the weight and the forces generated by the nutrunner by a movable mechanical structure. The assist arm is designed to allow free movement of the nutrunner in multiple directions by using a combination of articulated arms with rotational joints and/or linear bearings. This combination of articulated arms can allow up to six degrees of freedom of movement of the nutrunner. 
         [0006]    The position of the nutrunner in free space can be determined by placing rotational or linear encoders on the joints or linear bearings of the articulated arms of the assist arm and then using the encoder values to calculate the position coordinates via a positioning controller. This insures that the location of the nutrunner with respect to a particular joint is known before the nutrunner is activated. This also insures that the proper tightening or torque program is selected for the nutrunner for the joint currently engaged by the nutrunner. 
         [0007]    The assist arm technology can be used only if the assist arm carrying the nutrunner is in a stationary position relative to the vehicle which is moving past the assist arm station in the assembly line. Typically, the assist arm is installed on a dolly that is mechanically attached to each moving carrier as each carrier moves past the nutrunner work station. This allows the origin of coordinates to be located at the same location relative to the vehicle for the proper selection of the nutrunner program for each joint. 
         [0008]    However, there are applications where, due to the design of the assist arm, the assist arm is fixedly mounted to the assembly plant floor instead of on a dolly movable with the vehicle. In this application, the encoder positions would continuously change as the operator is following the vehicle in the process operation, thereby making the determination of the the coordinates of the position of the nutrunner relative to a joint on the vehicle impossible. This prevents the confirmation of the joint location for the application of the proper nutrunner program for that identified joint. 
         [0009]    It would be desirable to provide an apparatus and method for confirming joint location in all assembly applications to insure that the proper joint tightening program is selected for each different joint. 
       SUMMARY 
       [0010]    A method of selecting a stored tool operating program for a tool coupled to a tool controller and having a work piece engagement portion includes the steps of:
       engaging the work piece engagement member of the tool with the workpiece;   measuring, by a distance measurement device carried on the tool, a distance dimension between the distance measurement device and a surface feature dimensionally fixed with respect to the workpiece;   comparing, by a distance measurement apparatus controller, the measured distance dimension with a reference distance dimension;   transmitting by the distance measurement apparatus controller a match signal to a tool controller when the measured distance dimension equals one of the reference distance dimensions; and   selecting, by the tool controller, a tool operating program associated with the distance measurement apparatus output.       
 
         [0016]    The method can include mounting the distance measurement device on the tool. 
         [0017]    An improvement includes forming the distance measurement apparatus as a laser sensor capable of emitting a laser beam from a laser source and determining a distance between the laser source and the surface feature using the laser beam. 
         [0018]    The improvement can include adjustably mounting the laser on the tool. 
         [0019]    The tool can be provided as a nutrunner having selectable prestored torque programs, each associated with an identifiable joint on a workpiece. In this aspect, the method includes prestoring one joint location ID with a nutrunner torque program associated with the one joint, moving the nutrunner into an operating position engaged with the one joint, and identifying the joint location ID by matching a dimension from a laser sensor to a surface feature adjacent to the joint. When a dimensional match is determined, a nutrunner torque program prestored for the one joint is selected for operation of the nutrunner. 
         [0020]    An apparatus is disclosed for authorizing selection of one of a plurality of distinct tool operating programs each associated with one of a plurality of distinct tool operations on a workpiece includes a distance measurement sensor carried on the tool. The distance measurement sensor is capable of measuring a distance dimension between the distance measurement sensor and a surface feature adjacent to the location of the tool operation on the work piece. The distance measurement sensor outputs a signal when the measured distance dimension matches a reference distance dimension prestored in the laser sensor in the distance measurement apparatus. The tool controller, upon receiving the output signal from the distance measurement sensor, selects the one of the plurality of distinct tool operating programs associated with the one of the plurality of distinct tool operations on the work piece associated with the distance measurement for operating the tool according to the selected one tool operating program. 
         [0021]    The apparatus can include holder mountable on the tool. The distance measurement sensor can be mounted on the holder. The distance measurement sensor can be adjustably mounted on the holder. 
         [0022]    The distance measurement sensor can be a laser distance sensor. 
         [0023]    The tool can be a nutrunner. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         [0024]    The various features, advantages and other uses of the present invention will become more apparent by referring to the following detailed description drawing in which: 
           [0025]      FIG. 1  is a side elevational view of a laser location confirmation apparatus for a tool; 
           [0026]      FIG. 2  is a front elevational view of a nutrunner and nutrunner controller shown in  FIG. 1  as an example of a tool; 
           [0027]      FIG. 3  is a pictorial block representation of the tool, tool controller and electrical controls of the laser location confirmation apparatus; 
           [0028]      FIG. 4  is a perspective view of a laser location apparatus mounted on a nutrunner, as shown in  FIGS. 1 ,  2 , and  3 ; 
           [0029]      FIG. 5  is a perspective view showing the use of the apparatus in operating a nutrunner on a first joint; 
           [0030]      FIG. 6  is an electrical diagram showing the interface signals between the laser location confirmation apparatus and the tool; 
           [0031]      FIG. 7  is an enlarged, perspective view showing the first joint depicted generally in  FIG. 5 ; 
           [0032]      FIG. 8  is a perspective view of the use of the laser location confirmation apparatus with the nutrunner to tighten a second joint; and 
           [0033]      FIG. 9  is an enlarged perspective view of the second joint. 
       
    
    
     DETAILED DESCRIPTION 
       [0034]    The following description is a laser location confirmation apparatus for use with an automatic tool which confirms the location of the tool with respect to a joint or other location on a workpiece where the tool is to perform an operation, such as tightening a nut or bolt, drilling a hole etc. The laser location confirmation apparatus identifies the location of the tool at the joint and then sends a signal to enable the tool controller to select the proper operating program for that particular tool location or tool operation. 
         [0035]    By way of example only, the following description of the laser location confirmation apparatus uses a nutrunner operating several different control programs to tighten bolts in an automotive vehicle where at least two of the bolts require different tightening parameters. It will be understood that the laser location confirmation apparatus can be used with different tools for different tool operations, in addition to the following description of the use of the laser location confirmation apparatus with an automated nutrunner. 
         [0036]    Referring now to  FIGS. 1-3 , there is depicted a tool which, by example only, is a nutrunner  10 . The nutrunner  10  is coupled by a power cable  12  to a tool controller  14 . The tool controller  14  may include a central processing unit, such as a microprocessor or microcontroller, which executes a stored program containing individually selectable program parameters for operating the nutrunner  10 . The programs may be entered into the memory of the tool controller  14  via input push buttons  16  with the assistance of a display  18  on the face of the junction box  20  of the tool controller  14  or via computer software interface. 
         [0037]    The memory of the tool controller  14  stores a number of variables in each program associated with the operation of the tool or nutrunner  10 . Such variables can include, for example, the rotation speed, the torque, the torque angle, tool advance speed, and other variables, such as depth of cut, etc., for other types of tools. These variables are stored in the memory of the controller  14  and are individually selectable to meet the requirements of a particular tool operation. 
         [0038]    In the assembly of automotive vehicles, a number of different joints using bolts are used to join vehicle components together. The joints frequently have different assembly variables, such as final torque, torque angle, advance speed, etc. Thus, for proper assembly of the vehicle and for safe and reliable operation of the vehicle, it is important that each joint or work operation be completed correctly. 
         [0039]    In the present example of the nutrunner  10  used to tighten a number of different bolts on an automotive vehicle, the tool controller  14  operates to provide appropriate control signals via the cable  12  to the nutrunner  10  for the identified joint or work operation. 
         [0040]    As shown by example in  FIGS. 1 and 4 , the nutrunner  10  includes an elongated, generally cylindrical shaped body  26  having a first end  28  which is connectible to the power cable  12  and an opposed second end  30  which carries a rotatable socket head  32 . 
         [0041]    As shown generally in  FIG. 1 , an elongated socket extension  34  is coupled to the socket head  32  and terminates in a socket  36  sized to engage a particular size bolt on the vehicle. 
         [0042]    It will be understood, however, that any size socket or different sockets, each associated with different sized bolts or joints on a vehicle may be employed with a single nutrunner  10 . 
         [0043]    As shown by way of example only in  FIG. 1 , an optional assist arm assembly  40  is mounted to the assembly plant floor for supporting the tool or nutrunner  10  in the desired position and to reduce fatigue of the tool operator during operation of the nutrunner  10 . The assist arm  40  includes an extensible arm linkage  42  mounted on a stand  44  and attached to the nutrunner  10  to support and allow three dimensional or six plane movement of the nutrunner  10 . 
         [0044]    The power cable  12  extends from the nutrunner  10  to attachments on a frame  44  of the assist arm  40  and then to the tool controller junction box  20  as shown in  FIG. 1 . 
         [0045]    A separate junction box  48  is also mounted on the frame  44  to enclose the wiring terminals for a distance measurement apparatus or sensor, such as a laser location confirmation apparatus described hereafter. 
         [0046]    A trigger or activation switch  46  is mounted on the body  26  of the nutrunner  10  and is coupled to the conductors in the power cable  12  for activating the nutrunner  10 . 
         [0047]    Referring now to  FIG. 4 , a holder  50  is provided to fixedly, yet adjustably couple a distance measurement sensor, hereafter referred to as a laser location confirmation apparatus  52  to the body  26  of the nutrunner  10 . 
         [0048]    By way of example only, the holder  50  includes front and rear split connector plates  54  and  56 , respectively. Each of the plates  54  and  56 , which have a general linear configuration, have complimentary semicircular openings along a mating side edge. The semicircular openings  58  and  60  surround the body  26  of the nutrunner  10  and secure the connecting plates  54  and  56  to the body of the nutrunner  26  when mounting screws extend through the plates  54  and  56 . Only one of the mounting fasteners  62  is shown in  FIG. 4 . 
         [0049]    A pair of spaced legs,  66 , only one of which is shown in  FIG. 4 , project from an opposite side of the front connector plate  54  from the side edge carrying the semicircular opening  58 . The legs  66  provide an attachment support for a pair of pivot plates  68  and  70  which are attached to the legs  66  by bolts  72 . 
         [0050]    A slot  74  and  76  is formed in each of the pivot plates  68  and  70 , respectively. By way of example only, each slot  74  and  76  has an arcuate shape. A pair of fasteners, with only one fastener  80  shown in  FIG. 4 , extends through the slots  74  and  76  into the body or housing  53  of the laser location confirmation apparatus  52 . The second pair of fasteners  82  with only one fastener  82  being shown in  FIG. 4 , are provided through a separate opening in each pivot plate  74  and  76  and also engage in a lower portion of the housing  53  of the laser location confirmation apparatus  52 . The arrangement of the fasteners  80 , the slots  74  and  76  and the fixed fasteners  82  allow the orientation of the aiming axis  83  of the laser location confirmation apparatus  52  to be adjusted relative to the plane of the connecting plates  54  and  56  of the holder  50  and relative to the axis of rotation of the socket  32  of the nutrunner  10 . 
         [0051]    By way of example only, the housing  53  is shown at a nonparallel, acute angle relative to an axis of rotation  33  of the socket end  32 . To achieve this angular orientation or to adjust the aiming axis  83  of a laser source  84  in the laser location confirmation apparatus  52  to a different angle, the fasteners  80  and  82  are first loosened. The housing  32  is then adjusted until the axis  83  is at the desired angle relative to the longitudinal axis through the body  26  of the nutrunner  10  or to the axis of rotation  33  of the socket head  32 . The fasteners  80  and  82  are then tightening to fix the housing  53  into the desired position. 
         [0052]    Referring briefly to  FIG. 3 , as described above, the power cable  12  from the nutrunner  10  is coupled to the tool controller junction box  20 . A cable  100  also runs from the tool controller  20  to the junction box  48  with the communication of electrical signals between the laser location confirmation apparatus  52  via cable or a plurality of individual conductors. 
         [0053]    The tool controller junction box  20  is also coupled to the assembly plant Pokayoke system interface  106  via cable  107  to transmit go and no go signals from the tool controller  14  respectively indicative of a proper assembly operation or a non-proper assembly operation. The Pokayoke system interface  106  is coupled to the main assembly line controller  108  and is capable of sending a signal of stopping the main assembly line in the event of a no good assembly operation by the nutrunner  10 . 
         [0054]    A laser controller  120  is mounted inside the housing  53 . A display  122  may be coupled to the laser controller  120  and visible from the housing  53  to display distance values and other operating parameters. 
         [0055]    The laser controller  120  executes a program stored in a memory accessible by the laser controller  120 . The program stores distance information associated with each different work operation, such as the tightening of the bolts or joints in the following description. The stored distances or dimensions are referred to as reference distances. 
         [0056]    In operation, a vehicle will advance into a work station as shown in  FIGS. 5 and 7 . The Pokayoke system  106  requests the tool controller  20  to run the first tool operation program PSET# 1  which corresponds to the first joint  122  to be tightened in the work station process. The operator then engages the socket  36  of the nutrunner  10  with the nut  122  as shown in  FIG. 5  and depresses the trigger  46  on the nutrunner  10  to start the tightening sequence. 
         [0057]    The laser in the housing  53  attached to the nutrunner  10  continuously emits the laser beam  124  and computes the distance to the surface feature selected to correspond to joint # 1 . In the example shown in  FIG. 5 , the surface feature is the front suspension member of the vehicle which is located in close proximity to joint # 1 . The laser beam  124  is reflected from the surface feature  126  back to the laser housing  53  where the laser controller  120  computes the distance to the surface feature  126 . 
         [0058]    When the distance value computed by the laser controller  120  falls inside the range preprogrammed for the joint # 1  location, the laser output OU 1  is generated by the laser controller  120  and transmitted to the tool controller  20  where ladder logic is provided to control the operation of the nutrunner  10 . This sequence confirms the placement of a nutrunner  10  on the proper joint  122 . 
         [0059]    Output # 1  (Laser OU 1 ) is a condition programmed in the tool controller  20  logic shown in  FIG. 6  that allows the nutrunner  10  to run the PSET # 1  tool operating program. If output # 1  (Laser OU 1 ) is absent at the moment the operator depresses the trigger  46  on the nutrunner  10 , the nutrunner  10  will not run. Also, during the tightening cycle, if output # 1  is momentarily lost, the nutrunner  10  will stop and generate a false signal. 
         [0060]    When the tightening cycle for joint # 1  is completed, and the torque value target has been reached, a signal is sent by the tool controller  20  back to the Pokayoke system interface  106  confirming that joint # 1  has been successfully completed. 
         [0061]    The Pokayoke system  106  will now request the tool controller  20  to run PSET # 2  to tighten the second joint  130  shown in  FIG. 9 . The laser in the housing  53  attached to the nutrunner  10  continues to emit the laser beam  124  and computes the distance to any surface the beam  124  reflects from. In the specific case of joint # 2 , the proper preselected surface feature is the back door  132  of the vehicle located downstream of the one in the current work station. The laser controller  120  calculates the distance measurement provided by the laser beam  124  reflecting off of the surface feature  132 . When the computed distance value falls inside the range preprogrammed for the joint # 2  location, output # 2  signal is generated. This confirms the proper placement of the nutrunner  10  on joint # 2 . 
         [0062]    The logic shown in  FIG. 6  shows that a second signal is then generated by the tool controller  20  corresponding to PSET # 2 . 
         [0063]    Output # 2  is a condition programmed into the logic of the tool controller  20 , as shown in  FIG. 6 , which allows the nutrunner  10  to run at PSET # 2 . If output # 2  is absent at the moment the operator depresses the trigger  46 , the nutrunner  10  will not run. 
         [0064]    When the tightening cycle for the second joint  130  has been completed, and the target torque value has been reached, the tool controller  20  sends a signal back to the Pokayoke system  106  confirming that joint # 2  has been successfully completed. 
         [0065]    At this time, the Pokayoke system  106  has received confirmation that both joints # 1  and # 2  have been successfully tightened. The Pokayoke system  106  then sends a signal to the main assembly line controller  108  allowing the vehicle to advance to the next process workstation. 
         [0066]    The same nutrunner  10  can be used for additional joints on the same vehicle as long the reference distance to be measured by the laser  52  is distinct for each separate joint. 
         [0067]    It will also be understood that the nutrunner  10  may be used to provide the same set of work torque parameters for each of a plurality of joints, as long as a surface feature can be selected for each distinct joint or bolt head which has a completely unique or distinct distance measurement from all of the distance measurements associated with the other joints. This enables identical joints to be tightened with the same set of operating parameters, but with each distinct joint being uniquely identified along with its appropriate operating program for the nutrunner  10 .