Abstract:
An automated system for performing an operation on a component within a manufacturing workstation is disclosed. The system includes a robot controller having seven axes of motion control. A robotic manipulator is connected to the robot controller and has six axes of motion. The robotic manipulator includes tooling for grasping the component upon which the operation is performed. A fixed location tool is provided for performing the operation, and a servo mechanism is provided for operating the fixed location tool. The servo mechanism is controlled by one of the seven axes of motion control of the robot controller, whereby the robotic manipulator moves the component with respect to the fixed location tool for performing the operation.

Description:
BACKGROUND OF THE INVENTION 
     1. Technical Field 
     The present invention generally relates to a robot controlled sealant dispenser for use in a manufacturing environment. More particularly, the present invention is directed to a robot controlled sealant dispensing system which allows all six axes of the robotic manipulator to be utilized during the sealant dispensing and application process. 
     2. Discussion 
     Robot based manufacturing continues to find new applications as the technology for controlling and implementing robot based systems is improved. One particular use for robot based systems is the dispensing and application of sealant to individual parts to be assembled, such as those parts found in an automotive assembly facility. A variety of systems have been developed to implement this robot based automation technique. One such application involves utilizing one of the robot&#39;s motion axes to drive a dispensing pump mounted to the robot&#39;s end effector. This motion axis is sometimes referred to as the sixth axis of control. However, this application limits the motion of the robotic manipulator because only five of the typical six axes of motion are available. As a result, the robot manipulator is limited to applying sealant to a surface lying completely in a single dimensional plane. Thus, the functionality of this robotic manipulator design is severely limited for applications having a surface lying in two or more dimensional planes. 
     In addition, more complex hardware is required for supporting the sealant dispenser because it is always in motion with the end effector of the robotic manipulator. A substantial amount of weight is also placed on the robot end effector which can lead to uneven or inconsistent movement of the robotic manipulator. This inconsistent movement translates into error, which then reduces the benefits of using a high precision robot for the manufacturing task. 
     To achieve maximum flexibility in the manufacturing environment, it is desirable that the robot manipulator utilize all six axes of motion so that the end effector can be moved into any desired position. It is also desirable to remove the sealant dispenser from the robot manipulator, and mount the sealant dispenser in a fixed location. This in turn would remove a substantial amount of weight from the end effector of the robot, and increase the accuracy of the robot&#39;s movements. According to this envisioned design, the robotic manipulator can be used for moving parts to which sealant is to be applied about or underneath the fixed location sealant dispenser. Finally, it is desirable to operate the sealant dispenser with a feedback controlled servo mechanism for increasing the precision of the sealant application process. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention, an automated system for performing an operation on a component within a manufacturing workstation is disclosed. The system includes a robot controller having seven axes of motion control. A robotic manipulator is connected to the robot controller and has six axes of motion. The robotic manipulator includes tooling for grasping the component upon which the operation is performed. A fixed location tool is provided for performing the operation, and a servo mechanism is provided for operating the fixed location tool. The servo mechanism is controlled by one of the seven axes of motion control of the robot controller, whereby the robotic manipulator moves the component with respect to the fixed location tool for performing the operation. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Additional objects, advantages and features of the present invention will become apparent from the following description and appended claims, taken in conjunction with the accompanying drawings in which: 
     FIG. 1 is an environmental view of the robot based sealant dispensing system in accordance with a preferred embodiment of the present invention; 
     FIG. 2 is a top plan view of the robot based sealant dispensing system shown in FIG. 1; 
     FIG. 3 is partial sectional view of the sealant dispensing pump associated with the present invention; 
     FIG. 4 is a block diagram of the control system for implementing the robot based dispensing system according to a preferred embodiment of the present invention; and 
     FIG. 5 is a schematic diagram of the robot based dispensing system. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to FIGS. 1 and 2, the robot based dispensing system  10  is shown according to a preferred embodiment of the present invention. More particularly, FIGS. 1 and 2 are environmental views which show the manufacturing workstation  12  in which the robot based dispensing system  10  operates. A six-axis robotic manipulator  14  operates within the manufacturing workstation  12  and is outfitted with an end effector gripping tool  16 . The preferred robotic manipulator  14  for this application is the IRB 6400 manufactured by ABB Flexible Automation Inc., the assignee of the present invention. A seven-axis robot controller  18  executes the control algorithms for operating the robotic manipulator  14 . The preferred robot controller is the S4C controller, also manufactured by ABB Flexible Automation Inc. A PLC unit  68  is used as the programming and operator interface for robot controller  18 . It should be noted that the robot controller  18  can communicate with many types of PLC or personal computer based controllers  68  through a standard field bus. 
     As will be discussed in greater detail below, six of the seven axial control ports associated with robot controller  18  are used for controlling the six axes of motion of the robotic manipulator  14 . Thus, in the present implementation, all six axes of motion provided by the robotic manipulator  14  are utilized so that the end effector or gripping tool  16  has a complete range of motion within a three-dimensional coordinate space. As will be appreciated, this complete range of motion becomes important when applying sealant to surfaces which lie in two or more dimensional planes, and a smooth and consistent robotic motion is required. 
     As disclosed, the robot controller  18  includes a seventh axis or control port  76 , which may be used for controlling an external source associated with robotic manipulator  14 . As part of the present invention, this seventh axis  76  is used for controlling a sealant dispensing system  20 . As shown in FIGS. 1 and 2, the sealant dispensing system  20  is also located within the manufacturing workstation  12 . In the preferred embodiment, sealant dispensing system  20  is used as a fixed location dispensing system having a fixed position dispensing nozzle  40  for delivering a controlled amount of RTV sealant onto a part or subassembly arriving at the workstation  12 . 
     A pedestal structure  22  supports the sealant delivery components  30  and sealant supply components  42  associated with the sealant dispensing system  20 . The pedestal structure  22  includes a fixed base  26  which is secured to the floor within the workstation  12 . A stanchion  28  is welded to the fixed base  26  and extends vertically therefrom for supporting a cantilevered support beam  32 , to which the sealant delivery components  30  are secured. A servo-controlled motor and resolver unit  34  is used to drive an applicator screw pump  36 . 
     With brief reference to FIG. 3, the dispensing end of the applicator screw pump  36  is outfitted with an anti-drip valve  38  and a tapered dispensing nozzle  40 . The pump  36  includes a housing  100  to which the servo motor  34  is secured. An intake port  102  is provided on one side of the housing  100  for delivering the RTV sealant into a reservoir  104 . The intake port  102  is connected to the delivery valve  60 . A shaft  106  is axially supported by the housing  100 , and driven by the servo motor  34 . The lower end of the shaft  106  drives the screw pump mechanism  108 . As the screw pump mechanism  108  is rotated by the shaft  106 , the RTV sealant is dispensed through the nozzle  40  and can then be applied to a subassembly. During the controlled operation of sealant dispensing system  20 , the servo-motor  34  and applicator pump  36  are controlled for delivering and applying a precise shape, size, and quantity of sealant to the subassembly arriving at workstation  12 . As part of the present invention, the robot  14  can pick up a plug (not shown) and place it on the nozzle  40  for shutting off the nozzle and preventing the RTV sealant from drying out. 
     Returning to FIGS. 1 and 2, the sealant supply components  42  associated with sealant dispensing system  20  include a sealant supply bucket  44  and one or more supply lines  46  through which the sealant is drawn by a supply pump assembly  48 . The supply pump assembly  48  also includes a supply pressure transducer  50  which allows the supply pressure within supply line  52  to be closely monitored. As shown, supply line  52  extends between supply pump assembly  48  and a pressure regulator  54  which is disposed along the sealant supply system to ensure a consistent RTV delivery pressure. The delivery side of sealant dispensing system  20  includes a delivery pressure transducer  56  so that the delivery pressure can be monitored in conjunction with the supply pressure. As will be described in greater detail below, the supply pressure and the delivery pressure is monitored by an algorithm implemented within robot controller  18 . These real time pressure valves can also be displayed through a personal computer display or a HMI display (not shown). A delivery line  58  extends between the delivery pressure transducer  56  and the delivery valve  60 . As shown, the intake port  102  of applicator screw pump  36  is connected to the delivery valve  60  so that the flow of RTV sealant to the applicator screw pump  36  can be precisely controlled. The delivery valve  60  is also controlled by robot controller  18 . 
     A suitable conveyor or material handling system  62  runs through workstation  12  for transporting any number of pallets  64  into the workstation  12 . Each pallet  64  supports a part or subassembly to which RTV sealant will be applied. In the present invention, the part or subassembly is a rear end cover  66  having a gasket surface to which RTV sealant is applied prior to its assembly with a rear end housing (not shown). However, it should be understood that the present invention can apply sealant to a variety of components including but not limited to oil pans, valve covers, transmission covers, and gaskets. 
     In operation, sealant dispensing system  20  is used for delivering precise placement of a predetermined size, shape and quantity of RTV sealant to the rear end cover  66 . This application of RTV sealant is more easily achieved by the dispensing system  20  associated with the present invention because the RTV sealant is dispensed from a fixed position dispensing nozzle  40 , while the robot  14  and end effector  16  are utilized for moving the rear end cover  66  in a predetermined pattern of motion beneath the fixed dispensing nozzle  40 . 
     The precision of the present invention is achieved in that servo-motor  34  is feedback controlled through the seventh axis of the robot controller  18 . More specifically, the robot controller  18  sends a control signal to servo-motor  34  for controlling the angular position and speed of the motor drive shaft. Accordingly, servo-motor  34  controls the precise angular motion of applicator screw pump  36 . A resolver unit contained within servo-motor  34  provides a feedback signal to the seventh axis of robot controller  18  which allows for the precise dispensing of the RTV sealant. The delivery valve  60  is opened and closed by the robot controller  18  at precise time intervals for controlling the application and dispensing of the RTV sealant. 
     In the prior applications discussed above, the sixth axis of the robot was utilized for driving the dispenser pump. However, this prior technique leaves the robot with only five axes of movement which limits the freedom of motion of the robot. In addition, smoother and consistent movement of the robot can be achieved by utilizing all six axes of motion control because jumping or skipping movement of the robotic manipulator is eliminated. 
     Turning now to FIGS. 4 and 5, a block diagram and schematic diagram (respectively) show the control scheme of the present invention. The components of the robot based dispensing system  10  are represented as functional blocks in FIG.  4 . The electrical connections between the components of dispensing system  10  are shown in FIG.  5 . As disclosed, the supply pump assembly  48  pumps the RTV sealant through pressure regulator  50 , and the supply pressure is monitored by supply pressure transducer  50 . A supply pressure signal  82  generated by pressure transducer  50  is provided as feedback to the supply pump  48 , and this supply pressure signal  82  is further monitored by the PLC  68  and the robot controller  18 . The RTV sealant flows through delivery valve  60  and into the intake port  102  of the applicator pump  36 . The delivery pressure of the RTV sealant is monitored via delivery pressure transducer  56 . A delivery pressure signal  84  generated by pressure transducer  56  is also provided as feedback to the PLC  68 . The supply and delivery pressure signals  82 ,  84  are communicated to the robot controller  18  over a data bus  86 , and are used to enhance the precise control of sealant dispensing system  20 , and especially the servo motor  34 . 
     A unique feature of the present invention is that a single control panel  92  is used for supporting PLC  68  and robot controller  18  within workstation  12 . Thus, the area within the workstation  12  for control panels is reduced. Additionally, only one PLC controller and control program needs to be maintained. 
     FIGS. 4 and 5 also disclose the interconnection between the robot controller  18 , servo motor  34 , and the robotic manipulator  14 . The control block  74  functionally represents the six bidirectional channels (axes  1 - 6 ) of axial control provided between the robot controller  18  and the robotic manipulator  14 . The control lines  90  connect between the robotic manipulator  14  and control block  74 . The control block  76  functionally represents the seventh axis bidirectional control channel which is used for controlling the servo motor  34 . This bidirectional control channel includes control line  78  and feedback line  80 . 
     In operation, the robot controller  18  sends a control signal to servo motor  34  via line  78  for controlling the angular position, acceleration and velocity of the motor drive shaft. Thus, the servo motor  34  in turn controls the precise angular motion of the applicator screw pump  36 . The resolver unit contained within servo motor  34  provides a feedback signal via feedback line  80  to the seventh axis control block  76 . Also shown is that the delivery valve  60  is controlled by one of the external control ports of robot controller  18  via control line  88 . As will be appreciated, the servo motor  34 , and thus the sealant dispensing system  20  is controlled in a closed loop fashion which greatly assists in the precise application of the RTV sealant to any number of parts. 
     Another advantage of the present invention is the elimination of a second control panel from the workstation  12 . In the prior applications for dispensing RTV sealant, a separately controlled servo motor and applicator pump were connected to a separate (second) control panel. The communication between the second control panel for the servo motor and the first control panel for the robotic manipulator was handled by one or more PLC units. In the present invention, a single electrical control panel  92  is used. Eliminating the second control panel significantly reduces the cost and complexity of installing and maintaining the robot based dispensing system  10  of the present invention. Moreover, the present invention provides a single point of control for making modifications to both the robotic control algorithms, and the servo motor and application pump control algorithms, because only one operator interface (i.e. control panel  92  and PLC  68 ) is used. This in turn makes change over and alternate production setups easier to implement and test before going into live production. 
     The foregoing discussion discloses and describes exemplary embodiments of the present invention. One skilled in the art will readily recognize from such discussion, and from the accompanying drawings and claims, that various changes, modifications, and variations can be made therein without departing from the spirit and scope of the invention as defined in the following claims.