Patent Description:
The production of complex assemblies such as vehicles, appliances, consumer goods, and furniture often requires the fabrication of welded subassemblies, such as sheet metal workpieces with one or more welded fasteners. In the production of an assembly as complex as a vehicle, there can be a considerable quantity and variety of such sheet metal workpieces that are produced in a stamping operation for later welding in batches to produce the required welded subassemblies. A machine operator must remove a randomly oriented and sometimes interlocked sheet metal workpiece from the storage bin before loading it into the welding machine. A second component is then added manually or by automation in preparation for welding. In the case of resistance welding, two electrodes close upon the workpiece and second component before applying force and a high current necessary for completing the resistance weld. The finished subassembly is then removed from the machine in preparation for repeating the welding operation.

As automotive component production costs continue to be pressured lower, labor productivity is under increased scrutiny. The common direction in the industry is to replace labor with significant automation. To be competitive, it is important to maximize the productivity of both the equipment and operator. Much effort is being directed to address this challenge by building equipment with elements such as one or more fixtures to orient the workpiece or complex vision systems that permit a robot to accurately grasp and position the workpiece. Such systems can be challenging to set-up and may require specialized and costly skills to configure, troubleshoot and maintain. The problem this approach has created is equipment that is too hard for many customers (or specific plants) to set-up, operate and maintain. Some cannot access skilled labor, or they do not have enough complex equipment to justify investment in skilled labor and tools. Excessive sophistication may limit the operational reliably in the production environment. The complexity also increases the capital cost of the equipment and the inventory of spare parts to keep it in operation.

It is desirable to use equipment that is simple to configure, operate, troubleshoot, and maintain. It is also desirable to minimize the equipment changeover time while also minimizing its complexity.

<CIT>) describes a method which involves continuously moving a workpiece by an industrial robot. <CIT>) describes a process for the control of the position of workpiece and tool with a robot in a production machine. <CIT>) describes a welding method and a welding apparatus. <CIT>) describes an example of a welding system.

A securing system according to the invention is described in independent claim <NUM>.

In a further embodiment of the above, the securing station is a welding station that includes a feeder supported by the frame. The first and second members are first and second electrodes. The feeder is configured to slide relative to the home position between feeder advanced and feeder retracted positions. The component is arranged over the second electrode in the feeder advanced position.

In a further embodiment of any of the above, the feeder is configured to provide the component to the gun with the second electrode in an electrode advanced position. The component is a fastener.

In a further embodiment of any of the above, the second electrode is movable between electrode retracted and electrode advanced positions.

In a further embodiment of any of the above, the second electrode includes a pin movable between pin advanced and pin retracted positions with the second electrode in the electrode advanced position.

In a further embodiment of any of the above, the pin engages the component with the feeder in the feeder advanced position and the pin in the pin advanced position.

In a further embodiment of any of the above, the feeder is configured to move from the feeder advanced position to the feeder retracted position with the component loaded on the pin. The component is configured to be released by a release mechanism when moving to the feeder retracted position.

In a further embodiment of any of the above, the feeder includes opposing jaws biased to a component retaining position by springs. The jaws are configured to release the component and overcome the springs as the feeder moves from the feeder advanced position to the feeder retracted position.

In a further embodiment of any of the above, the feeder includes a clamp that is configured to retain a second component behind a first component. The first component is loaded on the pin. The clamp is configured to cycle and permit the second component to advance to the jaws for subsequent loading onto the pin.

In a further embodiment of any of the above, the float assembly includes links that interconnect the gun to the frame. The links are configured to permit the gun to move in a horizontal plane.

In a further embodiment of any of the above, the homing assembly includes a pin that selectively cooperates with a guide to retain the gun in the home position.

In a further embodiment of any of the above, the guide includes arms that selectively engage the pin to locate the gun within a horizontal plane.

In a further embodiment of any of the above, the control system evaluates the electrode and pin positions to identify, contain, and remediate workpiece and operating fault conditions.

In a further embodiment of any of the above, the control system contains a schedule of parameters corresponding to a number of assembly configurations.

A method of manufacturing an assembly using the securing system of any one of appended claims <NUM> to <NUM> is described in independent claim <NUM>.

In a further embodiment of any of the above, the component is a fastener. The assembly station is a welding station. The securing step includes welding the fastener to the part.

In a further embodiment of any of the above, the loading step includes the step of robotically transferring the part to the assembly station with the assembly station in a home position. The permitting step includes releasing the assembly station from the home position subsequent to performing the step of robotically transferring the part.

In a further embodiment of any of the above, the method includes the step of loading the component onto an electrode with a feeder and retracting the feeder subsequent to the component loading step. The feeder retracting step is performed prior to the permitting step.

In a further embodiment of any of the above, the method includes the step of advancing the electrode to engage the part during the permitting step.

In a further embodiment of any of the above, the component is a first component and includes the steps of clamping a second component in the feeder, releasing the first component during the feeder retracting step and performing the step of unclamping the second component.

In a further embodiment of any of the above, the feeder retracting step includes overcoming spring biased jaws in the feeder.

In a further embodiment of any of the above, the method includes the step of picking up the part off of a drag conveyor prior to the part loading step.

The embodiments, examples and alternatives of the preceding paragraphs, the claims, or the following description and drawings, including any of their various aspects or respective individual features, may be taken independently or in any combination. Features described in connection with one embodiment are applicable to all embodiments, unless such features are incompatible.

The disclosed system provides low-cost automation to weld fasteners, or secure other parts such as pins, clips, or brackets to sheet metal stampings at high speeds. The same system can be applied to other assembly processes such as rivets, self-piercing fasteners, mechanical fasteners to a variety of workpieces including those made of plastic. Thus, although the disclosed system is discussed primarily in terms of a welding system and method, it should be understood that other types of securing systems are contemplated.

A welding system <NUM> is schematically illustrated in <FIG>. First and second conveyors 12a, 12b feed different parts, such as stampings, into a robot <NUM> within a welding station <NUM>. The robot <NUM> transfers the parts from the conveyors 12a, 12b to welding machines 16a, 16b. One welding machine 16a secures studs supplied by a vibratory feeder bowl 17a, and the other welding machine 16b secures nuts supplied by a vibratory feeder bowl 17b. The arrangement shown in <FIG> is exemplary only and may be configured differently than illustrated.

<FIG> shows one example welding system <NUM> for high-rate production in more detail that includes a drag conveyor <NUM>, high-speed robot <NUM>, welding machine <NUM>, unload chute <NUM>, and control system <NUM>. The drag conveyor <NUM> provides a number of equally spaced load stations, each having a transfer pins <NUM> for engaging a workpiece to which a component such as a fastener will be welded. The drag conveyor <NUM> advances workpieces loaded by an operator onto transfer pins <NUM> at one end towards an unload end (shown in more detail in <FIG>). The high-speed robot <NUM> is positioned in close proximity to the unload end of the drag conveyor <NUM> where it will grasp a workpiece and the welding machine <NUM> to which it will present the workpiece for welding. A control system <NUM> is interconnected to each of the elements of the welding system <NUM> to provide functional control and coordination of the motions of the elements to minimize the operating cycle time. In one example, the welding system <NUM> may be configured to weld than thirty or more different assemblies. The control system <NUM> maintains data for each assembly needed to manage the position and number of fasteners in each assembly, instructions for when the robot can release the assembly, error recovery protocols, weld signatures, and other information for automating the welding of the assembly.

With continuing reference to <FIG>, the welding system <NUM> is configured to accept a workpiece W (<FIG>) such as a sheet metal stamping and weld a component part to it, such as a fastener F (e.g., <FIG>), in the shortest time possible. The individual stations of a drag conveyor <NUM> include a transfer pin <NUM> which engages in a hole in the workpiece to pull the workpiece W from the loading point to an unloading point. The geometry and mass of the workpiece W will determine its attitude when resting on the drag conveyor <NUM> and engaged with the transfer pin <NUM>. Friction between the bed of the drag conveyor <NUM> and the workpiece W is sufficient to urge all of the workpieces into a sufficiently consistent orientation as they are moved towards the unload position.

The number and spacing of the transfer pins <NUM> will determine the length and width of the drag conveyor <NUM>. The diameter of the transfer pins <NUM> is selected to engage the hole in the range of workpieces to be welded, have sufficient strength to minimize bending, and to provide some clearance between the hole and workpiece W so the high-speed robot <NUM> can reliably remove the workpiece W. The length of the transfer pin <NUM> is based on the height above the drag conveyor <NUM> where the workpiece engages the transfer pin <NUM>. The height of the drag conveyor <NUM> depends on whether it is to be manually loaded at a convenient height for an operator, or by automation directly from the stamping equipment used in production of the workpiece.

The welding system <NUM> shown in <FIG> is includes a drag conveyor <NUM> having three rows of twenty four stations. The number of rows and stations depends on a number of factors such as permissible floorspace, workpiece loading time, welding sequence time, buffer inventory requirement, and interaction between workpieces in adjacent stations.

The high-speed robot <NUM> is programmed to properly grasp the workpiece W from a station at the unload end of the drag conveyor <NUM> and transition it to an attitude and position necessary to engage with the welding machine <NUM>. Since the tooling uses a simple transfer pin <NUM>, there is no requirement beyond programming, for tooling or tool set-up to accommodate different workpieces.

The high-speed robot <NUM> and the welding machine <NUM> are coordinated by a control system <NUM> to engage the workpiece W with the welding machine <NUM> as quickly as possible so the welding process can be completed and the completed assembly discharged from the welding system <NUM>. The welding machine <NUM> includes provisions, such as the float assemblies illustrated in <FIG>, for accommodating some misalignment of the workpiece due to variation of the attitude of the workpiece on the drag conveyor <NUM> and positioning error of the high-speed robot <NUM> plus any positioning error due to variations in the workpiece W, or movement of the workpiece W in the gripping device of the high-speed robot <NUM> during the workpiece transfer.

In further detail, with continuing reference to <FIG>, the size and configuration of the welding system are suited to the range of assemblies to be welded. The welding machine <NUM> capability, including its physical size, welding current or power capability, and electrode force range are determined by the workpiece characteristics and the requirements of the welding process. The configuration and height of the unload chute <NUM> is based on the type of container in which the completed weldment is discharging.

The welding machine <NUM> shown in <FIG> is a resistance welding machine configured for welding projection weld nuts. It could also be configured to weld projection weld studs, to weld by other means such as laser welding, or to perform other processes such as assembly. The versatility of the welding system <NUM> can be expanded by incorporating multiple welding machines <NUM> that weld different sized fasteners F (e.g., <FIG>) or different types of operations. These either can be located within easy reach of the high-speed robot, manually repositioned, or supplied with automation to index one or more welding machines <NUM> to the active position within the reach of the high-speed robot <NUM>.

The welding machine <NUM> as shown in <FIG> includes a welding machine frame <NUM> supporting a resistance welding gun <NUM> and a feeder <NUM> for delivering a fastener F to be welded to a workpiece W. The welding machine frame <NUM> maintains the alignment and orientation of the components and includes provisions for leveling to ensure the desired function. The resistance welding gun <NUM> supports a resistance welding transformer <NUM> to produce the required welding current and a welding actuator <NUM> for achieving the required coordinated motion of the welding electrodes and the necessary electrode force for welding. The resistance welding transformer can be of any type, such as alternating current or inverter. The resistance welding gun is oriented to exploit gravity to maintain engagement with the fastener F delivered by a feeder <NUM> as it is moved to the welding position. The feeder <NUM> dispenses one fastener F to be welded to the workpiece at a time onto the movable welding electrode <NUM>.

The feeder <NUM> shown is for feeding projection weld nuts. The design of the feeder <NUM> will be based on the requirements of the fastener F to be welded and may for example be a stud, pin, or bracket; or other process such as feeding of a rivet, screw, clinch nut, mechanical clip, or other mechanical fastener. Thus, the welding machine <NUM> can employ a process other than resistance welding or a process that does not involve such mechanical fastening involving riveting, self-piercing fastener, bolting, or the like.

The welding machine frame <NUM> is rigid enough to ensure consistency of the resistance welding gun <NUM> position when the mass of the gun is shifting and when it is subjected to external forces. When a welding cycle is requested, the welding actuator <NUM> extends to a position that is aligned with the feeder <NUM> when it advances to deliver a component to be welded. When the feeder <NUM> retracts to its home or feeder retracted position, the welding actuator <NUM> extends fully to close the electrodes and press the fastener F to be welded against the workpiece W positioned by the high-speed welding robot <NUM>. During the welding sequence, welding current delivered by the resistance welding transformer <NUM> creates the heat for welding. At the completion of the weld, the output of the welding actuator <NUM> is retracted to return the moveable welding electrode <NUM> to its home or electrode retracted position.

The welding machine frame <NUM> of <FIG> holds the resistance welding gun <NUM> at the required working height determined in large part by the required height of the unload chute <NUM> or by clearance necessary to ensure there is no interference with the operation of the resistance welding gun <NUM>. The resistance welding gun <NUM> is sized to accommodate the physical size of the workpiece W or workpieces, and the required electrode force and welding current. The stroke of the welding actuator <NUM> is determined by the required resistance welding gun <NUM> opening and that in turn determines the length of the welding actuator <NUM>.

The configuration of the welding machine frame <NUM> illustrated in <FIG> is a generic design for illustration purposes. The welding machine frame <NUM> can be a standardized version or a custom design created for a specific application. The welding machine frame <NUM> can stand alone, it can be mounted to a frame that supports the other components of the welding system <NUM>, or it can be incorporated into a larger piece of equipment providing multiple functions. The C-type resistance welding gun <NUM> shown employs a welding actuator <NUM> that moves the electrode in a linear motion towards an opposing stationary welding electrode <NUM> (<FIG>). Linear motion is desirable for projection welding because it is most effective for providing consistent force on each projection and to follow the projection collapse during the weld.

The resistance welding gun <NUM> can be of any design, construction or material that achieves the requirements for the particular project scope. The welding actuator illustrated is an electric servo type but it could also be a pneumatic cylinder with an intermediate stroke position, such as a retract cylinder or other similar device.

<FIG> shows elements of the welding machine <NUM> in more detail. The resistance welding gun <NUM> includes two spaced apart welding gun side frames <NUM> and <NUM> that provide the main structure to hold the components of the gun, contain the welding force, and provide a means for mounting within the welding machine <NUM>. A moveable welding electrode <NUM>, containing a fastener rough locating pin <NUM>, is connected to the output shaft of the welding actuator <NUM>. A stationary welding electrode <NUM> containing a fastener locating pin <NUM>, opposes the moveable welding electrode <NUM>. The fastener locating pin <NUM> is actuated by a locating pin cylinder <NUM> and its position is sensed by a locating pin position sensor <NUM>.

Examples relating to suitable pin position sensing can be found in <CIT> and PCT International Application No. <CIT>.

The sensor(s) can be used to track the electrode and welding pin movement to monitor situations that might generate an error leading to a defective part or a fault in the welding system <NUM>. For example, if the pin locating the fastener is depressed when the welding gun closes on the workpiece presented by the robot, the workpiece may not have a clearance hole, or the workpiece may have slipped in the robot gripper too far for the floating action of the welding unit to accommodate (discussed in more detail below). The control system <NUM> in this case can instruct the robot <NUM> to deliver the workpiece to a containment area and pick up a new workpiece from the drag conveyor <NUM>. In another example, if the electrode is not closed to the expected height, there may be an improper workpiece, fastener, or perhaps two fasteners. In this scenario, the system may first try to eject the fastener and reload. If the same error occurs, the workpiece is replaced as above.

The stationary welding electrode <NUM> and fastener locating pin <NUM> are specifically designed to suit the thickness of the workpiece W plus the clearance hole and fastener F locating diameter. The fastener locating pin <NUM> needs to be designed with gentle and smoothly transitioned curves to help urge the resistance welding gun <NUM> into the correct position. Excessive roughness, sharp angles, or steps on the fastener locating pin <NUM> may cause the pin to hang up on the workpiece, thereby inhibiting the locating pin cylinder <NUM> from advancing the fastener locating pin <NUM> to its fully extended position. Significant deviation of the workpiece W hole location can be accommodated by this arrangement. The maximum deviation would be in the range of <NUM>% of the fastener thread being gaged. Our demonstration system is somewhat higher - providing a <NUM> window of compensation for a fastener having an <NUM> thread.

The stroke and force capability of the locating pin cylinder <NUM> needs to be sufficient to overcome the force applied to the fastener rough locating pin <NUM> in the movable welding electrode <NUM>.

The resistance welding gun <NUM> is connected to the machine frame <NUM> by one or more float assemblies <NUM> which permit motion within a plane. For simplicity, the description of one mechanism will be described although <FIG> shows there is one such mechanism located on opposing sides of the resistance welding gun <NUM>. The planar alignment of bracket <NUM> on frame with the bracket <NUM> on welding unit is provided by link <NUM> to frame and link <NUM> to welding unit. Pins and bearings are provided at the attachment points between the components of this mechanism to enable welding gun <NUM> to float freely relative to the frame <NUM>. A homing assembly <NUM> includes a homing actuator <NUM> that engages guide pins <NUM> and <NUM> to urge the resistance welding gun to a fixed home position that is the nominal position of the fastener locating pin <NUM> where the high-speed robot <NUM> has been programmed to position the clearance hole for the fastener locating pin <NUM>. The float assembly <NUM> and homing assembly <NUM> illustrated in <FIG> are shown in more detail in <FIG>. Alternative configurations are illustrated in <FIG>.

The resistance welding gun <NUM> of <FIG> provides clearance between the welding gun side frames <NUM> and <NUM> to accommodate the feeder <NUM>. Like the welding gun side frames <NUM> and <NUM>, the feeder <NUM> represents a potential point of interference between the resistance welding gun <NUM> and the workpiece or high-speed welding robot gripper so it is desirable to keep it out of the way and this is accomplished by putting it in the throat of the resistance welding gun <NUM>. The feeder <NUM> is commonly provided with components, such as fasteners, from an automatic feeding system by way of a tube, track, or carrier (e.g., vibratory feeder bowls 17a, 17b shown in <FIG>). The feed path required to accommodate this apparatus can be quite long and it can be provided for and accommodated within the welding machine frame <NUM>.

To load the component such as a fastener, the rod of the welding actuator <NUM> is advanced (with the feeder <NUM> in the feeder retracted position) to raise the movable welding electrode <NUM> to the electrode advanced position (<FIG>) necessary to interact with the feeder <NUM>. The feeder <NUM> advances in a linear motion to a feeder advanced position (<FIG>) where the fastener is aligned with the fastener rough locating pin <NUM>. At this time, the fastener rough locating pin <NUM> is advanced to its fully extended pin advanced position (<FIG>) to capture the fastener. Then the feeder <NUM> is withdrawn to its home feeder retracted position (<FIG>), the action of which causes the feeder <NUM> to release the fastener on the fastener rough locating pin <NUM>. With the feeder <NUM> clear of the moveable welding electrode <NUM>, the welding actuator <NUM> is free to advance the moveable welding electrode <NUM>, as soon as the high-speed welding robot <NUM> confirms it has placed a workpiece over the fastener locating pin <NUM> in the stationary welding electrode <NUM>.

<FIG> is a perspective view of the feeder <NUM>. The feeder mounting plate <NUM> is used to establish a fixed position relative to the resistance welding gun <NUM> or welding machine frame <NUM>. A slide bar <NUM> engages a slide body <NUM> to which an escapement assembly is mounted so it can move between a returned position and an advanced position, which corresponds to feeder retracted and feeder advanced positions. The two articulating jaws <NUM> and <NUM> are biased in contact with each other by the springs <NUM> and <NUM> respectively. A top plate <NUM> and bottom plate cooperate with the jaws <NUM> and <NUM> to form a chamber which holds a fastener F in preparation for loading onto the fastener rough locating pin <NUM>. <FIG> is a top view of the feeder <NUM> with the clamp arm <NUM>, clamp pad <NUM>, and top plate <NUM> removed to show fastener F, retained fastener F2, and other fasteners queued for feeding to the welding machine <NUM>. A clamp cylinder <NUM> drives a clamp arm <NUM> that supports a clamp pad <NUM> to capture retained fastener F2 which is immediately adjacent and in contact with the fastener F which will be loaded onto the fastener rough locating pin <NUM>.

The feeder <NUM> of <FIG>, receives fasteners from an external system that sorts, orients and delivers fasteners. When the moveable welding electrode <NUM> is in position to receive a fastener F, a signal is given by the control system <NUM> to actuate the advance cylinder <NUM>. The slide body <NUM> moves along the slide bar <NUM> to advance the escapement mechanism into the position where the hole in fastener F will align with the fastener rough locating pin <NUM>. The control system <NUM> provides a signal to operate clamp cylinder <NUM> which drives clamp arm <NUM> to press clamp pad <NUM> against retained fastener F2. When the advanced position has been reached, the control system <NUM> provides a signal to advance the fastener rough locating pin <NUM> to its fully extended position at which it engages the fastener F. At this point in the sequence, the advance cylinder <NUM> retracts. The engagement of the fastener rough locating pin <NUM> with fastener F prevents fastener F from moving. The force of fastener F transferred to jaws <NUM> and <NUM> causes them to act against springs <NUM> and <NUM> so they will open to release fastener F. The feeder <NUM> therefore returns to a position clear of the moveable welding electrode <NUM>, after having deposited fastener F on the fastener rough locating pin <NUM>. Advance cylinder <NUM> retracts to release the clamp pad <NUM> to release retained fastener F2 so that it can advance to the position of fastener F.

The size and configuration of feeder <NUM> must be appropriate for the dimensions and requirements of a specific fastener F. Such fasteners are widely varied in thread type, size, and length; and other attributes such as pilot diameters, stepped faces, number and type of projections. The shape of the jaws <NUM> and <NUM> must be suitable to provide a channel which guides and contains the fastener F, plus permits fastener F to force the jaws <NUM> and <NUM> open when the advance cylinder <NUM> retracts. The size of the clamp pad <NUM> and the length of clamp arm <NUM> will depend largely on the diameter or effective size of the fasteners F and F2 so that fastener F2 is properly retained and there is no interference with fastener F that impairs the reliability of its ejection and placement. For suitable operating life, the components of the feeder <NUM> in contact with the fasteners need to be made of hardened materials that resist wear from impact and sliding friction. The cycle time of this feeding operation is very fast - typically <NUM> seconds or less.

While <FIG> illustrate a fastener F that is a projection weld nut for resistance welding, the component could be any of a variety including a pin, stud, or bracket. The shape of the jaws <NUM> and <NUM> would need to be suitable for the shape of the component and feeding function. The configuration of clamp pad <NUM> would be similarly changed to match the requirements to secure the retained fastener F2. This may involve for example, a pin to engage the hole in retained fastener F2 or a barrier to impede the travel of fastener F2 or provide separation between the retained fastener F2 and fastener F.

In another example, the clamp cylinder <NUM>, clamp arm <NUM> and clamp pad <NUM> may be eliminated (as shown in <FIG>). In this case, gravity urges the fasteners F to the end of the feeder <NUM>. The control system <NUM> tracks the number of fasteners F inside the feeder <NUM>, which is determined by the fastener size, to ensure a sufficient urging force. Since the releasing operation happens so fast, with the clamp jaws <NUM>, <NUM> following the contour of the fastener F there is no opportunity for a second fastener F2 to be released although there is no means for retention.

While waiting to receive the workpiece from the high-speed robot <NUM>, the resistance welding gun is locked into a fixed position by the homing actuator <NUM> advancing over guide pins <NUM> and <NUM>, as shown in <FIG> and <FIG>. This fixed position provides the high-speed robot with a target to align the fastener clearance hole in the workpiece W with the fastener locating pin <NUM> in the stationary welding electrode <NUM>. Once the high-speed robot <NUM> has completed the transit to the load position, the workpiece W will be in close proximity or resting against the stationary welding electrode <NUM>. The homing actuator <NUM> is then retracted to permit the resistance welding gun <NUM> to move freely in the plane of the weld. When the locating pin cylinder <NUM> advances the fastener locating pin <NUM> through workpiece W, any misalignment between the fastener locating pin <NUM> and the hole in the workpiece W will cause a force on one side of the locating pin <NUM>. This force will urge the resistance welding gun <NUM> to move in the plane of the weld into a compliant position where the fastener locating pin <NUM> is centered in the hole in the workpiece W and engaged with the fastener F on the other side. To fully extend, the fastener locating pin <NUM> must push the fastener rough locating pin <NUM> out of the fastener F and back into the moveable welding electrode <NUM>. The locating pin position sensor <NUM> verifies that the fastener locating pin <NUM> has reached the desired stroke extension and the displacement conforms with expectations.

To move the resistance welding gun <NUM> relative to the fixed welding machine frame <NUM>, the distance between the bracket <NUM> on frame and bracket <NUM> on welding unit will change. The change in the mounting bracket distance is easily accommodated by changing the angle between the link <NUM> to frame and link <NUM> to welding unit. The link to welding unit <NUM> incorporates provisions for adjusting the tension against the link to frame to ensure there is not excessive binding or looseness that impairs the function of the float assembly <NUM>.

For small assemblies, where the mass of the part is unlikely to affect the welding process, when the electrodes are closed on the workpiece W and fastener, the high-speed robot <NUM> may release the workpiece W to return to the drag conveyor <NUM> for another workpiece W. If there is an additional fastener F or fasteners to be welded, or the mass of the weldment is too much, the high-speed robot <NUM> will continue to hold the workpiece W. Then the welding process is completed to secure the fastener W to the workpiece W. If the assembly weldment was released, the action of opening the resistance welding gun <NUM> by retracting the welding actuator <NUM> will free the welded assembly to fall onto the unload chute <NUM> to be discharged from the machine.

If there is a requirement to weld additional fasteners the feeder <NUM> operating sequence and welding sequence can be repeated as soon as the moveable welding electrode <NUM> has returned to the feeder <NUM> cycling position. If the welding is complete, the high-speed robot <NUM> can move the assembly to the position where it can be released.

The force and stroke of the homing actuator <NUM> needs to be sufficient to engage the guide pins <NUM> and <NUM> urge the resistance welding gun <NUM> back to its home position. The travel speed of the homing actuator <NUM> and the shape of the guide pins <NUM> and <NUM> determine the rate at which the resistance welding gun <NUM> moves.

The mechanism for enabling the resistance welding gun <NUM> to move in the plane of the weld could be an air bearing or low-friction X-Y slide assembly. Other means for placing the fastener on the movable electrode can be used such as conventional spear type fastener loader. The homing actuator <NUM> and arrangement of guide pins <NUM> and <NUM> represents one way to guide the resistance welding gun <NUM> back to its home position. Tapered pins, wedges and expanding arbors or guides are examples of other devices for centering two items that are displaced from one another in one plane.

When the position of the hole provided in the workpiece W for access to the fastener F thread is not sufficiently accurate to be used for establishing the welding position of the fastener F, such as when the hole is cut by a laser slightly out of position, the principles of <FIG> can be applied to an external device which accomplishes the same function of urging the resistance welding gun <NUM> to a desired location, using a different hole or attribute of the workpiece W as a reference. In this case, another supplemental pin, performing the location function of the fastener locating pin <NUM> can be attached and driven by a supplemental actuator so that it can engage a hole or attribute of the workpiece that is desired for establishing the position of the fastener F in relation to the workpiece W. The supplemental actuator would advance the supplemental pin to engage the workpiece W. The shape of the pin would be selected to urge the resistance welding gun into the proper position for welding when it engages the workpiece W. Relocation of this function to the supplemental actuator and pin would not affect the ability of the fastener locating pin <NUM> to provide the function of monitoring and detecting the fastener F.

<FIG> is a top view of the resistance welding gun <NUM> in its home position with the guide pins <NUM> and <NUM> engaged in the homing guides <NUM> and <NUM> respectively. Each of the homing guides <NUM> and <NUM> provides a cylindrical hole corresponding to a <NUM>-dimensional position within the plane of movement. The two homing guides <NUM> and <NUM> work together to fix the position of the fastener locating pin <NUM> which the high-speed robot <NUM> will target for workpiece placement in the next welding machine <NUM> operating cycle.

<FIG> is a top view of the resistance welding gun <NUM> in a position where the guide pins <NUM> and <NUM> are no longer engaged or aligned with the homing guides <NUM> and <NUM> respectively. This position is achieved when the homing actuator <NUM> retracts the guide pins <NUM> and <NUM> from the homing guides <NUM> and <NUM> and force applied on the fastener locating pin <NUM> urges the resistance welding gun <NUM> into such an alignment. The difference in position of the resistance welding gun <NUM> in <FIG> is not visible in these figures.

When the homing actuator <NUM> is activated to return the resistance welding gun <NUM> to its home position, the homing guides <NUM> and <NUM> will be forced against and over the guide pins <NUM> and <NUM> respectively. In the position where the homing actuator <NUM> is fully advanced, the guide pins <NUM> and <NUM> will be securely contained by the homing guides <NUM> and <NUM>, as in <FIG>.

The homing guides <NUM> and <NUM> provide a cylindrical hole to establish a <NUM>-dimensional position within the plane of movement and the two cooperate together to establish the home position of the resistance welding gun <NUM>. The diameter of the cylindrical holes is determined by the diameter of the guide pins <NUM> and <NUM> with a minor amount of clearance necessary to ensure a slip fit. The guide pins <NUM> and <NUM> need to have a diameter sufficient to resist bending and a length accommodating the desired rate transition from the small diameter tip to the full diameter. The small diameter of the tip determines the maximum guide pin displacement at which the guide pins <NUM> and <NUM> can enter the homing guides <NUM> and <NUM>. In most cases, the guide pins <NUM> and <NUM> and homing guides <NUM> and <NUM> should be hardened and have a low friction coating to prevent galling and binding. The spacing and position of the homing guides <NUM> and <NUM> is a function of the resistance welding gun <NUM> and the distance from the center of the homing guides <NUM> and <NUM> to the center of the fastener locating pin <NUM>. The homing actuator <NUM> must have a force and travel speed sufficient to realign the guide pins <NUM> and <NUM> and homing guides <NUM> and <NUM> quickly and without excessive shock.

The hardware used to fix the position the resistance welding gun <NUM> can involve other approaches than described. For example, wedges or cams could be used in place of guide pins <NUM> and <NUM>. The homing guides <NUM> and <NUM> could also be split lengthwise to close onto the guide pins <NUM> and <NUM> to reduce friction. Using such an approach, the solid guide pins <NUM> and <NUM> could be surrounded or replaced with rollers to further reduce friction during repositioning.

Another homing assembly <NUM> is shown in <FIG> and <FIG>. The homing assembly <NUM> uses a pair of homing guides <NUM>, <NUM> that respectively cooperate with guide pins <NUM>, <NUM> to locate the welding unit to the home position. In the example, a first homing actuator <NUM> actuates a pair of arms <NUM> into engagement with opposing sides of the guide pin <NUM> to clamp the guide pin <NUM> and locate one side of the welding unit in a first direction within the horizontal plane. A second homing actuator <NUM> actuates a pair of arms <NUM>, which include notches <NUM>, into engagement with opposing sides of the guide pin <NUM> to clamp the guide pin <NUM> and locate the other side of the welding unit in both first and second directions within the plane. The first and second actuators <NUM>, <NUM> are typically operated simultaneously to locate both sides of the welding unit in the home position within the plane. The arms <NUM>, <NUM> are moved out of engagement with their respective guide pins <NUM>, <NUM> to permit the welding unit to float.

<FIG> is a perspective view of the drag conveyor <NUM> with the addition of a number of workpieces W. The workpieces W are engaged on number of evenly spaced transfer pins <NUM> are affixed to conveyor chains <NUM>. Three such conveyor chains <NUM> are supported and driven by a sprocket assembly at each end of the drag conveyor <NUM>. The conveyor chains <NUM> are aligned with spaces provided between adjacent friction bars <NUM> to permit the travel of the transfer pins <NUM> and thereby the workpieces W.

The workpiece W shown in <FIG> is used to illustrate the principles of operation and is not representative of the range and size of permissible workpieces W. While not defined in the hardware, a number of zones are illustrated in <FIG> to explain the operation of the drag conveyor <NUM>. An operator loading zone A, is within easy reach of an operator who will manually sort, orient, and place a workpiece W so the selected attribute of the workpiece W, such as a specific hole, engages a transfer pin <NUM>. Within zone A, the orientation of the workpiece W is not required to be precise and the number of occupied transfer pins <NUM>, as well as the sequence in which they are loaded is not important. The sprocket assembly <NUM> drives the conveyor chains <NUM> to advance the transfer pins <NUM> towards the unloading zone C. Along the length of the drag conveyor there is a workpiece orientation zone B in which the friction of the workpiece W acting against the friction bar <NUM> urges the workpiece W into a generally consistent orientation. Also illustrated is an empty zone B1 which corresponds to a time when the operator was unable to load a workpiece W. This could be for any number of reasons such as when convenient access to workpieces W is not possible. This could occur when there is an interruption of the supply of workpieces, such as might occur when the container holding them is empty and requires replacement. In the oriented part zone B2 the workpieces are progressively oriented such that when leaving this zone and entering the unloading zone C, they are in a position identifiable by the high-speed robot <NUM>.

In the unloading zone C, a detection method would be employed so the control system <NUM> can communicate the workpiece W location to the high-speed robot <NUM>. The detection method could be an inductive proximity switch, photo switch, laser, or imaging system. The detection method could detect and verify the workpiece W in the unloading zone C each of the transfer path, or it could be incorporated into the high-speed robot <NUM> tooling that is used to capture the workpiece W for loading into the welding machine. The drag conveyor <NUM> would be advanced to position at least one workpiece W in the unloading zone C within reach of the robot. The high-speed robot <NUM> could wait until a workpiece W has reached a fixed unloading position, or it could capture the workpiece while it is moving within the unloading zone C if the drag conveyor <NUM> and high-speed robot <NUM> are operated in coordinated motion.

The detection method employed to detect and verify the workpiece W is within the unloading zone C can also be used to verify an attribute of the workpiece W so that a misaligned or incorrect workpiece W can be discharged from the drag conveyor <NUM> simply by moving it past the point at which the workpiece W remains engaged with the friction bars <NUM> and transfer pin <NUM>.

The conveyor frame <NUM> shown in <FIG> is illustrative only. It can be a freestanding unit as shown or integrated with the frame supporting other components of the welding system <NUM>. The number and length of conveyor chains <NUM> is dependent on the number and spacing of transfer pins <NUM> required to support the welding system <NUM> operating requirements. The transfer pins <NUM> may not have a circular cross section and of any length required to engage the workpiece W while it is resting on a surface. The length and definition of the illustrated drag conveyor <NUM> zones is a function of the welding system <NUM> operating requirements and other factors such as machine guarding, and the duration of friction application required to ensure the workpieces W are consistently oriented. The friction bar <NUM> would commonly be made of sheet or plate steel with a width, length, and thickness suited to the size of the workpiece W. Instead of changing the length of transfer pins <NUM> to suit different workpieces W, provision can be made to change the spacing between the friction bar <NUM> and conveyor chain <NUM>.

The drag conveyor <NUM> shown in <FIG> is an example configuration. The transfer path does not need to be linear as illustrated. The transfer path could be circular as a rotary table, a serpentine shape, or have transitions to different shapes along the length of travel. The transfer path also does not need to be in one plane or in a plane parallel to the floor. The conveyor chain <NUM> can be driven by any number of means such as the high-speed robot <NUM> controller to provide for coordinated motion, a speed-controlled motor, or a ratcheting drive connected to a pneumatic cylinder. The friction bars <NUM> can be made of any number of metal, other material such as self-healing polymer, or a combination of materials. The friction bars <NUM> may also be supplemented with risers or guides if, for example, they are beneficial to speed up workpiece W orientation, reduce the chance the workpiece W will lock on the transfer pin <NUM>, or prevent motion that would cause interference between adjacent workpieces W. The space between friction bars could be occupied with conveyor chain <NUM> link, accessory, or cover that prevents the workpiece W from engaging with the gap between adjacent friction bars <NUM> if the such engagement would prevent the workpiece W from moving to the desired alignment.

An example operating sequence of each of the principle welding system <NUM> components is as follows. The equipment operator or automation will load workpieces on the drag conveyor <NUM> whenever there is an available station within reach. The drag conveyor <NUM> will advance workpieces W towards the unloading zone C whenever there are no workpieces W properly oriented for pick-up within the unloading zone C. The high-speed robot <NUM> will move to position to engage a workpiece W when it is free to begin the transfer sequence and a workpiece W has been detected in an orientation conducive to engagement. When the resistance welding gun <NUM> is opened sufficiently to accept the high-speed robot <NUM> to load a workpiece W, the high-speed robot <NUM> will move the workpiece W to a position in alignment with the stationary welding electrode <NUM>. Independently, or simultaneously with the operation of the high-speed robot <NUM>, when the moveable welding electrode <NUM> has been moved by the welding actuator <NUM> to the position to receive the fastener F from the feeder <NUM>, the feeder <NUM> will advance to the location in which the fastener F is aligned with movable welding electrode <NUM>. The fastener rough locating pin <NUM> is then advanced to engage with the fastener F while the clamp arm <NUM> advances to bring the clamp pad <NUM> into contact with the retained fastener F2. The feeder <NUM> is then retracted to its rest position, the action of which causes the jaws <NUM> and <NUM> to move against the biasing springs <NUM> and <NUM> to release the fastener F. When the feeder <NUM> has retracted, the fastener F will be raised towards the workpiece W by the movable welding electrode <NUM> on which it is resting. When the welding actuator <NUM> reaches the travel distance at which the workpiece W and fastener F should be in contact between the moveable welding electrode <NUM> and stationary welding electrode <NUM>, homing guide pins <NUM> and <NUM> will be released from the homing guides <NUM> and <NUM>. The fastener locating pin <NUM> will then advance to monitor and verify the part position as well as to bring the parts to be welded, if present, into alignment by urging the resistance welding gun <NUM> to move. The welding machine <NUM> will perform the welding operation. When the workpiece W does not require an additional fastener F and can be supported by the welding electrodes, the high-speed robot <NUM> will disengage from the workpiece W and move to retrieve another workpiece W from the drag conveyor <NUM>. Otherwise, it will continue to hold and support the workpiece W until the moveable electrode <NUM> has retracted sufficiently to either permit the high-speed robot <NUM> to index the subassembly to the next welding position, or to release the completed assembly so it can exit the welding system <NUM>. The welding actuator <NUM> will return the moveable welding electrode <NUM> to its fully lowered position to begin the fastener feeding and welding cycle over again.

The disclosed welding system welds fasteners at high speeds to maximize labor productivity while reducing complexity to minimize downtime and capital cost. Both the equipment and operator productivity are improved by freeing the operator from having to load components synchronously with the welding machine cycle. When the operator can grab a number of workpieces from the storage bin and load them into the equipment at a higher rate than the equipment cycle time, the time required for the operator to get more workpieces from the bin can be buried in the system cycle time so the welding process can proceed at the maximum production rate of the welding machine.

Maximizing the production rate allows the capital cost of the welding machine or assembly processes to be amortized over more assemblies. In addition to the labor savings that comes from increasing the rate of production welding, increased production volume provides an opportunity to amortize the cost of any supplemental error avoidance systems over more assemblies.

The system provides sufficient speed, versatility, and reliability to be located in the stamping bay where the stampings are produced or where injection molding occurs to eliminate storage of inventory and extra material handling.

It should also be understood that although a particular component arrangement is disclosed in the illustrated embodiments, other arrangements will benefit herefrom. Although particular step sequences are shown, described, and claimed, it should be understood that steps may be performed in any order, separated or combined unless otherwise indicated.

Although the different examples have specific components shown in the illustrations, embodiments of this invention are not limited to those particular combinations.

Claim 1:
A securing system comprising:
a robot (<NUM>) configured to transfer a workpiece (W) to a home position;
a securing station includes:
a frame (<NUM>);
a gun (<NUM>) supported on the frame (<NUM>), the gun (<NUM>) includes a stationary welding electrode (<NUM>) and a moveable welding electrode (<NUM>), the moveable welding electrode (<NUM>) opposing the stationary welding electrode (<NUM>), the gun (<NUM>) is suitable to secure a component to the workpiece (W) in a securing position during a securing operation; and
a float assembly (<NUM>) interconnects the gun (<NUM>) to the frame (<NUM>), the float assembly (<NUM>) suitable to permit the gun (<NUM>) to glide relative to the frame (<NUM>) between the home position and the securing position, wherein the stationary welding electrode (<NUM>) comprises a locating pin (<NUM>) and a locating pin cylinder (<NUM>), and wherein, in use, when the locating pin cylinder (<NUM>) advances the fastener locating pin (<NUM>) through the workpiece (W), any misalignment between the fastener locating pin (<NUM>) and a hole in the workpiece (W) will cause a force on one side of the locating pin (<NUM>), which will urge the resistance welding gun (<NUM>) to move in a plane of the weld into a compliant position where the fastener locating pin (<NUM>) is centered in the hole in the workpiece (W) and engaged with the fastener (F) on the other side;
a homing assembly (<NUM>, <NUM>) includes a homing guide (<NUM>, <NUM>) suitable to release the gun (<NUM>) from the home position during the securing operation and a homing actuator (<NUM>) which, when retracted, permits the resistance welding gun (<NUM>) to move freely in the plane of the weld.