End of travel arrangement

An end of travel arrangement for shutting down an assembly line conveyor when an ergo assist arm at a conveyor station moves beyond an end of travel limit point, the end of travel arrangement including a trolley rail mounted alongside one of a pair of runway rails for supporting an ergo assist arm carriage with the trolley movable along the trolley rail. One or more proximity switches are mounted aligned with a home position on the trolley and detect when the trolley is displaced from the home position by contact of a feature on the carriage with the trolley and generate signals immediately initiating shutting down of the assembly line conveyor.

BACKGROUND OF THE INVENTION

This invention concerns end of travel arrangements associated with a carriage for an ergo assist arm, used at workstations located along an assembly line to assist lifting and positioning of parts to be installed or for performing other operations. The end of travel arrangement stops an assembly line conveyor if the carriage reaches a predetermined limit in its range of motion alongside the assembly line.

Each ergo assist arm is typically supported on an associated carriage mounted on a pair of runway rails extending along one side of an assembly line conveyor, the carriage being movable along the runway rails so as to be able to move along with the auto body moved by the assembly line conveyor so as to be able to conduct an assembly or other operation on the moving auto body.

The ergo assist arm is disposed to enable an assembly line worker to carry out a particular operation while the carriage supporting the ergo assist arm is being moved parallel to the assembly line to match the motion of the auto body down the line. As a practical matter, there is a limited range of movement of the carriage and ergo assist arm along the runway rails, and the carriage will eventually reach an end of travel position if the assembly step or other operation is not completed in the normal interval allowed.

This is because the assembly line conveyor is continuously operated, and the auto body or other work will eventually advance beyond the limited range of travel of the ergo assist arm carriage.

This will cause the assembly line conveyor to pull the ergo assist arm from the station and possibly damaging the same.

Also, the auto body being assembled must not be advanced downstream to other stations along the assembly line where other assembly steps are to be carried out if an earlier assembly operation has not been completed in an upstream station.

For this reason, an end of travel arrangement has hereto been provided which is designed to stop the assembly line conveyor if movement of the carriage along the runway rails past a predetermined travel limit is detected. The end of travel arrangements have included one or more limit switches which when tripped sound an alarm when the end of travel arrangement trolley begins to exceed the limit of its normal range of motion. The assembly line conveyor control also receives a signal from a limit switch initiating a stoppage of the assembly line conveyor which stops after the inertia of assembly line motion is dissipated. The continuous nature of the alarm commonly leads to efforts by plant personnel in an attempt to disable the switches to turn off the alarm, often damaging the switches in the effort.

In these prior designs using mechanical limit switches, a dog feature on the carriage engages and trips the limit switch when the carriage reaches the designed for end of travel point, to thereby detect such over travel occurrence.

Since such limit switches have a trip element which is mechanically engaged in order to be operated, over time deformation of the trip element can result in a failure of the carriage dog feature to make contact with the switch trip element and result in a failure of the end of travel arrangement to shut down the assembly line conveyor when over travel occurs.

As noted above, vigorous efforts are often attempted after the alarm has sounded to physically deactivate the switch as with a pole or broom handle. The limit switches are typically mounted in an exposed location since a mechanical engagement with the switch trip element is necessary, and thus, vigorous efforts such as banging on the exposed limit switches by assembly line workers sometimes occur, often resulting in damage to the limit switches to the extent that the end of travel arrangement becomes inoperative. Extensive repairs and an extended assembly line shutdown may then be necessary.

In some situations, it would be desirable to allow continued limited manual movement of an ergo assist arm carriage by a substantial advance of the carriage after an automatic shutdown of the assembly line has occurred, as to enable repositioning a part carried by the ergo assist arm in order to prepare for a restart of the assembly line conveyor.

It is an object of the present invention to provide a more reliable and durable end of travel arrangement for automatically shutting down an assembly line conveyor when over travel of the carriage supporting the ergo assist arm is detected.

It is a further object to provide an end of travel arrangement which is shielded against being damaged by any attempt to interfere with an end of travel detection switch.

It is yet another object to provide an end of travel arrangement which allows a substantial manual movement of the ergo assist arm support carriage after a conveyor shut down so as to enable repositioning of the ergo assist arm after the conveyor has been shut down.

SUMMARY OF THE INVENTION

The above recited objects and other objects which will be understood by those skilled in the art are achieved by an end of travel arrangement installed on one of the carriage supporting runway rails, the end of travel arrangement including an end of travel trolley rail mounted to one of the runway rails and a trolley movable on the trolley rail to be movable alongside and parallel to the runway rails which extend alongside the assembly line conveyor. The trolley mounts support rollers enabling it to run along the trolley rail after the carriage makes contact therewith when the carriage reaches the end of the designed for range of travel.

The end of travel trolley is normally held positioned against a stop defining a home position along the trolley rail by a spring balancer which exerts a pull on the trolley holding it against the stop. The end of trolley in its home position is engagable by a tow plate fixed to the carriage when the carriage reaches the end of its normal range of travel along the runway rails.

One or more proximity sensors are located above a metal block on the trolley when the trolley is in the home position so as to detect the presence of the trolley at its home position and to also detect when the trolley is pushed away from its home position after being contacted by a tow plate on the carriage when it reaches the end of its designed for normal range of motion along the runway rails. Movement of the trolley away from its home position is detected by one or more proximity switches sending signals to the assembly line conveyor initiating a shutdown of the assembly line conveyor which ceases after a momentary lag. Two proximity switches are preferred to be used to keep the end of travel functional even if one of the proximity switches fail and also to make it more difficult to manually deactivate the switches as with a piece of metal. A single switch generating an alarm and shutting down the conveyor could also be employed.

Both proximity switches are preferably mounted side by side in a protective carrier housing which is mounted to one end of the trolley rail as by a bolt passing through the lower end of the carrier housing sides and the sides of the trolley rail.

A plastic nonmagnetic mounting bar may be mounted in the carrier housing so as to extend through two sides of the housing, the bar having threaded holes which each receive one of the two proximity switches to be held side by side and vertically upright within the carrier housing in a locked upright position. The bar is not made from ferromagnetic material so does not itself activate the switches.

A horizontal partition plate may be fixed within the carrier housing and projects over the end of the trolley rail, secured thereto as by a threaded fastener passing through a notch in the outer edge of the plate and threaded into a nut engaged with the top of the end of travel rail holding the carrier housing upright in a locked position.

Loosening the threaded fastener may allow the partition plate and attached carrier housing to be swung up to expose the lower ends of the proximity switches so as to facilitate adjustment of the positions of the lower ends of proximity switches to ensure that they are flush with the undersurface of the plastic mounting bar.

The end of travel trolley can be manually rolled along the trolley rail for a substantial distance beyond the home position to allow movement of the ergo assist arm supporting carriage along the runway rails to accommodate the continued brief movement of the assembly line conveyor after the shut down signal has been sent and also to enable further movement of the carriage necessary for a manual repositioning of a part supported by the ergo assist arm or to carry out some other maneuver necessary to prepare for restart of the assembly line conveyor.

DETAILED DESCRIPTION

In the following detailed description, certain specific terminology will be employed for the sake of clarity and a particular embodiment described in accordance with the requirements of 35 USC 112, but it is to be understood that the same is not intended to be limiting and should not be so construed inasmuch as the invention is capable of taking many forms and variations within the scope of the appended claims.

Referring to the Drawings and particularly toFIGS. 1 and 2, a linear assembly line power conveyor2is depicted diagrammatically, such as one typically used in assembling car bodies6conveyed along an assembly line by continuous operation of the conveyor2.

At various work stations along the assembly line conveyor2, there is typically provided an apparatus12including an ergo assist arm4or other similar device used to support and position a part to be assembled to the car body6or to perform some other operation on the car body6at the station. The ergo assist arm4has one member4A connected to a support carriage8mounted for movement along a pair of parallel runway rails8A,8B which extend parallel to the assembly line conveyor2.

The other member4B of the ergo assist arm4may carry tooling4C for performing an operation, holding a part, etc.

As noted, the runway rails8A,8B extend alongside and parallel to the assembly line conveyor2. The ergo assist arm4may be pulled along the runway rails8A,8B by the motion of the assembly line conveyor2during the operation at the station so as to not be moved relative to the car body as the operation is carried out.

That operation must be completed within a predetermined distance less than the length of the runway rails8A,8B so that no relative linear motion occurs between the car body and the tooling.

The end of travel arrangement10includes an end of travel trolley rail14attached by a pair of brackets16to one of the runway rails8B and extending alongside and parallel thereto, as seen inFIGS. 1 and 2.

The carriage8(a fragmentary portion shown inFIG. 2) moves from right to left as seen inFIG. 2in moving the ergo assist arm4matched to the car body movement caused by operation of the conveyor2. The ergo assist arm4may be conveying a part to be assembled to a car body6or performing some other operation as mentioned above.

A tow plate20(also referred to as a trip dog) is attached to a leading end of the ergo assist arm supporting carriage8, located so as to come into contact with one end of the trolley22which is mounted to movable along the trolley rail14as described further below.

If the tow plate20of the carriage8moves past the point of first contact with the end of travel trolley22, the trolley22is moved away from its home position, which change in position is detected and a shut down signal is sent to an assembly line conveyor control24to initiate shut down.

This is caused by signals received from a pair of proximity switches60A,60B, these signals generated when a block28(FIG. 2) made of a ferromagnetic magnetic material is moved away from a home position of the trolley22where it is normally closely positioned to the lower ends of the proximity switches60A,60B.

Both of the proximity switches60A,60B produce a signal which generate a signal transmitted to the assembly conveyor control24causing an initiation of shutdown of the assembly line conveyor2.

Alternatively, a single proximity switch able to produce both signals could be used.

The end of travel trolley22and ergo assist arm carriage8can continue to move due to the extension of the trolley rail14past the limited range of motion from the home position. This capability may be desirable in order to be able to move a part further after conveyor motion has ceased supported on the ergo assist arm carriage8or to carry out some other maneuver necessary to allow restart of the assembly line conveyor2.

Referring toFIGS. 3 and 3A, the trolley rail14may be constructed from an aluminum extrusion formed with a pair of interior lengthwise extending runner surfaces30separated by a slot32.

The end of travel trolley22has two sets of rollers34mounted on the upper side which allows free movement of the trolley22along the length of the runner surfaces30and the slot32formed in the trolley rail14, allowing the body of the trolley22to pass therebetween.

Guide rollers36maintain a vertical orientation of the trolley22.

The right end38of the trolley rail14is partially cut away as shown inFIG. 3removing a top slot portion40in the vicinity of the home position of the trolley22.

Referring toFIGS. 4, 4A, 5, 6 and 7, the end of travel arrangement10further includes a carrier housing42defined in part by a U-shaped piece44having sides45A,45B with a back plate46welded thereto and a support plate48extending across the piece44with ends50extending through cutouts52in the sides of the U-shaped piece44and welded thereto.

The carrier housing42preferably is of sturdy construction and substantially encloses the proximity switches60A,60B to protect the same from being damaged by misguided efforts to reset the same.

A thick plastic bar54overlies the support plate48also having ends extending through cut outs52A with screws56passing through the ends of the bar54and received in threaded holes in ends50A,50B to attach the plastic (nylon) bar54to the underside of support plate48.

The support plate48has a portion48A which projects out beyond the U-shaped piece44having a notch56formed therein at its outer end which overlies the top of the track40of the trolley rail14. A machine screw58secures the support plate48to the trolley rail14when tightened into a threaded plate59received within the track40of the trolley rail14.

The pair of proximity switches60A,60B pass through respective holes62in the support plate48to be aligned with threaded holes64in the bar54. Switch60A,60B when activated generate signals when the trolley22moves away from its home position, which are both sent to the conveyor control24to stop the power conveyor2, which control24occurs after a brief lag due to its inertia.

The carrier housing44is pivotably connected to the trolley rail14by a shoulder bolt66passing through aligned holes67in the sides45A,45B of U-shaped piece44as well as through aligned holes69in the sides of trolley rail14with a nut and washer70,71retaining the same in position.

A plastic spacer-stop block72is placed in the inside of the U-shaped piece44at the rear thereof with a through hole74allowing the bolt66to pass through and secure the spacer stop block72in position.

The spacer/stop block72has an upper bar portion76which extends across the surfaces30at the end of the trolley rail14.

The block72also has a bottom bar portion78integral with the upper bar portion76extending beneath and across the top portion76which is received in the slot32between the surfaces30of the trolley rail16and projecting forward of the top portion76to define a stop for the trailing edge23of the end of travel trolley22to locate the metal block feature28directly beneath the bar54and the lower ends of proximity sensors60A,60B so as to allow its presence to be reliably detected (FIG. 4A).

A spring balancer80has a cable connection82to trolley22to exert a moderate force pulling the trolley edge23against the end79of the spacer stop block lower portion.

Such spring balancers are commercially available and allow the end of travel trolley22to move a substantial distance down the trolley rail14as seen inFIG. 2without a great increase in the spring force to gently return the trolley22to its home position. This accommodates substantial movement of the carriage8after contacting the trolley22accommodating a brief continuance of the conveyor2and to allow repositioning of a part (not shown) as necessary.

A mounting bracket84(FIG. 8) attached to the spring balancer80and to the rear of the plate46with small screws as shown secures the spring balancer80to the housing42.

The machine screw58may be removed to allow pivoting back the housing44as seen inFIGS. 5 and 6.

This conveniently allows an adjustment of the position of the lower ends of the proximity switches60so as to be flush to the bottom of the bar54to be positioned very close to the block feature28while not contacting the same.

Locking nuts86secure the proximity switches60A,60B in a correctly adjusted position.

Referring toFIG. 9, details of the brackets16which connects the trolley rail14to a runway rail8B are shown.

An angle piece90is connected at one end to a U-shaped standard bracket piece92which rests atop the track40atop the trolley rail14. A small plate94is inserted within the track40and connected by two screws96received in threaded holes95to the bottom of the U-shaped piece92.

A bolt98passes through holes99in the sides of the U-shaped piece92and a tube100inserted between the sides of the U-shaped piece92to be captured.

A bracket122is installed in the runway rail8B and secured with a bolt104passing through a holes105,106in angle piece90, and a hole107in a plate108, secured together with a nut109.