US3791010A - Overload mechanism for cam operated linkages in a multistation assembly machine - Google Patents

Abstract

A station for an automatic nonsynchronous multistation assembly machine operated by a cam shaft extending transversely to the line of movement of the parts in the transport system, and featuring an individual overload mechanisms for each of the associated cam. The overload mechanism including a detent link pivot together with an associated drive disconnect and sensor system so that an overload condition causes displacement of the pivot link generating a sensor signal and a consequent disconnect of the drive system in response to the sensed signal.

Description

ll'nited States Patent 4 [191 Graham et -al.

[4 1 Feb. 12, 1974 OVERLOAD MECHANISM FOR CAM OPERATED LINKAGES IN A MULTISTA'IION ASSEMBLY MACHINE Inventors: James T. Graham, Sterling Heights;

Fred W. Hackstock, Birmingham,

both of Mich.

Assignee: The Bendix Corporation, Southfield,

Mich.

Filed: Feb.:l6 1973 Appl. No.: 333,436

Related US. Application Data Division of Ser. No. 204,755, Dec. 3, 1971, Pat. No. 3.724.052.

us. Cl 29/208 0 Int. Cl 823p 19/04 Field of Search29/208 c, 200 A, 200 P, 200 B,

[56] References Cited UNITED STATES PATENTS 3,648,346 3/1972 Graham et al. 29/200 A 3,724,052 4/l973 Graham ct al 29/200 P Primary Ixaminer-lhomas H. Eager Attorney, Agent, or Firm.lohn R. Bcneficl [5 7] ABSTRACT A station for an automatic nonsynchronous multistation assembly machine operated by a cam shaft extending transversely to the line of movement of the parts in the transport system, and featuring an individual overload mechanisms for each of the associated cam. The overload mechanism including a detent link pivot together with an associated drive disconnect and sensor system so that an overload condition causes displacement of the pivot link generating a sensor signal and a consequent disconnect of the drive system in response to the sensed signal.

6 Claims, 6 Drawing Figures Patented Feb. 12, 1974 4 Sheets-Sheet 1 FIGI W: M w Patented Feb.12,1974 339ml.

4 Sheets-Sheet 2 FIG.4

Patented Feb. 12, 1974 4 Sheets-Sheet 5 atemed Feb. 12, 1974 4 Sheet 4 FIG. 5

v OVERLOAD MECHANISM FOR CAM OPERATED LINKAGES IN A MULTISTATION ASSEMBLY MACHINE This is a division of application Ser. No. 204,755, filed Dec. 3,1971, US. Pat. No. 3,724,052.

BACKGROUND OF' THE INVENTION output declined because of the compounding of downtime which results from such an interrelationship, as a stoppage at any station would discontinue activity at every station.- In addition, problems of maintenance and trouble-shooting were'greatly aggravated.

In order to increase the size and number of stations in such machines, it was found to be necessary to disconnect the control systems of the individual stations from one another, tying them together only with the power and free-type transport system so that each station operated as a separate machine powered by its own individual drive system and activated by its own control system, i.e., the nonsynchronous type of automatic assembly machine. The back-up of parts available in this power and free transport system act as a reservoir or cushion of parts for each individual station, so that temporary cessations at individual stations will not affect the overall production of completed assemblies.

.In addition, maintenance and troubleshooting problems are greatly simplified due to the isolation of the stations and their relative individual simplicity.

However, this type of machine has in the past been arranged with a multiplicity of air or hydraulic cylinders, valves, and limit switches pro-viding endpoint sequential type control or by having each station operated with a parallel extending cam shaft either aligned with the line of movement of the parts or along side thereof. For reliability, a cam system is more desirable, but certain problems have existed in such systems.

A problem has concerned the protection overload mechanisms designed to protect the machine from jams and which frequently consist of overload yielding or releasing clutches located at the main drive of the operator cam. Such an arrangement senses only the aggregate loading of the various motion linkages and may not protect an individual linkage if the total torque applied to the cam is not excessive. Furthermore, the shifting mechanical advantages occurring as the linkages and cam are stroked lead to further uncertainties in detecting jams in the individual linkages.

It is therefore an object of the present invention to provide improved linkage mechanisms for this arrangement in which damage due to jamming of the individual linkages is effectively prevented.

SUMMARY'OF THE INVENTION This and other objects which will become apparent upon a reading of the following specification and claims are accomplished by a novel overload release mechanism incorporated in the individual motion linkage by providing a detent link pivot together with an associated drive disconnect and sensor system so that an overload condition causes displacement of the pivot link generating a sensor signal and a consequent disconnect of the drive system in response to the sensed signal.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a plan view of a multiple station nonsynchronous automatic assembly machine.

- FIG. 2 is a view taken along the section 22 in FIG. 1;

FIG. 3 is a view of the section taken along line 33 in FIG. 1.

FIG. 4 is a view of the section taken along line 4-4 in FIG. 3.

FIG. 5 is a view in partial section of the overtravel link shown in FIG. 4.

FIG. 6 is a view of the section taken along the line 66 in FIG. 5.

DESCRIPTION OF THE PREFERRED EMBODIMENT In the following detailed description, certain specific terminology will be utilized for the sake of clarity and a specific embodiment described in order to provide a full and clear understanding of the invention, but it is to be understood that the invention is not so limited and may be practiced in a variety of forms and embodiments thereof.

Referring to the drawings, and particularly FIG. .1, a multistation automatic assembly machine according to the present invention is depicted. The machine 10 includes a plurality of assembly stations 12 interconnected by sections of power and free transport conveyor l4 and may also include manual stations (not shown) for various operations which are better suited for manual performance.

As seen in FIG. 2, the conveyor system includes an inner and an outer roller chain l6, 18 which are continuously advanced by means of sprockets 20 and 22 at some point in the system (FIG. 1). The roller chains 16 and 18 are supported on bars 24, 26 and carry fixed thereto on their upper surface portion, plates 28, 30 which serve to support and frictionally engage a pallet 32 upon which the workpiece 34 is located. Inasmuch as the details of this system do not form a part of the present invention and are themselves known to those skilled in the art, it is not felt necessary to describe this in great detail.

In operation, base members such as housings of the workpiece 34 to be assembled are placed on a pallet 32, which advances successively to each station 12, each of which may add parts from a supply and feed mechanism 36, to the assembly or may merely manipulate elements previously added thereto.

Referring to FIG. 3, a station 12 with an operating mechanism according to the present invention is shown in some detail. This station is adapted to receive pallets 32 which are carried into the station by the roller chains 16, 18.

The station 12 includes a locating fixture 38. The pallet 32 is adapted to be stopped and located with respect to the fixture 38 immediately after it comes into approximate registry with the station 12, by means of a rough stop mechanism (not shown).

At this point a series of actions take place all controlled and operated means of a transversely extending drum cam assembly 40 which is driven by a motor 42, speed reducer 44 and clutch unit 45 and brake unit 46, preferably pneumatically operated, which actions are initiated by suitable controls, in order to intermittently rotate the cam assembly 40.

The cam assembly 40 includes a drum member 48 I which is supported by means of bearings 50, 52 mounted on partitions 54, 56, respectively, supported in the station base 58. Secured to the drum 48 are a plurality of cam groove sections 60, 62, 64, 66, and 68 which may be constructed of stand-ardized segments individually belted or otherwise secured to the drum member 48. Associated with each respective segment 60, 62, 64, 66, 68 is a linkage assembly 70, 72, 74, 76, and 78 for performing a specific motion with regard to the workpiece or in locating or providing auxiliary support for the pallet 32. Each linkage assembly 70, 72, 74, 78 is supported by a cross member 80 which is in turn supported by partitions 54, 56 as well as partition 82, while linkage assembly 76 is supported by a plate 84 in turn supported by appropriate bracketry.

Each linkage assembly 70, 72, 74, 76 and 78 includes an associated link 86, 88, 90, 92, and 94 rotatably supported by pivots 96, 98, 100, 102, 104. Each link 86, 88, 90, 92, 94 has an associated cam follower 105, 107, 109, 111, 113 disposed in its respective cam groove so as to constrain it to move in conformity with the particular contours thereof.

Each link 86, 88, 90, 92, 94 is drivingly associated with a mechanism designed to perform some motion function which is associated with the specific operation to be performed at the particular station 12.

For example, link 88 is adapted to operate a wedge pin device 114 which serves to locate the pallet and workpiece with respect to the registry fixture 38, link 92 is adapted to drive an auxiliary support clamp mechanism 116, link 88 is adapted to operate a bearing or seal feed mechanism 118, link 86 operates a bearing positioning mechanism 119, while link 94 drives a press mechanism 120, arranged to press a hearing or seal into the workpiece 34.

Inasmuch as the details of the particular motion mechanisms are not in themselves a part of the present invention and may be any of a great variety of such known movements, it is not felt necessary to describe these in great detail.

Suffice it to say that each of these mechanisms are operated in a sequence and in a manner determined by the particular contour of its associated cam groove to accomplish the intended station operation, after which time the cam drive is discontinued via a control arrangement (not shown) cooperating with the clutch unit 45 and brake unit 46 to await the next cycle.

From this description, it can be appreciated that the space occupied by the cam mechanism and its associated linkages occupies substantially less length of assembly line than a corresponding parallel disposed cam mechanism. Indeed in this arrangement, the several cam operated linkages occupy very little more space than a single such linkage, and hence the number of motions available is not dependent on the line space available and substantially more motions are possible at each station.- I

In addition, the cam may be located so that motions on either side of the line may be easily and directly taken therefrom.

As shown in FIG. 4, pivot 74, which is typical, includes a socket 122 secured to cross member and aligned with a corresponding bore 125 therein, and containing a ball 124 urged to the right as viewed in FIG. 4 by means of a compression spring 126. A bushing 127 may be included to lessen wear and maintain an accurate fit with the ball 124.

Disposed juxtaposed to the ball 124 is a pivot post 128 having a base portion 130 formed with a generally dished depression 132, normally disposed with the ball 124 centered therein. The pivot post 128 is maintained against the cross member 80 by means of a slotted bracket 136 secured to the cross member 80 and formed with an opening 138 so as to allow limited movement of the pivot post in the plane of its abutment with the cross member 80, while preventing movement out of this plane.

The link 90 is rotatably supported on a reduced end portion 140 of the pivot post 128, and retained thereon by means of a thrust washer 142 and a pneumatic fitting 144 threadedly engaging the end portion 140.

Associated with the fitting 144 is a source of pneumatic pressure 146 connected thereto via line 148, which communicates via the fitting 144 with a central passage 150 formed in the pivot post member 128, leading into the center of the dished depression 132. The source 146 is also connected via the fitting 144 and a line with a pressure switch 152 which is arranged to control the clutch unit 45 and brake unit 46 by means ofa solenoid valve 154 which is operatively connected thereto and serves to control communications of the pneumatic source 156 which in turn controls the application of the clutch 45 and brake 46 to discontinue drum movement. The solenoid valve 154 also may serve as the primary cycle control during normal operations.

An indicator 158 may also be operated by the pressure switch 152.

In operation, if a jam or other overload condition occurs in any one of the linkage assemblies as for example the linkage 74, the reaction force at the pivot 100 will cause the associated link 90 acting through the pivot post 128 and the dished depression 132 will cause the ball 124 to be cammed to the left as viewed in FIG. 4 against the bias of the compression spring 126, allowing the link 90 to move away from its pivot point in the direction tending to relieve the overload condition.

At this point, the passage is vented since the ball 124 no longer is centered in the depression 132 which in turn causes a pressure reduc-tion in line 145 and pressure switch 152, which is arranged to deactivate the clutch 45 and apply the brake 46, and cease further rotation of the cam assembly 40.

The indicator 158 is also activated thereby so that an operator may be apprised of the shutdown.

From this description, it can be appreciated that this arrangement is sensitive to overload conditions in the individual link mechanisms and acts to immediately relieve the excessive forces as well as to shut down all further activity at the station, and hence, providing a solution to the problem of detecting the individual jams. Furthermore, since the pivots are the locations where the excessive force levels are detected, the shifting mechanical advantage of the cam groove sections and the cam follower does not affect its function, and hence this arrangement also eliminates this source of error.

The overload level of each link mechanism 70, 72, 74, 76, and 78 also may be individually tailored by controlling the bias force applied to the ball by the compression spring and/or the ramp angle of the associated dished depression.

As noted above, a problem has existed in accurately locating a member by means of cam and linkage mechanisms due to the play involved therein and the effects of wear. An example of this type of situation is the positioning mechanism 119 referred to operated by the linkage 70. This mechanism serves to receive a part 160, such as a seal or bearing from the feed mechanism 118, into a holding member 162, and transport it into a proper position with respect to the workpiece 34 for emplacement by the press mechanism 120. Thus, the holding member 162 must accurately be brought into registry in these positions with respect to the feed mechanism 118, the press mechanism 120 and the workpiece 34.

The arrangement provided for accomplishing this includes a stationary block 164 fixed to the housing 58 and a pair of rods 166, 168 slidably disposed in bores formed in the block 164. The rods 166, 168 are connected at one end to an end plate 170 in turn connected to the holding member 162, and at the other end to end plate 172. The end plate is adapted to be driven by the link 86 by means of an overtravel link 174 pinned at 176 to the link 86 and at 178 to the end plate 172.

An adjustable positive stop 188 is threaded into the end plate 170, while a cooperating adjustable positive stop 190 is similarly threaded into the block 164. An adjustable stop 192 is threaded into end plate 172 and a cooperating stop 194 is threaded into the block 164.

The overtravel link 174, as shown in more detail in FIGS. 5 and 6, is adapted to provide a resilient limited lost motion connection between the link 86 and the end plate 172, and includes a pair of end rods 196 and 198 adapted to be pinned to the link 86 and end plate 172, respectively. End rod 196 is threadedly connected to a rod 200, extending into a housing 202 and received into an opening 204 formed in a cup member 204. The cup member 204 is threaded to the end rod 198.

Surrounding rod 200 and disposed in the housing 202 is a compression spring 206, bearing at one end against a shoulder 208 in the housing 202 and at the other end on a compression washer 210.

Compression washer 210 is forced thereby against the end 212 of the cup member 204, which in turn is abutting an internal shoulder 216 of a cap 218 threaded on the end of the housing 202.

Movement of the rod 200 in the housing 202 is limited by means of a compression washer 220 abutting the housing end 222 and adjusting lock nut 224. The compression spring 206 also acts on the rod 200 via a pair of protuberances 226 and 228 slidably received in a pair of slots 230, 232, in the cup member 204, with the compression washer 210 extending inwardly to engage the protuberances 226 and 228.

In the position shown with the cup member 204 abutting the spacer washer 214 and the compression washer 220, a lost motion clearance l is provided between the rod 200 and the cup member 204, whichallows relative movement between the end rods 196, 198 until the rod 200 abuts the bottom of the opening 203.

In operation, as the link 86 is pivoted in a clockwise direction as viewed in FIG. 3, the end plate 172 and connected rods 166, 168, end plate and holding member 162 are stroked to the right via the driving connection of the overtravel link 174 acting through its compression spring 206, until the stops 188, contact each other. This point is selected to be at the precise registry point required by adjusting one or the other or both of the stops 188, 190. At this point, the cup member 204 becomes relatively fixed, and the end rod 196 (acting through the compression washer 220) moves against the bias of the compression spring 206 to the right until the cam motion begins to pivot the link 86 in the return direction. Since a lost motion clearance l is provided, the cam motion and linkage does not need to be precisely adjusted and maintained to begin the return motion at the precise moment when the stops 188 and 190 come into contact.

Upon movement of the link 86 counter-clockwise, the end plate 172 is stroked by the overtravel link 174 to the left, together with the connected rods 166, 168, and plate 170, and holding member 162 until the stops 192, 194 contact each other, at which time the cup member 204 becomes fixed relative to rod 200. At that point, the rod 200 moves against the bias of the spring 206 acting thereon through the protuberances 228 and 226 and the thrust washer 210 (to the left as viewed in FIG. 5) until the link 86 is caused to either stop or reverse its pivotal motion by the cam groove section 60. Since the rod 200 is free to move relative to the cup member 204, if the contact of the stops 192, 194 does not precisely coincide with this stoppage or reversal of counter-clockwise pivotal movement the rod 200 is free to continue moving to the left as viewed in FIG. 5 until the spring 206 reaches its fully compressed length, and hence the registry of the holding member may be precisely adjusted independently of the linkage motion within the limits of this overtravel.

Additional thrust washers 210 or washers of differing thickness thereof may be utilized, as well as springs of varying rates in order to control the relative stiffness of the overtravel link 174 to provide the proper response for the particular velocities, masses, etc., involved in the particular motion.

From the above detailed description, it can be appreciated that a particularly advantageous station configuration for a nonsynchronous multiple station automatic assembly machine has been provided inasmuch as the number of motions which can be utilized at any given station is not limited by the station width and that motions on either side of the line are easily available.

In addition, a highly effective, relatively trouble and maintenance free individual link overload mechanism has been provided as well as a precision registry arrangement which is accurate, relatively simple to adjust initially, and which requires a minimum of maintenance to keep in the proper adjustment.

What is claimed is:

1. An overload release arrangement for a machine having a plurality of linkages operated by a common drive comprising:

means pivotally supporting at least one of said linkage link mem-bers;

overload release means causing said link member to be displaced relative said pivotal support means in response to an overload condition in said linkage, whereby an overload condition in an individual linkage may be prevented.

2. The arrangement of claim 1 wherein said pivotal support and said overload release means includes a depression in said link member and a ball member resiliently biased into engagement with said depression, whereby reac-tion loads of a sufficient magnitude cause said ball to be cammed against said bias by said depression.

3. The arrangement of claim 2 further including deactivating means causing said drive to be interrupted in response to said displacement of said link member relative said pivotal support.

4. The arrangement of claim 3 wherein said pivotal support and over-load release means include a depression in said link member and a ball member resiliently biased into engagement with said depression, and

wherein said deactivating means includes a source of fluid pressure in communication with said depression and means venting said source through said depression in response to displacement of said link member, and further includes means deactivating said drive in response to said venting.

5. An overload release arrangement for a link member comprising:

means pivotally supporting said link member;

overload release means causing said link member to be displaced relative said pivotal support in response to a predetermined pivot reaction load.

6. The arrangement of claim 5 wherein said pivotal support means and said overload release means includes a depression in said link member and a ball member resiliently biased into engagement with said depression.

Claims (6)

1. An overload release arrangement for a machine having a plurality of linkages operated by a common drive comprising: means pivotally supporting at least one of said linkage link mem-bers; overload release means causing said link member to be displaced relative said pivotal support means in response to an overload condition in said linkage, whereby an overload condition in an individual linkage may be prevented.

2. The arrangement of claim 1 wherein said pivotal support and said overload release means includes a depression in said link member and a ball member resiliently biased into engagement with said depression, whereby reac-tion loads of a sufficient magnitude cause said ball to be cammed against said bias by said depression.

3. The arrangement of claim 2 further including deactivating means causing said drive to be interrupted in response to said displacement of said link member relative said pivotal support.

4. The arrangement of claim 3 wherein said pivotal support and over-load release means include a depression in said link member and a ball member resiliently biased into engagement with said depression, and wherein said deactivating means includes a source of fluid pressure in communication with said depression and means venting said source through said depression in response to displacement of said link member, and further includes means deactivating said drive in response to said venting.

5. An overload release arrangement for a link member comprising: means pivotally supporting said link member; overload release means causing said link member to be displaced relative said pivotal support in response to a predetermined pivot reaction load.

6. The arrangement of claim 5 wherein said pivotal support means and said overload release means includes a depression in said link member and a ball member resiliently biased into engagement with said depression.

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