US8336286B2 - Push chain with a bias spring to prevent buckling - Google Patents
Motion-transmitting drive chains are well known. Such chains are alternately known as or referred to as push chains, drive chains, and thrust chains. Regardless of what they are called, motion-transmitting drive chains are able to transmit an axial compressive load as well as exert a tensile force. Common chain on the other hand is incapable of transmitting a compressive load and is only able to exert a tensile force.
Motion-transmitting drive chains and common chains are both made up of successive, flexibly-connected links which are joined to each other by pins. In a common chain, the links are freely able to rotate around the pins in both directions. Unlike the links of a common chain, the links of a motion-transmitting drive chain are able rotate in only one direction. When the links of a drive chain are urged to rotate in the opposite direction, the chain becomes rigid and thereafter able to transmit a compressive axial load.
A problem with prior art drive chains is their susceptibility to buckling, if the line of action of a compressive force tends to rotate the links in the wrong direction or if the links are not sufficiently loaded to keep them locked. A drive chain that pre-loads the links of a drive chain such that they are less susceptible to buckling would be an improvement over the prior art.
As can be seen in
Reference numeral 66 identifies a second geometric plane which is displaced “vertically” from the first plane 62 as the two planes are shown in the figures. The second plane 66 is also parallel to the first plane 62 and cuts horizontally through the geometric centerline of the projections 58 shown in the figure. The distance separating the first plane 62 from the second plane 66 is considered a separation distance of the pins 56 from the projections 58.
The force represented by the vector 68 is preferably supplied to a drive chain by one or more types of springs wrapped around the chain's links or contained within the links of the drive chain 50.
Piston movement toward the right side of
As shown in the figure, a compressive force exerted by the elastic string 82 will be applied “below” the pins 56 as shown, and therefore “below” the pins' axes of rotation. Applying a compressive load as shown in
Spring motors are spring-powered retraction devices. Spring motors are commonly used to retract seat belts, among other things. In an alternate embodiment of the chain shown in
Knuckle joints are themselves well known. One such joint is shown and described in U.S. Pat. No. 4,929,113, which was issued to Sheu and entitled “Knuckle Joint.” The teachings of Sheu are incorporated herein by reference, at least with regard to the structure and operation of a knuckle joint.
Paraphrasing Sheu, a knuckle joint comprised of two inter-engaging pieces. A first piece is formed to have two, spaced-apart and side-by-side projections that enter a mating jaw. The jaw or second piece is also comprised of two, spaced-apart side-by-side projections of a second piece, however, the space between the side-by-side projections of the jaw are wider than the space between the side-by-side projections of the first piece.
Both pairs of projections on each piece have a hole or an “eye” through which a pin member can be inserted and around which the pieces will rotate. Stated another way, the pin passes through the eyes formed in the two projections of the first piece, and through the two eyes of the mating projections of the second piece. Unless there is some external limiter, a knuckle joint can be pivotally rotated in both directions around the pin.
In the figures, the two projections of the narrow end identified by reference numeral 97 are sized, shaped, and arranged to freely slide within the interior walls of the jaw formed by two projections identified by reference numeral 99. A bearing sleeve 100 is sized, shaped, and arranged to fit within the interior walls of the narrow end projections 97. A similar bearing 98 fits within the internal space of the jaw projections 99.
Top “corners” 103 of the jaw portion 99 are rounded. Directly below the rounded corners 103 the corners 95 are squared off as shown. The rounded shoulders 103 allow the link bodies 94 to rotate in a counter-clockwise direction around each bearing 98, however, when the link bodies 94 are urged in a clockwise direction around the bearings 98, the squared-off corners 95 but up against opposing faces 105 on an adjacent link body 94. The chain 90 shown in
The convex shape of the chains at rest is important when a push chain or motion-transmitting drive chain is used to drive a load that will exert a torque on the chain that will tend to bend the chain downwardly, (as shown in the figures) such as a when a push chain is used in a rodless dispenser for extrudable materials shown in
The piston rod is located on the back side 75 of the piston such that an axial compressive force exerted on the piston 18 has a line of action through the piston that is below the center line of the piston but “above” the axis of rotation of the connecting pins holding the chain links together. In the chain shown in
When the piston 18 shown in the figure encounters a resistance from extrudable material, a reactive force distributed across the piston face will act through a line extending through the piston's center line. Since the compressive force from the chain is below the piston's center line and the reactive force from the piston face is above the piston's center line, a reactive torque 124 is will be produced at the bottom end of the piston rod that will tend to rotate the piston and piston rod counterclockwise as shown. The reactive torque from piston rod will thus tend to straighten or flatten the chain from its at-rest location to be parallel to the reference line 120. If the push chain were initially flat relative to the reference line 120 or concave (opening upwardly), a reactive torque 124 could deflect the center part of the chain to an extent where a reactive axial force from the piston rod acted on a line below chain's connecting pins. Compressive force that acts on a line below the link pins axis or rotation will cause the links to unlock, i.e., rotate. The resting curve shown in
Those of ordinary skill in the art will recognize that a method of operating the drive chain is preferably comprised of applying a compressive force to the links in order to cause the links to rotate in a direction by which the links and the interlocking projections engage each other. The method of applying that compressive force is preferably a step of applying the compressive force as part of retracting the drive chain.
Those of ordinary skill in the art will also recognize that a mechanism by which a compressive force is applied to a spring can apply the compressive force such that the line of action for the compressive force is actually outside the link body 52. Such a mechanism would include an arm or other projection extending away from the link body 52.
In a device such as the aforementioned rodless dispenser, the spring 74 has a second or rearward end 77 attached to a point that is fixed in space relative to the spring and chain. In an alternate embodiment, a spring that provides a bias to a drive chain can also be connected to the chain, albeit toward the rearward end of the chain such that the spring is maintained in tension.
In an alternate embodiment of the rodless dispenser, and as shown in the patent applications incorporated herein by reference, a spring that exerts a bias force on the chain also acts to retract the chain into a chain magazine 29.
The foregoing description and examples are for purposes of illustration only. The true scope of the invention is defined by the appurtenant claims.