This disclosure relates to fluid cylinder actuators that extend and retract structures. In particular, this disclosure describes flow mechanisms that influence the amount of air flow the cylinder releases to decelerate or cushion a piston or analogous structure as it ends its stroke. For example, such cylinders can be used to extend a rod into a polyethylene terephthalate (PET) preform used to make plastic bottles. The rod stretches the preform which is then blow molded into a bottle.
An air cushion is a volume of control released air that softens or “cushions” a moving piston inside a pneumatic cylinder as the piston ends its stroke. The air cushion prevents high pressure impact between the piston and the end of the cylinder which can damage both. It can also replace or supplement a conventional rubber stop.
When a piston inside a piston cylinder moves, air volume on one side of the piston cylinder increases while the volume on the other side decreases. The process of air cushioning involves slowly releasing air that would otherwise just escape from the piston cylinder as the air volume decreases. This creates resistance against the moving piston. To accomplish this, the exhaust passage in the cylinder is smaller than what is needed to exhaust the air at the same rate as the air entering the other side of the piston. Controlling the rate of release of air from the cylinder controls the amount of cushioning. A needle inserted into the exhaust passage influences how quickly air releases from the cylinder. More particularly, moving the needle in and out controls how much of the passageway is physically blocked. Moving the needle out means less of the needle blocks the passageway allowing a faster flow of air out of the cylinder. This translates into less cushioning force against the piston. Conversely, extending the needle into the passageway allows slower flow of air out of the cylinder. This translates into more air biasing the piston thereby providing more cushion force.
The needle is threaded so rotating it also moves it linearly to and from the passageway. It is believed that there is a small window of needle adjustment to give proper cushioning. The problem is that a small turn of an adjustment screw that is part of the needle could translate into a large change in the control effect of the needle. This effectively limits the ability to make fine or precise adjustments to the cushioning effect using the needle.
Attempts to solve this problem by using a very fine pitch thread on the needle introduce significant problems in manufacturing and assembly. This disclosure describes a system that includes a needle assembly offering more precise adjustments of the needle to achieve the “proper cushioning.” In an embodiment, the needle assembly precisely controls how much the needle blocks an air escape passageway. This is achieved by coupling an adjustment screw to the needle. This can illustratively be achieved using two unequal screw threads. One set of threads connects the adjusting screw to the cylinder structure while the other set of threads connects the adjusting screw to the needle. The difference in the two thread leads allows a large rotary adjustment to be converted into a small precise linear motion of the needle while preserving the use of robust, standard threads to ease manufacturing and assembly.
An illustrative embodiment of the present disclosure provides a fluid cylinder actuator assembly that comprises a cylinder tube, a cap, a head, a rod, a piston, a manifold assembly, a fluid transfer tube, an accumulator chamber, a fluid distribution assembly, a cushion stud, and a cushion control needle assembly. The cap is located at a first end of the cylinder tube. The head is located at a second end of the cylinder tube opposite the first end. The rod extends through the cylinder tube and the head. The piston couples to the rod inside the cylinder tube separating the cylinder tube into extend and retract sides. To that end, the rod is configured to move between extend and retract positions. The fluid transfer tube extends between the cap and the manifold assembly and is configured to distribute pneumatic fluid to the extend side of the cylinder tube. The accumulator chamber is positioned between the cap and the manifold assembly and is in fluid communication with the extend side of the cylinder. The fluid distribution assembly is attached to the cylinder actuator assembly and is configured to distribute fluid between retract and extend sides of the cylinder tube. The cushion stud extends from the piston opposite from the rod and is configured to selectively extend into a receptacle in the cap. Lastly, the cushion control needle assembly is configured to extend into an opening in the cap to control the amount of fluid that exits from the retract side of the cylinder tube.
In the above and other embodiments, the fluid cylinder actuator assembly further comprises: the cushion control needle assembly further including a threaded cushion control differential screw that selectively screws into a retainer having corresponding threads, a control needle that includes a stem that is selectively extendable through a bore formed in the retainer, wherein the stem of the control needle is engageable with a threaded bore formed inside the cushion control differential screw; the threaded bore of the threaded cushion control differential screw being engageable with complimentary threads formed on the stem so that rotating the threaded cushion control differential screw extends or retracts the control needle back and forth; the threaded surface of the threaded cushion control differential screw being different than the threads on the stem; the opening in the cap that receives the cushion control needle assembly forms a bore having surfaces that are not round; the bore having surfaces that are not round has surfaces that are hex shape and are complimentary to a nut located on the control needle to prevent the control needle from rotating as it moves back and forth in the bore of the cap to limit the amount of air that can escape the cap; the bore has at least one non-curved shape that is complimentary to a non-curved shape located on the control needle to prevent the control needle from rotating as it moves back and forth in the bore of the cap to limit the amount of air that can escape the cap; the head including a flange that is attachable to a blow mold machine; the rod further including an eyelet at its end thereof opposite its coupling to the piston; an accumulator needle extending through a second opening in the cap to control fluid that passes through a second passage in the cap that is in fluid communication with the accumulator chamber; a muffler and an orifice plug assembly that attach to the manifold; a visual pressure indicator that couples to the manifold; the cushion control differential screw being configured to rotate which translates minimal linear movement of the control needle; and about 34 turns of the cushion control differential screw being configured to move the control needle a linear distance of about 0.153 inches.
Another illustrative embodiment of the present disclosure includes a fluid cylinder actuator assembly that comprises: a cylinder tube, a cap, a head, a rod, a piston, and a cushion control needle assembly. The cap is located at a first end of the cylinder tube and the head is located at a second end of the cylinder tube opposite the first end. The rod extends through the cylinder tube and the head. The piston is coupled to the rod inside the cylinder tube separating the cylinder tube into extend and retract sides. The rod is configured to move between extend and retract positions. The cushion control needle assembly is configured to extend into an opening in the cap to control fluid that exits from the retract side of the cylinder tube, and comprises: a threaded cushion control differential screw that selectively screws into a retainer having corresponding threads; a control needle that includes a stem that is selectively extendable through a bore in the retainer opposite the cushion control differential screw; wherein the stem of the control needle is also engageable with a threaded bore inside the cushion control differential screw; wherein the threads of the threaded bore are complimentary to the threads formed on the stem so that rotating the threaded cushion control differential screw will extend or retract the control needle back and forth; and wherein the threaded surface of the threaded cushion control differential screw is different than the threads on the stem.
In the above and alternative embodiments the fluid cylinder actuator assembly may further comprise: the opening in the cap that receives the cushion control needle assembly including a bore having surfaces that are not round; the bore having surfaces that are not round has a hex shape surface complimentary to a nut located on the control needle to prevent the control needle from rotating as it moves back and forth in the bore of the cap to limit the amount of air that can escape the cap; the bore has at least one non-curved shape that is complimentary to a non-curved shape located on the control needle to prevent the control needle from rotating as it moves back and forth in the bore of the cap to limit the amount of air that can escape the cap; the head including a flange that is attachable to a blow mold machine; the rod further comprising an eyelet at its end thereof opposite its coupling to the piston; an accumulator needle that extends through a second opening in the cap to control fluid that passes through a second passage in the cap that is in fluid communication with an accumulator tube; a muffler and an orifice plug assembly that attach to a manifold; a visual pressure indicator that couples to the manifold; the cushion control differential screw being configured to rotate which translates minimal linear movement of the control needle; and about 34 turns of the cushion control differential screw being configured to move the control needle a linear distance of about 0.153 inches.
Another illustrative embodiment of the fluid cylinder actuator assembly comprises a cylinder tube and a cushion control needle assembly. The cushion control needle assembly is configured to extend into the fluid cylinder actuator assembly to control fluid that exits the cylinder tube and comprises: a threaded cushion control differential screw that selectively screws into a retainer having corresponding threads; a control needle that includes a stem selectively extendable through a bore in the retainer opposite of the cushion control differential screw; wherein the stem of the control needle is engageable with a threaded bore inside the cushion control differential screw that is complimentary to the threads formed on the stem so that rotating the threaded cushion control differential screw will selectively extend or retract the control needle back and forth; and wherein threads of the threaded cushion control differential screw is different than the threads in its threaded bore.
Additional features and advantages of the flow control micro adjustment needle assembly will become apparent to those skilled in the art upon consideration of the following detailed descriptions exemplifying the best mode of carrying out the flow control micro adjustment needle assembly as presently perceived.
The present disclosure will be described hereafter with reference to the attached drawings which are given as non-limiting examples only.
a-c are side cross-sectional and detail views of the cushion control needle extended into the cap;
Corresponding reference characters indicate corresponding parts throughout the several views. The exemplification set out herein illustrates embodiments of the flow control needle micro adjustment assembly, and such exemplification is not to be construed as limiting the scope of the cylinder slide assembly in any manner.
A perspective view of a pneumatic cylinder slide assembly 2 is shown in
An exploded view of slide assembly 2 is shown in
An exploded view of cap 6 with cushion control needle assembly 104 and accumulator needle 106 is shown in
An exploded view of cushion control needle 104 is shown in
A cross-sectional exploded view of needle 104 is shown in
Side cross-sectional and detailed views of needle 104 extended into cap 6 are shown in
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A partial cutaway view of cap 6 is shown in
Side views of needle 104 are shown in
The relative pitch difference in the two screw threads determines the linear motion of the needle adjustment as it relates to the angular motion or number of turns of the adjusting screw.
For example, the larger diameter slotted adjustment screw that is rotated to move the needle into or out of the orifice is a 28 pitch screw, a ¼ diameter may be used because it is a common screw size and is easily and inexpensively produced. A common 10-32 set screw may be used as the second pitch thread because it is easily obtained and is also a low cost part. The diameter of the #10-32 set screw is smaller than the ¼-28 slotted adjustment screw so it easily accepts the #10 set screw within the needle assembly.
The formula for differential screws may be: (1/(Pitch1))−(1/(Pitch2))=inches per turn. The reciprocal of this number is the equivalent pitch. In this case 1/28−1/32=0.004464 (inch/turn) equals 1/.004464 or 224 turns per inch. Note that if this number is negative, a clockwise rotation of adjusting screw will pull the needle out of the orifice, just opposite of the direction that is customarily seen when turning a screw clockwise. If the number is positive, turning the screw clockwise will push the needle into the orifice as is customarily expected.
The travel of the needle may be determined by taking the equivalent pitch multiplied by the number of revolutions to turn. In this case (1/224*revolutions)=travel. However if desired travel is known, in this case 0.153 inches of needle travel, the number of turns may be determined. This equates to, Equivalent Pitch multiplied by the desired travel. The formula being (0.153*224)=34.2 turns.
To determine how long each of the two screws may be and their individual travels, the number of turns, in this case 34.2 and for the first screw (¼-28) is multiplied by the 1/pitch of the first screw, in this case 34.2/28=1.224 inches. For the second screw (10-32) with a pitch of 32, travel will be equal; (34.2*1/32)=1.071 inches. When used as described in this disclosure each screw will travel as shown in the above description. The difference between the two travels is the actual needle travel adjusting the flow out of the orifice.
The charts below describe additional thread pitches and how they may affect travel and number of turns. Please notice that the second chart shows that a 5/16-28 and #8-32 combination gives an equivalent screw pitch as the ¼-28 and 10-32 combinations shown in the upper chart.
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Corresponding reference characters indicate corresponding parts throughout the several views. Although the present disclosure has been described with reference to particular means, materials and embodiments, from the foregoing description, one skilled in the art can easily ascertain the essential characteristics of the invention and various changes and modifications may be made to adapt the various uses and characteristics without departing from the spirit and scope of the invention.
The present application is related to and claims priority to U.S. Provisional Patent Application Ser. No. 61/410,073, filed on Nov. 4, 2010, entitled “Flow Control Needle Micro Adjustment Assembly.” To the extent not included below, the subject matter disclosed in that application is hereby expressly incorporated into the present application.
Number | Date | Country | |
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61410073 | Nov 2010 | US |