Abstract:
A miniature piston assembly composed of an elongated cylinder containing a piston head which may be displaced in response to digital hydraulic signals or otherwise and which is arranged to provide self-snubbing without requiring check valves. In the side wall of the cylinder are one or more ports spaced from one or more of the distal ends of the cylinder by a predetermined distance. When the piston is in juxtaposition with a port and approaching the proximate end of the cylinder, the cylinder and the piston define an annular clearance space of ever increasing length and fluid impedance for snubbing the motion of the piston with respect to the cylinder.

Description:
This is a continuation of application Ser. No. 319,818, filed Dec. 29, 1972, now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to miniature pistons, and more particularly it relates to controls for miniature piston adder actuators. 
     2. Description of the Prior Art 
     Snubbing the motion of a piston with respect to a cylinder is a common problem in many arts. Various solutions to this problem have been proposed, and it is believed that the article by Albert C. Saurwein, published at pages 80-83 of the July 8, 1971 issue of the magazine Machine Design is fairly representative of the state of the art. The kind of solutions to this problem set forth therein have been found satisfactory for many purposes involving conventional pistons and cylinders. However, such solutions have not been found satisfactory for miniaturized pistons which workers in the art have long desired to use in connection with extremely low energy level, fluidic logic circuitry. Such miniaturized pistons would be particularly well-suited for use in general purpose digital computers, for instance in piston adders. Attempts have been made to fabricate such miniaturized piston adders including check valves and ports in parallel with them at each end of each cylinder so that, when the piston approaches a port at the end of the cylinder, the check valve will gradually close so that the port will damp the motion of the piston. However, in miniaturized piston adders, the provision of check valves and accurate orifices is a very difficult engineering problem because the check valves require so much space, and the orifices must be made so very small and to such close tolerances that the mechanism is extremely expensive to manufacture. Again, attempts have been made to use miniaturized piston assemblies without any snubbing means, but this has proved grossly unsatisfactory, often being destructive to the pistons themselves. 
     SUMMARY OF THE INVENTION 
     The present invention is designed to overcome the drawbacks of the prior art insofar as miniaturized pistons are concerned. It accomplishes this objective in a deceptively simple, easy to manufacture fashion by providing in the side wall of the miniaturized cylinder one or more ports spaced from one or more of the distal ends of the piston cylinder by a predetermined distance. When the piston is in juxtaposition with one of the ports and approaching the proximate end of the cylinder, the cylinder and the piston define an annular clearance space of ever increasing length and fluid impedance for snubbing the motion of the piston with respect to the cylinder. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cross-sectional view of one embodiment of the present invention. 
     FIG. 2 is a cross-sectional view of another embodiment of the present invention, 
     FIG. 3 is a cross-sectional view of part of the embodiment shown in FIG. 2, showing specific dimensions of the device which was used in obtaining the data plotted in FIG. 4. 
     FIG. 4 is a graph giving a straight line idealization taken from the original data generated by the embodiment of the present invention, part of which is depicted in FIG. 3. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     In FIG. 1, a piston 10 is disposed in an elongated cylinder 12 formed by a cylinder wall 13. The piston 10 is bonded to a drive rod 14 which may be displaced in response to digital hydraulic signals or otherwise. The head of the piston 10 comprises three concentric cylindrical surfaces 16, 18 and 20. The cylindrical surface 18 fits very snugly against the inner surfaces of the cylinder 12, preventing substantially all flow of a fluid 22, such as oil, contained in the cylinder 12 from one side to the other side of the piston. The diameters of the cylinders 16 and 20 are a few mils smaller than the diameter of the cylinder 18, and they may or may not be equal. The cylinder 12 is closed at one end by the drive rod 14 which passes through and snugly engages a bore formed in the right end of the cylinder wall 13, thereby preventing flow of the fluid 22 out of the cylinder 12 at that end. The other end of the cylinder 12 is closed by a threaded plug 24, which likewise prevents flow of the fluid 22 out that end of the cylinder. 
     In the wall 13 of the cylinder 12 are two ports, 26 and 28, spaced a predetermined distance from either end of the cylinder 12. These ports are not to be confused with orifices, which are used in the art to restrict the flow of a fluid. Rather, they are simply ports whose diameters are large enough to permit substantially unrestricted flow therethrough. Above the ports 26 and 28 are hose assemblies 30 and 32, which may be of any suitable construction so far as the present invention is concerned. In the embodiments shown, they consist of threaded plugs 34 and 36, with hoses 38 and 40 passing therethrough into communication with ports 26 and 28, respectively. The hoses 38 and 40 are in turn connected to a conventional four-way valve (not shown), which controls the fluid 22 under pressure from a hydraulic power supply (also not shown). 
     In the preferred embodiment shown, the length of the portion 16 of the cylinder 10 is exactly equal to the snubbing distance, i.e., the distance from the inside edge of the port 26, where the deceleration begins, to the plug 24, which stops the piston at the end of its travel. Such an arrangement is preferred, but is not essential. If the portion 16 of the cylinder 10 were longer, the amount by which it was longer would be wasted, in the sense that it would not contribute to the snubbing action. On the other hand, if the portion 16 of the cylinder 10 were shorter, the portion 18 of the cylinder 10 would partially or wholly obstruct the port 26. If it only partially obstructed the port 26, this could serve as a drastic form of snubbing, but if it wholly obstructed the port 26 and if the fluid 22 is incompressible, it would bring the piston to a stop short of the desired terminus in contact with or immediately adjacent to the plug 24. 
     In use, when the piston is moving through the center portion of the cylinder 12, fluid flow through the ports is substantially unimpeded, since the ports function as conventional circular ports. The diameter of the ports, line losses, and valve losses are then the only limits on the velocity of the piston. 
     However, when the piston enters the area of port 26, for example, the effective size of the port is drastically altered. The clearance between the portion 16 of the piston and the inner wall of the cylinder 12 is on the order of 10% of the diameter of the port, and the cross-sectional area of the fluid escape path now becomes an annulus rather than a circle, thereby producing a sudden pressure increase opposing the direction of piston travel and acting as a deceleration force on the piston. 
     It should be noted that this pressure is not constant, but increases as the piston goes further toward the end of the cylinder. This increase is caused by the fact that the fluid must pass through a path formed by the relatively narrow clearance between the piston and the cylinder before entering the port, and this path gets longer and longer as the piston moves further toward the end of the cylinder. Consequently, it can be seen that the piston has been snubbed (decelerated) without the need for check valves or other devices used in the prior art. 
     It should also be noted that the port adjacent to the piston when it begins its travel from one end of the cylinder to the other acts as a restriction to the acceleration of the piston. This restriction occurs because the fluid 22 being pumped back into the space behind the moving piston 10 must pass through the annular space between the piston and the cylinder wall 13, and its flow therein is impeded. However, this effect is not as detrimental as might be supposed, because inertial considerations tend to preclude velocity build-up at the start of the stroke anyway. 
     It is obvious that an infinite number of embodiments of the present invention may be fabricated by varying port shape and diameter, snubbing distance, and clearance between piston and cylinder. One such embodiment is shown in FIG. 2, and it should be apparent that the embodiments of FIG. 1 and FIG. 2 produce equivalent results. The only difference between the FIG. 1 embodiment and the FIG. 2 embodiment is that undercuts 42 and 44 in the interior walls of the cylinder 12 have replaced the varying diameters of the three cylindrical surfaces 16, 18, and 20 in FIG. 1. Otherwise, the embodiments are identical, and so it is believed that the FIG. 2 embodiment need not be described further. 
     FIG. 3 is a cross-section of a portion of the embodiment shown in FIG. 2, giving specific dimensions which were used in obtaining the data shown in FIG. 4. As indicated in FIG. 3, both the inner diameter of the cylinder and the outer diameter of the piston are on the order of one-eighth inch in the illustrated embodiments. In FIG. 3, 46 is a flow measuring device, and the fluid contained within the cylinder is incompressible. 
     FIG. 4 clearly shows the rapid drop in oil flow as the piston enters the region of the port, followed by the gradual drop in oil flow as the piston goes beyond the region of the port. In this figure, X is the distance in inches the leading edge of the piston has travelled beyond the point at which it first draws even with the beginning or inside edge of the port, and each of the several curves respresents the flow rate for a given static pressure as a function of the piston position. It will be readily appreciated that, given the dimension of the piston and the cylinder, the figures for flow rate could be converted into the velocity of the piston. It should also be appreciated that the figure only shows the flow rate up to a cut-off point. In the preferred embodiments, the piston thereafter comes into contact with the end of the cylinder and is brought to a sudden stop thereby. However, if it were not required to stop the piston at a particular, fairly sharply defined spot, it would be possible to simply let the piston come to a gradual stop at an indeterminate spot as the result of the snubbing action. 
     CAVEAT 
     While the present invention has been illustrated by detailed descriptions of two preferred embodiments thereof, it will be obvious to those skilled in the art that various changes in form and detail can be made therein without departing from the true scope of the invention. For that reason, the invention must be measured by the claims appended hereto and not by the foregoing preferred embodiments.