US 2949098 A
Description (OCR text may contain errors)
- Au'g- 16, 196 F. s. FLICK 2,949,098
ACTUATOR FOR SERVICE IN PISTON AND CYLINDER DEVICES Filed March 21, 1956 United States Patent ACTUATOR FOR SERVICE PISTON AND CYLINDER DEVICES Francis S. Flick, Oak Park, Ill., assignor to Flick-Reedy Corporation, a corporation of Illinois Filed Mar. 21, 1956, Ser. No. 572,851
4 Claims. (Cl. 1211 i8) This invention relates to an actuator for service in piston and cylinder devices.
Many machine operations are performed in sequence which require controls to cause one operation to start after the completion of a previous operation. Piston and cylinder devices may be used to provide the mode of power for such machine operations so that a limit switch is a convenient means for effecting a sequence of operations. Often, the movement of a piston to the end of its stroke may be used to trip a switch starting the next operation or the return stroke of the piston.
This invention is concerned with an actuator which may be placed in the head of a cylinder in position to be struck by the piston and moved to operate a switch or the like. One difliculty with this type of actuator in the past has been the fact that the actuator was exposed to the pressure within the cylinder and might be moved by the pressure when the piston was moving away from the actuator. Springs have been used to bear against the actuator and oppose the pressure fluid on its exposed part; however, space limitations have not permitted the incorporation of suflicient spring pressure particularly in high pressure applications.
It is a principal object of this invention to provide a new and improved actuator of the type described.
Another object is to provide an actuator for piston and cylinder devices particularly adapted to high pressure applications.
Another object is to provide an actuator which by its structure cannot be operated by pressure fluid within the cylinder and will be operated only by physical movement provided by the piston striking the actuator.
A still further object is to provide an actuator of the character described requiring only suflicient spring loading to overcome friction of the sealing structures utilized insuring proper low pressure operation.
Other objects, features and advantages of the invention will be apparent from the following description of a preferred embodiment of the invention illustrated in the drawing in which:
Figure l is a fragmentary sectional view through one head of a piston and cylinder device showing the actuator of this invention mounted therein and positioned to operate a switch shown in elevation; and
Figure 2 is a fragmentary sectional view taken substantially along line 2--2 of Figure l.
The present invention is particularly intended for use in piston and cylinder devices operating at high pressure. Ordinarily, such devices use a hydraulic motive fluid and the operating pressures involved may be as high as 3000 pounds per square inch or more. At these pressures, the exposed part of the actuator will have considerable force applied to it by the pressure within the cylinder as the piston moves away from the actuator. In the past, this force has been opposed by the imposition of heavy springs against the movable part of the actuator.
There is normally no pressure fluid on the actuator 2,919,098 Patented Aug. 16, 1960 ICC as the piston moves toward it. The spring pressure on the actuator must be overcome by the piston movement and should not be suflicient to cause serious feed rate change or thrust loss which might aifect forward stroke normal operation.
In the figures of the drawings, a cylinder head 3 is shown as joined to a cylinder tube 4 held together by tie rods 5. A piston structure 6 is reciprocally mounted Within the cylinder and may travel until it strikes against the head structure. The head itself has a retainer plate 7 mounted thereagainst serving to hold bushings and sealing structure for the piston rod (not shown). A microswitch 8 having a base plate 9 is secured by screws 10 to the retainer plate. The switch has an operating stem 11 extending into an appropriately located bore 12 through the retainer plate. In order to operate the switch 8, its stem 11 may be depressed a short distance, ordinarily not appreciably more than a sixteenth of an inch. It will thus be evident that the drawings illustrating the invention are somewhat enlarged in scale.
The actuator itself involves a spool 15 having an outer stem 16 and an inner stem or actuating portion 17 with an enlargement 18 intermediate the two stem portions. A stepped bore 19 is formed through the head 3 in order to receive the actuator structure. This bore is in communication with the bore 12 through the retainer plate.
The structural parts of the actuator include a cylindrical cage 20 having a larger internal diameter portion 21 and a smaller portion 22. The stem portion 17 slides in the smaller diameter of the cage and is sealed thereagainst by an O-ring 23. The enlargement 1-8 slides within the larger portion 21 of the cage and is sealed likewise thereagainst by an O-ring 24. Thus, the stem and enlargement guide the spool in its longitudinal movement within the cage 20.
The portion of the actuator exposed to the internal pressure of fluid within the cylinder is sealed from the remainder of the actuator by an O-ring or packing 25 in engagement With the outer surface of the stem portion 16. A washer-like member 26 retains the O-ring against extrusion towards the switch. The cage itself is sealed Within the bore 19 in the head by an O-ring 27 so that fluid from within the cylinder is prevented from escaping through the bore 19 around the actuator parts, any leakage going to the vent 33.
When operating under extremely high pressure of the order of 3000 pounds per square inch, the stem 16 is subjected to a considerable force urging the spool toward the switch. In the present instance, this force is resisted by a structure permitting the application of the pressure fluid to the backside of the enlargement 18 on the spool. The particular means here employed includes a fluid pas sage 30 drilled longitudinally through the stem 16 and connecting with a cross passage 31 admitting fluid into the space or chamber 32 between the spool and cage. The area of the enlargement against which this pressure acts is slightly larger than the effective area of the stem 16. Since the pressure fluid acting upon the enlargement and the stem is the same, the net eifect is to yieldingly urge the spool toward the piston. While the passages 30 and 31 are herein shown as the preferred means of applying the pressure to the enlargement, obviously a separate passage through the head 3 could be provided.
Since the spool is sealed within the cage by the Oring 25 around the stem 16 and the O-ring 24 in the enlargement, a means is provided for venting the space between these O-rings. A small tapped vent 33 communicates with a space 34 around the forward end of the cage. As the spool moves there is thus no change in the atmospheric pressure around the forward end of the enlargement and thus no resistance to its movement because of any change in pressure. The spring 35 shown as abutting the enlargement and the rearward part of the cage is a light weight compression spring applying a force on the spool only suflicient to overcome the friction of the O-rings on the movable spool. This spring insures that the spool will be moved toward the piston even though the pressure within the cylinder might be quite low. When the enlargement is moved against the washer-like part 26, it is in proper position to be contacted by the piston and physically moved to operate the microswitch 8. The switch in turn will control the starting of a succeeding operation.
The actuator of the present invention may be used with equal facility in high and low pressure piston and cylinder devices. In either event, the pressure admitted to the rearward side of the enlarged portion of the spool will always urge the spool toward the piston within the cylinder. Slight modifications of the shape of the spool may be made in order to increase or decrease the differential force acting upon the spool because of the appli cation of motive fluid pressure. Also, the present actuator is shown as mounted within a cylindrical cage 29; however, modifications may be made in this regard should the bore 19 within the head of the cylinder be properly shaped to receive the spool. For convenience of manufatcure, the present structure is preferred.
In operation, the actuator spool is moved to the right in Figure 1 when struck by the piston structure 6. The spool abuts the stem 11 of a microswitch 8 and causes it to move thus operating the switch. Ordinarily, the pressure fluid moving the piston 6 is then reversed within the cylinder so that the piston will be moved away from the spool of the actuator. Upon this occurrence, the spool will return to the position shown wherein the enlargement engages the washer-like member 26. Should the pressure within the cylinder be quite low so that the force applied on the spool by the pressure will not overcome the friction of the O-ring seals, the light spring 35 will insure that the spool returns to the initial position.
The foregoing detailed description has been given for clearness of understanding only, and no unnecessary limitations should be understood therefrom, for some modifications will be obvious to those skilled in the art.
1. A limit switch actuator for a piston and cylinder device, comprising: an actuator spool adapted to be slidably mounted in a bore in a head of the cylinder and having a stem positioned to be contacted and moved by the piston at the end of its stroke for operating a limit switch; an enlargement on the spool adjacent the stem of a size to afford a chamber in the bore on the side of the enlargement remote from the piston, said stem having a fluid passage for admitting cylinder pressure fluid to said chamber; and sealing means for preventing application of cylinder pressure fluid to the side of the enlargement adjacent the stem so that the cylinder pressure fluid is prevented from moving the spool from a predeterminded desired position.
2. An actuator assembly for a piston and cylinder device adapted to move a means responsive to physical movement thereof by a piston in the cylinder, comprising: a spool slidably mounted in a bore in the cylinder head communicating with the interior of the cylinder, said spool having a stem portion extending into the cylinder for contact and movement by the piston and an intermediate enlargement, said stem and enlargement having sliding support in said bore; a seal about the stem preventing application of cylinder pressure fluid to one side of the enlargement; and said stem having a fluid passage leading to the other side of the enlargement so that pressure fluid within the cylinder may urge the spool toward the cylinder.
3. An actuator as specified in claim 2 in which said seal about the stem comprises a packing in fluid tight engagement about the stem portion and a spring is provided for urging the spool toward position to be contacted by the piston, said spring being adapted to overcome friction of said sealing means on the spool.
4. An actuator assembly for use in high pressure cylinders, comprising: a hollow cage adapted to be placed in a bore in a cylinder head and having a stepped bore with an internal shoulder near one end between the bores; a spool slidably mounted in the cage and having a rearward stem portion slidable in the smaller bore portion of the cage and an enlarged portion slidable in the larger bore portion of the cage; said spool carrying fluid sealing means in contact with said bore portions; a forward stem portion on said spool extending into the cylinder for physical contact with a member to move the spool within the cage for actuating another member; fluid sealing means between the forward stem and cylinder head preventing passage of fluid along said stem, and said forward stem having a fluid passage therein com municating with a space between the cage and enlargement to apply pressure fluid to the enlargement in opposition to the pressure fluid on said stem, said stem area and enlargement area being so related that pressure fluid in the cylinder urges the spool toward the interior of the cylinder; and spring means between said cage shoulder and spool enlargement additionally urging the spool toward the interior of the cylinder.
References Cited in the file of this patent