Self-excited Oscillator

Abstract

A self-excited pneumatic oscillator is described which includes a reciprocating hammer member adapted to impact an anvil. The hammer is disposed in a housing structure which includes a porting arrangement. As the hammer moves towards engagement with the anvil, it in sequence opens a discharge port and then an intake port in communication with a source of pressurized air. The space between the front surface of the hammer and an extended housing section which supports the anvil defines an active cavity. The space between the housing and the rear surface of the hammer defines a passive spring cavity. The hammer and these cavities define a system which is acoustically resonant and oscillates at a frequency determined by the dimensions and masses thereof to convert the flow of pressurized air into reciprocating motion of the hammer and provides isolation (minimizing pressure fluctuations) between the oscillator and the air source.

Description

The present invention relates to pneumatic oscillators and particularly to a self-excited pneumoacoustic vibration generator.

Heretofore, most pneumatic oscillators for driving a valve member or hammer in a reciprocal fashion were relaxation oscillators that operate on what is known as a dump-and-fill cycle. In such arrangements, pressurized air charges a chamber driving the valve member axially. Thereafter, the charge is discharged. The return stroke operates in a similar fashion with the exception that typically it uses a smaller porting arrangement. These devices are limited in frequency because they have inherent inertial problems in stating, accelerating, stopping and reversing the valve member. Further, these relaxation oscillators have an inherent upper frequency limit that is imposed by the supply pressure, the mass of the valve member and the travel of the stroke. In practical devices, the supply pressure is often limited to about 100 p.s.i. and the frequency of oscillation to about 20- 50 cycles per second. With relaxation oscillators in order to increase their frequency of oscillation, to a range 100 cycles per second, it is necessary to use a lightweight hammer and to decrease the stroke. In addition, such oscillators are subject to the so-called "wire-drawing" effect by virtue of the input porting arrangements used therein. Thus, the available operating pressure inside such oscillators is reduced. All of the foregoing disadvantages limit the application of these low-power devices.

Accordingly, it is an object of the present invention to provide an improved self-excited pneumatic oscillator capable of being used in an impact tool.

Another object of the present invention is to provide an improved self-excited pneumatic oscillator wherein the oscillator and the flow source are isolated without an acoustic transmission line filter mechanism which would complicate the oscillator mechanism and require additional space.

A further object of the present invention is to provide an improved pneumatic oscillator which is configured to provide for efficient power transmission from the oscillator to a load.

A still further object of the present invention is to provide an improved pneumatically driven oscillator which eliminates back pressure flow and provides for high compression which will increase efficiency of the power transmission to load.

Another object of the present invention is to provided an improved pneumatically driven oscillator which develops substantially higher power output than existing devices, but which still uses the same general level of inlet operating pressure.

Still another object of the present invention is to provide an improved pneumatic oscillator having an improved air inlet system such that the wire-drawing effect is substantially eliminated.

Briefly described, a pneumatic oscillator embodying the invention includes a self-excited hammer which is constrained to generally a single degree of freedom and is adapted to periodically impact upon an anvil system. The arrangement is such that between the hammer and an extended section of the housing there is defined an active cavity, whereas between the rear surface of the hammer and the housing there is defined a passive spring cavity. When the hammer is in its rearward position, the spring action of the passive cavity exerts a force on the hammer member which causes it to decelerate, reverses its movement and finally drives it forward towards the anvil. The hammer is adapted to open and close a multiplicity of intake and discharge ports in communication with the active cavity before the hammer impacts upon the anvil. This porting arrangement provides for higher effective operating pressures by eliminating the wire-drawing effect.

It is an important feature of the present invention to provide a porting arrangement which functionally provides for isolation between the oscillator and the flow source during the time intervals when the pressure in the cavities is higher than the flow source pressure.

The invention itself both as to its organization and method of operation, partitions well as additional objects and advantages thereof will become more readily apparent from a reading of the following description taken with the accompanying drawing, the sole FIGURE of which is a schematic, longitudinal sectional view of an oscillator constructed in accordance with a preferred embodiment of the invention.

Referring more particularly to the drawing, a representative oscillator 10 is shown to include a housing 12 which is comprised of two end pieces 14a and 14b, a cylindrical member 16 and an extended sectional member 18, somewhat conical in shape, all of which are secured together by means of a series of bolts 20. The housing 12 is configured to define a large interior hollow cylindrical area 21. The sectional member 18 extends from the forward end piece 14a into the interior cylindrical area 21 and terminates at a position where it defines a receiving hole 22. The hole 22 is adapted to receive the end portion 24a of an anvil 24. An O-ring 25 allows the anvil 24 to move axially. A flange portion 27 and an internal shoulder 29 form an end stop. Another stop (not shown) to prevent excessive motion forwardly (to the left) may also be provided. It is desireable to vent the space between the flange 27 and the member 18 to the atmosphere, and a vent hole (not shown) in the member 18 may be provided for this purpose. The interior cylindrical area 21 is positioned so that between the interior of the extended sectional member 18 and the end piece 14a, there is defined a supply chamber 26 which by means of an intake fitting 28 is in communication, via a channel, such as a pipe, with a source of pressurized air. The remaining portion of the cylindrical area 21 defines an actuation chamber which is partitioned into a passive spring cavity 30 located between the end piece 14b and the hammer 34 and an active cavity 32 located between the hammer and a surface 18a of the extended member 18. A fill hole 70 for the cavity 32 is provided in the member 18. The active and passive spring cavities are dimensioned so as to have approximately the same volume in the position shown. By means of the geometry of the cavities 30 and 32 and the geometry and mass of the hammer 34, the free or oscillating frequency of the device can be predetermined.

The hammer member 34 includes a cylindrical striking portion 34a and a somewhat web-shaped flange portion 34b. The hammer is made of a resilient metal (e.g. steel) and includes an outward cylindrical shoe portion 36 biased into a sliding engagement with the interior surface 16a, thereby, by virtue of the resiliency in the flange 34b; thus providing some bearing support. The rearward end of the hammer 34 is provided with an elongated cylindrical section 38 which is in sliding bearing relationship with an interior bearing surface 40 of a hole provided in the end piece 14b. Holes 39 in the section 38 may be provided so that the region 41 forms part of the spring cavity 30. The foregoing bearing arrangement stabilizes the hammer 34 as it moves to and from anvil 24 which desirably has predetermined spring characteristics. The hammer 34 is arranged so that its web portion 34b coacts with the anvil 24 during impact. The large diameter hammer 34 needed to achieve high frequency without sacrifice in hammer weight is specially proportioned to take advantage of all requirements, including the beneficial effect of an impact spring between the massive shoe section 36 of the hammer and the top 24a of the anvil 24. This massive shoe section 36 has negligible compliance.

The center section 34a acts as a mass too, but is a small percentage (say less than one-fourth to about one-twentieth) of the shoe 36 weight.

The conical spring provided by the web 34b deflects in a combination of tension and shear. Even if the oscillator is turned over the primary hammer stresses are a combination of compression and shear such that operation in the inverted position is possible. A feature of the invention is the compactness of the device and its ease of providing an air receiver.

Note the advantage of the approximately center placement of the spring web 34b on the shoe 36. The angles on the inside of the shoe top and bottom may be made about twice as great as would be possible with end placement of the spring web on the shoe. Tolerances on the upper and lower ends of the shoe 36 are large and the shoe is a rigid, acoustically short massive element.

The sliding bearing provided by the outer periphery of the shoe 36 are long enough to provide good protection against cocking (they may be slightly over one diameter in length). These bearings are however short enough to give a compact construction.

Pressurized air from the high volume source such as a compressor changes the supply chamber 26 by way of the intake 28. A series of channels 44 in the rear end of the section member 18 delivery air to a plenum 46 formed between the outer surface of the member 16 and an extended flange of the end piece 14a. The plenum 46 is in communication with the active cavity 32 when circumferentially spaced ports or holes 50 in the shoe portion 36 are in alignment with cooperating circumferentially spaced ports 48 in the member 16.

Similarly, a series of circumferentially spaced discharge ports 52 spaced rearwardly form the ports 48 in the member 16 will discharge the active cavity when the ports 50 are in alignment therewith. It should be noted that there is a channel 56 which leads from the plenum 46 to an adjustable screw orifice 58 for permitting the difference between the average pressure in the passive cavity 30 and that in the active cavity 32 to balance the average of the force pulses transmitted to the anvil 34 system, thereby to stabilize the average position of the hammer. A bleeding orifice 60 is also provided in the passive cavity 30 for adjusting the average pressure in the passive cavity as required.

In operation, assuming the hammer 34 is in its most rearward position (to the right as viewed on the drawing), the force exerted by the cavities 30 and 32 because of air compression and expansion is such that it urges the hammer 34 towards the anvil system 24 at a high velocity. Shortly thereafter, the ports 50 are in alignment with the ports 52 reducing the pressure in the active cavity 32 and increasing the force on the hammer 34. Just prior to impact the ports 48 and 50 will come into alignment but will not have sufficient effect to reduce the impact blow of an impact section 34a of the hammer and the surface 24a. However, the pressure in the active cavity will have increased and will in conjunction with the rebound of the hammer 34 off the impact system 24 drive the hammer in the reverse direction. Thereafter the ports 50 will again open up the ports 48 building the pressure in the active cavity 32 and driving the hammer 34 rearwardly at an increasing velocity until the port 50 aligns itself with the port 52 for a short period of time which will decrease the active cavity pressure. Thereafter the operation will repeat itself at the frequency determined by the geometry and masses as heretofore mentioned.

By means of the inlet porting arrangement in the form of an integral receiver and a multiplicity of short low-impedance ports, there will be high effective operating pressures. The wire-drawing effect common to prior air-operated percussive devices is substantially eliminated.

In order to start up the oscillator there is provided a stator port section 62 in the end piece 14b (normally closed) which permits a high burst of pressurized air into the passive cavity 30 which will rapidly drive the hammer 34 towards impact and thus initiates the start of oscillation. Thereafter the port 62 will be closed by appropriate valving means.

Starting may be accomplished as well without the port 60. Consider the hammer 34 to be in the down position. The air fills supply chamber 26.

Air starts to fill cavity 32 and 21 through vent 70 and bleed 58. Since vent 70 is bigger than bleed 58, cavity 32 fills faster. The hammer 34 then moves up.

When inlet ports 48 line up with hammer ports 50, the in rush of air rapidly increases the pressure in cavity 32, thereby accelerating the hammer 34 upwardly. The momentum of the hammer 34 will, when the air charge in cavity 30 is still low, move the hammer to open the exhaust ports 52. This will drop the pressure in cavity 32; thus allowing hammer to be accelerated downward. On this cycle, the hammer 34 will move to and slightly beyond the position that aligns the hammer ports 50 with the inlet 48. The hammer will be accelerated with greater momentum than on the previous cycle and will again reach exhaust ports 52, even through cavity 30 is at higher pressure than on the previous cycle. The open ports in cavity 32 will again drop the pressure, starting another cycle downward. This precess continues with each cycle building up to higher amplitude. As pressures stabilize in cavities 32 and 21 and as the hammer starts to impact on the anvil 24a and energy is extracted from the oscillation, the level of oscillation will stabilized so that force and energy balances are maintained. This is the condition of steady running.

While an embodiment of the invention has been described, variations thereof and modifications therein within the spirit of the invention will undoubtedly suggest themselves to those skilled in the art. Accordingly, the foregoing description should be taken as illustrative and not in any limiting sense.

Claims

What is claimed is:

1. A self-excited pneumatic oscillator comprising

a. a housing, an anvil, and a movable hammer for impacting upon the anvil,

b. the housing defining a hollow interior cylindrical space and including a section which extends into the cylindrical space and partitions said space into a supply chamber and an actuation chamber,

c. said hammer being disposed in and partitioning the actuation chamber into a passive spring cavity and an active cavity on opposite sides thereof,

d. intake and discharge ports for pressurized air in said housing both opening into the actuating chamber, and

e. said hammer being disposed in slideable engagement with the housing and including means for blocking said inlet and discharge ports and having a third port for sequentially communicating with the discharge port and the intake port as said hammer moves towards impact with said anvil, whereby said hammer executes self-excited oscillatory movement and periodically impacts upon the anvil.

2. The invention as set forth in claim 1 wherein said section has an opening in which said anvil is located in alignment with said hammer.

3. The invention as set forth in claim 1 wherein said hammer has a flexible web portion which interconnects a central anvil impacting section to a shoe section which rides on the wall of said housing, said web portion having spring characteristics.

4. The invention as set forth in claim 1 wherein the housing defines a plenum in communication with the intake port and the supply chamber.

5. The invention as set forth in claim 4 including means providing communication between said plenum and said passive spring cavity for stabilizing the axial position of said hammer.

6. The invention as set forth in claim 5 including means coupled to the spring cavity to start the oscillator by driving the hammer in one of a pair of directions, toward and away from the anvil.

7. The invention as set forth in claim 1 wherein said blocking means of said hammer includes a shoe providing bearing surface which is disposed in contact with a bearing surface provided by the internal wall housing, said shoe encompassing the housing wall in an area adjacent the intake and discharge ports.

8. The invention as set forth in claim 7 wherein the hammer includes a hammer striking portion for impacting said anvil, a web shaped portion which provides spring action during impact and which interconnects the striking portion and said shoe.

9. The invention as set forth in claim 8 wherein said third port is located in said shoe.

10. In a self-excited oscillator the combination comprising

a. means for providing a source of pressurized air,

b. a housing, an anvil system, and a movable hammer impacting upon the anvil system and movable in first and second successive strokes in each cycle of oscillation away from and toward said anvil system,

c. said housing defining active and passive spring cavities for acting upon said movable hammer,

d. means defining a supply chamber connected to said pressurized air source means, and

e. porting means for sequentially providing during each of said first strokes communication between said supply chamber and said active cavity and then communication between said active cavity and a discharge for said active cavity, and during each of said second strokes communication between said active cavity and a discharge for said active cavity and then between said supply chamber and said active cavity.