US2568450A

US2568450A - Reciprocating pneumatic motor

Info

Publication number: US2568450A
Application number: US756514A
Authority: US
Inventors: Hjarpe Erik Georg
Original assignee: SKF AB
Current assignee: SKF AB
Priority date: 1945-10-03
Filing date: 1947-06-23
Publication date: 1951-09-18
Anticipated expiration: 1968-09-18

Description

E. G. HJARPE RECIPROCATING PNEUMATIC MOTOR Sept. 18, 1951 2 Sheet-Sheet 1 Filed June 23, 1947 E Invcn 07 r/Z Gear Har e.

Patented Sept. 18, 1951 UNITED STATES PATENT OFFICE Aktiebolaget Svenska Kullagerfabriken,

Goteborg, Sweden, a corporation of Sweden Application June 23, 1947, Serial No. 756,514 In Sweden October 3, 1945 Section 1, Public Law 690, August 8, 1946 Patent expires October 3, 1965 2 Claims.

It is often necessary in machine tools, gauging devices transport mechanisms etc. to provide means for imparting a reciprocating motion to feed mechanisms, gauging motions or to move work pieces either in an uninterrupted series or according to certain manual or machine-actuated impulses.

The desired motions may be obtained conveniently by means of a pneumatic motor of suitable design. A suitable motor of this type is one having a piston reciprocable in a cylinder and driven by air under pressure, the chamber on one side of the piston being in continuous communication with a source of air under pressure and the chamber on the other side having valve members actuated directly or indirectly by the piston which alternately put the latter chamber into communication with the sourceof pressure and with an exhaust opening.

The present invention relates to devices by means of which the length of the stroke of a pneumatic motor of above mentioned type may be varied without varying the size of the clearance and thereby avoiding the increase in air. consumption which would result from the increase in the clearance which would otherwise follow upon a shortening of the stroke. The invention is characterized thereby that the member for reversing the stroke is adjustable to vary the length of the stroke by varying the reversing point of the piston at that end of the cylinder, which is continuously in communication with the source of air pressure.

An embodiment of the invention is illustrated in the accompanying drawings, in which Fig. 1

is a longitudinal section through the device; Fig.

2 is an external View seen in the direction of the arrow 11 in Fig. 1; Fig. 3 is a simplified longitudinal section through the device; Fig. 4 is a detail of Fig. 3 showing the parts in another position; Figs. 5 to 8 show various positions of the contacts for reversing the direction of movement and Fig. 9 shows on a larger scale the valves and reversing contacts of Fig. 3.

The device comprises a cylinder having a bottom I with holes 41 for receiving screws for fixing it to a support, for instance a machine part, a cylindrical member 2 and a cover 3. A diiferential piston 4 is movable in the cylinder.

Contacts

5 and 6 are operatively connected to the piston. Chambers 2| and 24 are formed under and over the piston. In the bottom I of the cylinder is a piston valve 1, which is magnetized and therefore always has a tendency to adhere to one of the

iron discs

8 or 9 and thus can not of its own accord change position. This makes it possible to mount the device in any desired position relative to the horizontal plane without in any way influencing its function. The piston valve should be located as near as possible to the cylinder chamber 2| so that the clearance space will be the least possible.

A pair of conical valves l0 and l l are provided in the cover 3 and are pressed against their

seats

35 and 29 by the pressure of air in a chamber 25. The valves can be opened through the action of a pair of arms [2 and [3 either by manual operation through a handle or by the action of the

contacts

5 and 9 against the arms l2 and I3 caused by the movement of the piston 4.

The contacts 5 and t are provided at their circumferences with a number of recesses l4 and i 5, which in certain angular positions of the

contacts

5 and 6 register with pins l9 and H mounted on the cover 3. A spring actuated ball 45 retains the

contacts

5 and 6 in the positions to which they have been adjusted.

A pair of needle valves l9 and 20 are provided in the bottom of the cylinder for governing the flow of air through the inlet and

outlet channels

34 and 35 to the cylinder chamber 2!.

The function of the channels in the cylinder will be apparent from a description of the function of the device, as disclosed in Fig. 3.

Air under pressure is admitted to the device through the connection 22 and passes through a channel 23 to the chamber 2'; above the piston and from there flows to the valve chamber 2 5 and also passes the needle valve 19 to the chamber 25 in the piston valve 1 and, in the position shown in Fig. 3, further through a channel 27! to the chamber 2i under the piston. The chamber 24 communicates continuously with the source of air pressure, but the chamber 2| is alternately put into communication with the air pressure and with the atmosphere by means of the piston valve 1'. By this means the action of the piston will be easier and smoother and its speed can better be controlled than in devices in which the chambers on both sides of the piston are alternately put into communication with the source of air pressure and with the atmosphere.

Since the area of the piston t in the chamber M is greater than the effective area of the piston in the chamber 2 the piston will he forced upwards with a velocity determined by the speed with which the air is permitted to pass the needle valve l9. When the contact 6 attached to the piston rod 28 engages the pin ll (see Fig. 5) further motion of the contact 6, and therefore also of the piston 4, is prevented and the piston stops in this position.

In order to again start the motion of the piston it is necessaryto depress the handle 45 either by hand or by any other impulse, for instance from some member of the machine. The valve II is then lifted by the arm i3 and the air in the chamber 25 escapes through the valve seat 29 into a channel 39, which leads to a chamber 3| to the left of the piston valve '1, which is thereby forced towards the right to its other end position against the disc 9 (see Fig. 4). right hand end of the piston valve is then in communication with the atmosphere through the channels 3?, 4| and 39. While the valve II is in raised position the arm it keeps the channel 32 in the valve H at least partially closed, whereby air is completely or partially prevented from escaping from the chamber 25 through the

channels

33 and 32.

In the position now assumed by the piston valve 1 (see Fig. 4) the inlet channel 34 to the chamber 26 is closed by the cylindrical part 40 of the piston valve and the channel 2'! from the chamber 2.! has been put into communication with an outlet channel 35 through the chamber 25. The channel 35 communicates with the atmosphere through the needle valve 20. As the pressure in the chamber 2| drops the pressure in the chamber .24 forces the piston 4 downwards at a speed, which is determined by the speed with which the air can pass the adjustable needle valve 20.

' When the contact attached to the piston rod 28 engages the pin I'6 (see Fig. 5) further movement of the contact 5 and of the piston 4 is pre vented and the piston remains in this position.

In order to again start the motion of the piston it is necessary to lift the handle 45 either by hand or in some other suitable manner. The valve E8 is hereby depressed by the arm l2 and the pressure air in the chamber 25 passes through thevalve seat 36 into the channel 31 and further to the chamber 33 and forces the piston valve I to the left against the disc 8. The chamber 3| at the left hand end of the piston valve 1 is now' in communication with the atmosphere through the

channels

30, 33 and 32. Meanwhile the arm I? at least partially covers the opening of the channel 39 in the valve l9, whereby the air is entirely or partially prevented from escaping this way through the channels 4| and 39.

In the position .now assumed by the piston valve 1, the chamber 2% has again been put into communication with the inlet 3 and the pressure air passes through the channel 21 to the chamber 2| and the piston is raised. In this manner the piston can make a single stroke and then automatically remain in its end position.

If on the

other hand thecontacts

5 and 6 are turned with aid of the knob it to such a position that a recess [5, for instance in the contact 6, registers with the pin l1, while the pin l5. does not register with any of the recesses in the contact 5 (Fig.6) the contact 6 will not engage the pin I! during the upward movement of the piston 4 but will instead engage the arm is, which will lift the valve andthe piston valve 1 will be forced by the air pressure to its right hand position, as above described, whereupon the motion of the piston will be reversed for a return stroke. Since the pin It still prevents the contact 5 from engagingthe arm l2 the piston 6 stops in its lower position until it receives a new impulse by the raising of the handle 45.

If the

contacts

5 and 6 are adjusted to a posi- 7 tion in which a recess M in the contact 5 regisers with the pin It but no recess in. th con,-

The chamber. 38 at the tact 6 registers with the pin I (Fig. 7) the piston will move downwards and reverse but stop again in the upper position.

If the

contacts

5 and 6 are adjusted so that recesses register with both of the pins I6 and I! *(Fig. 8) the piston 4 will automatically reverse in both upper and lower ends and continue its 7 reciprocating motion indefinitely until the air pressure is out 01f, or until the

contacts

5 and 6 are adjusted to such a position that one of the pins L6 or I? prevents either of the valves Ill or II from being opened;

The stroke of the piston can be adjusted by adjusting the contact 6 axially along a bar 42 connected to the piston rod 44 by means of screws 43. a 7

An adjustment of the length of the stroke therefore takes place only by altering the upper reversing point. On the other hand the piston is always reversed at the same place at the lower reversing point. This means that the volume of the clearance space in the cylinder chamber 2| is not altered. Since practically all air consumptiontakes place through the chamber 2| this results in a saving in the air consumption, since it is not necessary to consume air to fill the clearance from atmospheric pressure at each stroke Since the air can immediately force the piston in the opposite direction this arrangement also results in quicker reversal of the direction of movement of the piston. No air consumption takes place in the chamber 24 and there is consequently no disadvantage in altering the reversingpoint at this end of the cylinder. 7

Fig. 9 shows a device whereby the period of time required for reversing the stroke at the end positions can be varied, for instance be extended, so that a slight delay will take place before the piston is reversed. Screws 487are screwedinto the arms I 2 and I3 and are provided with flat heads 49 so positioned that they may be brought into contact with thervalves l9 and H. The screws have fine threads so that they may be adjusted with great accuracy and are provided with lock nuts 50 so that they may be-locked in the desired position. By a suitable adjustment of the screws it is possible to adjust the area of flow of the valves l9 and H and thereby control the flow of air through the

valves

29 and 36 so that a suitable interval of time will lapse before the pressure in the channel 39, the chamber 3| andthe channel 37 and chamber 38 respectively has increased sufficiently to reverse the piston valve 1. The period of time is of course a function of the volumes of the channels and chainbers. These volumes may therefor be made greater in cases in which greater delay is re- 'quired. Since the piston valve "I is magnetized a certain pressure must be attained in the cham bers. 3| and 38 in order to displace the piston valve and reverse the direction of movement of a catedat a distance from other parts of the motor and may be connected to them by means of suitable ducts. The valves may be actuated from any suitable part of the machine, which may be actuated by the piston. The chambers 2| and 24 may be connected to difierent sources of air :pressure having different pressures. The d v ce 1 be scribeda o e as being driven by air pressure, but may of course be driven by any suitable pressure medium, for instance by fluid or by gas. The pins 16 and H ma be replaced by any suitable contact device. The pins may be mounted on the contacts and the recesses be provided in the cover of the cylinder. The contact devices may be so arranged that they may be moved out of the way of the contacts. The piston need not have the form of a differential piston but in cases where both sides of the piston have the same area either the chambers on opposite sides of the piston must be connected to sources of difierent pressures or a pressure reducing valve must be introduced in the duct leading to one of the cylinder chambers.

Having thus described my invention, 1 claim and desire to secure by Letters Patent the following:

1. A pneumatic motor having a cylinder and a piston reciprocable therein, a source of air pressure, the cylinder at one side of the :piston being in continuous communication with said source, valve means actuated by the piston for putting the other side of the cylinder into connection alternatel with the source of air pressure and with the atmosphere so as to afford uninterrupted reciprocatory operation of the motor, contact members for actuating the said valve means, said members being operatively associated with the piston for operation by the latter, one of said contact members being adjustable for varying the point at which said valve means is actuated during travel of the piston toward that end of the cylinder which is in continuous connection with the source of air pressure to reverse the direction of said travel and for thereby regulating the effective length of the stroke of the piston, stop members to prevent the contact members from actuating the valves, and means for suspending the function of the stop membets.

2. A pneumatic motor according to claim 1 characterized thereby that the contact members are provided with recesses or the like, which register with the stop members to suspend the function of the latter and that the contacts are rotatable to bring the recesses out of register with the contacts.

ERIK GEORG HJARPE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 968,453 Daellenbach Aug. 23, 1910 1,336,171 Trace Apr. 6, 1920 1,456,050 Benbow May 22, 1923 1,816,829 DeLeeuw Aug. 4, 1931 1,817,180 Drake Aug. 4, 1931 FOREIGN PATENTS Number Country Date 496,591 Great Britain Dec. 2, 1988