GB2359590A

GB2359590A - Improvements in pneumatic or hydraulic rams

Info

Publication number: GB2359590A
Application number: GB0004570A
Authority: GB
Inventors: Richard Arthur Lindsay
Original assignee: Vitec Group PLC
Current assignee: Videndum PLC
Priority date: 2000-02-25
Filing date: 2000-02-25
Publication date: 2001-08-29
Also published as: GB0004570D0; WO2001063130A1; AU2694601A

Abstract

The disclosure relates to a pneumatic/hydraulic ram (10) having a cylinder (11), a piston rod (24) extending into the cylinder through an open end thereof with a clearance between the rod and cylinder for sliding of the rod into and out of the cylinder. A tubular diaphragm (30), rolling back on itself with its inner periphery attached to the piston rod and the outer periphery attached to the cylinder provides a seal between the piston rod and cylinder which defines a pressure chamber in the cylinder. The cylinder and piston rod as have substantially equal circumferential lengths so that the rolling diaphragm readily transfers from the wall of the piston rod to the wall of the piston and vice-versa during the extension/retraction of the piston rod. The equal circumferential lengths may be achieved by forming the piston rod with a waveform or undulation on its circumferential surface.

Description

2359590 IMPROVEMENTS IN OR RELATING TO PNEUMATICIHYDRAULIC RAMS This

invention relates to pneumatic/hydraulic rams for moving for positioning loads such as the ram used for operating a vertical column of a pedestal which supports a TV video camera.

Typically, a pneumatic or hydraulic ram has a cylinder and piston rod projecting from the cylinder with a seal on the piston rod sealing with the cylinder or vice versa. When fluid pressures in the cylinder are high, the seal has to be pressed in to engagement with the piston rod or cylinder (as appropriate) to prevent leakage but this results in a high frictional engagement requiring some force to move. Such an arrangement is not suitable for delicate positioning of a load such as a TV/video camera where accurate positioning without shudder or jerking, that is smooth controlled movement is essential.

This invention provides a pneumatic/hydraulic ram having a cylinder a piston rod extending into the cylinder through an open end thereof with a clearance between the rod and cylinder for sliding of the rod into and out of the cylinder, and a tubular diaphragm rolling back on itself with its inner periphery attached to the piston rod and the outer periphery attached to the cylinder to provide a seal between the piston rod and cylinder which defines a pressure chamber in the cylinder; wherein the cylinder and piston rod are so formed as to have substantially equal peripheral lengths so that the rolling diaphragm readily transfers from the wall of the piston rod to the wall of the piston and vice-versa during the 2 extension/retraction of the piston rod.

For example, the cylinder may have a circular cross section and the piston rod may have a generally circular cross section with an undulating or ripple form surface such that the circumferential length of the cylinder and piston rod are substantially the same.

More specifically the piston rod may have a wave form cross section, and in particular a sinusoidal wave form cross section.

In any of the above arrangements the diaphragm may comprise a parallel side seamless tube formed from a woven material coated or impregnated with a plastic or elastic material for sealing purposes.

In one arrangement the diaphragm may be formed in finely woven thread (eg. silk) with a neoprene or other rubber like coating.

In an alternative arrangement the diaphragm may be extruded from plastic sheet material and a woven fabric tube is located on the outer, ie., nonpressured side.

In any of the above arrangements the diaphragm may be attached to the end of the piston projecting into the cylinder.

Also the outer diameter of the piston may be substantially smaller than the inner diameter of the cylinder to provide an extensive space around the piston in the cylinder and the open end of the cylinder has a reduced diameter section in which the piston rod is mounted for sliding movement into and 3 out of the cylinder.

is In the latter construction the cylinder may have a support tube extending co-axially from said reduced diameter section of the cylinder and projecting into the enlarged space within the cylinder, the piston being slidably mounted in the tube at the open end of the cylinder and projecting through the tube into the cylinder with a clearance between the piston and tube and the diaphragm being attached to the tube.

More specifically the tube may terminates partway along the cylinder and the diaphragm may be attached to the end of the tube.

Further, the tube may have a low friction bearing or bearings adjacent the open end thereof to guide the piston rod for movement into and out of the cylinder.

The following is a description of some specific embodiments of the invention, reference being made to the accompanying drawings in which:

Figure 1 is a cross sectional view through a pneumatic/hydraulic ram taken along a longitudinal axis of the ram according to the invention; and Figure 2 is a crosssectional view taken on the line 2-2 on Figure 1; Referring to the drawings, there is shown a pneumatic ram indicated generally at 10 intended for use in a vertically adjustable telescopic column of a pedestal for supporting a TV/video camera.

The ram comprises a cylinder 11 closed at one end 12 and having a large cylindrical cavity 13 extending over the greater part of its length. At the other end of the cylinder, the wall of the cylinder is stepped 4 inwardly at 14 to form a reduced diameter open ended bore 15 coaxial with the main cylindrical cavity. A tube 16 is mounted at one end in the bore 15 and projects coaxially into the cylinder cavity and has a free end 17 some two thirds of the way along the cavity.

A piston rod 24 of hollow cylindrical form projects into the cylinder through the tube and is supported in a spaced pair of low friction DELRIN or NYLON bushes 25 mounted in the tube 16 within the bore 15. The end 26 of the piston rod projecting into the ram cylinder has an annular end cap 27 engaging in the end of the piston rod. The other end of the piston rod projects from the ram cylinder and is closed by an end bung 28 adapted to be connected to a further component.

The cylinder of the piston rod has a slightly smaller outer diameter than the inner diameter of the ram cylinder to provide a clearance gap between the two which is indicated at 29. To provide a seal between the piston rod and cylinder, a rolling diaphragm 30 is provided. One end of the diaphragm is secured in the open end of the piston rod being trapped between cap 27 and inner end of the piston rod as indicated at 31. The other end of the diaphragm which is clamped to the free end of the tube by an encircling collar 32. Thus, as the piston rod moves into and out of the cylinder, the diaphragm unrolls from the piston rod onto the cylinder and vice-versa to provide a frictionless seal between the piston rod and cylinder.

The diaphragm is a low stretch finely woven parallel tube formed for example in silk and has a neoprene or other rubber like coating on its pressurised side, that is the side facing the closed end of the cylinder.

To accommodate the rolling of the diaphragm between the piston rod and cylinder, the piston rod 24 is formed with longitudinally extending convolutions 33 of sinusoidal wave form, as shown in Figure 2. The wave form is designed so that the circumferential length of the piston rod, taking into account the peaks and troughs of the waves is substantially the same as the inner circumference of the plain tube of the cylinder. Thus the diaphragm has the same circumferential length whether it is engaging with the tube or engaging with the piston rod and will therefore lay onto the cylinder or onto the piston rod without distortion.

In the arrangement shown in the drawings, the ram has 24 equi-spaced sign wave convolutions, although this will be determined in each case to suit the particular relative sizes of the ram and tube/cylinder.

The cylinder 11 and piston rod do not, of course, have to be of geometric cylindrical form. other cross-sections may be used. for example the cylinder may have a multi-faceted form, - e.g. hexagonal or octagonal form and the piston rod has a sinusoidal wave form spaced opposite each such faces and being of the same peripheral length of each facet.

1 1 6 -

Claims

1. A pneumatic/hydraulic ram having a cylinder, a piston rod extending into the cylinder through an open end thereof with a clearance between the rod and cylinder for sliding of the rod into and out of the cylinder, and a tubular diaphragm rolling back on itself with its inner periphery attached to the piston rod and the outer periphery attached to the cylinder to provide a seal between the piston rod and cylinder which defines a pressure chamber in the cylinder; wherein the cylinder and piston rod are so formed as to have substantially equal peripheral lengths so that the rolling diaphragm readily transfers from the wall of the piston rod to the wall of the piston and viceversa during the extension/retraction of the piston rod.

2. A ram as claimed in claim 1, wherein the cylinder has a circular cross section and the piston rod has a generally circular cross section with an undulating or ripple form surface such that the circumferential length of the cylinder and piston rod are substantially the same.

3. A ram as claimed in claim 2, wherein the piston rod has a wave form cross section.

4. A ram as claimed in claim 3, wherein the ram has a sinusoidal wave form cross section.

5. A ram as claimed in any of the preceding claims, wherein the diaphragm comprises a parallel side seamless tube formed from a woven material coated or impregnated with a plastic or elastic material for sealing purposes.

6. A ram as claimed in claim 5, wherein the diaphragm is formed in finely woven thread (eg. silk) with a neoprene or other rubber like coating.

7. A ram as claimed in claim 5, wherein the diaphragm is extruded from plastic sheet material and a woven fabric tube is located on the outer, ie., nonpressured side.

8. A ram as claimed in any of the preceding claims, wherein the diaphragm is attached to the end of the piston projecting into the cylinder.

9. A ram as claimed in any of the preceding claims, wherein the outer diameter of the piston is substantially smaller than the inner diameter of the cylinder to provide an extensive space around the piston in the cylinder and the open end of the cylinder has a reduced diameter section in which the piston rod is mounted for sliding movement into and out of the cylinder.

10. A ram as claimed in claim 9, wherein the cylinder has a support tube extending co-axially from said reduced diameter section of the cylinder and projecting into the enlarged space within the cylinder, the piston being slidably mounted in the tube at the open end of the cylinder and projecting through the tube into the cylinder with a clearance between the piston and tube and the diaphragm being attached to the tube.

11. A ram as claimed in claim 11, wherein the tube terminates part-way along the cylinder and the diaphragm is attached to the end of the tube.

12. A ram as claimed in claim 10 or claim 11, wherein the cylinder has a low friction bearing or bearings adjacent the open end thereof to guide the piston rod for movement into and out of the cylinder.

13. A pneumatic/hydraulic ram substantially as described with reference to and as illustrated in the accompanying drawings.

: 64909: GCB: JB: FURNDOCS