US3911627A

US3911627A - Belt grinding machine adapted to grind a flat or curved surface

Info

Publication number: US3911627A
Application number: US460722A
Authority: US
Inventors: Karl Heesemann
Original assignee: Individual
Current assignee: Individual
Priority date: 1973-04-21
Filing date: 1974-04-15
Publication date: 1975-10-14
Anticipated expiration: 1992-10-14
Also published as: ES425525A1; SE407915B; IT1011313B; GB1437908A; DE2320345A1; AT325451B; JPS5030197A; CH568817A5; PL90677B1

Abstract

The invention concerns a belt grinding machine or finisher, adapted to grind a flat or curved surface. The belt is driven and endless and passes over a conveyor on which workpieces each having a face to be ground, are located. The belt runs over a flexible beam which can be bent by one or more of a plurality of piston and cylinder units some of which are fixed to and some mounted displaceably on the frame of the machine, each cylinder having a feeler-actuator which during the passage of a workpiece past the belt, comes into contact with the surface to be ground, or a template, and follows the curvature thereof. Each feeler operates a valve to admit pressure fluid to or drain it from its cylinder so that the various cylinder actuations cause the beam and hence the belt to follow a path the curvature of which is that desired on the workpiece surface.

Description

United States Patent Heesemann Oct. 14, 1975 1 BELT GRINDING MACHINE ADAPTED TO Primary ExaminerA1 Lawrence Smith GRIND A FLAT OR CURVED SURFACE Assistant ExaminerNicholas P. Godici [76] Inventor: Karl Heesemann, 54 Friedenstr., Attorney Agent or Firm Learman & Mccuuoch 4970 Bad Oeynhausen-Rehme, Germany ABSTRACT [22] Filed: Apr 15 1974 The invention concerns a beltgrinding machine or fin- Appl. No.: 460,722

isher, adapted to grind a flat or curved surface. The belt is driven and endless and passes over a conveyor on which workpieces each having a face to be ground, are located. The belt runs over a flexible beam which can be bent by one or more of a plurality of piston and cylinder units some of which are fixed to and some mounted displaceably on the frame of the machine, each cylinder having a feeler-actuator which during the passage of a workpiece past the belt, comes into contact with the surface to be ground, or a template, and follows the curvature thereof. Each feeler operates a valve to admit pressure fluid to or drain it from its cylinder so that the various cylinder actuations cause the beam and hence the belt to follow a path the curvature of which is that desired on the workpiece surface.

9 Claims, 4 Drawing Figures US. Patent Oct. 14, 1975 Sheet 1 of 3 3,911,627

BELT GRINDING MACHINE ADAPTED TO GRIND A FLAT OR CURVED SURFACE The present invention concerns a belt grinding machine or finisher for grinding plane, concave or convex workpiece surfaces, and comprising a motor-driven conveyor device, such as endless chains, belts or the like, moving the workpieces to be ground, an endless grinding belt circulating transversely or longitudinally to the direction of movement of the workpieces and located above the conveyor device, and a resilient pressure member, associated with the grinding belt, moving and holding the grinding belt against the surface of the workpiece to be ground by a plurality of pressure units spaced from eachtother in the direction of movement of the grinding belt and loaded on one or both ends.

Such belt grinding machines, of which various embodiments are known, can grind plane plate-shaped workpieces having regular or irregular external shapes.

If the workpiece surfaces are not plane, but highly concave or convex, grinding such surfaces involves special problems and the grinding operation must be carried out manually by methods which may be expensive and not particularly effective.

It is an object of the present invention to provide a belt grinding machine of the above mentioned type which makes it possible to grind plane and strongly concave or convex workpiece surfaces the curvature of which is greater than I mm, on workpieces having regular and/or irregular outer shapes such as chair seats, perfectly and fully automatically.

In one form of the present invention, the belt grinding machine is provided with a grinding belt which is adaptable in a simple, reliable and accurate manner, to any particular shape of workpiece surface to be ground.

Furthermore, the grinding belt exerts a uniform specific grinding pressure on the entire grinding surface.

Again, it is proposed, without the use of attachments, to avoid grinding through the edges of the workpiece and to achieve accurate control of the grinding belt position relatively to the workpiece.

According to the present invention there is provided a belt grinding machine comprising a motor-driven conveyor device, carrying the workpieces to be ground, an endless grinding belt travelling above the conveyor transversely or longitudinally of the direction of movement of the workpieces, and a resilient pressure member associated with this grinding belt which is moved to keep the grinding belt against the workpiece surface to be ground by a plurality of pressure units spaced from each other in the direction of movement of the grinding belt of single or double acting type, wherein at least some pressure units are displaceable towards or away from the workpiece surface independently of the displacement of the pressure member of the pressure unit to adapt the pressure member to the form of the workpiece, whether concave or convex, to be ground.

In a preferred embodiment, the vertically displaceable hydraulic cylinders are connected by means of a transmission means, preferably a flexible transmission member, such as a Bowden cable pressure and traction device, to a control member which scans either the actual workpiece surface to be ground, a workpiece surface opposed to the workpiece surface to be ground and having an identical shape, or a template, circular template and translates its movement by the transmission means into a vertical displacement of the hydraulic cylinders; each hydraulic cylinder has its own control member and transmission means. It is preferable to arrange this control member below the hydraulic cylinder and to form it as a vertically pivotable scanning roller which scans the negative side of the workpiece and to connect it to the housing of the hydraulic cylinder by means of the Bowden cable device.

Each hydraulic cylinder is attached to a vertically displaceable member, such as a non-rotatable ball race, a second hydraulic cylinder or a track and pinion, vertically displaceable on a supporting beam carrying all the hydraulic cylinders. All the cylinders are provided in a housing, and may be hydraulically double-acting or single-acting with spring return, the piston rod of each cylinder extending downwardly out of the housing where it is connected to the resilient pressure member.

A pressure force normally keeps each piston in a raised position with respect to the pressure member, and the hydraulic fluid when applied, is subject to such a pressure that it moves the piston and, thus the pressure member, downwardly, overcoming any opposing force towards the workpiece surface to be ground so that a uniform pressure and, consequently, a uniform grinding pressure are exerted over the entire area of the pressure member by the hydraulic fluid.

The belt grinding machine of the present invention makes it possible, in a continuous process, to effect fully automatic grinding of plane or highly concave or convex workpiece surfaces, such as, for example, the surfaces of chair seats. The workpiece is ground over its entire surface in a single operation, the edges of said workpiece being protected so that grinding attachments are avoided and a good quality of grind is achieved.

This belt grinding machine is particularly advantageous for high operating speeds so that it has a high output rate of good quality work. The resilient pressure member is adapted to the surface to be ground, according to its shape, in a simple, reliable and accurate manner by individual, vertically displaceable units (single or double-acting hydraulic cylinders, mechanical or motor-driven pressure devices) so that the pressure member is deformed with the grinding belt into the shape of the surface to be ground. All the pressure units (cylinders) exert a uniform force by their pressure member (hydraulic fluid loaded piston) on the grinding belt, so that a uniform predetermined surface pressure is produced over the entire surface of the pressure member.

Due to the vertical displacement of individual pressure units, the pressure member and the grinding belt are exactly shaped to the surface of the workpiece, and the grinding pressure is then produced independently by the members of the pressure units.

The vertical displacement of the hydraulic cylinders is simply and reliably carried out by means of a control member that scans the shape of the surface which corresponds to the surface of the workpiece to be ground, and which is formed by the workpiece itself, such as a matrix or a template, and transmits its movements to the corresponding hydraulic cylinder without loss or delay.-

Since the entire pressure beam is deformed in dependence on the shape of the workpiece, accurate surface grinding without rounding or spoiling of the workpiece edges is possible.

An embodiment of the present invention is illustrated in the accompanying drawings, in which:

FIG. 1 shows a front view of a belt grinding machine,

FIG. 2 shows a longitudinal section through a hydrau' lic cylinder and associated machine parts taken on the line I I of FIG. 1,

FIG. 3 shows a longitudinal section through a hydraulic cylinder, taken on the line II II of FIG. 1 for grinding a plane surface,

FIG. 4 shows a front view of a plurality of adjacent hydraulic cylinders, with a pressure member and a workpiece to be ground, in the lowered and deformed position of the pressure member.

A belt grinding machine according to the present invention for grinding plane and highly concave or convex plate-like workpieces having regular or irregular outlines such as chair seats, is provided, in a frame 1 1, with a motor-driven conveyor device 12, which may include two endless chains or a belt continuously moving the workpieces 10 to be ground. The two chains of the conveyor device 12, are arranged to be adjustable in the frame 11 in a horizontal plane relatively to the width of the particular workpiece, and spaced from each other transversely to the direction of travel.

Arranged above this conveyor 12 there is an endless grinding belt 13 circulating transversely to the direction of movement of the workpiece, the belt being driven independently of the conveyor device 12 and held by a resilient pressure beam 14 extending substantially over the entire length of the lower portion of the grinding belt, between the two guide pulleys 15 of the grinding belt, in the grinding position against the workpiece surface 10a to be ground.

A plurality of pressure units, in this case

hydraulic cylinders

16, 17 are provided spaced apart in the direction of movement of the grinding belt and associated with the pressure member 14. They produce a movement of the pressure member 14 against the surface of the workpiece to be ground and hold it in the grinding position in order to achieve a uniform predetermined grinding pressure over the entire area of the pressure member, and they can also bring the pressure member 14 back to the raised position (no contact between grinding belt 13 and workpiece 10).

Each of the hydraulic cylinders l6, 17 has a

housing

18, 19 which is indirectly supported on the machine base 11 and in which there is a double-acting piston 20 which is connected to a piston rod 21 extending at the workpiece end (lower end) out of the

housing

18, 19. This piston 20 is reciprocated (displaced up and down) by a hydraulic fluid, preferably air, and thus the pressure member 14 connected to the piston rod 21 receives the movement in the pressure and raised position; instead of air, oil or any other fluid may be used as hydraulic fluid.

Each

hydraulic cylinder

16, 17 is provided with a

supply channel

22, 23 feeding hydraulic fluid to each cylinder to bring its position to the raised (resting) position of the grinding belt, and a

supply channel

24, 25 feeding hydraulic fluid to the piston to bring it to the pressure (working) position of the grinding belt. A magnetically operated control valve 26, feeding the fluid for the grinding pressure to the

hydraulic cylinder

16, 17 against the lifting pressure, or evacuating it from the

cylinder

16, 17, is inserted in the

fluid supply channel

24, 25. The valve 26 is connected by means of an electric switching and control device, such as an adjustable time delay relay to a scanning member 27, actuating this time relay in dependence on the moving workpiece 10.

Individual hydraulic cylinders 17 may be displaceable (lowerable) towards the surface 10a of the workpiece, independently of the displacement of the piston effecting the grinding pressure, thus pre-adapting the pressure member 14 to the surface 10a of the workpiece in dependence on the concave or convex surface 10a of the workpiece to be ground, so that the pressure member 14 is set to the form of the surface of the workpiece by a vertical displacement of the hydraulic cylinder or cylinders 17, the piston 20 only providing the grinding pressure.

All the

hydraulic cylinders

16, 17 are secured to a supporting beam 29 mounted by arms 28 on the machine frame 11 and extending in the direction of movement of the grinding belt. Some cylinders (16) are fixed and others (17) are vertically displaceable.

The pressure member 14 is divided over its length extending in the direction of movement of the grinding belt, into a centre portion grinding a concave or convex section of the surface, and into two end portions (left and right ends) grinding less curved or plane sections. The vertically adjustable hydraulic cylinders 17 are provided in the centre portion, and the fixed hydraulic cylinders 16 being in both end portions. The number of fixed and vertically displaceable

hydraulic cylinders

16, 17 may be provided or added as desired.

Two

pipes

30, 31 extending one above the other and closed at the ends are mounted on the supporting beam 20. They are hydraulic fluid channels. The upper pipe 30 contains hydraulic fluid for lowering the pressure member, and the lower pipe 31 contains hydraulic fluid for raising the pressure member, the fluid in the pipe 30 being at a higher pressure than that in pipe 31.

The flxed hydraulic cylinders 16 are secured to the

hydraulic pipes

30, 31 by screws 32 some of these screws being hollow and establishing a path for the flow of hydraulic fluid from the

pipes

30, 31 into the hydraulic cylinders 16. Each screw 32 forms part of a

supply duct

22, 24.

The vertically displaceable hydraulic cylinders 17 also receive their hydraulic fluid from the two pipes 30, 3I through

flexible tubes

23a, 25a, which extend from each

pipe

30, 31 to each

hydraulic cylinder supply

23, 25.

The double-acting piston 20 separates the

cylinder housing

18, 19 into a lower chamber 33a, with which the

supply channel

22, 23 communicates, and into an upper chamber 33b with which the

supply channel

24, 25 from the valve 26 communicates.

The pressure medium in the lower chamber 33a always holds the piston 20 in the upper position determining the raised position of the pressure member.

The lowerable hydraulic cylinders 17 are in driving engagement with control members 34 scanning the surface 10a to be ground on the workpiece 10, a workpiece surface 10b opposed to the surface 10a to be ground and corresponding in shape to the surface 10a or a template corresponding to the surface 10a, so that a vertical displacement of the hydraulic cylinders 10 and, consequently, of the pressure member 14 is effected according to the movement of the control member. Each hydraulic cylinder 17 is in driving engagement with its own control member 34.

Each hydraulic cylinder 17 is mounted to be reciprocated with its housing 19 at an angle, preferably at a right angle, to the plane of movement of the workpiece on a displaceable member 35. This displacement is parallel to the movements of the piston rods 21 which are also displaceable at an angle, preferably at a right an gle, to the plane of movement of the workpiece.

The vertically adjustable member 35 is a non-rotating ball race secured to the supporting beam 29 of the frame. Each hydraulic cylinder 17 has its own ball race 35 which has a guide sleeve 37 which is secured in position in a receiving member 36 mounted on the supporting beam 29 and in which a guide rod 38 connected to the hydraulic cylinder housing 19 is mounted so as to be vertically displaceable but without rotation. This ball race 35 is a preferred adjusting device; however, it is within the scope of the present invention to set the vertical position of each hydraulic cylinder 17 by a second hydraulic cylinder, a rack and pinion, or any other similar system, instead of using the ball race.

The control member 34 is located below each hydraulic cylinder 17 and includes a scanning roller or pin; the control member 34 may be located above the workpiece 10.

The control member 34 is held with pressure against the shaped surface to be scanned and is connected by a transmission member 39, such a Bowden cable or hydraulic pipe line with the displaceable pistons at the control member end, and at the hydraulic cylinder end, by a lever or rack to the control member 34.

A Bowden cable remote control means operating with pressure and traction is preferably used as the flexible transmission member 39. It has a steel strip mounted on balls and the strip is secured at one end to a projecting arm 40 of the hydraulic cylinder housing 19 and at its other end to a lever 41 carrying the control member 34, near the control member. Such a Bowden cable remote control transmission member 39 transmits both pressure and traction forces.

The control member 34 includes a scanning roller 34a mounted to rotate on one end of the lever 41, and this lever 41 is mounted to pivot at its other end about an axis 42 which extends parallel to the plane of movement of the workpiece and transversely to the direction of movement of said workpiece; it is mounted on a bracket 43 secured to the frame 11.

A force pivoting the lever 41 in the direction of the surface b to be scanned, acts on the lever 41 between the scanning roller 34a and pivot axis 42. The force is derived from a hydraulic cylinder 44 with a doubleacting piston 45 and a piston rod 46 pivoted on the lever 41. The housing 47 of the hydraulic cylinder 44 is provided with two

hydraulic fluid connections

48, 49 through which hydraulic fluid flows through the connection 49, urging the piston 45 towards the lever 41 and thus always holding the scanning roller 34 in contact with the underside of the workpiece 10. The other connection 48 evacuates the fluid during the lowering of the cylinders.

Instead of the hydraulic cylinder 44, a compression spring may be provided, said spring urging the lever 41 towards the workpiece.

The compressiondevice formed by the hydraulic cylinder 44 or a compression spring, is mounted on the bracket 43.

One end of the flexible transmission members 39 is fixed to the supporting beam 29, and the other end on the bracket 43 for the transmission of movement without lost motion.

The double-acting

hydraulic cylinders

16, 17 are replaced in another embodiment (not shown), by single acting cylinders, the piston 20 thereof being driven by a hydraulic fluid towards the workpiece 10 in the applied pressure position, and into the raised position by an opposing force such as a compression spring. The

pressure units

16, 17 may also be pressure devices (pressure units) which are reciprocated mechanically, for example, by springs, or they may be reciprocated by a motor.

Each pressure unit l6, 17 has a vertically displaceable pressure member (displaccable ram) which acts on the pressure member 14.

The scanning roller 27 is mounted on a pivotable lever 50 which co-operates with an electric switch which switches the time relay on and off.

All the electrical switching and control devices for the entire operation of the machine are located in a switch box 52 mounted on the machine frame 11.

The pressure beam 14 has a plurality of pressure rams 53 extending transversely to its length and secured to each piston rod 21 with a resilient compression plate 54 (preferably a steel plate) extending over the entire length and width secured to said rams. On this steel plate 54 there is a layer of felt 55, a layer 56 of foam rubber and a second layer of felt 57 which is thinner than the layer of felt 55, adjacent to the steel plate 54, and a sliding mat 58 acting on the grinding belt 13. These parts are connected together to form an elastic unit extending towards the workpiece 10. This elastic pressure beam 14 has increased elasticity because of the above mentioned layers.

In an alternative embodiment the pressure beam 14 may be provided with an air-filled cushion which replaces the layers and 56.

The above described belt grinding machine operates as follows:

The workpieces 10 to be ground are moved through the machine by means of the conveyor device 12. All the

hydraulic cylinders

16, 17 are first held in an inoperative postion by the hydraulic fluid or compression spring acting upwardly on the piston 20, so that the pressure member 14 is disposed above the grinding plane.

When the front edge of the workpiece, in the direction of movement, comes into contact with the scanning roller 27, the roller is swung upwardly by its lever 50 and the switch 51 actuated which then switches on the time relay which in turn actuates the magnetically operated valve 26 coupled thereto; this valve 26 which shuts off the

supply

24, 25 in the inoperative position of the pressure member, now releases the

flow

24, 25 and a hydraulic fluid can now flow into the chamber 33b of each

hydraulic cylinder

16, 17 to exert a greater pressure than the opposing force and thereby displace the piston 20 downwardly in the direction of the workpiece 10.

Only the pistons 20 move downwardly which receive hydraulic fluid under control of their valves 26.

The hydraulic fluid pressure determines the grinding pressure with which the grinding belt 13 is held by the beam 14 against the workpiece surface 10a to be ground, and which is uniform over the entire length of the pressure beam. The stroke of the piston 20 in the directin of the workpiece 10 is small, but sufficient for grinding contact with the workpiece 10 to be established with the desired pressure. Plane workpiece sur faces 10a are disposed in the region of the fixed hydraulic cylinders 16 and in this case the slight descending movement of the pressure member 14 is only to obtain the necessary grinding pressure.

Concave or convex or mixed concave and convex workpiece surfaces 10a, which project by at least 1 mm out of a plane surface, are machined by the other section of the pressure member in which the vertically dis-' placeable hydraulic cylinders 17 are located, said cylinders producing by their additional vertical displacement the shaping of the pressure member 14 to the workpiece surface 10a to be ground.

Each scanning roller 34a associated with a vertically displaceable hydraulic cylinder 17 scans a shaped surface which is preferably formed by the workpiece surface lb opposed to the surface a to be ground, and identical in shape. In response to the greater or lesser curvature of this surface 10b the scanning roller 34a is pivoted about its pivotal axis 42 and transmits this pivotal movement to the transmission member 39 which effects a vertical displacement of the individual hydraulic cylinders 17 which then deform the pressure beam 14 by their displacement and shape it to the workpiece surface 100 to be ground. Grinding pressure from the vertically displaced hydraulic cylinders 17 is applied by their piston rod displacement, effected independently of the vertical displacement by the hydraulic fluid. When the workpiece 10 has passed through under the driving belt 13, the scanning roller 37 leaves the workpiece 10 and resets the switch 51 which in turn deenergizes the time relay and the valve 26 so that the supply of fluid is interrupted and a return flow of fluid simultaneously applied so that the piston rod 21 returns upwardly and the pressure member 14 moves into the raised inoperative position.

As shown, the grinding belt 13 moves transversely to the flow direction of the workpieces 10. However, it is also within the scope of the present invention for the driving belt 13 to move in the direction of travel of the workpieces. The hydraulic cylinders l6, 17 not required in a grinding operation may be switched on or off manually, individually or in groups or automatically switched on or off by elements scanning the workpieces 10.

The scanning of the shape of the workpiece surface 10a to be ground may be effected on the reverse side of the workpiece or on a substitute workpiece 10, or on a template located near the grinding area, above or below the plane of movement of the workpiece.

The grinding belt 13 with pressure member 14 and

hydraulic cylinders

16, 17 is preferably made as a unit to be vertically adjustable in the machine frame 11 relatively to the plane of contact of the conveyor device 12.

I claim:

1. A belt grinding machine comprising a frame, conveying means on said frame for conveying workpieces to be ground along a first path, endless grinding belt means operably overlying said first path, a flexible pressure member overlying a portion of said belt means and extending transversely entirely across said first path, a support member fixedly mounted on said frame overlying said pressure member, a plurality of motor means having cylinders supported upon said support member and plunger means displaceable within said cylinders and engageable with spaced portions of said pressure member for pressing said pressure member against said belt means to press said belt means against workpieces conveyed along said first path, mounting means mounting at least some of said cylinders on said support member for movement toward and away from said pressure member, a plurality of first control means respectively coupled to each of said motors for independently displacing the plunger means of each motor to provide grinding pressure, and a plurality of second control means respectively coupled to each of said at least some of said cylinders for independently shifting the individual last mentioned cylinders toward and away from said pressure member in accordance with the curvature of a workpiece longitudinally of said first path.

2. The invention defined in claim 1 wherein each of said second control means comprises scanning means engageable with a scanning surface on said workpiece having a curvature variable longitudinally of the direction of movement of said workpiece along said first path, pressure means for pressing said scanning means against said scanning surface, and motion transmitting means for transmitting displacement of said scanning means to one of said at least some of said cylinders.

3. The invention defined in claim 2 wherein said motion transmitting means comprises a Bowden wire.

4. The invention defined in claim 2 wherein said scanning means comprises an arm pivotably mounted at one end on said frame, and a scanning roller rotatably mounted at the opposite end of said arm, said pressure means being engaged between said frame and an intermediate portion of said arm and said motion transmitting means being coupled between said arm and said one of said cylinders.

5. The invention defined in claim 1 wherein said mounting means comprises a guide member fixedly secured to each of said at least some of said cylinders and a ball guide mounted upon said support member for slideably guiding said guide member in non-rotary reciprocating movement.

6. The invention defined in claim 1 where said at least some of said cylinders comprise a second group of cylinders and additional ones of said cylinders comprise a first group of cylinders, said first group of cylinders being equally divided into two similar groups fixedly secured to said support member to overlie the opposite outer side edge portions of a workpiece moving along said first path and said second group of cylinders being disposed between the two similar groups of said first group of cylindrs.

7. The invention defined in claim 6 wherein said first control means comprises first scanning roller means engageable with the upper surface of a workpiece and said second control means comprises second scanning roller means engageable with the lower side of a workpiece.

8. The invention defined in claim 7 wherein said first scanning roller means comprises a first scanning roller for each of said cylinders of both of said first and said second groups, each first scanning roller means being operable to control the displacement of its plunger means in accordance with-the position of its first spanning roller, and said second scanning means comprises a second scanning roller for each of said second group of cylinders only, and means for transmitting displacement of each second scanning roller to its associated cylinder.

9. The invention defined in claim 8 wherein said means for transmitting displacement comprises a Bowdenwire.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3v9llr627 D d October 14, 1975 lnvent s) Karl Heesemann It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 1, line 58, after "piece" insert surface.

Column 6, line 67, change "directin" to direction.

Q Column 8, line 41, change "where" to wherein--.

Column 8, line 50, change "cylindrs" to cylinders--.

' Signed and Salad this sixth D y of January 1976 [SEAL] A ttest:

RUTH c. MASON c. MARSHALL DANN Arresting Officer Commissioner of Parents and Trademarks

Claims

8. The invention defined in claim 7 wherein said first scanning roller means comprises a first scanning roller for each of said cylinders of both of said first and said second groups, each first scanning roller means being operable to control the displacement of its plunger means in accordance with the position of its first spanning roller, and said second scanning means comprises a second scanning roller for each of said second group of cylinders only, and means for transmitting displacement of each second scanning roller to its associated cylinder.

9. The invention defined in claim 8 wherein said means for transmitting displacement comprises a Bowden wire.