EP0179818A4

EP0179818A4 - Linear motion resistance cell.

Info

Publication number: EP0179818A4
Application number: EP19850901930
Authority: EP
Inventors: Reginald Trethewey
Original assignee: Comdox No 70 Pty Ltd
Current assignee: Comdox No 70 Pty Ltd
Priority date: 1984-04-24
Filing date: 1985-04-24
Publication date: 1987-09-21
Also published as: NO855326L; WO1985004935A1; EP0179818A1

Abstract

The linear motion resistance cell comprises a cylinder (51) in which a piston (23) moves under the influence on an actuation rod (28) sealed within the cylinder by end seals (29). The piston (23) divides the cylinder into two chambers (52) and (53) which are filled with a working fluid which is forced from one chamber to the other through passages (31) and (32) in the piston during movement of the piston. Valve means (54, 55) are provided in conjunction with the passages controlled by the rotation of a control disk (30) by a control shaft (30a) and a control wheel (21), opening and closing selected ones of the passages through the piston [some of which are provided with variously orientated non-return valves (54, 55)]. Rotation of the control disk (30) enables operation of the cell to be effected in a selected one of the following three modes: (i) controlled resistance to movement in both directions; (ii) controlled resistance to movement in one predetermined direction only with relatively low resistance to movement in the other direction; and (iii) controlled resistance to movement in the opposite predetermined direction to (ii) with relatively low resistance to movement in the other direction. The linear motion resistance cell has a particular application to use in exercise machines.

Description

"LINEAR MOTION RESISTANCE CELL"

TECHNICAL FIELD This invention relates to a linear motiion resistance cell and has been devised particularly though not solely for use in a multi-station physical exercise machine.

BACKGROUND ART There are many applications in many different machines where it is desired to provide a resistance to linear motion which can be adjusted so as to enable the operator or user to select various modes of resistance. Typical modes may- provide resistance to motion in both opposite linear directions or a controlled resistance to motion in one direction with a relatively low resistance to motion in the opposite direction. A typical application of such a linear motion resistance cell is in an exercise machine where it is desired to provide resistance to motion in different types of exercise. Various exercise machines have attempted to provide this multi-purpose function. in the past by providing a number of hydraulic resistance cylinders which may be substituted into the machine for various different applications. For example, one hydraulic piston and cylinder assembly may be set up to provide resistance to movement in two directions and another hydraulic piston and cylinder assembly may be set up to provide resistance to movement in one direction only.

Such arrangements are awkward and time consuming to use as the user must replace the hydraulic piston and cylinder assembly in the machine each time it is desired to change the function of the machine. DISCLOSURE OF THE INVENTION

It is therefore an object of the present invention to provide a linear motion resistance cell which will go at least part of the way toward meeting the foregoing desiderata, or which will obviate or minimise the foregoing disadvantages in a simple yet effective manner, or which will at least provide the public with a useful choice.

Accordingly the invention consists in a linear motion resistance cell comprising a cylinder, a piston operable by an actuation rod for linear movement within the cylinder, sealing means at both ends of the cylinder de ining two chambers within the cylinder, one on either side of the piston, one or more passages from one said chamber to the other said chamber, a working fluid within the chambers arranged to be forced from one said chamber to the other through the passages by movement of the piston within the cylinder, and valve means in association with the passages arranged to control the flow of fluid therethrough, the valve means being operable by control means so as to provide predetermined resistances to the movement of the piston within the cylinder selectable between at least two of the following three operating modes: (i) controlled resistance to movement in both directions; (ii) controlled resistance to movement in one predetermined direction only with relatively low resistance to movement in the other direction; (iii) controlled resistance to movement in the opposite direction to (ii) with relatively low resistance to movement in the other direction. Preferably the valve means and the control means are arranged to allow selection of any one of the three said operating modes.

Preferably three said passages are provided, said valve means including two non-return valves incorporated, one in each of two said passages, and orientated such that one said non-return valve closes during movement of the piston in one direction, and the other non-return valve closes during movement of the piston in the opposite direction.

Preferably the passages all terminate at one end at a surface and the valve means include a cover plate engaging the surface and being provided with openings therein, said control means being arranged to move the cover plate over the surface causing the openings to come into and out of register with the passages in a predetermined manner. opening and closing the passages to provide the selected operating mode. Preferably at least one of the openings within the cover plate is arranged to progressively open and close the passage in register therewith, allowing the said controlled resistance to movement to be varied by operation of the control means.

Preferably the linear motion resistance cell is incorporated into an exercise machine provided with operation means arranged so that movement of the operation means by the user is transmitted to the actuation rod causing the piston to move linearly within the cylinder. BRIEF DESCRIPTION OF THE DRAWINGS Notwithstanding any other forms that may fall within its scope, one preferred form of the invention will now be described by way of example only with reference to the accompanying drawings, in which:-

Fig. 1 is an exploded perspective view of a multi-station physical exercise machine incorporating a linear motion resistance cell according to the invention; Fig. 2 is a side elevation of the component of the exercise machine shown in Fig. 1 incorporating the linear motion resistance cell;

Fig. 3 is a plan view of the component shown in Fig. 2; Fig. 4 is a longitudinal cross-section through a linear motion resistance cell according to the invention;

Fig. 5 is a plan view of the cover plate used in the valve means of the linear motion resistance cell shown in Fig. 4; Fig. 6 is a plan view of the disk incorporating the fluid transfer passages used in the linear motion resistance cell shown in Fig. 4;

Fig. 7 is a longitudinal cross-section of an alternative form of linear motion resistance cell according to the invention;

Fig. 8 is a plan view of the linear motion resistance cell shown in Fig. 7; Fig. 9 is a perspective view of a motion transfer device used in the multi-station physical exercise machine shown in Fig. 1;

Fig. 10 is a block circuit diagram of electronic monitoring equipment used with the multi-station physical exercise machine shown in Fig. 1;

Fig. 11 is a perspective view of the electronic monitoring equipment; and

Fig. 12 is a transverse cross-section through a pressure reducing device used in conjunction with the electronic monitoring equipment shown in Figs. 10 and 11. MODES FOR CARRYING OUT THE INVENTION In the preferred form of the invention the linear motion resistance cell is incorporated into a multi-station physical exercise machine although it will be appreciated that a linear motion resistance cell of this type has many other applications in different types of machine.

Turning now to Fig. 1, the multi-station physical exercise machine comprises a base (1) having a standing platform (2) at one end and an upright work post (9)- The exercise machine is provided with a seat (3) mounted on seat support rails (4) which are in turn supported in a seat bracket roller cage (5) so that the seat is free to slide within the cage (5) in a direction parallel to the base (1). The roller cage (5) is in turn supported by a seat support post (6) which is telescopically adjustable for height and may be positioned by way of a locking pin (8). The linear motion of the seat relative to the seat bracket roller cage (5) may also be locked by way of a locking pin (7).

The linear motion resistance cell is located within a housing (10) mounted on the work post (9) by way of a mounting clamp (20) so that the housing may be adjusted to a desired height on the work post. The linear motion resistance cell is connected by way of a linkage [described below] to a splined shaft (11) which protrudes from either side of the housing (10) and is engageable on either side by a handle (12) .

The exercise machine is also provided with a combined attachment for lateral exercises and footrests (13) which is attachable to the work post (9) by way of locking pins and which will be described further below.

Turning now to Figs. 2 and 3, it can be seen that the linear motion resistance cell housing (10) incorporates sleeve portions (50) which encircle the work post (9) and which may be secured thereto at a desired height by the clamping device (20).

In the remainder of the housing there is positioned a hydraulic piston and cylinder assembly (51) mounted in the housing by way of a pivot pin (17) adjacent the upper end of the cylinder. An actuation rod (28) protrudes from the lower end of the cylinder and terminates in a swivel block (16) which is journalled between the outer ends of crank arms (15) mounted on splined shaft (11). The splined shaft (11) is in turn journalled in the housing (10) so that rotation of the shaft (11) causes the crank arms (15) to rotate and move the actuation rod (28) in and out of the cylinder (51). Under a no-load condition the actuation rod is retracted into the cylinder by way of a tension spring (18) extending between the swivelling block (16) and an anchor point (19) at the upper end of the housing (10). The splined shaft (11) is also provided with a quadrant plate (40) extending downwardly below the lower edge of the housing (10). provided with a plurality of transverse pins (39) equispaced adjacent the periphery of the quadrant. The quadrant (39) and pins (40) are used in conjunction with the combined attachment for lateral exercises and footrests shown in Fig. 9 as will be described further below.

The linear motion resistance cell comprises the cylinder (51) [Fig. 4] in which is incorporated a piston (23) controlled and operated by an actuation rod (28) for linear motion within the piston. The piston is provided with an O-ring seal (35) between the piston and the cylinder wall and a nylon wear ring (34) providing a sliding bearing between the piston and the cylinder (4). The piston and cylinder assembly further comprises sealing means in the form of end caps (24) and (25) together with accompanying seals (29) which define two chambers (52) and (53) within the cylinder, one on either side of the piston (23).

The piston is further provided with passages (31). (32) and (33) extending through the piston from the upper to the lower side. The cylinder is filled with a working fluid such as an hydraulic fluid so that motion of the piston within the cylinder causes the fluid to be forced from one chamber to the other through at least one of the passages. The passages (31) and (32) are provided with non-return valves (54) and (55) orientated in opposite directions such that movement of the piston in one direction will cause one of the non-return valves to close, and movement of the piston in the opposite direction will cause the other non-return valve to close and the first referred to non-return valve to open.

The piston is also provided with a cover plate (3) rotatably mounted on the upper surface of the piston. rotatable by a hollow shaft (30A) coaxial with the actuation shaft (28). The control shaft (30A) is in turn rotatable by way of a control wheel (21) provided with indicia on its upper face [Fig. 3] which can be read against pointer (22) affixed to the actuation rod (28).

An upper plan view of the piston (23) can be seen in Fig. 6 showing the passages (31) and (32) [incorporating the non-return valves (54) and (55)] and a third passage (33) which is an open passage without any valve therein. The configuration of the cover plate (30) can be seen in Fig. 5 which shows an aperture (36) therein and a cutaway portion (37) having an edge which varies in its distance from the centre A of the actuation rod which passes through a hole in the centre of the disk (30). The aperture (36) and cutaway portion (37) are positioned such that when the cover plate (30) is in position on the upper surface of the piston (23). the aperture (36) may be in register with one of the passages (31) or (32) and the edge of the cutaway portion (37) may partly cover the other said passage. To this end the two passages (31) and (32) are diametrically opposed in the piston disk (23). and the third passage (33) is located on a diameter angularly spaced from the diameter on which the first two passages (31) and (32) are located, and preferably on a diameter located at 90 to the diameter incorporating the passages (31) and (32).

The operation of the linear motion resistance cell can be controlled to provide predetermined resistances to the motion of the piston within the cylinder in any one .of the following three operating modes:

(i) controlled resistance to movement in both directions; (ii) controlled resistance to movement in one predetermined direction only with relatively low resistance to movement in the other direction; an (iii) controlled resistance to movement in the opposite predetermined direction to (ii) with relatively low resistance to movement in the other direction.

The selection of the required mode is controlled by rotating the control wheel (21) as indicated by the pointer (22) so that in position 1 [as indicated by the indicia shown in Fig. 3] resistance to downward movement only of the piston (23) occurs. When the control wheel is rotated to this position the aperture (36) in the cover plate (30) is aligned with passage (31) and the cutaway portion (37) is aligned with passage (32). The passage (33) is completely covered by the cover plate (30). Downward movement of the piston causes the non-return valve (54) to close allowing fluid to pass from the chamber (53) to the chamber (52) solely through the passage (32). The degree of resistance to downward movement can be finely adjusted by rotating the control wheel (21) through a predetermined arc as indicated by the symbols + and - shown in Fig. 3 on either side of the numbered position 1 to progressively open and close the passage (32) by covering and uncovering that passage by the edge of the cutaway portion (37) which varies in radius from the centre of the cover plate (30). For example when the cover plate is rotated so that the edge portion (56) is aligned with the passage (32). the passage (32) is relatively unobstructed allowing fluid to flow comparatively freely through the passage (32) and giving little resistance to the movement of the piston within the cylinder. When the cover plate (30) is rotated so that edge portion (57) of the cutaway portion (37) is aligned with the passage (32). then that passage is largely covered providing a comparatively high degree of resistance to the passage of fluid and therefore a high resistance to movement of the piston downwardly within the cylinder. When the piston is moved upwardly in the cylinder by operation of the actuation rod (28). the non-return valve (55) closes and the. non-return valve (54) opens, closing off passage (32) and opening passage (31). Because passage (31) is aligned with the aperture (36) in the cover plate (30) there is a relatively low resistance to the movement of fluid through the passage and hence relatively low resistance to movement of the piston upwardly in the cylinder.

In a second mode of operation the control wheel (21) may be rotated until the indicia (3) is aligned with the pointer (22) whereupon the aperture (36) will be in register with the passage (32) and the cutaway portion (37) in register with the passage (31). The operation of the linear motion resistance cell in this mode is similar to that described for the mode above, except that the position of the two non-return valves is now reversed, giving a controlled resistance to movement of the piston upwardly within the cylinder and a relatively low resistance to movement of the piston downwardly within the cylinder. Once again the degree of resistance to movement in the upward direction may be controlled by rotating the cover plate (30) using the control wheel (21) over the arc indicated by the symbols + and - on either side of the numbered position 3 on the control wheel. In the third mode of operation when the indicia (2) on the control wheel (21) is aligned with the pointer (22). the cutaway portion is moved into register with the passage (33). As the opposite side of the piston (23) from the passage (33) is solid, the aperture (36) in the cover plate (30) is totally blanked off. In this mode there is a controlled resistance to movement of the piston in both directions within the cylinder.

Although the preferred operation of the linear motion resistance cell has been described as allowing selection between three different operating modes, and also allowing control of the resistance to "fine tune" the degree of resistance to movement, it will be appreciated that the apparatus could be simplified for other operations. For example by omitting one of the passages. (31) (32) or (33), selection of modes of operation may be made between only two choices. The cutaway portion (37) could also be provided with an edge of constant radius from the centre of the cover plate so that the resistance to movement in the predetermined direction is fixed and not able to be "fine tuned". It is however preferred to provide selection between all three possible modes of operation and to be able to control the degree of resistance of movement in the predetermined direction. Although one form of the linear motion resistance cell has been described with reference to Fig. 4. it will be appreciated that the cell may be arranged in other configurations. One such configuration will now be described with reference to Figs. 7 and 8 in which corresponding reference numerals denote similar parts to those described with reference to Fig. 4.

In the configuration shown in Fig. 7 the actuation rod (28) does not extend through the top of the cylinder (51) and the piston (58) is a plain piston without any passages therethrough. The passages are instead provided in a disk (59) incorporated in the upper end of the cylinder (51) forming a compartment (60) adjacent the upper end of the cylinder. The disk (59) is very similar in configuration to the piston (23) of the embodiment shown in Fig. 4 and incorporates passages (31) (32) and (33) of a similar layout to that shown in Fig. 6, with non-return valves (54) and (55) incorporated in the passages (31) and (32) respectively. The cover plate (61) is also similar in configuration to the cover plate (30) shown in Fig. 5 and is rotatable by a control rod (62) operable by a control wheel (63). The control wheel (63) is provided with similar indicia [Fig. 8] read against a pointer (64).

A fluid conduit is provided between the compartment (60) and the lower end of the cylinder (51) by way of a sleeve (64) spaced from and coaxial with the cylinder and sealed thereto at either end by way of end portions (65) coacting with the seals (29). Openings (66) are provided in the wall of the cylinder into the interior portion (67) of the sleeve (64). through the compartment. (60) and adjacent the lower end of the cylinder (51).

The operation of the linear motion resistance cell shown in Figs. 7 and 8 is very similar to the embodiment shown in Fig. 4 except that upward movement of the piston within the cylinder causes fluid to be forced through the selected passage in the disk (59) and into the compartment (60) whereupon it passes through the apertures (66) into the interior portion (67) of the sleeve (64) to move downwardly over the outside of the cylinder and pass inwardly through the apertures (66) at the lower end of the cylinder into the chamber (53). Downward movement of the piston within the cylinder causes the flow of fluid to be reversed. The flow of fluid is however controlled by rotation of the cover plate (61) on the disk (59) moving the aperture (36) and cutaway portion (37) into and out of register with selected ones of the passages (31) (32) and (33) in a similar manner to that described above. Because the movement of the actuation rod (28) into and out of the cylinder (51) causes the volume within the cylinder to vary, it is necessary to provide an air pocket [or some other means for compensating for the change of volume] within the cylinder (51).

Returning now to Fig. 1. it can be seen that exercise movement on the handles (12) causing the splined shaft (11) to rotate causes the actuation rod (28) to move in and out of the piston (51) in a manner which can be controlled by rotation of the control wheel (21) relative to the pointer (22). In some exercises it is desirable to provide resistance to movement in one direction only, in other exercises in the opposite direction only, and in other exercises resistance to movement in both directions. The required mode can simply be selected by the user rotating the control wheel (21) and the degree of resistance "fine tuned" by movement of that wheel in the + or - directions on either side of the marked indicia.

In some forms of exercise it is desirable for the user to move two components, such as handgrips, toward or away from one another in synchronisation. To provide this facility, the exercise machine is equipped with a combined attachment for lateral exercises and footrests (13) which will now be described with reference to Fig. 9. The device incorporates a mounting bracket (68) from which protrude footrests (70) which can be used when the user is seated on the seat (3). The mounting bracket (68) is secured to the post (9) by way of a pin passed through the apertures (71). A support flange (72) is'provided protruding outwardly from the bracket (68) and equipped with two upwardly protruding splined pivot spigots (14). Each spigot is free to rotate in the plate (72) by being mounted in a suitable bearing [not shown].

The end of each handle (12) is provided with a crown wheel segment (38) having a plurality of teeth which extend upwardly when the handle (12) is engaged with the splined pivot spigot (14) [note that the crown wheel segment is permanently fixed to the handle (12) but is not shown on the handle in Fig. 1 for the clarity of that drawing].

When it is desired to perform a lateral exercise, the handles (12) are removed from the splined shaft (11) and are positioned on the splined pivot spigots (14) as shown in Fig. 9. The linear motion resistance cell housing is then lowered on the post (9) by operation of the clamp (20) until the quadrant plate (40) is located between the two crown wheel segments (38) and the pins (39) mesh with and engage the teeth on the crown wheel segment. The housing (10) is then locked in place by securing the clamp (20). also causing the handles (12) to be securely positioned on the spigots (14) and preventing inadvertent removal of the handles from those spigots. Synchronised contra-rotating movement of the handles (12) causes the crown wheel segments (38) to rotate on the spigots (14) and the teeth on the crown wheel segments to mesh with the pins (38) causing the quadrant plate (40) to rotate about the shaft (11). In this manner the crank arms (15) are caused to rotate and the actuation rod (28) connected to the pivot block (16) to move in and out of the cylinder (51). The operation mode of the linear motion resistance cell can be selected as before to provide the required form of resistance to operation of the handles (12).

It is also desirable to provide the exercise machine with electronic monitoring equipment to enable the user to determine his rate of work. Referring now to Figs. 10 and 11. the monitoring equipment comprises an electrical pressure transducer which is fitted to the cylinder (51) to monitor the oil pressure within the cylinder during operation. The oil pressure in the cylinder is directly proportional to the force applied to the handles (12) by the operator. The transducer is connected to the electronic circuitry by way of a flexible electrical cable (48). _m

This circuitry is housed in a case (41) with a magnetic back (42) allowing the monitor to be attached in any convenient position on any metallic part of the exercise machine.

The monitoring circuit performs two basic functions. In function one the force applied in any mode to the handles (12) by the operator will be displayed on a digital display (43). In function two the operator is provided with a digital readout of total energy usage. Initially the unit is reset to zero the display (44). During operation the circuitry automatically monitors and accumulates the operator's exertion level. At regular intervals an accumulated total exertion level is appended to the display (44).

Referring now to Fig. 10 the basic operation of the electronics is as follows. The pressure transducer converts oil pressure in the cylinder (51) to a voltage at point (45). Some impedance buffering and linear amplification is performed and the amplified voltage appears at point (46) where it is routed in two directions. The operation of the circuit will first be described in relation to function one defined above. The voltage at point (46) appears on the input of an analogue to digital converter (ADC) which gives a corresponding binary coded decimal (BCD) output. This BCD number then appears at the inputs of seven segment display decoders, the output being routed through a liquid crystal display (LCD) driver and then onto a three and a half digit LCD (43).

In function two, the circuitry operates as follows. The voltage at point (46) appears as the input of voltage to a frequency converter which gives a linearly related frequency output at point (47). Initially the reset button shown is pressed to zero the counters [and thus the exertion level display (44)]. It should also be noted that when there is no pressure in the cylinder (51), there is a zero frequency output at point (47). The frequency is accumulated by the BCD counters, the output being stored in the memories. Once every second the pulse generator sends a short pulse to the memories enable line causing the latest BCD number on the counters to be stored [and displayed] for the next second. The outputs of the memories pass through a BCD to seven segment display decoder and on through an LCD driver. The final result is displayed on a four and a half digit LCD (44).

In some situations the pressure from the cylinder (51) is fairly high and would require the use of an expensive pressure transducer to cope with this high pressure. It is therefore desirable that the pressure from the cylinder (51) can be proportionately reduced to enable the use of a cheaper pressure transducer. This pressure reduction is accomplished by the device shown in Fig. 12. The pressure divider device comprises a main body (73) in which is located a floating piston (74) having a larger end (75) moving in a cylinder (76) and a smaller end (77) moving in a cylinder of smaller diameter (78). O-ring seals (79) and (80) are provided to seal the piston within the respective cylinders. The cylinder (76) is closed at one end by an adaptor (80) secured in the main body by way of a circlip (81).

In use the pressure from the linear motion resistance cell is applied to the cylinder (78) and hence to the smaller end (77) of the piston (74). This pressure is transmitted through the piston to a further hydraulic fluid in the chamber (82) created within the cylinder (76) where, due to the larger surface area of the piston at (75) the pressure is proportionately reduced compared with the pressure in the cylinder (78). The outlet (83) from the chamber (82) may then be connected to the pressure transducer which can be calibrated to account for the known drop in pressure across the unit shown in Fig. 12.

In this manner an exercise machine is provided which enables the user to perform a large number of different exercises. The exercises are performed by operating the handles (12) by either the hands or feet of the operator, either when seated on the seat (3) or when standing on the platform (2). The orientation of the handles may be adjusted as required and the position of the seat may also be adjusted as necessary. The main feature of the exercise machine however is the nature of the linear motion resistance cell, which can be simply and quickly adjusted by the operator to provide the required degree of resistance i any one of the three selected modes of operation.

It will be appreciated however that the linear motion resistance cell, although particularly suitable for use in an exercise machine, can also be used in any other type of machine where it is required to provide controlled resistance to movement in different modes as may be selected by the operator.

Claims

1. A linear motion resistance cell comprising a cylinder, a piston operable by an actuation rod for linear movement within the cylinder, sealing means at both ends of the cylinder defining two chambers within the cylinder, one on either side of the piston, one or more passages from one said chamber to the other said chamber, a working fluid within the chambers arranged to be forced from one said chamber to the other through the passages by movement of the piston within the cylinder, and valve means in association with the passages arranged to control the flow of fluid therethrough, the valve means being operable by control means so as to provide predetermined resistances to the movement of the piston within the cylinder selectable between at least two of the following three operating modes: (i) controlled resistance to movement in both directions

(ii) controlled resistance to movement in one predetermined direction only with relatively low resistance to movement in the other direction, (iii) controlled resistance to movement in the opposite predetermined direction to (ii) with relatively low resistance to movement in the other direction.

2. A linear motion resistance cell as claimed in claim 1 wherein two said passages are provided, said valve means including a non-return valve incorporated in at least one of said passages.

3. A linear motion resistance cell as claimed in claim 1 wherein the valve means and the control means are arranged to allow selection of any one of the three said operating modes.

4. A linear motion resistance cell as claimed in claim 3 wherein three said passages are provided, said valve means including two non-return valves incorporated one in each of two of said passages, and orientated such that one said non-return valve closes during movement of the piston in one direction, and the other non-return valve closes during movement of the piston in the opposite direction.

5. A linear motion resistance cell as claimed in either claim 2 or claim 4 wherein said passages all terminate at one end at a surface and wherein said valve means include a cover plate engaging the surface and being provided with openings therein, said control means being arranged to move the cover plate over the surface causing the openings to come into and out of register with the passages in a predetermined manner, opening and closing the passages to provide the selected operating mode.

6. A linear motion resistance cell as claimed in claim 5 wherein at least one of the openings within the cover plate is arranged to progressively open and close the passage in register therewith, allowing the said controlled resistance to movement to be varied by operation of the control means.

7. A linear motion resistance cell as claimed in either claim 5 or claim 6 wherein the passages are axially aligned in a disk transversely orientated across the cylinder, and wherein the cover plate comprises a circular plate, coaxial with and rotatable on the surface of the disk by the control means.

8. A linear motion resistance cell as claimed in claim 7 when dependent upon claim 4 wherein the two said passages incorporating non-return valves are diametrically opposed in the disk and the third said passage is located on a diameter angularly spaced from the diameter on which the first two passages are located, all three passages being equispaced from the centre of the disk, and wherein the cover plate incorporates a first opening arranged to allow unrestricted opening of a passage in register therewith over a. predetermined arc of rotation of the cover plate relative to the disk* and a second opening, diametrically opposed to the first opening, arranged to progressively close the passage in register therewith over said predetermined arc of rotation.

9. A linear motion resistance cell as claimed in either claim 7 or claim 8 wherein the disk is attached to or integral with the piston so that the passages extend through the piston between the two chambers, and wherein the cover plate is rotatable by a shaft coaxial with the said actuation rod.

10. A linear motion resistance cell as claimed in either claim 7 or claim 8 wherein the disk is fixed to the cylinder wall adjacent one end of the cylinder forming a compartment at that end. and wherein a fluid conduit is provided between the compartment and the opposite end of the cylinder.

11. A linear motion resistance cell as claimed in claim 10 wherein the said fluid conduit comprises an outer sleeve, spaced from and coaxial with the cylinder and sealed thereto at either end. and openings through the cylinder wall into the interior of the sleeve, located in the compartment and toward the opposite end of the cylinder.

12. An exercise machine incorporating a linear motion resistance cell as claimed in any one of the preceding. claims.

13. An exercise machine as claimed in claim 12 when provided with operating handles attachable to a shaft so as to rotate the shaft upon force being applied to the handles, the shaft being provided with a crank arranged to move the actuation rod of the linear motion resistance cell upon rotation of the shaft.

14. An exercise machine as claimed in claim 13 wherein the linear motion resistance cell is mounted on a post such that the handles extend on either side of the post and wherein a seat is provided in front of the post and a standing platform behind the post.

15. An exercise machine as claimed in claim 14 wherein the shaft is provided with downwardly facing gear means and wherein a mounting bracket is provided on the post providing upwardly extending pivots adapted to rotatably support the handles which are provided with upwardly extending gear means arranged to engage and mesh with the downwardly extending gear means on the shaft when the linear motion resistance cell is lowered on the post to a position above the mounting bracket, so that synchronised contra-rotating movement of the handles on the pivots causes the gear means to rotate, causing rotation of the shaft.

16. An exercise machine as claimed in any one of claims 12 to 15 wherein electronic monitoring means are provided, actuable by a transducer measuring fluid pressure within the linear motion resistance cell to give a display of the effort applied to the handles.

17. An exercise machine as claimed in claim 16 wherein the transducer is used in conjunction with a pressure reducing device comprising a piston floating within the housing, the piston having a larger surface area at one end than the other, and wherein fluid pressure from the linear motion resistance cell is applied to the smaller end of the piston, and a correspondingly reduced pressure applied by the larger end of the piston to a second fluid in communication with the transducer.