U.S. patent application number 10/611870 was filed with the patent office on 2004-07-15 for resistance assembly.
Invention is credited to Puzey, Michael Roydon, Van Straaten, Willem Johannes.
Application Number | 20040138032 10/611870 |
Document ID | / |
Family ID | 30444592 |
Filed Date | 2004-07-15 |
United States Patent
Application |
20040138032 |
Kind Code |
A1 |
Van Straaten, Willem Johannes ;
et al. |
July 15, 2004 |
Resistance assembly
Abstract
A resistance assembly for use in an exercise machine which
includes a cylinder and a piston with a hollow piston rod which is
slidably engaged with the cylinder. The interiors of the cylinder
and the piston rod are pressurised using a compressor to provide a
controllable resistance force against which a user can
exercise.
Inventors: |
Van Straaten, Willem Johannes;
(Sandton, ZA) ; Puzey, Michael Roydon; (Sandton,
ZA) |
Correspondence
Address: |
YOUNG & THOMPSON
745 SOUTH 23RD STREET 2ND FLOOR
ARLINGTON
VA
22202
|
Family ID: |
30444592 |
Appl. No.: |
10/611870 |
Filed: |
July 3, 2003 |
Current U.S.
Class: |
482/112 |
Current CPC
Class: |
A63B 21/00069 20130101;
A63B 21/0557 20130101; A63B 21/0428 20130101; A63B 21/4043
20151001; A63B 2208/0233 20130101; A63B 21/04 20130101; A63B 21/156
20130101; A63B 2208/0228 20130101; A63B 21/0087 20130101; A63B
21/00065 20130101; A63B 21/0552 20130101; A63B 21/154 20130101;
A63B 2210/50 20130101 |
Class at
Publication: |
482/112 |
International
Class: |
A63B 021/008 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 15, 2003 |
ZA |
2003/0392 |
Claims
1. A resistance assembly for use in an exercise machine which
includes an elongate first cylinder with a first cross sectional
area, an interior of the first cylinder, in use, being pressurised
with a gas, an elongate member with a first end and a second end,
the elongate member extending partly into the interior of the first
cylinder with the first end inside the first cylinder and the
second end outside the first cylinder, the elongate member being
mounted for reciprocating movement, in its longitudinal direction,
relatively to the first cylinder, the elongate member upon being
moved by a distance l into the interior of the first cylinder
displacing a volume of gas which is given by the expression
l.times.a where a is a second cross sectional area which is smaller
than the first cross sectional area, and a formation at a location
selected from a position on the elongate member which is outside
the first cylinder and a position on the first cylinder for
connection to an actuator whereby a user can cause movement of the
elongate member relatively to the first cylinder.
2. A resistance assembly according to claim 1 which includes
apparatus for pressurizing the interior of the first cylinder with
a gas.
3. A resistance assembly according to claim 1 wherein the elongate
member is tubular with a hollow interior and the first end is open
and in communication with the interior of the first cylinder, and
the second end is sealed.
4. A resistance assembly according to claim 3 wherein the cross
sectional area of the hollow interior is equal to the second cross
sectional area.
5. A resistance assembly according to claim 1 wherein the elongate
member has a cross sectional area which is equal to the second
cross sectional area.
6. A resistance assembly according to claim 5 wherein the elongate
member is solid.
7. A resistance assembly according to claim 1 which includes a
piston head, with inner and outer sides, which is fixed to the
first end of the elongate member and which is engageable with an
internal surface of the first cylinder and which acts to guide the
reciprocating movement of the elongate element and wherein, within
the interior of the first cylinder, the pressure of the gas on the
inner side of the piston head is the same as the pressure of the
gas on the outer side of the piston head.
8. A resistance assembly according to claim 7 wherein the piston
head includes at least one formation which allows for free movement
of gas, inside the interior of the first cylinder, between the
inner side of the piston head and the outer side of the piston
head.
9. A resistance assembly according to claim 8 wherein the at least
one formation is a passage in the piston head between the inner
side and the outer side thereof.
10. A resistance assembly according to claim 1 which includes a
second cylinder which is located at least partly within the first
cylinder and which includes an inner end through which at least
part of an interior of the second cylinder is placed in gas
communication with the interior of the first cylinder and an outer
end, the elongate member extending partly into the second cylinder
with the first end of the elongate member inside the second
cylinder and the second end of the elongate member extending from
the outer end of the second cylinder, the reciprocating movement of
the elongate member taking place inside the second cylinder, and a
piston head at the first end of the elongate member which is in
sealing and reciprocating contact with an opposed inner surface of
the second cylinder.
11. A resistance assembly according to claim 1 wherein the size of
the first cross sectional area is at least six times the size of
the second cross sectional area.
Description
BACKGROUND OF THE INVENTION
[0001] This invention relates to a resistance assembly for use in
an exercise machine.
[0002] Exercise machines make use of diverse devices such as free
weights, weight plates, elastic bands, springs and the like to
provide a resistance force against which a user can exercise. It
has been found that, in many of these machines, the stroke length,
which is the distance against which a user moves his arms or legs,
as the case may be, against a resistive force, must be reasonably
long and this, in turn, means that an exercise machine must also be
of substantial dimensions.
[0003] It is preferable to have a substantially constant resistance
force, against which a user exercises, over the stroke length. If
use is made of a spring or similar component, to provide the
resistance force then, as is known, the spring characteristic is
such that the resistance force increases more or less linearly with
spring deformation. In other words the more the resistance device
is moved the greater is the resistance force which acts against
movement from the user. This is not necessarily a desirable
characteristic.
[0004] If one or more weights are used to provide the resistance
force then a substantially constant resistance force is obtained
over the stroke length. When a user who is physically strong makes
use of the exercise machine then the number of weights which must
be provided is substantial and this carries with it a penalty in
that the exercise machine is then not necessarily easily
transportable and, inevitably, the exercise machine is cumbersome
and expensive to ship to a customer.
[0005] Another factor is that the positive resistance force, which
is the resistance force displayed by the resistance device when
energy is put into an exercise machine by a user, should, as far as
is possible, be the same as the negative resistance force which
results when energy which is stored in the exercise machine is
released, on a return stroke. These forces can only be matched to
one another, at least to some extent, if frictional and similar
losses are minimised.
[0006] It should be possible, particularly for a device which is
intended for a home user, to be able to adjust the resistance
force, exhibited by an exercise machine, with relative ease. The
exercise machine should, as noted, be compact and light so that it
is suited for easy storage and transport. It is also desirable to
be able to use the machine in one of at least two modes eg. by
working against a resistance force by pulling downwardly on an
actuator which may be of any suitable form eg. a handle, a bar, an
ankle or wrist cuff, or the like, or by working against a
resistance force by pulling upwardly on an actuator. These modes
are given merely by way of example for the exercise machine could
be constructed to provide the resistance force against other types
of movement eg. a pushing or a rotating movement by the user.
SUMMARY OF INVENTION
[0007] The invention provides a resistance assembly for use in an
exercise machine which includes an elongate first cylinder with a
first cross sectional area, an interior of the first cylinder, in
use, being pressurised with a gas, an elongate member with a first
end and a second end, the elongate member extending partly into the
interior of the first cylinder with the first end inside the first
cylinder and the second end outside the first cylinder, the
elongate member being mounted for reciprocating movement, in its
longitudinal direction, relatively to the first cylinder, the
elongate member upon being moved by a distance t into the interior
of the first cylinder displacing a volume of gas which is given by
the expression l.times.a where a is a second cross sectional area
which is smaller than the first cross sectional area, and a
formation at a location selected from a position on the elongate
member which is outside the first cylinder and a position on the
first cylinder for connection to an actuator whereby a user can
cause movement of the elongate member relatively to the first
cylinder.
[0008] The resistance assembly may include apparatus for
pressurizing the interior of the first cylinder with a gas.
[0009] In one embodiment the elongate member is tubular with a
hollow interior and the first end is open and in communication with
the interior of the first cylinder, and the second end is
sealed.
[0010] Preferably the cross sectional area of the hollow interior
is equal to the second cross sectional area.
[0011] In a second form of the invention the elongate member has a
cross sectional area which is equal to the second cross sectional
area.
[0012] In this form of the invention the elongate member may be
solid or, if tubular, its inner end is sealed.
[0013] The assembly may include a piston head, with inner and outer
sides, which is fixed to the first end of the elongate member and
which is engageable with an internal surface of the first cylinder
and which acts to guide the reciprocating movement of the elongate
element and wherein, within the interior of the first cylinder, the
pressure of the gas on the inner side of the piston head is the
same as the pressure of the gas on the outer side of the piston
head.
[0014] The piston head may include at least one formation which
allows for free movement of gas, inside the interior of the first
cylinder, between the inner side of the piston head and the outer
side of the piston head.
[0015] The at least one formation may be a passage in the piston
head between the inner side and the outer side thereof.
[0016] In another form of the invention the resistance assembly
includes a second cylinder which is located at least partly within
the first cylinder and which includes an inner end through which at
least part of an interior of the second cylinder is placed in gas
communication with the interior of the first cylinder and an outer
end, the elongate member extending partly into the second cylinder
with the first end of the elongate member inside the second
cylinder and the second end of the elongate member extending from
the outer end of the second cylinder, the reciprocating movement of
the elongate member taking place inside the second cylinder, and a
piston head at the first end of the elongate member which is in
sealing and reciprocating contact with an opposed inner surface of
the second cylinder.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] The invention is further described by way of examples with
reference to the accompanying drawings in which:
[0018] FIG. 1 is a side view of an exercise machine which includes
a resistance assembly according to the invention, in a ready-to-use
state;
[0019] FIG. 2 is a perspective view from the front of the machine
with certain components removed to simplify the illustration;
[0020] FIG. 3 illustrates moving components of the exercise machine
of FIG. 1;
[0021] FIG. 4 illustrate a different type of resistance assembly to
what is employed in the machine of FIGS. 1 to 3;
[0022] FIG. 5 shows another type of resistance assembly, according
to the invention, and
[0023] FIG. 6 schematically depicts a prior art type of resistance
assembly.
DESCRIPTION OF PREFERRED EMBODIMENTS
[0024] FIGS. 1 to 3 of the accompanying drawings illustrate an
exercise machine 10 which uses a resistance assembly according to a
first form of the invention.
[0025] The exercise machine includes a frame 12 to which is
attached a seat 16 on which a user can be seated, and a backrest 18
for the back of a user positioned on the seat. For storage and
transport purposes the seat 16, which is normally braced by one or
more stays 20, can be folded downwardly so that it is substantially
parallel to the frame while, in a similar fashion, the backrest 18
which is braced by one or more stays 22 can be pivoted towards the
frame to take up a compact position. A structure 24 can be used at
an upper end of the frame as a holder for a card which carries
information on exercise sequences particularly if the backrest is
moved to a compact storage position adjacent the frame.
[0026] The frame is supported at an inclined position relatively to
the ground 26 by a downwardly depending U-member 28 which is
attached at a pivot point 30 to brackets 32 on a rear side of the
frame 12. The U-member 28 can be moved inwardly towards the frame
12 for storage and transport purposes or, as is shown in FIG. 1,
can be moved away from the frame to provide a maximum degree of
stable support for the frame.
[0027] The exercise machine includes a footpiece 36 at a foot of
the frame. The footpiece forms a housing in which are located an
electric motor 38 and an air pump or compressor 40 which is driven
by the motor and which delivers air via a flexible pipe 42 to a
cylinder 44 which is supported by the frame 12.
[0028] An upper surface 46 of the footpiece housing is serrated or
roughened and provides a reactive surface against which feet of a
user, positioned on the seat, react.
[0029] A flexible electric cord 50 extends from the motor to a main
electrical supply point, not shown. A switch 52 on the footpiece 36
can be actuated by a foot of a user to connect the motor 38 to the
main supply or turn the electrical supply off. In this way the
operation of the motor 38 can be controlled. A pressure relief
valve 60 is connected to the cylinder 44 via a flexible line 62.
The pressure relief valve can also be operated by means of a foot
of a user. Thus it is possible for the user to turn the compressor
on and thereby pressurise the cylinder 44; turn the compressor off;
or reduce the pressure inside the cylinder by actuating the valve
60.
[0030] The cylinder 44 is connected to a piston 70 to make up a
resistance assembly 72, according to a first form of the invention,
which provides a resistance force for a user. The manner in which
this is achieved is described hereinafter. The cylinder 44 has a
lower end 74 which is sealed and which is mounted to a lower
wheeled carriage 76. The piston 70 has a piston head 78 which is
mounted for reciprocating movement inside the cylinder and a piston
rod 80 which extends from the head. An upper end of the rod is
mounted to an upper wheeled carriage 82.
[0031] A first pulley and cable system 84 is mounted to act on the
lower carriage 76 while a second pulley and cable system 86 is
mounted to act on the upper carriage 82. The system 84 includes a
pair of handles 88A and 88B which are connected to each other by
means of a cable 90 which passes over a succession of pulleys 92A
to 92E respectively. The pulley 92C is connected to the carriage 76
by means of a cable 98 which passes over pulleys 100A and 100B on
the carriage. An end of the cable 98 is attached to an anchor point
102 on the frame 12.
[0032] The system 86 has handles 108A and 108B respectively at a
lower side of the frame which are connected to a cable 110 which
passes over pulleys 112A to 112E respectively. The pulley 112C is
connected to the carriage 82 by means of a cable 114 which passes
over pulleys 116A and 116B which are mounted to the carriage. An
end of the cable is tied to an anchor point 118 on the frame.
[0033] It is evident from FIG. 2 that the piston head 78 acts only
in a guiding capacity within the cylinder. The piston head is
formed with a plurality of formations in the form of notches or
cut-outs 120 which define passages through the piston head and
consequently the pressure inside the cylinder on one side of the
piston head is the same as the pressure on an opposing side of the
head.
[0034] The piston rod 80 is tubular with a hollow interior 122. A
plug 124 seals an upper end of the rod 80. A lower end of the rod,
which is connected to the piston head 78, is open and forms a mouth
126 which places the interior of the cylinder 44 in communication
with the hollow interior of the rod.
[0035] When the exercise machine is to be used the frame 12 is
positioned so that it has the orientation shown in FIG. 1. A user
could be seated, kneeling or standing while exercising. Assume the
user positions himself on the seat 16 with his back against the
backrest 18. The user activates the switch 52 with one of his feet
and the motor 38 is energised and then drives the compressor 40.
Once the interior of the cylinder 44 has been pressurised to a
desired air pressure the motor is turned off. If the pressure
inside the cylinder is too high the pressure relief valve 60 is
actuated to allow air to escape from the cylinder. It is therefore
relatively easy for a user to adjust or control the pressure inside
the cylinder using the foot-operated controls 52 and 60.
[0036] Assume that the user grips the upper handles 88A and 88B and
pulls downwardly on the handles as is indicated by arrows 130 in
FIG. 3. Due to the pulley and cable system 84 the lower carriage 76
is elevated and the cylinder rises with the piston moving with a
telescoping action into the cylinder. A resistance force is
generated which tends to act against the aforementioned movement as
the rod 80 is forced into the cylinder. The effective volume which
is occupied by the pressurized air inside the cylinder and the
hollow piston rod 80 is reduced depending on the extent to which
the rod extends into the cylinder 44.
[0037] If the pressure inside the cylinder 44 is relatively high
then a significant force is needed to move the rod 80 into the
cylinder. However as the volume of the interior of the rod 80 is
comparatively small compared to the volume of the cylinder 44, the
force which is needed to move the rod into the cylinder increases
only slightly as the rod extends to a greater extent into the
cylinder. In other words over the stroke length represented by the
downward movement of the handles 88A and 88B, the resistance force
displayed by the piston and cylinder assembly 72 increases only
slightly.
[0038] Due to the mechanical advantage of the system 84 the stroke
length of the handles 88A and 88B is four times the stroke length
of the piston into the cylinder. Thus the piston and cylinder
assembly can be relatively compact compared to the stroke length of
the exercise machine. This carries a further benefit in that the
change in pressure, inside the cylinder, as the assembly is
telescoped is restricted because the extent of movement of the
piston relatively to the cylinder is limited.
[0039] During the aforementioned telescoping movement of the
assembly 72 the upper end of the piston rod is supported by the
carriage 82 which in turn is supported by a bracing member or
formation 140 on the frame 12. On the other hand when the handles
108A and 108B are gripped and pulled upwardly, in the direction of
arrows 142, the upper carriage 82 moves downwardly and the lower
end 74 of the cylinder 44, which is mounted to the lower carriage
76, is prevented from moving by a support or bracing member 146 of
the frame.
[0040] The handles 108A and 108B exhibit the same relatively long
stroke length, compared to the stroke length of the piston into the
cylinder, as the handles 88A and 88B.
[0041] The exercise machine 10 has a number of significant
benefits. Firstly, it is possible for a user to adjust the pressure
inside the cylinder 44 and this in turn means that the user can
adjust the resistance force according to his physical condition
even while exercising. The adjustment is done without the user
needing to disengage his hands from the handles 88 or 108, as the
case may be. Secondly, as noted, the stroke length which results
when the handles 88 or 108 are used is four times the stroke length
of the piston into the cylinder. This allows for a compact
construction of the exercise machine.
[0042] Thirdly, the number of pulleys in each of the systems 84 and
86 is relatively low and this means that frictional losses are kept
to a minimum. Consequently the positive resistance force displayed
by the piston and cylinder assembly 72 (ie. the force which results
when the handles 88 are moved in the direction of the arrows 130 or
when the handles 108 are moved in the direction of the arrows 142)
is only slightly greater than the negative resistance force which
is the force produced when the air inside the cylinder 44 expands
to restore the piston and cylinder assembly to its extended
position.
[0043] A further benefit, already alluded to, is that the force
which is needed to drive the piston rod deeper into the cylinder
increases only slightly as the rod extends into the cylinder. This
force is a function of the pressure inside the cylinder and if the
pressure is sufficiently high the relative increase in the force,
as the piston moves into the cylinder, is comparatively low. The
extent to which the force increases is a function of the relative
volumes of the cylinder 44 and of the interior of the hollow rod
80.
[0044] The exercise machine is lightweight. The resistance force
results from the use of a cylinder and piston assembly which is
pressurised with air by a user to a chosen, controlled level which
is readily adjustable. The need for heavy weights is therefore
eliminated. The exercise machine can be folded compactly into a
fairly flat arrangement which can, for example, be stored under a
bed or behind a door when not required. In this respect it should
be observed that the compressor and motor are mounted in the
housing 36 and are therefore integrally associated with the
exercise machine. As is indicated by a curved arrow 158 in FIG. 1
the housing can be folded upwardly to a compact storage position,
adjacent the frame, when required. The exercise machine is thus a
fully self-contained unit and only requires connection to an
electrical supply to become operational. The same principles could
however be employed to provide an exercise machine, which may be
one of a plurality of similar machines, which is pressurized from a
remotely installed compressor. The pressure in each machine could
then be controlled as required by each respective user.
[0045] In each case the controls could be foot-operated. However
hand-operated, remotely activated, and voice actuated controls
could also be used to regulate the pressure in the cylinder.
[0046] FIG. 4 illustrates a resistance assembly 160, according to a
second form of the invention, which can be used in place of the
resistance assembly 72 shown in FIGS. 2 and 3. The resistance
assembly 160 has a number of similarities to the assembly 72 and
consequently, where appropriate, like reference numerals are used
to designate like components. The assembly 160 is not shown
installed in an exercise machine. It can be used in the same way as
the assembly 72, as shown in FIGS. 1 to 3, or in any other exercise
machine of appropriate design. A similar comment applies to the
assembly 72.
[0047] The principal difference between the assembly 72 and the
assembly 160 is that the piston rod, designated 80A in the assembly
160, is solid. Alternatively, if the rod is hollow, the lower end
of the rod, designated 126A, is sealed by means of a plate or plug
so that it is airtight.
[0048] The interior of the cylinder 44 is, as before, pressurized
by means of a compressor or a gas cylinder.
[0049] The piston head 78 also has notches or cut-outs 120 which
ensure that the pressure inside the cylinder on an upper side of
the piston head is the same as the pressure on a lower side of the
piston head.
[0050] When the piston rod is caused to move relatively to the
cylinder (with the cylinder stationary) or if the cylinder is
caused to reciprocate relatively to the piston rod (with the piston
rod stationary) the air inside the cylinder is further pressurized
as the rod 80A extends to a greater extent into the cylinder while
the pressure is slightly reduced as the rod is retracted from the
cylinder. The operation is substantially the same as for the
resistance assembly 72 except that for the assembly 72 the maximum
volume occupied by the pressurized air is equal to the sum of the
volume of the cylinder and of the volume of the interior of the
hollow piston rod while the minimum volume is equal to the volume
of the cylinder minus the volume of the wall of the piston rod.
With the assembly 160 the maximum volume occupied by the
pressurized air is slightly less than for the assembly 72 and is
equal to the volume of the cylinder. The minimum volume is also
slightly decreased in that it is equal to the volume of the
cylinder minus the volume of the solid or sealed piston rod. In
substance however the resistance assembly 160 offers the same
benefits as the resistance assembly 72.
[0051] FIG. 5 illustrates a third resistance assembly 166 which is
also equivalent to the assembly 72. The assembly 166 includes a
first or outer cylinder 168 and a second cylinder 170 which is
positioned inside the cylinder 168. A lower end 172 of the cylinder
170 is open and is supported by a plate 174 in which is formed a
plurality of holes 176. An upper end of the cylinder 170 is
supported by a plate 180 which is sealingly engaged with the
cylinders 168 and 170 and which includes a hole or plug 182 through
which a piston rod 184 extends. A leading end 186 of the piston rod
carries a piston head 188 which is slidingly and sealingly engaged
with an inner surface 190 of the second cylinder 170. An outer or
upper end 192 of the rod 184 is engaged with carriage structure 82
on an exercise machine (not shown). Similarly a lower end of the
cylinder 168 is attached to carriage structure 76 of the exercise
machine. The resistance assembly 166 can for example be used in a
manner similar to that shown in FIG. 2 although this is by no means
limiting for the resistance assembly can be used in an exercise
machine of any appropriate design.
[0052] The cylinder 168 and the cylinder 170 are simultaneously
pressurized with pressurized air from a suitable compressor or gas
cylinder, not shown.
[0053] The piston head 188 performs the same function as the hollow
rod 80 in FIG. 2 or the solid rod 80A in FIG. 4 for as the piston
head 188 advances into the cylinder 170 the air in both cylinders
is pressurized depending on the total volume of air which is
displaced by the advancing piston head.
[0054] The situation which arises when the resistance assembly of
the invention is used should be contrasted with the prior art
situation shown schematically in FIG. 6 which illustrates a
reservoir or accumulator 200 which is pressurized with air from an
air source 202 eg. a compressor. A separate resistance cylinder 204
of relatively small construction is connected to the reservoir via
a pipe 205. The cylinder 204 includes a piston rod 206 with a
piston head 208 which is mounted for reciprocating and sealing
movement inside the cylinder 204. As is evident from prior art
documents exercise machines which make use of the prior art
arrangement shown in FIG. 6 are bulky for they require at least two
separate cylinders. If the prior art arrangement is employed in an
exercise machine then it is difficult to provide a compact exercise
machine which, in an inoperative storage mode, is adapted for easy
transport or storage. This specific objective is met by an exercise
machine which makes use of a resistance assembly according to the
invention.
[0055] With the resistance assemblies 72 and 160 the effective
cross sectional area of the piston rod determines the volume of air
which is displaced when the piston rod is moved into the cylinder.
Referring to FIG. 2 assume that the piston rod has a cross
sectional area a in its hollow interior and that the cylinder 44
has a cross sectional area A. When the rod is moved into the
cylinder by a distance l the volume of air which is displaced is
given by the expression l.times.a. As the cross sectional area a is
substantial less than the cross sectional area A of the cylinder 44
the change in pressure inside the cylinder is relatively small and
to a substantial extent the piston moves against a force which does
not increase significantly with piston rod movement.
[0056] In the FIG. 4 embodiment the cross sectional area of the
solid piston rod 80A is a and when the piston rod is advanced into
the cylinder 44 by a distance l the volume of air displaced is
a.times.l which, again, is substantially less than what would be
case if the piston head 78 were large and were sealingly engaged
with the cylinder 44.
[0057] In the FIG. 5 embodiment the cross sectional area of the
piston 188 is a and, when the piston is advanced by a distance l
into the cylinder 170, the volume of air displaced is given by the
expression a.times.l.
[0058] In all three embodiments if a is substantially less than the
cross sectional area A of the cylinder 44 or the effective cross
sectional area of the cylinder 168, as the case may be, then there
is only a marginal increase in the resistance force as the piston
is moved from a position at which it is fully retracted from the
cylinder to a position at which it is fully inserted into the
cylinder. Although it is possible with the prior art arrangement
shown in FIG. 6 to achieve a similar relatively small variation in
air pressure this is at the expense of at least one additional
space consuming component.
[0059] The ratio of A to a should be at least 6 but preferably is
higher. In this respect a compromise must be struck between the
resistance force which is generated (this is a function of the
product of a and the air pressure force during a piston stroke.
* * * * *