referring now to fig1 a , a typical exercise machine 10 includes a pair of rotary arm steps 12 which are articulated or pivoted at points 13 so as to simulate stair climbing by virtue of the movement of the arms 25 and 26 about the pivots . the exercising individual stands at the distal end of the arms and is permitted stair climbing exercise due to the action of the arms under the control of a hydraulic phasing system 14 comprising cylinders 55 which will be described hereinafter . the exercise machine in general is provided with hand rails 17 and a display 18 to provide the user of the equipment with an indication of the amount of exercise accomplished . the phasing of the arms of the stairs refers to the control of the position of the arms during exercise such that when one stair or exercise arm is down , the other is in an up position and vice versa . the user of the equipment therefore is provided with exercise in a body lift mode in which the user steps from the lower arm to the upper arm thereby raising his body weight . as will be described , in the past it has been possible to phase the exercise stairs through the utilization of ram cylinders . one of the problems with ram cylinder systems is that there is no convenient way to regulate step height . another of the problems with the ram cylinders is the fact that when the fluid in the system expands , there is a stroke increase due to temperature . &# 34 ; stroke &# 34 ; refers to cylinder excursion . &# 34 ; step height &# 34 ; refers to step excursion . they are proportional but not equal . thus stroke is related to the distance between the lower stair and the upper stair which is the amount of distance that the person raises his or her body during the exercise process . referring now to fig1 b , the ram cylinder hydraulic system of fig1 a is shown having two hydraulic cylinders 5 and 6 which have rods 11 . it is this system which suffers from a lack of ready step height adjustment , is affected by thermal expansion of the fluid in the system , and has no compensation for fluid loss due to carry out . as illustrated , a throttling valve 15 is connected between the cylinders by hose 20 . steps 25 and 26 are connected to the rods directly or through linkages ( not shown ). the position of the bottom most portion of the step excursion 40 and deepest penetration of the rods into the cylinders , is set by stops 30 , 31 , 32 and 33 . the highest most position 50 of the step excursion is set by the length of the rod and the amount of fluid 55 in the system . l s , or the stroke , is the difference between positions 40 and 50 . it can be seen that if the amount of fluid in the system is reduced , the &# 34 ; up &# 34 ; rod 11 will descend further into its cylinder and the stroke height l s will be reduced . it can be further seen that if the fluid expands as a result of heat , the larger volume of fluid will force rod 11 further out , increasing the stroke height an amount which equals the volume of fluid expansion in cubic inches divided by the cross - section area of the rod in square inches . the determination of the amount of stroke or step height loss due to fluid carried - out past the rod seals 65 and 66 is identical to the thermal expansion calculation . it will be readily apparent that the system described in fig1 b has a fixed initial step height that is established by the geometry of the cylinder and the amount of fluid put into the system . it is also readily apparent that the step height will change due to fluid expansion or fluid loss . practical hydraulic fluids expand about 3 % when raised from ambient to typical operating temperatures . a given percentage increase of fluid volume due to temperature increase will result in a much larger percentage change in step height . here the t stroke height increase is shown by the dotted outline 26 &# 39 ; and stroke increase 60 . for instance , in a ram cylinder system , a 1 / 2 inch diameter cylinder and 7 / 16 inch diameter rod will have a percentage step height increase approximately 5 times the percentage increase resulting from thermal expansion . for such a system , 15 % expansion of step height is common and unwanted . fluid loss due to carry out is proportional to the diameter of the rod . the impact of the loss on step height is proportional to the square of the rod diameter . in the typical fourteen inch step height system with cylinders as previously described , 1 cubic inch of fluid loss , or 7 % of the total , results in a decrease of step height of nine inches , or 64 %, which would render the machine essentially useless . fig2 shows the subject invention having two operating ram cylinders 105 and 106 , plus a third cylinder 107 . each ram cylinder has a ram , respectively shown at 108 , 109 , and 110 . means 112 including a lever 113 rotated about pivot 114 to a coupling 115 at the back end of ram 110 , via a lost motion linkage 116 is used to control the amount of hydraulic fluid in the system . movement of lever 113 in the directions shown by double - ended arrow 120 increases or decreases step height . thus , movement of the lever moves ram 110 in and out to selectively add fluid to the two operating cylinders from reserve v r , or to remove fluid from the operating cylinders into volume v s created by withdrawing ram 110 . the hydraulic system shown has more cubic inches of fluid than that of the conventional two cylinder system shown in fig1 b . as a result , the apparent response to thermal expansion is greater than that of the prior art system shown in fig1 b in proportion to the ratio of fluid in v r to the fluid in the operating cylinders . however , as can be seen from fig2 an increase in cylinder diameter allows a more favorable rod diameter to cylinder diameter , which approaches 1 : 1 . a 2 inch diameter cylinder , a 1 5 / 8 inch diameter rod , and a fluid reserve equal to 20 % of the operating system , results in a step height expansion of only 1 . 5 times the percentage of fluid expansion . moreover , as to carry out , with the increased diameter shown , the loss of step height for a lost cubic inch is much reduced compared to the loss of step height for the same lost cubic inch when applied to a rod of smaller diameter . fig3 shows a ram cylinder absorption system in a low profile rotary arm exercise machine 125 designed to store under a bed . here the rotary arms are shown at 126 and 127 , with the step phasing being controlled by respective ram cylinders , one of which is shown at 127 . an appropriate linkage system 128 positions the respective arms . the arms rotate up and down , with the distal ends 129 and 130 of arms 126 and 127 providing the steps for the user . the preferred maximum step height 140 in exercise machines is 14 inches . because depression of the rotating arm more than 6 ° below the horizontal raises the user &# 39 ; s forefoot uncomfortably higher than the heel , most of the step height is generated by rotation above the horizontal . as a result , the lowest profile that can be obtained occurs when the two steps are parallel at the mid - point 150 . consequently , it is geometrically impossible to clear the typical 8 inch frame bed structure unless the step height can be mechanically adjusted , or unless enough fluid is removed to drop the steps . in operation and referring back to fig2 the initial rate at which exercise intensity is performed is controlled by a valve 15 which provides a restriction in the hydraulic line 16 between cylinders 105 and 106 . in this hydraulic ram embodiment , the step height adjustment , here illustrated by dotted outline 118 and double ended arrows 119 , is accomplished by moving ram 110 to the left , at which time additional fluid is added to the system which raises top portion 120 of ram 109 with respect to top portion 121 of ram 105 . thus a difference in step height can be added merely by moving a lever 113 to add fluid to the system . likewise the step height can be reduced by withdrawing ram 110 . it will also be appreciated that the movement of ram 110 in the auxiliary cylinder may be used to add fluid to the system such that carry out is no longer a problem due to the utilization of the auxiliary cylinder . when this system is utilized in the rotary arm exercise apparatus of fig3 withdrawing ram 110 in the auxiliary cylinder of fig2 results in an almost complete removal of the fluid in the operating cylinders . this results in the ability to drop both of the rotary arms 126 and 127 into the base 132 of the rotary arm device such that the device can be wheeled by wheels 134 underneath a bed . it will also be appreciated that the ability to remove fluid from the system so as to collapse the exercise device down onto the base permits storage in tight areas such as small closets . referring now to fig4 while the subject invention has been described in connection with ram cylinder type systems , in this embodiment , piston cylinders are utilized in which single acting piston cylinders 160 and 162 are utilized . within each of the cylinders is a piston 164 and 166 which is sealed to the cylinder walls via appropriate seals 168 and 170 . this provides that the hydraulic working fluid 172 is always beneath the respective piston . it will also be appreciated that the cylinders are provided with ports 174 and 176 respectively so as to be able to vent the top portions of the pistons to atmosphere . note that the single acting pistons are provided with a fluid linkage connection as illustrated at 178 , with a control valve 180 disposed therein . as can be seen this system can be used in the rods down configuration , with rods 182 and 184 depending from respective pistons 164 and 166 through rod seals 186 and 188 . an auxiliary cylinder 190 is provided with a ram 192 for the purpose of step height adjustment and to replenish fluid lost to carry out . this cylinder is coupled to the operating cylinders via a fluid conduit 194 such that cylinder 190 is in communication with both cylinders 160 and 162 . what will be appreciated from the single acting cylinder embodiment is that a rods down reliable exercise machine can be built with the advantages of step height adjustment provided by the auxiliary cylinder . piston seals 168 and 170 are available from parker hannifin corp . of cleveland , ohio as ptfe slip ring seals , model number 1 . 5bb2hku4a4 . what will be seen in fig4 is that rather than utilizing the bypass system provided for phasing the stairs in piston cylinder systems in which hydraulic fluid exists above and below each piston , the step height adjustment can be accomplished with the single acting piston system of fig4 through the utilization of the subject auxiliary cylinder . having above indicated a preferred embodiment of the present invention , it will occur to those skilled in the art that modifications and alternatives can be practiced within the spirit of the invention . it is accordingly intended to define the scope of the invention only as indicated in the following claims :
an auxiliary cylinder is provided as an adjustable volume accumulator in communication with the two hydraulic ram cylinders utilized to phase the steps utilized in stair climbing apparatus . step height adjustment is facilitated by providing the auxiliary cylinder with a ram and a positioning lever , with step height adjustment being accomplished through the removal of oil from the system by backing off the ram . moving the ram forward replaces oil lost during carry out . the subject system facilitates rapid step height adjustment , facilitates lowering of the steps for permitting under - bed storage through the dropping of the steps , and makes up fluid loss during carry out for preventing step height loss . additionally , operating cylinder component sizing is used to minimize step height growth due to thermal expansion of the fluid in the system .