a detailed description of a conventional wheelchair structure will be discussed hereinbelow for the purposes of assisting in the detailed description of the anti - rollback assembly of the present invention and explaining the manner in which the anti - rollback assembly is operatively supported on a wheelchair . it is understood , however , the present invention is not restricted to the illustrated wheelchair or the construction and arrangement of the individual components of the illustrated wheelchair . referring now to the drawings , there is shown in fig1 a , and 2 b a wheelchair generally is designated by reference numeral 10 . the wheelchair 10 includes a frame structure 12 comprising a pair of opposing side frames 14 a and 14 b laterally spaced from and substantially parallel with one another . the opposing side 20 frames 14 a and 14 b have respective front upright members 16 a and 16 b and respective rear upright members 18 a and 18 b . in the illustrated embodiment , the front upright member 16 a and the rear upright member 18 a of the side frame 14 a 25 include longitudinal axes oriented substantially vertical , and are interconnected with crossbars 19 a and 20 a . the front upright member 16 b and the rear upright member 18 b of the other side frame 14 b are arranged and interconnected in a similar manner with crossbars 19 b and 20 b . handles 22 a and 22 b are fitted onto upper ends ( unnumbered ) of the rear upright members 18 a and 18 b , respectively . arm rests 24 a and 24 b are secured to upper surfaces of the crossbars 19 a and 19 b , respectively . the wheelchair 10 further includes a flexible seat member 26 extending between the opposing side frames 14 a and 14 b and arranged in a substantially horizontal orientation so as to permit an occupant to sit thereon . a flexible back support member 28 extends between the rear upright members 18 a and 18 b and , together with the seat member 26 , define a seating area ( unnumbered ) for supporting the wheelchair occupant . as shown in fig1 ., the wheelchair 10 further includes rear drive wheel assemblies comprising two large rear drive wheels 30 a and 30 b which are manually rotatable by the occupant to rotate about hubs 32 a and 32 b , respectively . the hubs 32 a and 32 b are respectively attached to the rear upright members 18 a and 18 b with axle bolts ( unnumbered ) and each include a plurality of spokes ( not shown ) extending therefrom to interconnect the hubs 32 a and 32 b to their respective drive wheels 30 a and 30 b . front wheel assemblies comprise small wheels 34 a and 34 b swivably connected to the front upright members 16 a and 16 b , respectively , to facilitate turning of the wheelchair 10 . although not shown , it is understood that in accordance with the present invention , the wheelchair 10 can include additional components , such as footrests . it is further understood that in accordance with the present invention the wheelchair can omit one or more of the components discussed above and illustrated in the drawings , so long as the wheelchair is characterized as being capable of operatively supporting the anti - rollback feature of the present invention . one embodiment of the automatic anti - rollback assembly of the present invention , which is generally designated by reference numeral 40 , will now be described with greater specificity hereinbelow . referring to fig3 and 4 , the illustrated automatic anti - rollback assembly 40 includes two mounting assemblies . for explanatory purposes , only one of the two mounting assemblies , which is generally designated by reference numeral 42 , will be described below . the mounting assembly 42 includes a mounting bracket 44 with a discontinuous circular clamping end 46 , which accommodates the rear upright member 18 a . nut - bolt combinations 48 and 50 serve to secure the mounting bracket 44 to the rear upright member 18 a . reinforcement spacers 52 may be used in combination with the nut - bolt combinations 48 and 50 to prevent bowing of the bolts . the reinforcement spacers 52 can be made of , for example , nylon or other plastics . as shown in fig1 a , and 2 b , the clamping end 46 of the mounting bracket 44 is positioned immediately above the axle bolt associated with hub 32 a . the mounting assembly 42 further includes a movable brake - arm supporting member 54 ( also referred to as a brake - member supporting member or pivotable collar ), which is substantially configured as a clevis yoke . in the illustrated embodiment , the brake - arm supporting member 54 is rotatable about its longitudinal axis between first and second positions . opposing sides of the mounting bracket 44 define aligned apertures , one of which is designated by reference numeral 56 in fig4 . the apertures 56 are sized to receive a shaft 58 co - axially extending from and integral with the pivotable collar 54 . the shaft 58 is secured to the mounting bracket 44 with , for example , a lock cap 60 . as shown in fig5 a torsion spring 62 is accommodated in the mounting bracket 44 and connected to the shaft 58 of the pivotable collar 54 via pin 63 to urge the pivotable collar 54 into its first position . the opposite end ( unnumbered ) of the pivotable collar 54 defines a slot 66 diametrically positioned and axially extending a certain depth into pivotable collar 54 . a first s bore 68 is diametrically defined within the pivotable collar 54 , and arranged orthogonally relative to the slot 66 to intersect the slot 66 . second and third bores 70 and 72 are each diametrically disposed , arranged orthogonally relative to each other to intersect each other , and are interposed between the slot 66 and the shaft 58 . the functions of the slot 66 and the first , second , and third bores 68 , 70 , and 72 will be described below . still referring to fig3 the automatic anti - rollback assembly 40 further includes a brake releasing assembly , which is generally designated by reference numeral 74 . the brake releasing assembly 74 includes a substantially l - shaped actuator lever 76 , adjustor plate 78 , and connector plates 80 . for explanatory purposes , the connector plate 80 and the side of the adjustor plate 78 operatively associated with mounting assembly 42 will be described below . the actuator lever 76 is cantilevered at a central portion ( unnumbered ) of the adjustor plate 78 . the end ( unnumbered ) of the adjustor plate 78 defines an exposed lateral port 82 , which receives a portion of the connector plate 80 . the upper region of the adjustor plate 78 has an elongated slot 84 defined therethrough in communication with the lateral port 82 . ( as shown in fig3 the slots 84 are located on each side of the central portion of the adjustor plate 78 .) a nut - washer combination 86 engages a first aperture 88 of the connector plate 80 and the elongated slot 84 to thereby secure the adjustor plate 78 to the connector plate 80 . the end of the connector plate 80 opposite to the first aperture 88 defines a second aperture 90 . as shown in fig2 a and 2b , when the brake releasing assembly 74 is connected to the mounting assembly 42 , the brake releasing assembly 74 is positioned immediately underneath the seat member 26 . the connection of the brake releasing assembly 74 to the mounting assembly 42 will now be described with reference to fig3 . the slot 66 of the pivotable collar 54 receives the end of the adjustor plate 78 containing the second aperture 90 so that the first bore 68 and the second aperture 90 are aligned . a quick - release pin 92 is inserted through the aligned first bore 68 and second aperture 90 to secure the brake releasing assembly 74 to the mounting assembly 42 . the provision of the quick - release pin 92 or similar connecting device facilitates the quick and easy separation and removal of the brake releasing assembly 74 . when the wheelchair 10 is of the collapsible variety , the frames 14 a and 14 b and associated wheels on either side of the seat member 26 can thereby be folded together for convenient stowage . the provision of a quick - releasing mechanism to facilitate the ability of the wheelchair 10 to be collapsed and stored represents one of the many advantages of the present invention . another of the advantages of the illustrated embodiment rests in the configuration of the elongated slots 84 of the adjustor plate 78 , which provides for an adjustable positional relationship with the first aperture 88 of connector plate 80 . this feature makes the illustrated anti - rollback assembly 40 adaptable and retrofittable to wheelchairs of various widths . although not shown , it is noted that the elongated slots 84 can be replaced with , for example , a series of spaced apertures . the anti - rollback assembly 40 also includes a brake member ( or brake arm ) 94 , a proximal end portion 96 of which is received in the second bore 70 of the pivotable collar 54 and secured thereto with a set screw 98 ( fig3 ). ( the brake member 94 and mounting assembly 42 collectively form a one - way brake assembly in this embodiment .) as respectively shown in fig2 a and 2b , a distal end portion 99 of the brake arm 94 either is spaced from a rear region of the drive wheel 30 a ( when the wheelchair 10 is occupied ) or rests on the drive wheel 30 a ( when the wheelchair 10 is unoccupied or the occupant attempts to rise from or sit down into the wheelchair 10 ). as is believed evident from this description , the positional relationship - of the brake arm 94 to the pivotable collar 54 can be adjusted ( by loosening set screw 98 ) to make the brake arm 94 adaptable and retrofittable to wheelchairs of various drive wheel sizes . the operational movement of the anti - rollback assembly 40 will be described below with reference to fig1 a , 2 b , and 3 . in its unoccupied state , the torsion spring 62 imparts a biasing force to urge the brake - arm supporting member 54 towards the first position , which in turn urges the seat member 26 towards its upper position and the distal end portion 99 of the brake arm 94 into the activated position . in the activated position , the distal end portion 99 of the brake arm 94 prevents the first drive wheel 30 a from rotating about a central axis thereof in a rearward direction , yet does not prevent the first drive wheel 30 a from rotating about the central axis thereof in a forward direction . when a patient attempts to rest into the seating area of the wheelchair 10 , the weight of the patient imparts a downward force on the seat member 26 , which causes the seat member 26 to flex , bend , slide , or otherwise move in a downward direction to its lower position . the downward movement of the seat member 26 translates the downward force to the actuator lever 76 , thereby pivoting the actuator lever 76 downward as indicated by the arrow in fig2 a . as the actuator lever 76 pivots , the adjustor plate 78 is rotated about its longitudinal axis to translate a corresponding rotational movement to pivotable collar 54 . as the collar 54 rotates about its axis , the brake arm 94 operatively associated therewith is pivoted about the region of its proximal end portion 96 accommodated in the second bore 70 so that the distal end portion 99 is moved from the activated position to a non - activated position . in the non - activated position , the distal end portion 99 is radially spaced from the drive wheel 30 a and , hence , does not interfere with manual operation ( including both forward and rearward motion ) of the wheelchair 10 . conversely , when an occupant of the wheelchair 10 attempts to rise from the seating area , the torsion spring 62 imparts a biasing force to urge the brake - arm supporting member 54 towards the first position , which in turn urges the seat member 26 towards its upper position and the distal end portion 99 of the brake arm 94 to move in a downward manner along an arcuate path ( as shown by the arrow in fig2 b ) into the activated position . in the illustrated embodiment , the arcuate path that the distal end portion 99 of the brake arm 94 follows between the activated and non - activated positions intersects the circumference of the drive wheel 30 a . consequently , the amount of frictional force applied to the brake arm 94 by the drive - wheel 30 a is proportional to the rearward force applied to the wheelchair 10 . stated differently , when the wheelchair 10 is moved rearwardly , frictional force between the drive wheel 30 a and the brake arm 94 causes the distal end portion 99 of the brake arm 94 to move in a generally radially inward direction towards the hub 32 a , which further presses the distal end portion 99 into the drive wheel 30 a . consequently , continued rearward motion of the wheelchair 10 has a corresponding immobilizing effect on the drive wheel 30 a of the wheelchair 10 . accordingly , even though the occupant of the wheelchair 10 may neglect to set a conventional parking brake ( not shown ), the chair 10 is automatically immobilized against backward movement by the anti - rollback device when the occupant is attempting to rise from or seat himself in the seat member 26 . referring now to fig6 and 7 , according to another embodiment of the present invention the wheelchair is equipped with an ambulation monitor , generally designated by reference numeral 100 , for activating an alarm when the occupant of the wheelchair 10 attempts to rise from the seat member 26 . as shown in fig7 the ambulation monitor includes a housing structure 102 , which houses a horn 104 , an on / off switch 106 and a switch jack 108 electrically connected to the horn 104 , and an energy source 110 , e . g ., a battery , electrically connected to the on / off switch 106 . the housing structure 102 is supported on the mounting bracket 44 with a mounting bracket 112 , a mounting bracket clamp knob 114 , and screws 116 a and 116 b . referring now to fig6 a connector wire 120 electrically connects the switch jack 108 to a cam actuator switch 122 . a cam 124 is cooperatively associated with the pivotable collar 54 by providing the cam 124 with an eccentrically disposed aperture 126 through which a portion of the pivotable collar 54 is disposed . accordingly , when the occupant begins to rise from the seat member 26 , the pivotable collar 54 is rotated about its longitudinal axis as described above . the cam 124 , by virtue of its cooperative association with the pivotable collar 54 , rotates to actuate the switch 122 , thereby activating the horn 104 to alert staff of the occurrence . in its broadest aspects , several variations and modifications to the above - discussed anti - rollback assembly can be implemented without departing from the scope of the present invention . for example , the anti - rollback assembly 40 may include a separate biasing member or members , such as springs , to urge the seat member into its upper position independent of or in conjunction with the torsion spring 62 . also , although in the illustrated embodiment each of the drive wheels 30 a and 30 b and a one - way brake assembly ( that is , a mounting assembly and brake arm ) associated therewith , it is understood that the anti - rollback assembly 40 may include only one mounting assembly 42 and brake arm 94 , in which case , for example , a pivotable bar ( not shown ) may interconnect the brake releasing assembly 74 with the side frame 14 b not associated with the mounting assembly 42 and brake arm 94 . where the anti - rollback assembly includes one - way brake assemblies respectively associated with each of the drive wheels 30 a and 30 b ( as shown in fig1 a , and 2 b ), a second torsion spring ( not shown ) may be accommodated in the mounting bracket associated with the second drive wheel 30 b ; alternatively , the anti - rollback assembly 40 may include only a single torsion spring , since the pivotable collar 54 associated with the first drive wheel 30 a rotates in unison with the pivotable collar associated with the second drive wheel 30 b due to the interconnection provided by the brake releasing assembly 74 . the one - way brake assemblies may respectively engage portions of the rear drive wheel assemblies at positions other than the rear drive wheel . for example , although not shown , the assemblies could include ratchet and pawl wheel assemblies to accomplish the anti - rollback function of the present invention . these and other modifications to the assembly , when viewed with reference to this disclosure , are within the purview of those skilled in the art . if desired , the automatic anti - rollback assembly 40 of the present invention may be used in conjunction with conventional supplemental braking devices well known in the art , including , for example , a manually - operated parking brake to immobilize the wheelchair from forward or rearward movement when occupied . this application claims priority of provisional patent application no . 60 / 039 , 485 , the complete disclosure of which is incorporated herein by reference . the foregoing detailed description of the preferred embodiments of the invention has been provided for the purposes of illustration and description . it is not intended to be exhaustive or to limit the invention to the precise embodiments disclosed . the embodiments were chosen and described in order to best explain the principles of the invention and its practical application , thereby enabling others skilled in the art to understand the invention . while the invention has been described in connection with what is presently considered to be the most practical and preferred embodiments , it is understood that the invention is not limited to the disclosed embodiments , but , on the contrary , is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims .
an anti - rollback assembly adapted or adaptable for use in combination with a wheelchair . the anti - rollback assembly includes a one - way brake assembly automatically immobilizing the wheelchair against rearward movement when the occupant attempts to rise from or sit in a seat member of the wheelchair , yet at the same time does not prevent the wheelchair from moving in a forward direction . conversely , when the occupant is fully seated in the seat member , the one - way brake assembly is disengaged so that the wheelchair can move freely in forward or rearward directions . the assembly can be retrofitted onto existing wheelchairs , and is adjustable to fit various size wheelchairs .