referring now to the drawings , and more particularly to fig1 there is shown a preferred embodiment of the present invention , generally indicated as 1 . lower leg exerciser 1 is operated by supine patient 8 , depicted by dotted lines , on training table 3 . the exerciser 1 is constructed with a support , preferably in the form of &# 34 ; l &# 34 ; shaped bearing block 4 attached to baseplate 5 , which rests on table 3 . a handle 6 is rigidly connected to bearing block 4 and is preferably long enough to permit supine patient 8 to grip it with one hand while operating exerciser 1 . when gripped by patient 8 during exercise , handle 6 prevents baseplate 5 rocking back and forth . baseplate 5 is preferably long enough to extend under all parts of exerciser 1 to prevent exerciser 1 tilting to the side during exercise . a pivot bracket 9 is rigidly connected to a threaded shaft 10 , which extends through and is rotatably mounted on bearing block 4 , with its longitudinal axis substantially parallel to baseplate 5 . a footplate 7 is rigidly attached to pivot bracket 9 . pivot bracket 9 serves to provide rotational forces to shaft 10 , in response to movement of footplate 7 by the foot of patient 8 during the exercise cycle . the foot of patient 8 is located on footplate 7 such that the longitudinal axis of shaft 10 is substantially aligned with the ankle joint of patient 8 . the distance from the longitudinal axis of shaft 10 to footplate 7 is preferably about 3 inches ( 7 . 6 cm ). adjustable footstrap 11 , preferably cloth belting with velcro fasteners , secures the ball of the foot of patient 8 to footplate 7 for dorsiflexion exercises . in this exercise the patient &# 39 ; s foot pulls footplate 7 counterclockwise when viewed from the footplate end of exerciser 1 . alternatively , a rigid metal bar could replace footstrap 11 . if adjustable along the length of footplate 7 , it too could secure the foot of patient 8 to footplate 7 . heel blocks 21 at the lower end of footplate 7 support the heel of patient 8 . because the axis of rotation of pivot bracket 9 is substantially aligned with the ankle of patient 8 , a footstrap is preferably not used to secure the heel of patient 8 to footplate 7 . pressing footplate 7 clockwise in the plantarflexion exercise does not result in the heel of patient 8 lifting off footplate 7 when the ankle and pivot bracket alignment are close . therefore , once the footstrap 11 is adjusted to one of the feet of patient 8 , either foot of patient 8 can easily be slid in and out of closed footstrap 11 without loosening it . this arrangement enhances the ease with which patient 8 can operate exerciser 1 from a supine position . attached to threaded shaft 10 on the opposite side of bearing block 4 from pivot bracket 9 is rotatable friction disk 12 . coaxial , fixed friction disk 13 is substantially the same size as disk 12 and is urged against disk 12 preferably by compression spring 16 , shown more clearly in fig2 . friction disk 13 is preferably secured from rotation by engagement with angle bracket 15 mounted to the side of bearing block 4 . a handwheel 17 , threaded onto shaft 10 against the opposite end of spring 16 from disk 13 , is rotated to adjust the compression force of spring 16 against friction disk 13 . fig2 discloses more detail of the preferred embodiment of the present invention , shown as 1 . this sectioned view is taken along a horizontal plane which passes through the longitudinal axis of shaft 10 . friction disk 13 preferably has pin 14 extending radially to engage an axially oriented slot in angle bracket 15 . this means of preventing rotation of disk 13 allows disk 13 to slide along shaft 10 in order that spring 16 may press the friction surface of disk 13 against that of disk 12 . angle bracket 15 is preferably attached to bearing block 4 by bolts 26 and 27 , which also extend through handle 6 to secure it to bearing block 4 . bearing block 4 preferably has two flanged ball bearings 24 and 25 pressed into opposite sides of a clearance hole for shaft 10 through bearing block 4 . pivot bracket 9 is preferably welded to threaded shaft 10 . rotatable disk 12 is preferably pinned to shaft 10 by pin 20 after shaft 10 is inserted through bearings 24 and 25 . this sequence insures the axial play of shaft 10 in bearings 24 and 25 is minimized . shaft 10 oscillates in a rotary path about its longitudinal axis along with footplate 7 during operation . handwheel 17 is threaded onto shaft 10 . in order to maintain the compression on spring 16 constant during operation of exerciser 1 , handwheel 17 preferably rotates with shaft 10 . however , friction disk 13 cannot rotate because of its engagement with angle bracket 15 , and compression spring 16 is compressed against disk 13 and also cannot rotate . therefore , washer 19 and thrust bearing 18 are preferably inserted between handwheel 17 and spring 16 to enable handwheel 17 to rotate while compressing non - rotating spring 16 . footplate 7 is preferably attached to pivot bracket 9 by means of two flat head screws , 22 and 23 . several pairs of screw holes in footplate 7 for screws 22 and 23 permit footplate 7 to be located on pivot bracket 9 such that different length feet can have ankles aligned with the longitudinal axis of shaft 10 . fig3 shows the interface between friction disks 12 and 13 . rotatably - fixed friction disk 13 has preferably four equally - spaced , 50 ° arc length , raised , sector - shaped friction pads 28 attached to it . rotatable friction disk 12 also has preferably four equally - spaced , 50 ° arc length , raised , sector - shaped friction surfaces 29 that contact those on disk 13 . the orientation of pins 14 and 20 is such that when handle 6 is horizontal and footplate 7 is vertical , surfaces 28 substantially overlap matching surfaces 29 . there is preferably a 40 ° gap between each raised friction surface 28 and 29 . because this gap is less than the 50 ° arc length of the friction surfaces , rotation of one disk relative to the other cannot cause the raised surfaces of one disk to fall into the gaps of the other . fig4 shows the right foot of patient 8 with three centerlines extending from the ankle joint . centerline n is parallel to the bottom of the foot and is substantially vertical when the leg of patient 8 is horizontal . this represents the neutral or resting position of the foot . centerline d represents the extreme dorsiflexion position of the foot , typically 15 °- 25 ° from centerline n . centerline p represents the extreme plantarflexion position of the foot , typically 35 °- 45 ° from centerline n . fig5 a , 5b , and 5c diagrammatically show the overlap of sector - shaped friction surfaces illustrated on disks 12 and 13 . surfaces 28 on disk 13 are identified by vertical lines . surfaces 29 on disk 12 are identified by horizontal lines . their overlap is represented by areas having both vertical and horizontal lines . fig5 b shows both sets of friction surfaces substantially overlapped . this is the preferred condition when the foot of patient 8 is in the neutral position . fig5 a shows the partial overlap of friction surfaces 28 and 29 when disk 12 is rotated by the foot of patient 8 to the extreme dorsiflexion position . the overlap area is substantially reduced from what it is in fig5 b . fig5 c shows the partial overlap of friction surfaces 28 and 29 when disk 12 is rotated by the foot of patient 8 to the extreme plantarflexion position . again the overlap area is substantially reduced from what it is in fig5 b . it is believed that the reduction in friction contact area under the same spring pressure results in reduced torsional resistance as one disk is rotated relative to the other . measurements of six inch ( 15 . 2 cm ) diameter disks , with the preferred friction surface materials of polished aluminum against silicone grease - coated cork , indicate percent of maximum torsional resistance for different overlaps . when overlap arc length is 50 ° at each sector , friction torque is maximum . when overlap arc length is 35 ° at each sector , friction torque is 88 % of maximum . when overlap arc length is 15 ° at each sector , friction torque is 72 % of maximum . the reduction in torsional resistance as disk 12 is rotated in either direction from the neutral position corresponds to the reduction in leverage of the lower leg muscles . although the correspondence is not exact , any such reduction of resistance as the muscle leverage decreases enables the range of motion of the exercise to be beneficially increased . the variable - contact - area method of matching resistance to muscle leverage is preferred for the lower leg exerciser of the present invention . other more complicated methods of varying resistance with footplate angular position , which are not preferred , are cams and linkages between footplate and source of resistance . these change the mechanism leverage rather than the resistance . for other friction resistance devices , alternate contact surface shapes may better fit the desired angle of rotation and resistance criteria . some alternatives are shown in the remaining figures . fig6 a and 6b show an alternative to the preferred four sector - shaped surfaces of the present invention . the substantially overlapped surfaces 30 and 31 of fig6 a define a four - pointed star . fig6 b shows one disk rotated relative to the other by 45 °. not only is the resulting overlap area reduced to a minimum , but also , the radius to the perimeter of the overlap area is reduced to a minimum . it is believed that the reduction of the radius to the perimeter of the overlap area reduces torsional resistance , and that a combined reduction of overlap area and radius to its perimeter reduces torsional resistance more substantially than if either area or radius to perimeter of area is reduced independently . fig7 a and 7b show coaxial disks with two 100 ° arc length sector - shaped surfaces 32 and 33 . in fig7 a surfaces 32 and 33 are substantially overlapped . in fig7 b the overlap is reduced by 50 % when one disk is rotated 50 ° relative to the other . at a rotation of 80 ° in either direction the overlap area would reach its minimum . fig8 a and 8b show coaxial disk surfaces 34 and 35 , each with two opposing circular segments removed . in fig8 a the surfaces are substantially overlapped . in fig8 b one disk is rotated 90 ° to the other to where the overlap area is minimized . fig9 a and 9b show circular disk surfaces 36 and 37 which have rotational axes offset from the centers of the disks . in fig9 a the circular surfaces are substantially overlapped . in fig9 b one disk is rotated 180 ° relative to the other to a minimum overlap area . the preferred embodiment of the present invention is preferably constructed of common materials . referring to fig2 bearing block 4 , for example , is preferably a lightweight material that is easily machined from a 2 inch by 5 inch by 6 inch ( 5 . 1 cm by 12 . 7 cm by 15 . 2 cm ) block of rigid polyvinyl chloride ( pvc ) or phenolic . baseplate 5 is preferably a 0 . 25 inch by 2 inch by 14 inch ( 6 . 4 mm by 5 . 1 cm by 35 . 5 cm ) long rigid pvc or phenolic strip which is fastened by screws or adhesively bonded to one end of bearing block 4 . extending from a pilot hole in the other leg of &# 34 ; l &# 34 ; shaped bearing block 4 is preferably a hollow one inch ( 2 . 5 cm ) diameter by 3 foot ( 91 cm ) long handle 6 made of preferably rigid pvc or phenolic tubing . footplate 7 is preferably an aluminum casting 0 . 38 inches ( 9 . 6 mm ) thick by 5 inches ( 12 . 7 cm ) wide by 12 inches ( 30 . 5 cm ) long , with preferably 1 . 4 inch ( 3 . 6 cm ) high heelblocks 21 cast perpendicular to the foot contacting surface of footplate 7 . each heelblock 21 is preferably angled 45 ° to the longitudinal axis of footplate 7 . this configuration forms a wedge to center the foot of patient 8 on footplate 7 . pivot bracket 9 , to which footplate 7 is attached by two flathead screws 22 and 23 , is preferably made of a 1 . 25 inch ( 3 . 2 cm ) wide section of 0 . 38 inch ( 9 . 6 mm ) thick 5 inch by 5 inch ( 12 . 7 cm by 12 . 7 cm ) structural steel angle . preferably plug - welded substantially perpendicular to pivot bracket 9 is threaded shaft 10 , preferably 0 . 749 inch ( 1 . 902 cm ) diameter by 8 inches ( 20 . 3 cm ) long and made of cold rolled steel . shaft 10 preferably has 3 / 4 - 10 nc thread cut along the outer 3 inches ( 7 . 6 cm ) opposite its welded end . shaft 10 preferably slips through non - precision , 0 . 750 inch ( 1 . 905 cm ) bore steel ball bearings 24 and 25 , such as heim model rf - 12 - 22 - 14 . these bearings are preferably press fit into opposite sides of bearing block 4 . rotatable friction disk 12 and rotatably - fixed friction disk 13 are preferably circular disks made of cast aluminum , with 0 . 755 inch ( 1 . 918 cm ) diameter bores , 0 . 25 inch ( 6 . 4 mm ) and 0 . 5 inch ( 1 . 3 cm ) thick faces respectively , and 6 inch ( 15 . 2 cm ) outer diameters . disk 12 has a hub which is preferably pinned to shaft 10 by means of a 0 . 25 inch ( 6 . 4 mm ) diameter by 1 . 5 inch ( 3 . 8 cm ) long steel spring pin 20 . preferably pressed into and extending radially from disk 13 is a second spring pin 14 of the same material and size as pin 20 . it preferably engages a 0 . 28 inch ( 7 . 1 mm ) wide by 0 . 5 inch ( 1 . 3 cm ) long slot in angle bracket 15 , bolted to the side of bearing block 4 . angle bracket 15 is preferably a 1 . 25 inch ( 3 . 2 cm ) wide section of 0 . 25 inch ( 6 . 4 mm ) thick by 2 inch by 2 inch ( 5 . 1 cm by 5 . 1 cm ) aluminum structural angle . attached to disk 13 are preferably four raised sector - shaped friction surfaces 28 , made of 0 . 13 inch ( 3 . 3 mm ) thick cork . these are preferably attached to disk 13 by means of double - sided foam urethane tape . cast aluminum raised sector - shaped surfaces 29 of disk 12 are preferably lathe faced smooth . reducing the coefficient of friction between surfaces 28 and 29 is preferably a silicone grease lightly coating cork surfaces 28 . compression spring 16 is preferably a 0 - 200 pound ( 0 - 91 kg ) force helical - wound spring made of 9 coils of 6 gage music wire . its outside diameter is preferably 1 . 25 inches ( 3 . 2 cm ) and its free length is preferably 3 inches ( 7 . 6 cm ). hand wheel 17 is preferably an aluminum or zinc diecast part with 3 / 4 - 10 nc internal thread and 2 . 5 inch ( 6 . 35 cm ) outside diameter . thrust bearing 18 is preferably the same as bearings 24 and 25 , with one race in contact with handwheel 17 and the other race contacting washer 19 . washer 19 is preferably a 7 / 8 inch ( 2 . 2 cm ) sae flat washer . it is though that the lower leg exerciser of the present invention , and many of its attendant advantages , will be understood from the foregoing description ; and it will be apparent that various changes may be made in form , construction , and arrangement without departing from the spirit and scope of the invention or sacrificing all of its material advantages ; the form hereinbefore described being merely a preferred or exemplary embodiment thereof .
apparatus for lower leg exercise wherein dorsiflexion and plantarflexion movements of the foot , about a machine axis substantially aligned with the axis of the ankle , are resisted by a frictional torque that varies in a predetermined manner with the angular position of the foot . reducing the extent of friction contact surface overlap and / or reducing the radius to the perimeter of friction contact surface overlap causes torsional resistance to decrease . as the foot rotates about the ankle to either side of its neutral position , the natural leverage of the leg muscles opposing torsional resistance decreases . corresponding reduction of resistance with reduction of muscle leverage permits the range of motion of lower leg exercise to be increased . in the preferred embodiment the apparatus has a handle and base which permit operation from a supine position on a bed , training table , or floor , with leg extended horizontally .