Ratcheting mechanism for tightening cuff or blood pressure monitor

A ratcheting device for use in tightening the cuff of a blood pressure monitor has a lever, a lever mounting which is attached to one end of the cuff and which holds the lever so that it can be moved in a given direction or an opposite direction. An elastic body is disposed between the lever and the lever mounting to transmit a force applied to the lever into the lever mounting by elastic deformation of the elastic body. Interdental spaces are formed between saw teeth on the inner surface of a cam and extend in the given and opposite directions in which the lever moves. A ratchet having pawls thereon which can engage with the interdental spaces is provided; this rachet is immobilized by the engagement of the pawls in the interdental spaces when the pressure applied to the lever exceeds a given value.

FIELD OF THE INVENTION 
This invention relates to a ratcheting device which can be used in the 
wrapping mechanism of a cuff on a blood pressure monitor of the type which 
measures blood pressure by obstructing the flow of blood in a finger 
artery. 
BACKGROUND OF THE INVENTION 
To facilitate the wrapping of the cuff onto the finger, prior blood 
pressure monitors used on a finger employ the cuff wrapping mechanism 
shown in FIGS. 12 and 13. In FIG. 12, 122 is the case, and 123 is the cuff 
within the case. Rubber chamber 123b is attached to cuff 123. 
The protruding end 123a of cuff 123 is fixed to lever 124. This lever is 
installed on case 122 in such a way that it can slide both in direction A, 
which tightens the cuff, and in direction B, which loosens the cuff. An 
elastic pawl 125 is provided on lever 124. As shown in FIG. 13, pawl 125 
engages interdental spaces 126, which are located in two parallel rows 
along the path of movement of lever 124. Thus, the pawl prevents the lever 
from moving in direction B and loosening the cuff. 
To measure a person's blood pressure, the person inserts a finger, usually 
the index finger, into opening 122a in case 122. Lever 124 is then moved 
in direction A to tighten the cuff. During tightening, pawl 125 is 
elastically deformed and passes over interdental spaces 126. When the 
appropriate cuff pressure has been attained, the operator releases lever 
124, and pawl 125 engages in interdental spaces 126. This fixes the 
position of lever 124 and keeps cuff 123 wrapped around the patient's 
finger. Air is then pumped into rubber chamber 123b until the flow of 
blood in the finger artery is obstructed, and the blood pressure is 
measured. 
When the blood pressure measurement has been completed, button 127 is 
pressed, causing pawl 125 to move down so that it is released from 
interdental spaces 126. Lever 124 slides in direction B, allowing cuff 123 
to loosen. 
With the existing cuff wrapping mechanism described above, the operator has 
a tendency to apply great force to lever 124 at the moment pawl 125 is 
slipping past teeth 126. This causes the pressure with which the cuff is 
wrapped to vary. For this reason, the tightness of the cuff is variable, 
and there is a pronounced tendency to overtighten it. 
If cuff 123 is not wrapped sufficiently tightly, the volume of rubber 
chamber 123b will be increased, which will cause it to take longer for the 
cuff to be pressurized. Further, the area of the surface of rubber chamber 
123b which contacts the finger will be decreased, which increases the 
chance that the rubber will wrinkle. If this happens, the blood pressure 
will not be measured correctly. Problems such as these are well known in 
blood pressure monitors employing the oscillation technique, in which the 
change in air pressure inside rubber chamber 123b is used to detect the 
pulse wave. 
In contrast, if cuff 123 is wrapped too tightly, the blood in the finger 
can be completely obstructed, which will cause pain to the patient. To 
prevent cuff 123 from being wrapped too tightly, one could conceivably use 
deeper teeth for the toothed portions of 126, but this would cause the 
tightness to vary even more, and the operating noise would become much 
louder. 
SUMMARY OF THE INVENTION 
In view of the above problems, the purpose of this invention is to provide 
a ratcheting device which, when used in a blood pressure monitor, will 
allow the cuff easily to be wrapped to the appropriate tightness while 
minimizing operating noise. 
The ratcheting device with which this invention is concerned includes a 
mounting for a lever which can be moved in a given direction or its 
opposite as the cuff is to be tightened or loosened. A lever which is 
capable of moving in the given direction or its opposite is installed on 
the mounting. An elastic body is situated between this lever and its 
mounting which can transmit the force applied to the lever into the lever 
mounting by elastic deformation. There is a ratchet with pawls and 
interdental spaces provided along the two directions in which the lever 
moves into which the pawls can fall. Finally, there is a means for 
immobilizing the ratchet, so that the pawls engage in the interdental 
spaces when the pressure applied to the lever exceeds a given value. With 
this design, the lever mounting can move smoothly until the pawls of the 
ratchet engage in the interdental spaces, thus minimizing the operating 
noise of the lever mounting. 
In operation, the lever mounting runs into a stop, and the elastic body is 
compressed. When the compressive force exceeds a given value, the means 
for immobilizing the lever cause the pawls to engage in the interdental 
spaces. The lever mounting can move no further in the given direction, 
even if additional force is applied in that direction. Thus, it is 
impossible to apply excessive force to the person's finger.

DETAILED DESCRIPTION OF THE INVENTION 
We shall now explain an embodiment of this invention with reference to 
FIGS. 1 through 6, starting with a summary of how the invention works in 
this embodiment. 
In FIG. 6, finger-cuff electronic blood pressure monitor 1 has a liquid 
crystal display 3, which displays blood pressure values and other 
information, and operating buttons 4 and 5 are located on case 2, which 
encloses blood pressure monitor 1. The cuff tightening unit 10, as 
depicted in FIGS. 1(a) and (b), FIG. 4 and FIG. 5, is attached to case 2. 
A finger can be inserted into part 2a. Slot 2b, in which the lever slides, 
is also provided. 
FIG. 1(a) is a cross sectional view of cuff tightening unit 10 when the 
cuff is loose. FIG. 1(b) illustrates the relationship between cam 15 and 
ratchet 48 by showing an overhead view of cuff tightening unit 10 with 
cover 19 removed. FIGS. 2(b) and 3(b) show the same view. FIG. 4 shows an 
enlarged cross section along the area in FIG. 1(a) indicated by line 
IV--IV. FIG. 5 shows an oblique exploded view of the disassembled 
components of cuff-tightening unit 10. With its housing 10a removed, 
cuff-tightening unit 10 includes base 11 and cover 19, cam 15, lever 
mounting 23, lever 33, stop 42, ratchet 48 and coil springs 18, 32 and 37 
as its major components. For the sake of convenience and simplicity, the 
unit is broken down vertically in the following explanation. 
The ratcheting device of this invention includes a mounting 23 for a lever 
which can be moved in a given direction (A) or its opposite (B). A lever 
33, capable of moving in either direction (A) or (B), is installed on 
mounting 23. An elastic body 32 is situated between lever 33 and its 
mounting 23 which can transmit the force applied to the lever into the 
lever mounting by elastically deforming. A ratchet 48 is provided with 
pawls 49 which can fall into interdental spaces 17 provided along the two 
directions (A) and (B) in which the lever moves. The means for 
immobilizing the ratchet is depicted by reference numerals 45, 50; this 
means causes the pawls 49 to engage in the interdental spaces 17 when the 
pressure applied to the lever 33 exceeds a given value. 
In this embodiment of the invention, when the lever 33 is moved in 
direction (A), the force is transmitted through the elastic body 32 to the 
lever mounting 23, which also moves in direction (A). When the lever has 
reached a certain point, the lever mounting 23 is stopped, and the elastic 
body 32 is compressed. When the compressive force exceeds a given value, 
the means for immobilizing the lever 45, 50 causes the pawls 49 to engage 
in the interdental spaces 17, thus securing the ratchet. As a result, the 
lever mounting 23 is locked into its position and can move no further in 
direction (A), even if more force is applied to the lever. Therefore it is 
not possible to apply an excessive force to the finger disposed in the 
cuff because of this arrangement. When this ratcheting device is employed 
in a blood pressure monitor, it prevents overtightening of the cuff. Also, 
because the lever mounting moves smoothly until the pawls of the ratchet 
engage in the interdental spaces, operating noise is kept to a minimum. 
Base 11 as shown in FIG. 5 includes cylindrical cuff sleeve 12 and cam 
sleeve 13, which form a single unit. Inside cam sleeve 13 is U-shaped cam 
15. This cam is constructed in such a way that it can slide a certain 
distance within cam sleeve 13 in either direction (A), which tightens the 
cuff, or direction (B), which loosens the cuff. Guide rails 14 are 
provided on the inner surface of cam sleeve 13. As shown in FIG. 4, these 
guide rails 14 contact corresponding ridges 16 on the underside of cam 15 
in order to guide it so that it can move smoothly. 
The inside of cam 15 has parallel rows of sawteeth defining interdental 
spaces 17. One end of the cam, 15a, is slightly shorter than the other 
end, 15b. Coil spring 18 is interposed between cam end 15a and vertical 
wall 13a of the cam sleeve so that it can absorb the force when cam 15 
slides in direction (A) to tighten the cuff. Cam sleeve 13 is enclosed by 
cover 19, and is constructed in such a way that cam 15 and coil spring 18 
cannot slip out of the sleeve. As shown in FIGS. 4 and 5, cover 19 is 
fastened to the cam sleeve by tabs 20, which engage on the bottom of cam 
sleeve 13 to secure the cover. Cover 19 has a long slot in it, slot 21, 
into which tabs 22 are inserted. 
Lever mounting 23 is seated on tabs 22. The end 24 of lever mounting 23 
protrudes downward between tabs 22. This end 24 has projections 25 on 
either side to prevent it from coming out of the tabs, and it also has an 
anchor pin, 26. This pin is anchored to the protruding end 9 of the cuff, 
which extends out of cuff cover 12. Lever 33 is mounted on lever mounting 
23 in such a way that it can slide in direction (A) to tighten the cuff or 
in direction (B) to loosen the cuff. Tabs 34 on lever 33 are engaged, 
respectively, in slots 27 on lever mounting 23. These tabs serve to guide 
lever 33 in directions (A) and (B). 
Pin 35 depends vertically from lever 33, passes through guide track 28 on 
lever mounting 23, and protrudes downward, as shown in FIG. 1(a). Coil 
spring 32 is interposed between spring pressure plate 31 on lever mounting 
23 and the base of pin 35. 
Button 38 is mounted on lever mounting 23. Button shaft 40 protrudes 
downward through hole 30 in lever mounting 23. Lever 33 has an opening 36 
in it so that the head 39 of button 38 will not contact it. Coil spring 37 
is attached to button shaft 40 and provides force in an upward direction. 
As shown in FIGS. 1(a), 4 and 5, stop 42 is mounted to the bottom surface 
of lever mounting 23 in such a way that it, too, can slide in directions A 
and B. On the top surface of stop 42 there are two guide teeth 43, which 
fit into guide track 28 on lever mounting 23. These teeth engage, 
respectively, with guide rails 29. The lower end of the pin 35 inserts 
into hole 44 on stop 42 so that lever 33 and stop 42 move as a single 
unit. 
Slot 45 is cut in stop 42 on a diagonal with respect to directions (A) and 
(B). Depression 45a is on the side toward direction (B), which loosens the 
cuff. It is cut one step deeper than the rest of the slot. Button shaft 40 
goes through slot 46, which allows it to protrude downward. Ratchet 48 is 
mounted to this protruding shaft 40 in such a way that it is free to 
rotate. Detent 41 prevents ratchet 48 from coming loose. Ratchet 48 has 
two pawls 49 and two projections 50, 51 on its upper surface. Projection 
50 fits into slot 45 as a guide. When the cuff is loosened, it is on the 
side of the slot closer to direction (A). The other projection, 51, 
contacts the bottom of stop 42 when the cuff is loosened. These 
projections are provided in order to insure that ratchet 48 can rotate 
smoothly. 
The following is an explanation of the cuff tightening operation in the 
embodiment with reference to FIGS. 2 and 3. When force is applied to lever 
33 in direction (A), which tightens the cuff, this force is transmitted to 
lever mounting 23 through coil spring 32, and lever mounting 23 begins to 
slide in direction (A). The protruding end 9 of the cuff is pulled in 
direction (A), and the cuff is tightened around the finger. 
When the cuff is tightened, coil spring 32 is deformed by compression, and 
lever 33 and stop 42 slide against lever mounting 23 in direction (A). At 
this time the center of rotation of ratchet 48, i.e., button shaft 40, is 
anchored to the top surface of lever mounting 23, so projection 50 is 
guided by slot 45, and ratchet 48 rotates in direction (C). 
When the value for the cuff tightening force is exceeded, pawls 49 on 
ratchet 48 engage in interdental spaces 17 can be seen in FIGS. 2(a) and 
(b). At the same time, projection 50 is pulled into depression 45a, 
projection 51 is pulled into slot 46, and ratchet 48 is secured by stop 
42. When pawls 49 engage interdental spaces 17, lever mounting 23 is 
immobilized with respect to cam 15, and the cuff cannot be tightened any 
further. 
When the operator's hand is removed from lever 33, air begins to enter the 
rubber chamber on the cuff, and cam 15 slides distance b in direction (B), 
the direction which loosens the cuff, while lever mounting 23 remains 
immobilized. This can be seen in FIGS. 3(a) and (b). This causes the cuff 
to loosen very slightly so the value for the tightening force of the cuff 
at the start of pressurization can be fixed at close to zero, and a 
correct blood pressure reading can be obtained. This distance b can be 
adjusted by varying the elasticity of coil spring 1B. Thus the movement of 
cam 15 can be controlled such that the cam does not move in direction (B) 
farther than is necessary. 
To loosen the cuff, the operator pushes button head 39. When this button 
head is pushed, ratchet 48 moves downward, projections 50 and 51 are 
released from depression 45a and slot 46 respectively, and ratchet 48 
becomes free to rotate. The force of coil spring 32 causes lever 33 and 
stop 42 to resume their former positions with respect to lever mounting 
23. Ratchet 48 rotates in the direction opposite C, and pawls 49 disengage 
from interdental spaces 17. Lever mounting 23 can then slide in direction 
(B), and the cuff can be loosened. The force of coil spring 18 causes cam 
15 to resume its former position. 
In the embodiment described above, coil spring 18 is used to control the 
travel of cam 15. This structure acts to regulate rachet travel by 
permitting the rachet to travel either in direction (A) or in direction 
(B) while regulating the distance in either direction through which the 
rachet is permitted to travel. However, the invention is not limited to 
the use of such a coil spring. Any appropriate design modification can be 
made. 
Another embodiment of this invention is explained below with reference to 
FIGS. 7 through 11. FIG. 11 is a frontal view of finger cuff-type 
electronic blood pressure monitor 101, in which the ratcheting device of 
this second embodiment is employed. The end of case 102 of this blood 
pressure monitor is formed into finger insertion unit 102a, within which a 
cuff with an air chamber [not pictured] identical to those of previous 
versions is provided. Case 102 has a slot 102b on it, in which the 
wrapping device for the cuff is located. 
The wrapping device for the cuff, as shown in FIG. 10, includes button 110, 
lever 108, coil springs 109 and 111, lever mounting 107, cover 104, cam 
105, stop 112 and ratchet 113. Cover 104 is fastened to the inner surface 
of case 102 and projects from slot 102b as shown in FIGS. 7, 9 and 11. Cam 
105 is inside case 102, and is attached to the inner surface of cover 104. 
Cam 105 has sawteeth on either side of slot 102b extending along its 
length. The sawteeth are positioned beneath cover 104 but do not come in 
contact with it. 
Lever mounting 107 is retained in slot 102b on the exterior of case 102. It 
can slide on cover 104 in either direction (A), which tightens the cuff, 
or direction (B), which loosens the cuff. The end portion 107a of lever 
mounting 107 depends within the case between the two portions of cover 
104. Projections 107b prevent the lever mounting from coming loose. Anchor 
pin 107c depends from the end 107a of the lever mounting and secures the 
protruding end 103 of the cuff as shown in FIGS. 7(a) and 10. Lever 108 is 
mounted on lever mounting 107 in such a way that it can slide on the 
mounting in direction (A), which tightens the cuff, or in direction (B), 
which loosens the cuff. Tabs 108a on lever 108 engage in respective slots 
107d on lever mounting 107. They serve to guide lever 108 in directions 
(A) and (B). Pin 108b depends from lever 108, passes through guide slot 
107e on lever mounting 107, and protrudes downward. Coil spring 109 is 
interposed between lug 107h and the lower end of pin 108. 
Button 110 is mounted on lever mounting 107. The shaft of this button, 
110b, passes through hole 107g on lever mounting 107 and protrudes 
downward. Lever 108 has an opening 108c on it, so that the top 110b of the 
button Will not contact the lever. Coil spring 111 is attached to button 
shaft 110b. It provides a force to move button 110 upward. 
Stop 112 is mounted to the bottom surface of lever 107 in such a way that 
it allows the lever to slide in directions (A) and (B) against the lever 
mounting. Stop 112 has two tabs 112a on it. These tabs insert into guide 
slot 107e on the lever mounting and engage, respectively, with projections 
107f. The lower end of pin 108b inserts into hole 112b so that lever 108 
and stop 112 can move as a single unit against lever mounting 107. 
Stop 112 has a slot 112c on it, which is oblique with reference to 
directions (A) and (B). On the side of this slot closer to direction (B), 
which loosens the cuff, there is a depression, 112d, which is one step 
deep. Hole 112e is for button shaft 110b. The button shaft passes through 
the hole and protrudes into the interior of the device. Ratchet 113 is 
mounted to this protruding button shaft 110b in such a way that it is free 
to rotate. Ratchet 113 has two pawls 113a and a projection 113b, which is 
higher than the rest of the ratchet. This projection 113b is guided by 
slot 112c. When no force is being applied to tighten the cuff, the 
projection will be on the end of slot 112c in the direction of direction 
(A). 
We shall next explain the operation of the cuff wrapping mechanism in this 
second embodiment, with reference to FIGS. 8(a) and (b). When force is 
applied to lever 108 in direction (A), which tightens the cuff, this force 
is transmitted to lever mounting 107 through coil spring 109, and lever 
mounting 107 begins to slide in direction (A). The protruding end 103 of 
the cuff is pulled in direction (A), and the cuff is wrapped around the 
finger. 
When the cuff is wrapped around the finger, coil spring 109 is 
compressively deformed, and lever 108 and stop 112 slide against lever 
mounting 107 in direction (A), which tightens the cuff. Because the center 
of rotation of rachet 113 is fixed to lever mounting 107, projection 113b 
is guided by slot 112c, and ratchet 113 rotates in direction C. 
When the tightening force exceeds a given value, pawls 113a on ratchet 113 
engage respective interdental spaces 106. At the same time, projection 
113b engages in slot 112c, and ratchet 113 is fixed in that position. When 
pawls 113a engage interdental spaces 106, lever mounting 107 is arrested 
in its position at that moment, and the cuff cannot be tightened or 
loosened any further. Because pawls 113a and interdental spaces 106 do not 
come in contact until lever mounting 107 is arrested, the force used to 
tighten the cuff is not variable as in former designs. As a result, there 
is less chance of overtightening the cuff, and operating noise is kept to 
a minimum. 
When the measurement of blood pressure has been completed, the operator 
pushes button head 110b, and the entire ratchet 113 is moved downward 
toward the interior of the device. When ratchet 113 moves downward, 
projection 113b disengages from slot 112c, and the ratchet becomes free to 
rotate in the opposing direction. Consequently, pawls 113a disengage from 
interdental spaces 106, and lever mounting 107 moves in direction (B), 
enabling the cuff to be loosened. 
Although the invention has been described with respect to two embodiments 
depicted in this application, persons skilled in this art will readily 
recognize and be able to practice other equivalent embodiments of the 
invention upon consideration of the specification, claims and drawings of 
this application.