GB2346190A - Ratchet mechanism - Google Patents

Abstract

A releasable ratchet mechanism having single-handed operation comprising a rotatable input member 140, a rotatable output member 133 and mutually engageable ratchet means 143, 144 effecting selective coupling between the input and output members 140, 133. Rotation of the input member 140 in a first direction rotates the output member 133 in that direction but prevents rotation of the output member in a second, opposite direction. Rotation of the input member 140 in the opposite second direction permits rotation of the output member 133 in that second direction. The ratchet mechanism preferably forms part of sphygmomanometer cuff means.

Description

IMPROVEMENTS IN OR RELATYNG TO RATCHET MECHANISMS DESCRIPTION Technical Field This invention relates to ratchet mechanisms and in particular to ratchet mechanisfns involving relative arcuate movement between the ratcheting parts.

Background Art It is a well-known to provide a rotary ratchet mechanism in which the ratchet and pawl may be disengaged by depressing a button in a generally radial direction to deflect the pawl out of enagagement of the ratchet teeth. Where the rotary ratchet mechanism has no spring or like resilient means to effect counter-rotation when the ratchet and pawl are disengaged, the disengagement procedure is generally an inconvenient two-handed operation requiring one hand to effect rotation or counter-rotation of the rotary member of the ratchet mechanism and the other hand to effect depression of the disengagement button.

It is considered desirable to provide a releasable, i. e. disenageable, ratchet mechanism that does not require twohanded operation.

Summary of the Invention According to this invention thore is provided a releasable ratchet mechanism that is one-hand operable and comprises a rotatable input member, a rptatable output member, and mutually engageable ratchet means effecting selectively disengageable coupling between, the said input and output members such that rotation of the input member in a first direction effects rotation of the output member in that direction but prevents rotation of the output member in a second, opposite direction, and such that rotation of the input member in the opposite second direction permits rotation of the output member in that second direction.

Preferably the ratchet mechanism comprises first and second mutually engageable ratchet means that, when the input member is rotated in said first direction are in mutual cooperative engagement to prevent said rotation of the output member in the second direction and that are disengaged when the input member is rotated in the said opposite, second direction-to permit said rotation of the output member in the second direction.

Advantageously, the mechanism comprises a pawl fast with one member (preferably the output member) for extension through a slot in the other member (preferably the input member) and to engage an arcuate array of fixed ratchet teeth, one of the bounding edges of said slot deflecting the pawl inwardly when the other member is rotated in said second direction.

Brief Description of the Drawings By way of example, embodiments of this invention will now be described with reference to the accompanying drawings of which: Figure 1 is a diagrammatic perspective view of a sphygmomanometer incorporating a ratchet mechanism according to the present invention, Figure 2 is an exploded view of parts of the sphygmomanometer of Fig 1 and showing, generally, the ratchet mechanism, Figure 3 is an enlarged view showing parts of the ratchet mechanism shown in Fig 2, Figure 4 is an exploded view of ratchet mechanism parts shown in Fig 3, Figure 5 is a perspective view of the ratchet mechanism parts that are shpwn in Fig 4 when they are interengaged, Figure 6 is a perspective view of the end of a spindle part that is shown in Figs 2 to 5, Figure 7 is a perspective view of the end of a knob unit that is shown in Figs 2 to 5, Figure 8 is a perspective view, corresponding generally to Fig 5, of interengaged ratchet mechanism parts of another embodiment'-a modification of the embodiment of the present invention shown in Figs 1 to 7, Figure 9 is a perspective view of the end of a spindle part that is shown in Fig 8, Figure 10 is a perspective view of the end of a knob unit that is shown in Fig 8, and Figure 11 is a view similar to that of Fig 7 and Fig 10 but of a further modification of the knob unit.

Detailed Description of Example (s) of the Invention The illustrated sphygmomanotneter 110 has cuff means comprising a single inflatable compartment 12 (Fig 2) in the form of an elongate bag or bladder of generally rectangular shape. As is conventional, one wall of the inflatable compartment 12 is provided with a pair of hollow spigots (not shown) for the passage of air into and/or out of the compartment 12. One hollow spigot is connected via a rubber tube and a one-way relief valve to a compressible rubber inflating bulb. The other hollow spigot is connected via a rubber tube to an appropriate pressure guage (e. g. a mercury column guage or an'aneroid or other pressuremeasuring instrument).

The elongate rectangular inflatable compartment 12 is sealed along its edges, and the two spigots are located adjacent one shorter end or edge 13 of the compartment 12.

The sphygmomanometer 110 of Figs 1 to 7 has an end unit 115 that fits into an elongate recess 127 in the outer surface of a generally cylindrical, elongate casing 132 of a cuff constrictive unit 130. The end unit 115 comprises two mutually co-operating elongate parts 128,129 (Fig 2) that together form a main body or cross-piece. The sealed end 13 of the inflatable compartment 12 is sandwiched between the parts 128,129 and secured to them with screw fastenings through holes 123.

The two parts 128,129 of end unit 115 also clamp between them a clip 150 of generally J-shaped form having a short tab-like limb 125 and a longer detent-like limb 152. The tab-like limb 125 can enter a recess 125r in the wall of casing 132, and the detent-like limb 152 has a rib 151 that can co-operate with the edge of a cavity 153 provided in the outer surface of the wall of casing 132. This clip 150 provides a very reliable detent device for fastening the end unit 115 to the casing 132, yet permits their separation by appropriate lifting of limb 152.

The clip's bight wall 154 (Fig 2) is provided with a central bead 155 or like line of greater thickness and with a decreasing wall thickness approaching the bight wall's side edges. In addition, the opposed edges 158a, 158b and 159a, 159b of the recess in parts 128,129 of end unit 115 that accommodates the clip, are provided as oppositely directed, mutually divergent surfaces having a form substantially that of the symbols > < in elision. This oppositely angled arrangement of the side surfaces of the clip's bight wall 154 and of the opposed edges 158a, 158b and 159a, 159b of the clip accomodating recess, allows the clip's bight wall 154 to be pivotable in each direction about its bead 155 (that is located between the divergent walls 158a, 159a and 158a, 159b).

It is this co-operation between clip 150 and casing 132 that permits a measure of twisting angular movement, e. g. of the order of between 5 apd 15 , between the end unit 115 and the casing 132 without those parts becoming separated from one another.. This measure of twisting angular movement permits the looped portion of inflatable compartment 12 (that extends from end unit 115 to a slot 135 in the wall of casing 132) to accommodate the tapering nature of the patient's upper arm-and can do this whether the arm thickness decreases or (in some patients) increases as the arm extends towards the patient's hand, and whether the inflatable cuff is placed on the left arm (as is usual) or (for some patients) is place on the right arm.

As the elongate rectangular cuff or compartment 12 extends through slot 135 of casing 132 it follows a path whereby it bends back or reverses upon it$elf-i. e. it approaches the slot from the same left or right side both internally and externally of the casing 1t2. This tends to provide mutually opposing inflation forces to each of the internal casing surface and the external casing surface adjacent the slot 135 such as to aid in th constrictive effect and in minimising any tendency for the inflation forces internally of the casing to separate the t, wo co-operating casing parts 146,148.

The casing 132 houses and rotatably supports an internal spindle 133 comprising a pair of inter-fitting elongate parts 134,136. The sealed end t7 of the cuff or compartment 12 is sandwiched and clamped between two parts 134,136 and, to enhance this clamping attacment, a plurality of screws or other fasteners may extend through holes 131 provided in the inter-fitting parts 134,136 (and, optionally, also through the cuff's sealed end 17). Part 136 of spindle 133 is provided with both of the spindle's end discs 137 and is also provided with an axially outward extension 138 that is to co-operate with a knob unit 140 projecting through an apertured end wall 141 of the casing 132. This apertured end wall 141 is provided as a separate element (e. g. of a more rigid plastics material to that employed for the casing parts 146,148) that is retained firmly in position by the casing's main co-operating parts 146,148. The casing end wall 141 has its aperture formed as a ring of saw-like ratchet teeth 143, i. e. having sequential steep-rake and shallow-rake surfaces.

As best shown in Figs 3 to 7, the spindle's extension 138 is molded integrally with a pair of diametrically opposite, spirally directed, resilient pawl limbs 144 of which the free ends are to engage and co-operate with the positionally fixed, saw-like ratchet teeth 143. The spindle's extension 138 is also molded integrally with a pair of diametrically opposite lobes 160 defining a first pair of diametrically aligned radial shoulders 169 and, angularly spaced therefrom, a second pair of diametrically aligned radial shoulders 139. The radial shoulders 139 are in use engageable by a pair of diametrically opposite radial flanges 149 molded integrally on knob unit 140. The knob unit 140 is also provided with a pair of diametrically opposite slots 145 through which the resilient limbs 144 extend.

To tighten the external loop of the cuff or compartment 12 about the upper arm of a patient, the knob unit 140 is rotated clockwise. This clockwise rotation of knob unit 140 will cause its flanges 149 to abut against steps 139 of the spindle extension 138 and cause spindle 133 to rotate clockwise to wind in excess lengths of compartment 12. Such clockwise rotation of the spindle 133 is unimpeded since the resilient pawl limbs I44 slip past and over the shallow-rake surfaces of the saw-like teeth 143 in the end wall 141. The limbs 144 may possibly also be slightly deflected radially inwardly (towards the spindle's axis) as they ratchet past the saw-like internal teeth 143.

In contrast, any tendency t6 anti-clockwise rotation of spindle 133 due to tension in the inflatable compartment or cuff 12 will be prevented by engagement between the end tips of the pawl limbs 144 and the steeply raked surfaces of the saw-like teeth 143.

However, when it is desired'to effect loosening of the external loop of inflatable compartment or cuff 12 from off the patient's arm, the knob'unit 140 is rotated anticlockwise. As soon as such anti-clockwise rotation is initiated, the (now leading) trailing edge 145t of each slot 145 engages the outer surface of the spirally directed resilient pawl limb 144 that'projects through that slot, and deflects it inwardly towards the common axis of the knob and spindle. This action moves the free ends or tips of the limbs 144 out of their engagement of the saw-teeth 143 and removes the restraint to the anti-clockwise rotation of spindle 133 and to compartment 12 being unwound from it.

To ensure that any further anti-clockwise rotation of knob unit 140 does not cause damage to the parts and/or does not move co-operating parts to positions in which their subsequent co-operation (upon ; clockwise rotation of the knob unit) would be prejudiced, the spindle extension 138 and the knob unit 140 may be provided with co-operating detent means 147,157. As illustrated, the co-operating detent means on knob unit 140 comprises a pair of diametrically opposite, generally arcuate, resilient limbs 147 molded integrally at the free end of knob unit 140, each limb 147 having an undercut recess 147r in its radially inward surface. The co-operating part on spindle extension 138 is provided by a pair of diametrically opposite, triangular lobes 157 that can snap into the undercut recess 147r in each limb 147 as the knob unit 140 is rotated anti-clockwise past the leading end of each arcuate resilient limb 147 (which is deflected resiliently outwardly to permit this motion).

It will be appreciated that the above-described parts 138 to 157 provide a one-hand operable ratchet mechanism having a rotatable input member (knob unit 140) and a rotatable output member (spindle 133), rotation of the input member in a first direction effecting rotation of the output member in that direction but preventing rotation of the output member in a second, opposite direction, and rotation of the input member in the opposite second direction permitting rotation of the output member in that second direction. It will be noted that the embodiment of Figs 1 to 7 achieves this by providing first and second mutually engageable ratchet means that, when the input member is rotated in said first direction are in mutual co-operative engagement to prevent said rotation of the output member in the second direction and that are disengaged when the input member is rotated in the said opposite, second directionto permit said rotation of the output member in the second direction.

It will be apparent from the foregoing description of the embodiment of Figs 1 to 7 that, after the subject's blood pressure has been measured, and the pressure in the cuff 12 released, the cuff means can be released from off the subject's arm in one and/or other of two ways. One way is by disengaging the ratchet mechanism's co-operatively engageable parts 143,144 to permit withdrawal of a wound-up cuff portion from the housing 132, the thus-extended length of cuff externally of the housing being then freely movable with respect to the subject's arm and allowing the apparatus to be slipped off the subject's arm. The second way is by simply uncoupling the resilient clip 150 from off the casing 132 to free the apparats as a whole from off the subject's arm.

It will be appreciated that the embodiment of Figs 1 to 7 can be modified in a number of ways.

In one modification, the end wall 141 is not a separate component but, instead, is molded integrally with one or other of the two mutually co-operating parts 146,148 of casing 132.

In another modification, illustrated as the embodiment of Figs 8 to 10, the co-operatinq detent means 147,157 of the embodiment of Figs 1-7 are omitted and, instead, the angular extent of each slot 145 in knob unit 140 and of each lobe 160 on spindle end 138 is altered. Each slot 145 is widened to permit the pawl arm 144 normally projecting therethrough to be deflected wholly inwardly of slot 145 as the (now leading) trailing edge 145t engages that arm 144 upon anti-clockwise rotation of knob 140. Thus the arms 144 do not impede anti-clockwise rotation of the knob 140. In addition, the angular extent of each lobe 160 on the spindle end extension 138 is reduced to provide a pair of diametrically opposite radial shoulders 169 angularly spaced from the shoulders 139. The arrangement is such that, upon anti-clockwise rotation of knob 140, the shoulder 169 of each lobe 160. is engaged by an associated radial flange or surface 168 provided by the knob 140 unit.

This arrangement ensures that anti-clockwise rotation of knob unit 140 can release ratchet co-operation between parts 134,144 but not move so far anti-clockwise that the inherent co-operative relationship between the parts is disturbed to an extent preventing their subsequent cooperation upon later clockwise rotation of the knob unit 140 for re-use of the cuff means. In other words, after initial anti-clockwise rotation of the knob unit 140 with respect to the spindle 133, further anti-clockwise rotation of the knob unit 140 is accompamied by corresponding anticlockwise rotation of the spindle to unwind the cuff 12 therefrom.

Optionally, the knob unit 140 of Fig 10 is (or, indeed, that of Fig 7) may be provided with a pair of diametrically opposite arcuate limbs 170 which, when the knob unit 140 is rotated clockwise, enage root-adjacent portions of the pawl members 144 and urge the pawl members 144 outwardly through the slots 145. These limbs 170 thus aid the inherent resiliency of the pawl members 144 and ensure that they engage the ratchet teeth 143 during such clockwise rotation of the knob unit 140.

In a still further modification illustrated in Fig 11, parts 147 and 157 are again omitted but the latching cooperation between them is replaced by providing the knob unit 140 with an elongate arcuate recess 167 in the interior face of the wall defining the edge 145t of the slot 145. The ends of this elongate arcuate recess 167 are defined at one end by a generally radially directed bounding surface 166 adjacent slot 145 and at the other end by a somewhat curved surface 165, the distance between surfaces 165 and 166 being sufficient to accomodate a pawl 144. When the knob unit 140 of Fig 11 is rotated anticlockwise to disenage (i. e. release) the ratchet mechanism between pawl 144 on spindle 133 (of either Fig 6 or Fig 9) and ratchet teeth 143, the pawl 144 slides relatively past the wall's edge 145t and, due to its inherent resiliency, enters somewhat fittingly into the recess 167 to engage behind the bounding surface 166 of the recess. Thus, here again, after initial anti-clockwise rotation of the knob unit 140 with respect to the spindle 133, further anticlockwise rotation of the knqb unit 140 is accompamied by corresponding anti-clockwise rotation of the spindle to unwind the cuff 12 therefrom.

It will be appreciated that in use of the illustrated embodiments of sphygmomanometer to measure a subject's blood pressure, the end unit 115 is snap-connected to the constrictor unit 130 to form the inflatable bladder or bag as a loop that encompasses the subject's arm (usually the left arm) above elbow. The knob unit 140 is then rotated to wind up the cuff 12 about the spindle 133 and draw the cuff 12 into the housing 132 until the cuff-with units 115 and 130-provides a snug fit around the subject's upper arm.

It will be appreciated that the arrangement allows the cuff element 12, on its own, to encompass at least 80% of the circumference of the upper arm of any subject (i. e. whatever size of upper arm the subject may have) and that the cuff 12 is in a position appropriate to shut off blood flow in the brachial artery when the bag (which the cuff 12 defines or contains) is inflated.

It will also be appreciated that the above-described ratchet mechanism permits rotation of the spindle 133 in this"cuff-winding-in"direction and, as long as it is not subject to counter-rotation, prevents spindle rotation in the contra-direction which would allow loosening of the cuff 12 from conforming engagement of and around the subject's upper arm.

Using the inflation bulb, air is pumped into the bag 12 via the one-way valve 20 and its associated tube and spigot, the effective volume of the bag being only that which conforms to the perimeter of the subject's upper arm, i. e. which is external of the constriction provided by the constrictor unit 130. This is because the ratchet mechanism prevents any air-pressure-induced unwinding of the cuff from off the spindle 133 and thus prevents any increase in the inflatable length of the cuff beyond that to which it was initially set when the cuff was initially wound into the casing 132. The pumped air supply is continued until the subject's pulse in the brachial artery in the upper arm disappears. The reading of the guage at this moment gives the systolic blood pressure, i. e. the pressure necessary to suppress the maximum pressure of blood in the artery. The air pressure within the bladder is then allowed to decrease slowly via the one-way relief valve whilst the (expected) pulse beat is monitored by the user's stethoscope. As the air pressure compressing the artery is diminished, the pressure reading on the gauge at which the maximum pulse wave is (again) obtained marks the diastolic pressure, i. e. provides a measure of the pressure when the heart is in diastole with arterial pressure at its minimum.

After the subject's blood pressure has been measured, the knob unit 45 can be rotated in the opposite direction so as to permit loosening of the cuff 12 from around the subject's arm. Such counter-rotation pushes additional length of cuff outwards of the casing 132 and/or simply enables pulling of the cuff 12 outwards from the casing 132. Once the cuff is loose, the subject or the person (e. g. nurse or doctor) responsible for obtaining the subject's blood pressure can, using a thumb or their fingers, disengage the two units 115 and 130 from one another by separating the inter-latched parts 151 and 152.

Other modifications and embodiments of the invention, which will be readily apparent to those skilled in this art, are to be deemed within the ambit and scope of the invention, and the particular embodiment (s) hereinbefore described may be varied in construction and detail, e. g. interchanging (where appropriate or desired) different features of each, without departing from the scopie of the patent monopoly hereby sought. For example the guage 26 may be a simple mercury manometer, or may be an aneroid instrument, or may be an electronic pressure mqasuring instrument. Also for example, and either additionally or alternatively, the fasteners provided to attach either or each end 13,17 of the cuff 12 to its associated unit 115,130 may be other than screws. For example they'may comprise spigots provided with undercut tips to snap fit into the holes 123 and/or 131.

Claims (6)

1. CLAIMS 1. A releasable ratchet mechanism that is one-hand operable and comprises a rotatable input member, a rotatable output member, and mutually engageable ratchet means effecting selectively disengageable coupling between the said input and output members such that rotation of the input member in a first direction effects rotation of the output member in that direction but prevents rotation of the output member in a second, opposite direction, and such that rotation of the input member in the opposite second direction permits rotation of the output member in that second direction.
2. 2. A ratchet mechanism according to Claim 1 and comprising first and second mutually engageable ratchet means that, when the input member is rotated in said first direction, are in mutual co-operative engagement to prevent said rotation of the output member in the second direction and that are disengaged when the input member is rotated in the said opposite, second direction-to permit said rotation of the output member in the second direction.
3. 3. A ratchet mechanism according to Claim 2 and comprising a pawl fast with one member for extension through a slot in the other member and to engage an arcuate array of fixed ratchet teeth, one of the bounding edges of said slot deflecting the pawl inwardly when the other member is rotated in said second direction.
4. 4. A ratchet mechanism according to Claim 3 wherein the pawl is fast with the output member and said slot is provided in the input member.
5. 5. A ratchet mechanism susbstantially as herein described with reference to and/or as illustrated in the accompanying drawings.
6. 6. A ratchet mechanism according to any preceding Claim forming part of sphygmomanometer cuff means.