Display device for the number of heatings performed

Abstract: A display device is described which indicates the number of heatings performed, especially for the purpose of autoclave sterilization. The display device comprises a temperature-sensitive mechanical element (22) which essentially reversibly transforms from a first spacial state to a second spacial state when the temperature-sensitive mechanical element (22) is heated in excess of a predetermined temperature. The temperature-sensitive mechanical element (22) is coupled to the actuating element (32) of a counter mechanism (32, 4), and upon the transformation to the second spacial state effects movement of the actuating element (32) into an actuation position.

Description: The present invention is directed to a display device for the number of heatings performed, particularly for the purpose of autoclave sterilization. Conventionally, surgical instruments have been made of metal. In this case there is no problem in sterilizing the instruments using an autoclave where they are heated up to 120°C or 135°C. The application of plastics, however, has some advantages over metal: it can easily be molded in complicated shapes, it has a light weight, and it is less expensive than metal. Especially for elaborate instruments, as they are used, e.g. in minimally invasive surgery or in laparoscopic operations, there is a trend to apply plastics. In many cases the whole instrument or part of the instrument is designed to be disposed of after the operation. To save costs it is often advantageous if the instrument has some reusable parts which have to be sterilized in an autoclave after the operation. Some plastic materials can resist the temperatures during this process (120°C to 135°C), e.g. polyetherimide. Generally, they can be treated in an autoclave only for a limited number of times (in the order of 10 times), because they age, crack, etc.. Consequently the instruments are not reliable anymore after having been heated too often. US-A-4 235 842 discloses a contact lens disinfector unit which includes an indication device indicating the number of sterilizing cycles which have been employed since the contact lenses were last cleaned. The indication device comprises a drum, which has indicia on its lateral wall and is rotated by means of a ratched wheel which is driven by a bimetallic strip having pawl elements. The preamble of Claim 1 is based on US-A-4 235 842. It is an object of the present invention to provide a means for indicating the number of heatings performed which is reliable, inexpensive and small. This problem is solved by the display device for the number of heatings performed, particularly for the purpose of autoclave sterilization, having the features of Claim 1. The dependent claims describe advantageous embodiments of the invention. The display device according to the invention can be manufactured in small size, so that it can be easily attached to a semi-disposable surgical instrument for indicating the number of times the instrument has been subjected to high heat. It is also possible to equip a reusable instrument with the display device according to the invention, e.g. to indicate the need for maintenance. In the display device according to the invention a temperature-sensitive mechanical element changes its size when it is heated to high temperature. This element is coupled to an actuating element of a counter, thus increasing the number or symbol displayed by the counter by one each time the temperature-sensitive mechanical element actuates the actuating element. The number or other kind of symbol displayed by the counter is easily visible, so that the person using a surgical instrument having the display device according to the invention is informed on the number of times the instrument has been heated and thus on its residual lifetime. The temperature-sensitive mechanical element is made of a memory metal, for example of a nickel titanium alloy. A memory metal element can be made to expand or contract at a predetermined temperature. A memory metal has faster response time than bimetallics and the alloy can be custom-designed to actuate the temperature-sensitive member at a desired temperature. For example, the temperature-sensitive mechanical element can be made in the form of a memory metal spring that strongly expands when heated and which essentially reversibly returns to its original shape after cooling to the original temperature. Preferably, in its original shape or first spacial state the memory metal spring is somewhat biased by a reset spring in order to define the original shape precisely. When the memory metal spring is heated above the predetermined temperature and it expands to its second spacial state, it is strong enough to depress the reset spring. Preferably the counter comprizes a ratcheting device. In an advantageous embodiment a first blocking element coupled to the counter moves to a blocking position, after a given number of actuations of the counter has been exceeded. In this way the blocking element may inhibit use of the whole surgical instrument, e.g. by blocking an actuation knob. Similarly, a second blocking element may be coupled to the temperature-sensitive mechanical element or to a second temperature-sensitive mechanical element being responsive at a higher temperature than the ordinary temperature experienced during autoclave sterilization, in order to inhibit the surgical instrument completely and irreversibly when it has been heated to too high a temperature by accident and is not reliable any more. In the following the present invention is described in more detail by reference to some embodiments. The drawings show: Figure 1 a sectional view of a first embodiment of a display device; Figure 2a a top view of a second embodiment of a display device, having a top plate of the housing removed; Figure 2b a bottom view of the second embodiment; Figure 3a an exploded side view of a third embodiment of a display device, showing some parts in section; Figure 3b a side view of the third embodiment; Figure 3c a top view onto the inside of one of the half-shells of the housing of the third embodiment; Figure 3d a top view of one of the counting wheels of the third embodiment; Figure 3e a diagrammatic view illustrating the function of the display device according to the third embodiment; and Figure 3f a side view of the display device according to the third embodiment attached to a surgical instrument. Figure 1 illustrates a first embodiment of a display device. In a housing 2 a ratchet wheel 4 having teeth 5 is rotatably mounted by means of a pivot 6. In an upper portion 10 of the housing 2 a shaft 13 is slidably supported in guide holes 11, 12. A safety spring 18 is located between an abutting surface 14 and a first disk 16 being slidably mounted on the shaft 13. A spring 22 serves as temperature-sensitive mechanical element and is made of a suitable memory metal alloy. Spring 22 abutes against the first disk 16 and a second disk 20 which is rigidly attached to the shaft 13. A reset spring 28 made of ordinary metal is held between a third disk 24 which is rigidly attached to the shaft 13 and an abutting surface 26. In the resting position of the device in which the temperature-sensitive mechanical element (spring 22) is in its first spacial state, the reset spring 28 presses the third disk 24 against a protrusion 30, as shown in Figure 1. In this state spring 22 is slightly compressed. One end of a ratchet 32 in form of a leaf spring is fixed to the bottom side of shaft 13. The ratchet 32 is biased against the ratchet wheel 4, so that its free end 33 touches the ratchet wheel 4 along its periphery, i.e. at the low-slope sides of the teeth 5. A safety ratchet 34 in form of a leaf spring is fixed at the upper side of shaft 13 close to the third disk 24. The free end 35 of safety ratchet 34 is biased away from shaft 13, so that the safety ratchet 34 can be depressed by means of a protrusion 36. In the lower part of the housing 2 a second ratchet 38 is attached by means of a support member 39. On the ratchet wheel 4 there are provided display numbers 42, each display number 42 being associated to one tooth 5. A cover plate of housing 2 comprises a window (not shown in Figure 1) through which one of the display numbers 42 is visible. Preferably the display numbers 42 are arranged in consecutive order; it is also possible to use some other kind of display signs or symbols, e.g. a colour code. In the following the way is described how the display device according to the first embodiment works. Figure 1 displays the resting position of the device in which spring 22 is its first spacial state, i.e. a compressed state. It has to be noted that it is not necessay to bias spring 22 to a compressed configuration, because it is made of a memory metal and will strongly expand in this embodiment upon heating and almost reversibly return to its original size upon cooling. Some compression of spring 22 in its resting position is advantageous, however, because in this way the resting position of the ratchet 32, which serves as the actuating element of the counter, is well defined by means of the reset spring 28, the third disk 24 and the protrusion 30. When the display device and the surgical instrument it is attached two are heated, e.g. in an autoclave, spring 22 strongly expands whereas safety spring 18 keeps its original size as long as the device is not heated to too high a temperature. The expanding spring 22 moves the shaft 13 to the right side and it is strong enough to compress the reset spring 28. During the movement of the shaft 13 the free end 33 of ratchet 32 engages to the steep-slope side of the tooth 5 closest to it and rotates the ratchet wheel 4 in a clockwise sense. When the ratchet 32 has reached its actuating position (spring 22 is in its second spacial state now), the ratchet wheel 4 has been rotated by one tooth, i.e. until the second ratchet 38 snaps across the tip of the tooth it is biased against. When the temperature decreases the spring 22 returns to its first spacial state, i.e. the resting position shown in Figure 1. The friction between the free end 33 and the ratchet wheel 4 cannot cause the ratchet wheel 4 to rotate counterclockwise again, because such rotation is inhibited now by second ratchet 38. This embodiment comprises the safety spring 18 by means of which it is possible to lock the whole surgical instrument the display device is attached to, for the case the instrument is exposed to a dangerously high temperature which would render it inoperative for future use. If the temperature exceeds a predetermined level (being higher than the response temperature of spring 22) the safety spring 18 (as well as spring 22) expands, so that the total displacement of shaft 13 is large enough for the free end 35 of safety ratchet 34 to engage on the right side of protrusion 30. When that happens shaft 13 cannot retract to its original position after cooling. Furthermore, the end 40 of shaft 13 will project from the upper portion 10 of the housing 2 as shown in dotted lines in Figure 1. The end 40 can serve as a blocking element by locking, e.g. an actuating knob of the surgical instrument. Figure 2 shows a second embodiment of a display device. In a housing 52 a ratchet wheel 54 is rotatably mounted by means of a pivot 56. The ratchet wheel 54 has the general shape of an open cylinder having a toothed ring 55 on the inner lateral area. A spring member 60 comprising a first leg 62, a second leg 64 and a resilient arcuate portion 66 is biased in a way as to increase the distance between the first leg 62 and the second leg 64, as shown in Figure 2a. The first leg 62 of spring member 60 is rigidly fixed to housing 52. A spring 68 made of a memory metal alloy is attached to the spring member 60 by inserting the ends of the spring 68 through holes 69 in the first leg 62 and the second leg 64. Along the side of the second leg 64 the fixed end 72 of a ratchet spring 70 is rigidly attached to the second leg 64. The ratchet spring 70 is a kind of arcuate leaf spring with its long side extending along approximately half of the inner periphery of ratchet wheel 54, whereas its small side extends perpendicularly to the plane of Figure 2a. The free end 74 of ratchet spring 70 is bent outwardly. In order to enable a safety function which will be described later the toothed rang 55 comprises a gap 80 and the housing 52 includes a side window 82. Figure 2b shows the display device of Figure 2a from the other side, i.e. the bottom side. A bottom plate 84 comprises a window 86 through which one of the display numbers 88 is visible. The display numbers 88 are arranged along a circle line on the bottom side of ratchet wheel 54. Instead of display numbers it is possible to use other kinds of symbols. This embodiment of the inventive display device works in the following way. In its first spacial state, i.e. at low temperature, the spring 68 has a short length, and it is strong enough to bias the arcuate portion 66 of spring member 60. In this state (which is not shown in Figure 2a) the second leg 64 is moved to the left and consequently the free end 74 of the ratchet spring 70 is moved downwardly. Now, when the temperature is raised above the predetermined temperature the spring 68 expands and allows the spring member 60 to relax. Consequently, the second leg 64 moves to the right and the free end 74 of the ratchet spring 70 moves upwardly (Figure 2a). Because it engages the steep-slope side of a tooth 76 of the ratchet wheel 54 it rotates the ratchet wheel 54 in a clockwise sense by one tooth width, exhibiting the next display number 88. As the temperature decreases the spring 68 contracts, biases the spring member 60 and moves the free end 74 of the ratchet spring 70 downwardly until it snaps across the tip of the subsequent tooth. The safety feature provided by this embodiment is able to block the surgical instrument the device is attached to after a predetermined number of sterilizations has been performed. After the last allowed heating process the free end 74 of the ratchet spring 70 engages at the edge 78. When the device is sterilized another time, on cooling the free end 74 reaches the upper end of gap 80. Because the ratchet spring 70 is biased outwardly, in this moment it is not supported anymore by the toothed ring 55 and penetrates the side window 82, as shown in Figure 2a and Figure 2b in dotted lines. In a similar manner as the blocking device according to the first embodiment, the protruding free end 74 is able to lock the whole surgical instrument in order to inhibit its future use. A third embodiment of a display device is illustrated in Figure 3. Figure 3a shows the individual members of this embodiment in exploded side view. A first half-shell 100 of the housing of the display device, a second half-shell 101 of the housing, a first counting wheel 120, and a second counting wheel 121 are concentrically aligned along an axis A-A which is the rotation axis of the counting wheels 120, 121. The first half-shell 100 of the housing comprises a bottom portion 102, a lateral area 104 forming the outer periphery, and a generally cylindrical bearing member 106 whose axial extension is somewhat smaller than that of the lateral area 104 (see Figure 3a). Radially extending ribs 108 are formed on the inner surface of the bottom portion 102, as shown in Figure 3c. A window 110 is located in the lateral area 104. The construction of the second half-shell 101 of the housing is the same as that of the first half-shell 100. Preferably both half-shells 100, 101 are molded from a suitable temperature-resistive plastic material. A first counting wheel 120 generally has the shape of an open cylinder. A hub portion 122 is supported by the bearing member 106 of the first half-shell 100 of the housing, and a lateral area 124 is adapted to fit into the first half-shell 100 of the housing. Display numbers 126 or similar display signs are arranged on the outer lateral area 124, see Figure 3a. On the hub portion 122 is formed an arcuate ratchet 128 which is bent toward the facing bottom portion 102, so that the free end 129 of the ratchet 128 resiliently abuts against the bottom portion 102 including the ribs 108, see also Figure 3d. In the center of the first counting wheel 120 is provided a center hole 132 the diameter of which corresponds to that of the bearing member 106. A generally tangentially extending arcuate first opening 134 having a nose 135 is formed close to the periphery of the hub portion 122. A similar second opening 136 having a nose 137 is provided approximately diametrically opposite to the first opening 134. If the first counting wheel 120 is inserted in the first half-shell 100 of the housing, the ratchet 128 enables rotation of the first counting wheel 120 in one direction only, which is the clockwise sense in Figure 3d. A counterclockwise rotational movement is inhibited, because in this case the free end 129 of the ratchet 128 engages an edge between the bottom portion 102 and a rib 108 and cannot come across the rib 108. The second counting wheel 121 which is inserted into the second half-shell 101 of the housing, so that the hub portions of the counting wheels 120, 121 face each other (see Figure 3a), is constructed in essentially the same way as the first counting wheel 120, except for that its ratchet is arranged in a way that both counting wheels 120, 121 can be rotated in the same direction only. Preferably the counting wheels 120, 121 are made of stainless steel. The second counting wheel 121 is arranged with respect to the first counting wheel 120, so that the first opening 134 of the first counting wheel 120 roughly coincides with a corresponding first opening in the hub portion of the second counting wheel 121. The same holds for the second opening 136 of the first counting wheel 120 and a corresponding one in the second counting wheel 121. A helical spring 140 made of a memory metal alloy is inserted into the first opening 134 of the first counting wheel 120 where its first end 142 (see Figure 3e) is held by the nose 135. The second end 143 of the helical spring 140 is similarly held by a corresponding nose in the first opening of the second counting wheel 121. In this way the helical spring 140 exerts a force onto the first counting wheel 120 via its first end 142 and a force onto the second counting wheel 121 via its second end 143. Another helical spring which is a compression spring made of an ordinary material is inserted into the second opening 136 of the first counting wheel 120 and into a corresponding second opening of the second counting wheel 121. This helical spring 144 presses against the first counting wheel 120 via its first end 146 where it is held by the nose 137, and it presses against the second counting wheel 121 via its second end 147 where a similar nose is provided. The position of the helical springs 140 and 144 with respect of the planes of the hub portions of the counting wheels 120 and 121 is illustrated in Figure 3b. The way how the display device according to the third embodiment works is explained using Figure 3e. Part (A) of Figure 3e shows the resting position of the device in which the helical spring 140 of memory metal, which is the temperature-sensitive mechanical element, is in its first spacial state and in which the first counting wheel 120 serving as the actuating element of the counter is in its resting position. When the display device is heated the helical spring 140 of memory metal expands while it is able to exert a higher force than the ordinary helical spring 144. The helical spring 140 tries to rotate the first counting wheel 120 in a clockwise sense via its first end 142 and to rotate the second counting wheel 121 in a counterclockwise sense via its second end 143. The latter is not possible, because the free end of the ratchet of the second counting wheel 121 abutes against an edge between the bottom portion and a rib of the second half-shell 101 of the housing. As a result of the clockwise rotation by an amount corresponding to the width (better said, angle) between two adjacent ribs, the next display number 126 is moved to the window 110 to indicate the heating process. Furthermore, the helical spring 144 is compressed, see part (B) of Figure 3e where the line 150 serves to aid the eye. Now the helical spring 140 of memory metal is in its second spacial state and the first counting wheel 120 is in its actuating position. In the last step of the counting process which is illustrated in part (C) of Figure 3e the display device cools, the helical spring 140 of memory metal contracts and the helical spring 144 of ordinary material is able to exert a larger force than the memory metal spring. This means that the helical spring 144 tries to rotate the first counting wheel 120 in a counterclockwise sense and to rotate the second counting wheel 121 in a clockwise sense. The former is not possible, because for this direction the ratchet 128 of the first counting wheel 120 blocks. As a result, the second counting wheel 121 is rotated by an amount corresponding to the width between two adjacent ribs in the bottom portion of the second half-shell 101 of the housing. For the case the second half-shell 101 comprises a window, display numbers or symbols, preferably the first digit of a display number, can be provided on the lateral area of the second counting wheel 121, as shown in Figures 3a and 3b. It has to be noted, however, that during each actuation of the display device both counting wheels 120, 121 are rotated by the same angle. Consequently the counting wheels 120, 121 do not form a counter having a decimal reduction ratio. As an alternative, one window and display numbers or symbols associated to one of the counting wheels 120 or 121 is sufficient. Figure 3f illustrates how the display device according to the third embodiment can be attached to a surgical instrument. In this example the surgical instrument 162 is applied in laparoscopy and comprises a handle member 166, an instrument tube 164 and at the distal end (not shown) an operational tool like a needle holder or a clamp, etc.. To reduce costs, some parts of the instrument are semi-reusable, e.g. the instrument tube 164 and the handle member 166. For monitoring the number of times these parts have been exposed to high temperatures during sterilization, a display device 160 is attached to the instrument tube 164, the inner diameter of the bearing member 106 and the diameter of the center hole 132 fitting to the outer diameter of the instrument tube 164. There are various ways to attach a counter device according to the invention to a surgical instrument. Another example is to include it in the handle member of the surgical instrument.

Claims: Display device for the number of heatings performed, particularly for the purpose of autoclave sterilization, comprising a temperature-sensitive mechanical element (140) which essentially reversibly transforms from a first spacial state to a second spacial state during heating in excess of a predetermined temperature, and a counter mechanism (100, 101, 120, 121) being responsive to an actuating element (120) movable from a resting position to an actuating position, said temperature-sensitive mechanical element (140) being coupled to said actuating element (120) and effecting a movement of said actuating element (120) into said actuating position during the transformation into said second spacial state, characterized in that said temperature-sensitive mechanical element (140) is made of a memory metal, preferably a nickel titanium alloy, said display device comprises two half-shells (100, 101) of a housing being provided with radially extending ribs (108) on the inner surfaces of their bottoms (102), in each of both half-shells (100, 101) a counting wheel (120, 121) is rotatably supported, from which counting wheel (120, 121) extends a ratchet (128) having the form of a leaf spring bent away from a hub portion (122), which ratchet (128) being able to abut with its free end (129) against one of said ribs (108) in said assigned half-shell (100, 101) of said housing, so that both counting wheels (120, 121) being coaxially positioned with respect to each other are rotatable in a common rotational direction and block in the opposite direction, both counting wheels (120, 121) are coupled via two tangentially extending, essentially diametrically opposing helical springs (140, 144), each of said helical springs (140, 144) engaging with one end (142, 146) to one of said counting wheels (120) and with the other end (143, 147) to the other counting wheel (121), one of both helical springs (140) being made of a memory metal, at least one of both counting wheels (120, 121) is provided with consecutive display numbers (126) or display symbols in peripheral direction, and a window (110) is provided in said respective half-shell (100, 101) of said housing, one of said display numbers (126) or said display symbols, respectively, being visible through said window (110). Display device according to Claim 1, characterized in that a first blocking element coupled to said counter mechanism is movable to a blocking state when the number of actuations of said counter mechanism exceeds a predetermined number. Display device according to Claim 1 or 2, characterized in that a second blocking element coupled to said temperature-sensitive mechanical element is movable to a blocking state when the temperature exceeds a second predetermined temperature being greater than said predetermined temperature. Display device according to Claim 1 or 2, characterized in that a second blocking element coupled to a second temperature-sensitive mechanical element is movable to a blocking state when the temperature exceeds a second predetermined temperature being greater than said predetermined temperature. Display device according to one of Claims 1 to 4, characterized in that said display device (160) is positioned on a surgical instrument (162) in order to indicate the number of autoclave sterilizations of the surgical instrument (162) performed.

Inventors: SCHULZE DALE, SCHULZE, DALE
Applicants: ETHICON INC, ETHICON INC.
Application year: 1993
Main classification: G06M1
IPC codes: G01K5, A61B17, G06M1, A61L2, G01K11