Pipette.

0001The subject of the invention is a plain pipette being a laboratory instrument and serving for drawing in, pipet­ting and dispensing the fluid of a strictly specified volume.

0002From the FRG patent specification No. 2,921,442 there is known a plain volume-controlled pipette, which consists of a casing, being simultaneously a hand grip, in its lower end comprising a joint cylinder with tubular terminals; of a piston placed in the said cylinder, being pressed down by means of a push and of a piston rod, contrary to the for­ce being exerted by a spring, which urges the piston to re­turn to its upper position; of an upper internal thread re­ducer sleeve, which is screwed upon the piston rod threading and which defines the upper position of the piston. The up­per sleeve and the casing are provided with a co-operating groove/projection assembly, which prevents turning thereof but enables the movement of the sleeve along the piston rod, and thereby, after turning the push which defines the upper position of the piston, the sleeve can be displaced up and down relative to the piston rod, changing the pipette's vo­lume which is monitored on the scale in the casing.

0003In the course of pipetting, the push is pressed, what makes the sleeve and piston move downward until the push is pres­sed down to a support. Starting from this point, it is pos­sible to further press down the push of the piston, together with a portion of the support being outside the end of the casing. The upward movement of the piston is limited by a flange in the casing, whereto the upper reducer sleeve is pressed, on return of the piston to its upper position.

0004From the other FRG patent specification No. 2,549,477, there is known a hand-held pipetting device, comprising a slim, conical body, the upper portion whereof is a handle, while the lower portion is terminated with an outlet member projecting outside the body, whereon a replaceable working tip of the pipette is fitted. Inside the body, there is mounted a dispensing mechanism being activated by means of a push projecting over the upper portion of the body. The mechanism of the pipette principally consists of a few ope­rating systems placed in tandem on a single axis running alongside the whole symmetry axis of the pipette. The up­per part of the mechanism constitutes the dosage measuring system. The said system comprises a piston rod being termi­ nated with a push projecting over the body, a return spring being fitted on the piston rod and a limiter with a hole in its bottom, wherethrough there passes the end of the piston rod. In the lower part, along the height of the limiter, on the periphery of the piston rod, there are six stops, being symmetrically spaced in pairs, having the three different heights determining the three different lengths of stroke of a plunger. Whereas in the bottom of the limiter, there are made pass-through conduits corres­ponding to the spacing of the two pairs of stops. In the body above the limiter, there is screwed a constant ring setting the upper basic position of the plunger and the whole mechanism. The said ring and limiter are made as per­manent magnets, and the limiter mechanism in its state of rest, due to the magnetic field effect, adheres with its upper flange periphery to the cylindrical stop.

0005Another solution is known from the US patent specification No. 4,009,611. The pipetting and blowing mechanisms are in fact placed on a single axis, but they are completely separated from the release mechanism of the actuating tip.

0006A pipette, as disclosed in the US patent specification No. 4,009,611, has a cylindrical body being a handle and an outerly step-by-step slimmer cylinder, being an elong­ation thereof, with a correspondingly step-by-step slimmer ejector's sleeve, being mounted thereon. Inside the body there is placed a long piston rod also terminated with a long rod plunger embedded into the cylinder, and periphe­ rally sealed from the top of the system.

0007Into the upper part, inside the body, a sleeve is forced, the length whereof is determined by the plunger's one-­length stroke. Under the sleeve, there is a movable ring threaded through the piston rod and held down from the bot­tom by means of a spiral spring in such a manner that a se­parable sleeve bottom is formed. Beneath the ring there is another sleeve, being also permanently forced inside the body. Inside the said sleeve there is a return spring mounted on the piston rod, with its lower end resting upon the bottom of the body, whereas with its upper end resting upon a peripheral limiter, being fitted on the piston rod beneath the ring which forms the bottom of the upper sle­eve. The upper end of the piston rod passes through the interior of the upper sleeve and projects above the body, where the piston rod is terminated with a push. The said push is a right-angled triangle in cross-section with a rounded and profiled leg for better support of a thumb. On the piston rod, in the upper sleeve area, there is fit­ted a ring-shaped stop, which in the state of rest of the mechanism is by means of return springs held down to the upper inner wall of the body.

0008Furthermore, from the Polish patent application No. P. 242,647, there is known a laboratory micro-pipette for drawing in the dispensing the predetermined volumes of fluid with a high precision rate.

0009The said laboratory micro-pipette is characterized in that in the upper separable two-segment body, in the por­tion above the piston, there is a partition wall, whereunder there is placed a main spring co-operating with the piston.

0010Above the partition wall, there is an auxiliary spring acting upon the sleeve, being centrically and movably placed inside the piston stroke control spring which is screwed in the aperture of the upper portion of the bo­dy, above the auxiliary spring. Inside the sleeve there is centrically placed a movable push rod of the piston, provided with a push head.

0011The hitherto-known pipettes are of a quite complicated design as they comprise a great number of component parts. Moreover, in the hitherto-known solutions of pipettes, the pressing movement is at length accompanied by the movement of a plunger. The force barrier is car­ried out by a bending stop. It results in a risk of weaker or stronger pressing down to a stop because of a fear of exceeding the force barrier, and the steps of pressing movement are not properly differentiated, what makes it possible that a high repeatability of results in drawing in the fluid for examination is not entire­ly ensured.

0012The plain pipette as per the present invention is charac­teric by the fact that in the middle of the symmetry axis of the body of the casing, right under a push, there is a calibration unit.

0013The said calibration unit comprises a multi-step calibra­tion sleeve resting upon the inner projection of the body of the casing, the said sleeve being blocked from the top by means of a hold-down element being screwed into the body of the casing. Inside the calibration sleeve, there freely slides an arbor which is connected to a press means, being with a part of its flattened diameter placed inside a flat­tened oblong sleeve being a push rod, which from the top rests with its flange upon the face of a stop, being screwed into the internal thread of the calibration sleeve. From the top, upon the flange of the push rod, pressure is exer­ted by the blow-out mechanism spring, which from the top rests upon a multi-step washer being blocked by a ring which is slid into the recess of an arbor. The lower part of the push rod contacts the flange of the plunger, whereas there remains a narrow slot between the said flange and the end of the arbor. The inner bottom flange of the cali­bration sleeve forms a resistance point for the push rod, being displaced downwards together with the arbor. The plun­ger of the pipette comprises a two-step flange and a trunca­ted cone portion, being with its smaller diameter directed towards the oblong arbor of the plunger terminated with the other conical portion. At the place of joint of the body of the casing and of a shank, there is a plunger sea­ling unit, comprising a nut with a flanged sleeve screwed into the internal thread thereof, being a hold-down element, which through the said sleeve presses down the ring and the sealing sleeve to the face of the main body.

0014In the other version of the pipette as per the present invention, a plunger comprises a two-step flange, a short cylindrical portion and then an oblong arbor and a thin plunger rod. At the place of joint of a body of a casing and of a shank, there is a plunger sealing unit comprising a nut, inside whereof a hold-down element is screwed, which through a spring exerts pressure upon a hold-down sleeve, which, being slid into the hole of the shank, presses down the ring and the sealing sleeve to the face of the shank. The press means of the pipette is in the shape of a round, one end-closed sleeve, whereto from the inside an arbor is rigidly fitted. From the outside, it has a transparent plastics cover mounted thereon. At the top, around the periphery of the press means, there is a rectangular gro­ove, wherein an information strip is placed.

0015The pipette as per the present invention, due to its plain design, is technologically more feasible.

0016Moreover, the pipette as per the present invention, due to the application of a calibration unit, in the course of pressing down the press means, is capable of differentia­ting the three steps of movement and the two force bar­riers and of separating them, where only the first and the third step of pressing movement is accompanied by the mo­vement of the plunger. In the second step of movement of the said plunger, the pipette performs an idle movement, which separates the draw-in cycle from the blow-out cyc­le. By such a capability of the pipette, a high repeat­ability of results in the course of operation in drawing in the fluid for examination is ensured.

0017The subject of the invention is presented in the example of embodiment in the drawing, where <ul id="ul0001" list-style="none"><li>Fig. 1 is a plain pi­pette in view,</li><li>Fig. 2 and 3 - is the plain pipette in a long-operation cycle in its longitudinal section,</li><li>Fig. 4 and 5 - is the plain pipette in a short-operation cycle in its longitudinal section,</li><li>Fig. 6 - is a calibration unit in the state of rest in its along-axis section,</li><li>Fig. 7 - is the calibration unit in the first step of mo­vement of the press means in its along-axis section.</li><li>Fig. 8 - is the calibration unit in the second step of move­ment of the press means in its along-axis section, and</li><li>Fig. 9 - is the calibration unit in the third step of mo­vement of the press means in its along-axis section.</li></ul>

0018In Figs. 1, 2 and 3, the plain pipette is shown which ser­ves for drawing in the fluid within the range of 100 - 1000 µl. It comprises a round body of a casing <u style="single">1</u>, which is made of plastics material, simultaneously being a handle for the persons applying it. To the lower portion of the body of easing <u style="single">1</u>, a shank <u style="single">3</u> is fitted through a round nut <u style="single">2</u> being screwed into the end of the body of casing <u style="single">1</u>, being in the shape of a step-by-step elongated sleeve. Inside nut <u style="single">2</u>, there is a sealing unit of a plunger <u style="single">4</u>, which comprises a hold-down element <u style="single">5</u> being in the shape of a flanged sleeve. Hold-down element <u style="single">5</u>, being screwed inside the internal thread of nut <u style="single">2</u>, through a sleeve <u style="single">6</u> presses down a ring <u style="single">7</u> and a sealing sleeve <u style="single">8</u> to th face of shank <u style="single">3</u>, which together seal the arbor of plunger <u style="single">4</u>, which slides into the opening of shank <u style="single">3</u>. The free and of shank <u style="single">3</u> is made in such a manner that it enables inser­ting therein a tip for drawing in the examined fluid, not being shown into the drawing.

0019Inside the body of casing <u style="single">1</u>, being a cylinder <u style="single">9</u>, there is placed a plunger <u style="single">4</u>. Plunger <u style="single">4</u> consists of a two-step flange <u style="single">10</u> being connected to a conical portion <u style="single">11</u> which is narrower towards the bottom, and then of a cylindrical portion being an arbor <u style="single">21</u>, which is again at the bottom terminated with a conical portion <u style="single">12</u> being narrower to­wards the bottom. On the side of conical portion <u style="single">11</u>, resting from one side on flange <u style="single">10</u> and from the other side on hold-down element<u style="single">5</u>, there is a cylindrical spring <u style="single">13</u> lifting plunger <u style="single">4</u> upwards. From the top, flange <u style="single">10</u> is pressed down by a push rod <u style="single">14</u> provided with an arbor <u style="single">15</u>, which has a press means <u style="single">16</u> fitted upon its upper end, whereas the movement of push rod <u style="single">14</u> and arbor <u style="single">15</u>. Arbor <u style="single">15</u> is in the shape of a two-step round rod, having an un­dercut in the fitting place of pressing element <u style="single">16</u>, and the other one in the fitting place of ring <u style="single">17</u>, and of a step washer <u style="single">18</u>. Directly beneath press means <u style="single">16</u>, there is a calibration unit, serving to impart the particular sta­ges of movement to plunger <u style="single">4</u> which comprises a multi-step calibration sleeve <u style="single">19</u>, being inserted inside the body of casing <u style="single">1</u>, inside whereof there is screwed a short step <u style="single">20</u> being in the shape of a sleeve. Inside the calibration unit, arbor <u style="single">15</u> is placed with its bigger diameter in the middle of elongated push rod <u style="single">14</u>, being in the shape of a step sleeve which is pressed down from the top to the flange of arbor <u style="single">15</u> by means of a blow-out mechanism spring <u style="single">22</u>. The flange of push rod <u style="single">14</u>, being in the state of rest, rests upon the face of short stop <u style="single">20</u>. At the same time, push rod <u style="single">14</u>, through plunger flange <u style="single">10</u>, is pressed from the bottom by lift up spring <u style="single">13</u>, whereas there remains a narrow slot <u style="single">23</u> between plunger flange <u style="single">10</u> and the end of arbor<u style="single">15</u>. The inner flange of a calibration sleeve <u style="single">19</u> forms a lower resistance point for push rod <u style="single">14</u> sliding down together with arbor <u style="single">15</u>. The calibration unit is closed from the top by a hold-down element <u style="single">24</u> which is screwed into the internal thread of the body of casing <u style="single">1</u>, the said element being in the shape of a nut, which blocks cali­bration sleeve <u style="single">19</u> from the top. Simultaneously, the blow-­out mechanism spring <u style="single">22</u> rests upon step washer <u style="single">18</u>, which slides down along arbor <u style="single">15</u>, and is displaced relative to calibration sleeve <u style="single">19</u> together arbor <u style="single">15</u>.

0020At the end of arbor <u style="single">15</u> there is rigidly mounted a press means <u style="single">16</u>, serving for actuating the pipette, which slides along the body of casing <u style="single">1</u>. Press means <u style="single">16</u> is in the form of a round sleeve, being closed from the top. From the outside, a transparent plastics cover <u style="single">25</u> is put upon press means <u style="single">16</u>.

0021In the upper part, around its periphery, press means <u style="single">16</u> has a rectangular groove <u style="single">26</u>, wherein information strip <u style="single">27</u> is placed, showing the pipette's volume.

0022At the top of casing <u style="single">1</u>, at the point where press means <u style="single">16</u> is fitted, there are hand grips <u style="single">28</u> placed on both sides of casing <u style="single">1</u>, being in the form of wings with half-round lower surfaces making handling the pipette easier, which are inte­grated with the body of casing <u style="single">1</u>, forming together a handle. The both hand grips <u style="single">28</u> are covered from the top with a re­ctangular cover <u style="single">29</u>.

0023In Figs. 1, 4 and 5 a plain pipette is shown, which serves for drawing in small volumes of fluid renging 5 + 50 µl, which is different by the design of plunger <u style="single">4</u>, by the manner of sealing plunger <u style="single">4</u> in handle <u style="single">3</u>, and which is provided with stop <u style="single">30</u>. Plunger <u style="single">4</u> is in the form of multi-step arbor, which consists of two-step flange <u style="single">10</u>, whereon lift-up spring <u style="single">13</u> is supported, and further of a short cylindrical portion <u style="single">31</u> being terminated with an elongated arbor <u style="single">32</u>, having a thin arbor of plunger <u style="single">4</u> at its end, which slides in the opening of shank <u style="single">3</u>. At the place of point of the body of casing <u style="single">1</u> and of shank <u style="single">3</u>, there is a sealing unit of the arbor <u style="single">21</u>, comprising nut <u style="single">6</u> being screwed onto the body of casing <u style="single">1</u>, inside whereof hold-down element <u style="single">5</u> is screwed being in the form of a sleeve with its flange turned down, whereon lift-up spring <u style="single">13</u> is supported. Hold-down element <u style="single">5</u>, through spring <u style="single">33</u>, exerts pressure on hold-down sleeve <u style="single">34</u>, which is slid inside the first opening of shank <u style="single">3</u> and then it presses down a ring <u style="single">35</u> and a sealing sleeve <u style="single">36</u> to the face of shank <u style="single">3</u>, the said elements sealing the arbor <u style="single">21</u> of plun­ger <u style="single">4</u>, which slides in the other opening of shank <u style="single">3</u>.

0024The above disclosed plain pipette operates in the following manner: when the pressing element is being pressed down, the three steps of movement are differentiated, being se­parated therefrom by the two force barriers.

0025Fig. 6 is a calibration unit of the pipette in its state of rest, when press means <u style="single">16</u> is extended and in Fig. 7 the first step of movement of press means <u style="single">16</u> is shown. The pre­ssing down movement of press means <u style="single">16</u> is accompanied by the movement of push rod <u style="single">14</u>. The flange of push rod <u style="single">14</u> is de­tached from the surface of stop <u style="single">20</u> or <u style="single">30</u>. Push rod <u style="single">14</u> ac­tuates plunger <u style="single">4</u> causing lift-up spring <u style="single">13</u> bend down. The first step of movement is over when the flange of push rod <u style="single">14</u> rests upon the projection of calibration sleeve <u style="single">19</u>. Then the first force barrier is sensed. On release of press means <u style="single">16</u>, in this step of movement, the fluid is drawn in. Fig. 8 shows the second step of movement of press means <u style="single">16</u>. When press means <u style="single">16</u> is being pressed down, the pretension of blow-out mechanisms spring <u style="single">22</u> is to be overcome, the said spring causing the first force barrier. On passing thereof, the movement of press means <u style="single">16</u> causes arbor <u style="single">15</u> displace re­lative to immovable push rod <u style="single">14</u>. At that moment, blow-out mechanism spring <u style="single">22</u> of plunger <u style="single">4</u> is bent down, whereas plunger <u style="single">4</u> remains in the state of rest. The second step of movement continues up to the moment of contact of the face of arbor <u style="single">15</u> with plunger's flange <u style="single">10</u>. Then the second force barrier is sensed. The second step of movement is separated by the first and the third force barrier. In this step of movement no operation of the pipette occurs; it is a protective step. Fig. 9 is the third step of mo­vement of press means <u style="single">16</u>. When press means <u style="single">16</u> is being pressed down, the second force barrier is to be further overcome.

0026At the moment when plunger <u style="single">4</u> starts to be pushed by the face of arbor <u style="single">15</u>, both springs: lift-up spring <u style="single">13</u> and blow-out mechanism spring <u style="single">22</u> start to operate in a paral­lel system and not in a series system as before. The ten­sion of lift-up spring <u style="single">13</u> is added to the tension of blow-­out mechanism spring <u style="single">22</u>. On crossing the second force barrier, arbor <u style="single">15</u> drives plunger <u style="single">4</u> up to the moment when press means <u style="single">16</u> rests upon hold-down element <u style="single">24</u>. The move­ment is terminated then. This additional step of movement serves to exactly clean the pipette from the remaining fluid. Only the first and the third step of movement of press means <u style="single">16</u> is accompanied by the downward movement of plunger <u style="single">4</u>. Therefore, when press means <u style="single">16</u> is being pressed down, for drawing in the fluid the first force barrier is to be always crossed and press means <u style="single">16</u> is to be stopped before reaching the second force barrier. It ensures obtaining a higher repeatability of results.