Coupling device for a laboratory centrifuge actuated by centrifugal force

Abstract

The invention relates to a laboratory centrifuge (1) with a coupling device (4) actuated by a centrifugal force. According to the invention an eccentric mass (22), especially a roller (23), is guided through a guideway (26) and preferably another guideway (27, 32) in such a way that the centrifugal force (46) of the eccentric mass (22) is deflected in such a way that a coupling force is generated which presses a coupling element (24) radially inwards against the outer surface of a drive shaft (3).

Claims

1. A coupling device for a laboratory centrifuge actuated by centrifugal force comprising a) a driving element driven by a motor, b) an output element drivingly connected to a rotor of the laboratory centrifuge, c) said driving element and said output element rotating about a common rotational axis, d) a coupling element for releasably coupling the driving element with the output element, e) an eccentric mass being located remote from the axis of rotation, rotating together with the driving element or the output element, formed separately from the coupling element and generating a centrifugal force, f) said coupling element being actuated via a force flow between the eccentric mass and the coupling element by a coupling force which is dependent on the centrifugal force generated by the eccentric mass, g) a guideway interposed in the force flow between the eccentric mass and the coupling element, said guideway establishing a rolling contact with the eccentric mass and deflecting the centrifugal force of the eccentric mass, wherein the eccentric mass is built by a sphere or roller.

2. The coupling device according to claim 1, wherein another guideway which once more deflects the centrifugal force of the eccentric mass is provided in the force flow between the eccentric mass and the coupling element.

3. The coupling device according to claim 2, wherein the guideway is inclined at least in a partial region with respect to the centrifugal force acting on the eccentric mass, so that a force component F.sub.H is generated a) the absolute value of which depends on the centrifugal force acting on the eccentric mass and b) which has an orientation parallel to the rotational axis.

4. The coupling device according to claim 3, wherein the force component F.sub.H generated by the inclined guideway is converted into a force component F.sub.KK by the other guideway, said force component F.sub.KK biasing the coupling element in a radially inward direction.

5. The coupling device according to claim 4, wherein a receiving body is provided, which receives the centrifugal force deflected by the inclined guideway into a force component F.sub.H having an orientation parallel to the rotational axis, while the receiving body is guided by the other guideway, which is inclined with respect to the rotational axis and to the direction perpendicular to the rotational axis in such a way that the coupling force F.sub.KK biasing the coupling element in a radially inward direction is generated.

6. The coupling device according to claim 5, wherein the receiving body is formed by the coupling element.

7. The coupling device according to claim 6, wherein an inset retainer is provided, a) wherein the eccentric mass and the receiving body forming the coupling element are accommodated and b) which forms the guideway.

8. The coupling device according to claim 5, wherein an inset retainer is provided, a) wherein the eccentric mass, the receiving body and the coupling element are accommodated and b) which forms the guideway.

9. The coupling device according to claim 1, wherein the guideway is inclined at least in a partial region with respect to the centrifugal force acting on the eccentric mass, so that a force component F.sub.H is generated a) the absolute value of which depends on the centrifugal force acting on the eccentric mass and b) which has an orientation parallel to the rotational axis.

10. The coupling device according claim 1, wherein the coupling element engages in a form-locking way with a recess or groove of the driving element.

11. The coupling device according to claim 10, wherein the coupling element and the recess or groove of the driving element interact by contact surfaces, where the contact surfaces are inclined in such a way that the coupling force is converted into an axial force component which axially presses the output element with a friction surface against an opposite friction surface of the driving element.

12. A laboratory centrifuge with a coupling device according to claim 1.

13. A coupling device for a laboratory centrifuge actuated by centrifugal force comprising a) a driving element driven by a motor, b) an output element drivingly connected to a rotor of the laboratory centrifuge, c) said driving element and said output element rotating about a common rotational axis, d) a coupling element for releasably coupling the driving element with the output element, e) an eccentric mass being located remote from the axis of rotation, rotating together with the driving element or the output element, formed separately from the coupling element and generating a centrifugal force, f) said coupling element being actuated via a force flow between the eccentric mass and the coupling element by a coupling force which is dependent on the centrifugal force generated by the eccentric mass, g) a guideway interposed in the force flow between the eccentric mass and the coupling element, said guideway establishing a sliding contact with the eccentric mass and deflecting the centrifugal force of the eccentric mass, wherein the eccentric mass is a sliding body which forms a sliding contact with the guideway, the guideway being inclined such that the sliding movement of the eccentric mass along the guideway results in the eccentric mass moving radially outwards and in a lifting movement of the eccentric mass parallel to the rotational axis, wherein the lifting movement of the eccentric mass is transmitted to the coupling element through a sliding contact.

14. The coupling device according to claim 13, wherein another guideway which once more deflects the centrifugal force of the eccentric mass is provided in the force flow between the eccentric mass and the coupling element.

15. The coupling device according to claim 14, wherein the guideway is inclined at least in a partial region with respect to the centrifugal force acting on the eccentric mass, so that a force components F.sub.H is generated a) the absolute value of which depends on the centrifugal force of acting on the eccentric mass and b) which has an orientation parallel to the rotational axis.

16. The coupling device according to claim 15, wherein the force component F.sub.H generated by the inclined guideway is converted into a force component F.sub.KK by the other guideway, said force component F.sub.KK biasing the coupling element in a radially inward direction.

17. The coupling device according to claim 13, wherein the guideway is inclined at least in a partial region with respect to the centrifugal force acting on the eccentric mass, so that a force component F.sub.H is generated a) the absolute value of which depends on the centrifugal force acting on the eccentric mass and b) which has an orientation parallel to the rotational axis.

18. The coupling device according claim 13, wherein the coupling element engages in a form-locking way with a recess or groove of the driving element.

19. The coupling device according to claim 18, wherein the coupling element and the recess or groove of the driving element interact by contact surfaces, where the contact surfaces are inclined in such a way that the coupling force is converted into an axial force component which axially presses the output element with a friction surface against an opposite friction surface of the driving element.

20. A laboratory centrifuge with a coupling device according to claim 13.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In the following, the invention is further explained and described with respect to preferred exemplary embodiments illustrated in the drawings.

(2) FIG. 1 shows a partial section of a part of a laboratory centrifuge with an unlocked configuration of the rotor in a three-dimensional view.

(3) FIG. 2 shows the part of the laboratory centrifuge according to FIG. 1 in an unlocked configuration of the rotor in a longitudinal section.

(4) FIG. 3 shows the part of the laboratory centrifuge according to FIG. 1 in a locked configuration of the rotor in a longitudinal section.

(5) FIG. 4 shows the part of the laboratory centrifuge according to FIG. 1 in an unlocked configuration of the rotor in a different longitudinal section.

(6) FIG. 5 in an exploded view shows the part of the laboratory centrifuge according to FIGS. 1 to 4.

(7) FIG. 6 in a three-dimensional view diagonally from above shows a base body of an inset retainer.

(8) FIG. 7 in a three-dimensional view diagonally from below shows a closing lid.

(9) FIG. 8 shows a free body diagram of an eccentric mass realized as a roller and a coupling element of a coupling device.

(10) FIGS. 9 to 13 show further coupling devices in a schematic view.

DETAILED DESCRIPTION

(11) Referring now in greater detail to the drawings, FIGS. 1 to 5 illustrate a part of a laboratory centrifuge 1. The laboratory centrifuge 1 has a driving element 2 realized as a driving shaft 3 and an output element 50 coupled to the driving element 2 through a coupling device 4 realized by a rotor 5. For simplification, further parts of the laboratory centrifuge 1, especially a motor, control electronics and an interface with a display and input elements as well as a housing to be closed with a lid are not shown.

(12) For the embodiment shown, the driving shaft 3 is realized as a hollow shaft (cp. FIG. 5). The driving shaft 3 has a partial lateral surface 6 in the shape of a truncated cone with which an opposite friction surface 7 is realized. In an upward direction, that is in the direction of the interior of the rotor 5, the partial lateral surface merges into a cylindrical partial lateral surface 8 of the driving shaft 3. On its front side the cylindrical partial lateral surface 8 merges into an insertion slope 9. In the partial lateral surface 8 there is a circumferential groove 10 in which an elastic sealing element 11 is placed. Furthermore, the partial outer surface 8 has a recess 12, here a circumferential groove 13, by which the coupling of the driving shaft 3 with the rotor 5 is achieved in a way further specified in the following.

(13) The rotor 5 comprises a base body 14 which in a rough approximation is plate-shaped. Evenly distributed over its circumference in the base body 14 several receptacles 16 for containers not shown here containing the substances to be centrifuged are distributed with an equal distance to a longitudinal and rotational axis 15. The longitudinal axes 17 of the receptacles 16 are aligned with the longitudinal and rotational axis 15 and to planes comprising the corresponding radial direction and are inclined under an acute angle with respect to the longitudinal and rotational axis 15.

(14) The base body 14 forms a ring chamber 18 being open to the top and extending coaxially to the longitudinal and rotational axis 15. As can especially be seen from FIG. 5, into this ring chamber 18 an inset retainer 19 is inserted from the top. The inset retainer 19 is formed with a base body 20 and a covering body 21. Between the base body 20 and the covering body 21 in the inset retainer 19 four eccentric masses 22, which here are realized as rollers 23, and four coupling elements 24 are accommodated evenly distributed in a circumferential direction. The base body 20 of the inset retainer 19 has four slits 25 distributed evenly over the circumference, which extend in planes oriented radially (FIG. 6). In each of those slits 25 a roller 23 and a coupling element 24 are guided in such a way that the roller 23 can execute a rolling motion to be further described in the slit 25 having small play in the circumferential direction, and the coupling element 24 can be slid along in the slit 25 also with small play in the circumferential direction. In the bottom region the base body 20 forms a guideway 26, which for the given embodiment is formed by a plain guiding plane and is inclined with respect to a plane transverse to the longitudinal axis 15 by an angle of approx. 25 to 60°, preferably 30 to 50° or 45° increasing towards the top when looking radially outwards. In contact with each of the guideways 26 of the slits 25 there is a roller 23 (FIG. 1). The covering body 21 is set onto the base body 20 from the top in such a way that the slits 25 are closed from above by the covering body 21. The covering body 21 in the region of the boundary of each of the slits 25 forms further guideways 27. In the plane transverse to the longitudinal axis 15 the coupling elements 24 have a rectangular cross section, while in a radial plane including the longitudinal axis 15 they are trapezoidal in a rough approximation where two sides of the trapezoid are each arranged in a plane transverse to the longitudinal axis 15. The other side surfaces 28, 29 form guide surfaces 30, 31, which are inclined corresponding to the inclination of the further guideways 27. The coupling elements 24 are guided in the slits 25 on the further guideway 27 with the guiding surface 31 lying radially outwards and on a further inclined guideway 32 with the guiding surface 30 lying radially inwards in such a way that the coupling element 24 can only move in parallel to the further guideways 27, 32 (i.e. only in the direction of the longitudinal and rotational axis 15 if at the same time there is a motion in parallel to the longitudinal and rotational axis). For the embodiment shown the further guideway 32 is realized by an inclined front surface of a sleeve-like circumferential wall 33 of the base body 14.

(15) For the rotor 5 at rest due to their weight the coupling elements 24 rest from the top against the corresponding rollers 23. In this non-coupled position shown in FIG. 2, the rollers 23 rest against the outer lateral surface of the wall 33, the guideways 26 of the base body 20 and the lower side of the coupling elements 24.

(16) The inset retainer 19 formed with the base body 20 and the covering body 21 with the rollers 23 and coupling elements 24 placed within it is axially secured and braced by a closing lid 34 shown in FIG. 7. As can be seen especially from FIG. 4, to achieve this the closing lid is attached to the base body 14 of the rotor by a screw connection extending from the bottom side through the base body 14 through a bore 35 of the base body 20 into a threaded bore 36 of the closing lid 34 with the inset retainer 19 caught in between. The closing lid 34 forms four protrusions 37 distributed over the circumference which are accommodated without play in corresponding recesses 38 of the base body 20 of the inset retainer 19.

(17) Under provision of a sealing against fluids, a housing lid 39 is screwed onto the base body 14 with a screw connection 40 with the closing lid 36. For the embodiment shown, the housing lid 39 is formed in several parts with a housing nut 41 and a lid part 43 connected to the housing nut 41 through a non-unlockable latching element 42. Between the base body 14, the lid part 43 and the closing lid 34 a reception space 44 extending along the whole circumference around the longitudinal and rotational axis 15 and being sealed against fluids is defined, into which the receptacles 16 open.

(18) The laboratory centrifuge functions as follows:

(19) For the rotor 5 removed from the driving shaft 3 as a first step the housing lid 39 is removed by loosening the screw connection 40, so that the receptacles 16 are openly accessible and in these containers with the substance to be centrifuged may be arranged. By screwing tight the screw connection 40, the housing lid 39 is subsequently fixed to the base body 14 of the rotor 5. With this, the reception space 44 is sealed against fluids.

(20) Now the rotor 5 is set onto the driving shaft 3 from above under coaxial orientation of the longitudinal axes. The driving shaft 3 enters so far into the interior of the rotor 5 that a friction surface 45 in the shape of a truncated cone of the base body 14 of the rotor 5 comes into contact with the opposite friction surface 7 of the driving shaft 3 with preferably its full surface. Due to the weight of the rotor 5 a friction force is generated in the friction contact between friction surface 45 and opposite friction surface 7.

(21) If the driving shaft 3 is driven by the motor of the laboratory centrifuge 1, the rotational motion of the driving shaft 3 is transmitted onto the rotor 5 through the friction contact between the friction surface 45 and the opposite friction surface 7, while the contact between the friction surface 45 and the opposite friction surface 7 forms a kind of sliding clutch. As the rotational speed of the rotor 5 increases, an increasing centrifugal force 46 acts on the eccentric masses 22 formed by the rollers 23. This results in the rollers 23 moving rollingly along the guideways 26, which on the one hand results in the rollers 23 moving further radially outwards and on the other hand in a lifting motion of the rollers 23 in parallel to the longitudinal and rotational axis 15 occurring together with this radial motion. This lifting motion of the rollers 23 results in the coupling elements 24, which rest against the top of the rollers 23, being forced upwards with a lifting force F.sub.H due to the centrifugal force. Due to the guidance of the coupling elements 24 by the further guideways 27, 32, the upwards motion of the rollers 23 is converted into a motion of the coupling elements 24 in parallel to the further guideways 27, 32. Therefore, the rolling motion of the rollers 23 along the guideways 26 of the base body 20 of the inset retainer 19 causes a motion of the coupling elements 24 with a motion component which is oriented upwards parallel to the longitudinal axis 15 and a motion component which is oriented radially inwards towards the longitudinal and rotational axis 15. The latter motion component results in the coupling element 24 entering into the recess 12 or groove 13 of the driving shaft 3 with its latching nose 47 placed radially inwards, in which way an axial form-locking is caused. The coupling force F.sub.KK with which the latching nose 47 of the coupling elements 24 is pressed into the groove 13 of the driving shaft 3 depends on the centrifugal force 46 (i.e. the rotational speed of the rotor 5) as well as the deflection and the components of the centrifugal force 46 relevant for generating the lifting force F.sub.H on the roller 23 due to the inclined guideway 26 as well as on the coupling force F.sub.KK oriented radially inwards, which is generated from the aforementioned lifting force F.sub.H as a force component on the further guideways 27, 32.

(22) It is possible that the latching nose 47 only provides an axial securing of the rotor 5 with respect to the driving shaft 3, thus forming a locking which avoids the rotor 5 unintentionally detaching from the opposite friction surface 7 of the driving shaft 3. Preferably, however, the groove 13 and the latching noses 47 of the coupling elements 24 in their contact areas each have contact surfaces inclined with respect to the plane transverse to the longitudinal axis 15. Due to the inclination of the contact surfaces, the coupling force F.sub.KK applied by the coupling element 24 leads to an axial force component which increases the contact force of the friction surface 45 with the opposite friction surface 7 according to the rotational speed.

(23) In the context of the description and the claims occasionally the “centrifugal force of the eccentric mass” being deflected by the guideway 26 and the further guideways 27, 32 or the centrifugal force acting on the roller 23, the coupling element 24 or the latching nose 47 and the groove 13 is mentioned. Strictly speaking, this is not the centrifugal force, but a force (component) F.sub.H, F.sub.KK (correspondingly larger or smaller) which depends on the centrifugal force, which is generated by deflection by a guideway 26, 27 and the absolute value of which results from the corresponding geometrical conditions. In the region of the friction surface 45 the base body 14 of the rotor 5 forms the output element 50.

(24) When the laboratory centrifuge 1 stops after finishing the centrifuging, due to their weight the coupling elements 24 and the rollers 23 move back from the coupled position according to FIG. 3 to the decoupled position according to FIG. 2. To ensure this, the inclination angle of the guideway 26 and the further guideway 27, 32 as well as that of the contact surface between the coupling element 24 and the recess 12 or groove 13 of the driving shaft 3 are preferably chosen smaller than a self-locking angle. In this way with the rotor 5 at rest the rotor 5 can be lifted upwards and away from the driving shaft 3 without further measures and especially without actuating a manual unlocking element.

(25) FIG. 8 shows a free body diagram of the roller 23 and the coupling element 24 for the embodiment according to FIGS. 1 to 7:

(26) A centrifugal force F.sub.ZFR (reference sign 46 in FIG. 3) acts on roller 23. The centrifugal force F.sub.ZFR results from the product of the mass of the roller 23, the distance of the center of gravity of the roller 23 from the rotational axis 15 and the square of the angular velocity of the rotor 5. Furthermore, the lifting force F.sub.H exerted on the coupling element 24 and a force F.sub.26 exerted on the roller 23 by the guideway 26 act on the roller 23. If α denotes the angle of the guideway 26 with respect to a transverse plane to the rotational axis 15, then the force F.sub.H results from F.sub.H=F.sub.ZFR/tan α.

(27) On the one hand, a centrifugal force F.sub.ZFK resulting from the product of the mass of the coupling element, the distance of the center of gravity of the coupling element 24 from the rotational axis 15 and the square of the angular velocity of the rotor 5 acts on the coupling element 24. Furthermore, the lifting force F.sub.H, a force F.sub.27,32 exerted onto the coupling element 24 by the further guideway 27, 32 and the coupling force F.sub.KK acting between the coupling element 24 and the groove 13 of the driving shaft 3 act on the coupling element 24. If the angle β describes the inclination of the further guideway 27, 32 with respect to a transverse plane to the rotational axis 15, from the free body diagram according to FIG. 8 it follows that the coupling force F.sub.KK results from F.sub.KK=F.sub.H tan β−F.sub.ZFK, so that
F.sub.KK=F.sub.ZFR(tan β/tan α)−F.sub.ZFK
holds.

(28) From the above it can be seen that to cause a coupling force as large as possible it is necessary that the influence of the mass of the coupling element 24 and the distance of the center of gravity of the coupling element 24 from the rotational axis 15 should be smaller than the influence of the mass of the roller 23 and the distance of the center of gravity of the roller 23 from the rotational axis 15.

(29) FIGS. 9 to 13 in a highly schematized way show further embodiments of a coupling device 4:

(30) For the embodiment according to FIG. 9 the eccentric mass 22 forms a sliding contact with the guideway 26. The lifting motion of the eccentric mass 22 is also transmitted to the coupling element 24 through a sliding contact. Finally, the coupling element 24 also forms a sliding contact with the further guideway 27, 32. As the rotational speed of the rotor 5 increases, the eccentric mass 22 migrates radially outwards while the coupling element 24 is moved radially inwards with a sliding relative motion between the eccentric mass 22 and the coupling element 24.

(31) For the embodiment shown in FIG. 10 a rolling bearing 57 is placed between the eccentric mass 22 and the coupling element 24 (with the way of functioning being the same as in FIG. 9 apart from that).

(32) According to FIG. 11, the eccentric mass 22 is realized as roller 23 which rolls on the guideway 26 and is coupled with an receiving body 52 by a cage 51. The receiving body 52 is here also realized as a roller 53. The roller 53 rolls along the further guideway 27. At the same time, the roller 53 rests against the coupling element 24 and exerts pressure on it radially inwards towards the rotational axis 15.

(33) For the embodiment shown in FIG. 12, between the eccentric mass 22, here guided slidingly, and the coupling element 24 a deflecting transmission device 54 guided through a guideway 26 is inserted. For the embodiment shown, the transmission device 54 is formed with rolling bodies 55 guided in a channel or tube along the guideway 26.

(34) According to FIG. 13 the eccentric mass 22 is realized as a roller 23. Here, the guideway 26 is formed directly by the coupling body 24.

(35) Many variations and modifications may be made to the preferred embodiments of the invention without departing substantially from the spirit and principles of the invention. All such modifications and variations are intended to be included herein within the scope of the present invention, as defined by the following claims.