Cam mechanism for the implementation of a variable stroke

Abstract

A cam mechanism for converting a swiveling movement of a drive-side shaft into a linear output movement. A cam disk is attached to the drive-side shaft, a slider is shiftable in a linear guide, and a cam follower is applied against the circumferential surface of the cam disk. Swiveling movement of the cam disk leads to a linear output movement of the slider in the linear guide. The circumference of the cam disk is spiral-shaped at least in sections, and the radius of the cam disk increases monotonically in the spiral-shaped section from a start radius to an end radius along a swiveling direction. By selecting two reversal points within the spiral-shaped section, the setting of a variable stroke can occur. A piston pump is provided with the cam mechanism and a method is provided for using the cam mechanism and the piston pump.

Claims

1. A piston pump for high performance liquid chromatography, the piston pump comprising: a cam mechanism configured to convert a rotational movement of a drive-side shaft into a linear output movement, the cam mechanism comprising: a) a cam disk attached to the drive-side shaft, b) a slider configured to be shifted in a linear guide at least in sections, and c) a cam follower which is applied against a circumferential surface of the cam disk, whereby a rotational movement of the cam disk leads to a linear output movement of the slider in the linear guide, wherein the circumference of the cam disk is designed as spiral-shaped at least in sections, and the radius of the cam disk increases monotonically in the spiral-shaped section from a start radius R.sub.1 to an end radius R.sub.2 along a rotational direction; a motor configured to drive a drive-side shaft, the drive-side shaft connected to the cam disk; a motor controller; and a piston attached axially on an end of the slider facing away from the cam follower, wherein the motor controller is configured so that the cam disk performs a back and forth rotational movement between two reversal points with radial distances R.sub.3 and R.sub.4, wherein R.sub.1<R.sub.3<R.sub.4<R.sub.2 and the slider performs an axial movement with a stroke corresponding to a difference between R.sub.4 and R.sub.3.

2. The piston pump according to claim 1, wherein a difference R.sub.2R.sub.1 is between 1.5 mm and 50 mm.

3. The piston pump according to claim 1, wherein, in the spiral-shaped section, the radius of the cam disk increases linearly with a rotational angle.

4. The piston pump according to claim 1, wherein the spiral-shaped section of the cam disk extends over an opening angle between 90 and 340.

5. The piston pump according to claim 1, wherein in the spiral-shaped section, the radius of the cam disk increases linearly with a rotational angle, and the linear increase is between 0.005 mm/ and 0.5 mm/.

6. The piston pump according to claim 1, wherein a contact surface of the linear guide for receiving the slider and an opposite-shaped matching sliding surface of the slider comprise a downward directed narrowing with a symmetry plane which coincides with a central axis of the slider.

7. The piston pump according to claim 1, wherein a contact surface of the linear guide for receiving the slider and an opposite-shaped matching sliding surface of the slider are v-shaped in cross section.

8. The piston pump according to claim 1, wherein an arrangement of the cam follower, of the cam disk and of the slider is present such that, for a region of a rotational movement, while the cam follower is applied against the cam disk in the spiral-shaped section, a radial force A acts from the cam follower onto the cam disk, forming an angle with the axial force B leading to the shifting of the slider, such that a transverse force C presses the slider in an area of the sliding surface vertically downward into a contact surface of the linear guide.

9. The piston pump according to claim 1, wherein a rotation axis of the cam disk lies in a plane of a central axis of the slider, and a rotation axis of the cam follower is offset vertically upward by a distance D.sub.1 relative to the central axis of the slider.

10. The piston pump according to claim 1, wherein a rotation axis of the cam disk is offset vertically upward by a distance D.sub.2 relative to a central axis of the slider, and a rotation axis of the cam follower is offset vertically upward by a distance D.sub.3 with respect to the rotation axis of the cam disk.

11. A method of using a cam mechanism for converting a rotational movement of a drive-side shaft into a linear output movement, the cam mechanism comprising: a) a cam disk that can attach to the drive-side shaft, b) a slider that can be shifted in a linear guide at least in sections, and c) a cam follower which is applied against the circumferential surface of the cam disk, so that a rotational movement of the cam disk leads to a linear output movement of the slider in the linear guide, wherein the circumference of the cam disk is designed as spiral-shaped at least in sections, and the radius of the cam disk increases monotonically in the spiral-shaped section from a start radius R1 to an end radius R2 along a rotational direction for driving a piston pump the method comprising: rotating the cam disk back and forth between first and second reversal points while the cam follower is applied against the cam disk in the spiral-shaped section, so that the piston is shifted linearly between two dead points, wherein, by determination of the reversal points, a predetermined piston stroke is set, which corresponds to a difference between the radius of the cam disk at a first reversal point R.sub.3 and the radius of the cam disk at a second reversal point R.sub.4.

12. The piston pump according to claim 1, wherein the difference R.sub.2R.sub.1 is between 5 mm and 30 mm.

13. The piston pump according to claim 1, wherein the difference R.sub.2R.sub.1 is between 10 mm and 20 mm.

14. The piston pump according to claim 1, wherein the spiral-shaped section of the cam disk extends over an opening angle between 220 and 330.

15. The piston pump according to claim 1, wherein the radius of the cam disk in the spiral-shaped section increases linearly with a rotational angle, and the linear increase is between 0.02 mm/ and 0.2 mm/.

16. The piston pump according to claim 1, wherein the radius of the cam disk in the spiral-shaped section increases linearly with a rotational angle, and the linear increase is between 0.03 mm/ and 0.08 mm/.

17. The piston pump according to claim 1, wherein a contact surface of the linear guide for receiving the slider and the opposite-shaped matching sliding surface of the slider are v-shaped in cross section, with an angle of between 30 and 170.

18. A cam mechanism for converting a rotational movement of a drive-side shaft into a linear output movement, the cam mechanism comprising: a) a cam disk configured to be attached to the drive-side shaft; b) a slider configured to be shifted in a linear guide at least in sections; and c) a cam follower which is applied against a circumferential surface of the cam disk, so that a rotational movement of the cam disk leads to a linear output movement of the slider in the linear guide, wherein a circumference of the cam disk is designed as spiral-shaped at least in sections, and a radius of the cam disk increases monotonically in the spiral-shaped section from a start radius R1 to an end radius R2 along a rotational direction, wherein a contact surface of the linear guide for receiving the slider and an opposite-shaped matching sliding surface of the slider comprise a downward directed narrowing with a symmetry plane which coincides with a central axis of the slider, and wherein (a) a rotation axis of the cam disk lies in the plane of the central axis of the slider, and a rotation axis of the cam follower is offset vertically upward by a distance D.sub.1 relative to the central axis of the slider, or (b) a rotation axis of the cam disk is offset vertically upward by a distance D.sub.2 relative to the central axis of the slider, and a rotation axis of the cam follower is offset vertically upward by a distance D.sub.3 relative to the rotation axis of the cam disk.

19. The cam mechanism according to claim 18, wherein the contact surface of the linear guide for receiving the slider and the opposite-shaped matching sliding surface of the slider are v-shaped in cross section.

20. The cam mechanism according to claim 19, wherein the contact surface of the linear guide for receiving the slider and the opposite-shaped matching sliding surface of the slider are v-shaped in cross section with an angle of between 30 and 170.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) FIG. 1 Diagrammatic representation of a preferred embodiment of the cam mechanism, wherein the slider is in the maximum retracted position

(2) FIG. 2 Diagrammatic representation of the preferred embodiment of the cam mechanism according to FIG. 1, wherein the slider is in a half-extended position

(3) FIG. 3 Diagrammatic representation of a preferred embodiment of the cam mechanism according to FIG. 1, wherein the slider is in the maximum extended position

(4) FIG. 4 Diagrammatic representation of a preferred embodiment of the cam mechanism, wherein the rotation axis of the cam disk and of the cam follower coincides with the central axis

(5) FIG. 5 Diagrammatic representation of a preferred embodiment of the cam mechanism with a doubled axial offset between the central axis, the rotation axis of the cam disk and the rotation axis of the cam follower

(6) FIG. 6 Diagrammatic representation of a preferred embodiment of the cam mechanism, wherein the slope of the radius in the spiral-shaped section is increased in comparison to the embodiment according to FIG. 1-3

(7) FIG. 7 Diagrammatic representation of a preferred embodiment of the cam mechanism to illustrate a v-shaped contact surface of the linear guide

DETAILED DESCRIPTION OF THE FIGURES

(8) FIG. 1-3 show a preferred embodiment of the cam mechanism, wherein the cam disk 1 is shown in different positions, so that the movement of the slider 3 is illustrated.

(9) The preferred embodiment of the cam mechanism has a cam follower 7 against which the cam disk 1 is applied. The cam follower 7 is connected to a slider 3 which can move axially with a sliding surface 11 along the contact surface 12 of a linear guide 5.

(10) The rotation axis of the cam disk 17, on the other hand, is stationary with respect to the linear guide 5. Therefore, by rotation of the cam disk 1, the slider 3 is moved axially within the linear guide 5 in accordance with the shape of the margin of the cam disk 1.

(11) The circumference of the cam disk 1 has a spiral-shaped section. At the start of the spiral-shaped section 19, the radius of the cam disk 1 is R.sub.1. In the preferred embodiment shown, the radius of the circumference of the cam disk 1 increases linearly with the rotation angle, until it reaches a radius R.sub.2 at the end of the spiral-shaped section 21. For the performance of an oscillating movement of the slider 3, the cam disk 1 performs an oscillating movement between the positions represented in FIG. 1-3. For this purpose, it is preferable that the cam disk 1 is connected to a drive-side shaft which performs, via a motor, an oscillating rotation movement (swiveling movement).

(12) In FIG. 1, the cam disk 1 is applied against the cam follower 7 in the position which corresponds to the start of the spiral-shaped section 19. Since the circumference in this position has the smallest radius R.sub.1, the slider 3 is in the maximum retracted position. In the embodiment shown, this corresponds to a movement position 25 of the slider at 2.8 mm. In the represented embodiment, the total length of the sliding surface is 51 mm and the total length of the contact surface of the linear guide is 72 mm. The radius of the cam follower is 20 mm, wherein R.sub.1 is 16 mm and R.sub.2 is 31 mm.

(13) FIG. 2 shows the positioning of the slider 3 and of the cam disk 1 after said cam disk has been rotated by a swiveling angle of 145. This corresponds to half the maximum swiveling angle possible for the preferred embodiment within the spiral-shaped section. The opening angle 23 of the spiral-shaped section is 290. In the swiveling position shown in FIG. 2, the slider 3 accordingly is in a half-extended movement position 25 at 10.45 mm.

(14) FIG. 3 shows the cam mechanism after the cam disk 1 has been rotated by an additional swiveling angle of 145 along the spiral-shaped section. In this position, the cam disk 1 is applied to the cam follower 7 with a radius R.sub.2 which corresponds to the end of the spiral-shaped section 21. In comparison to FIG. 1, the cam disk has been rotated by the maximum swiveling angle of 290 for the embodiment, which corresponds to the opening angle 23 of the spiral-shaped section. FIG. 3 thus shows the slider 3 in the maximum extended position. Said extended position corresponds in the example to a movement position 25 at 18.11 mm.

(15) In order to set the slider 3 into an oscillating linear movement, the cam disk 1 is rotated between the positions represented in FIGS. 1 and 3 of the reversal points of the swiveling movement. The maximum retracted position (FIG. 1) and the maximum extended position (FIG. 3) correspond to the dead points of the oscillating movement of the slider 3, wherein the converted stroke corresponds to the difference between R.sub.2 and R.sub.1. In the present example, a stroke of 15.3 mm has been implemented. The linear increase between R.sub.1 and R.sub.2 over the maximum swiveling angle of 290 is 0.053 mm/. In order to achieve a movement of the slider 3 with a different stroke, the swiveling movement can be selected so that the reversal points are located between the start of the spiral-shaped section 19 and the end of the spiral-shaped section 21.

(16) In the preferred embodiment, the rotation axis of the cam disk 17 and the central axis 13, i.e., the force exertion axis of the slider 3 lie in a plane, while the rotation axis of the cam follower 15 is offset vertically upward by an axial offset D.sub.1. As shown in FIG. 1, the radial force A: acting from the cam follower 7 onto the cam disk 1 forms an angle with the axial force B leading to the shifting of the slider 3 and extending along the force exertion axis 13, such that a transverse force C acts on the slider 3, pressing said slider vertically downward into the contact surface of the linear guide 12. For the present example, the axial offset is 0.6 mm and the distance 9 of the transverse force C from the start of the sliding surface 3 has a value of 19 mm. As can be seen in FIG. 1, the transverse force C acts in the center on the slider 3, so that said slider undergoes a stable guiding in the linear guide 5.

(17) The person skilled in the art knows that, by selecting the axial offset D.sub.1, the position 9 of the transverse force C within the sliding surface 11 can be shifted. Thus, an increase in the axial offset D.sub.1 leads to a shifting of the position 9 of the transverse force C towards the rear end of the sliding surface 11. The rear end refers to the side facing away from the cam disk, while the front end denotes the end facing the cam disk. For example, for an axial offset of D.sub.1=1 mm, other parameters remaining unchanged, the transverse force C would lie in a position at 28.1 mm. In contrast, a decrease of the axial offset D.sub.1 would lead to a shifting of the position 9 of the transverse force C towards the front end of the sliding surface 11. I.e., for example, for an axial offset of D.sub.1=0.3 mm, other parameters remaining unchanged, the transverse position C would be in a position at 14 mm.

(18) In the preferred embodiment of FIG. 1-3, the spiral-shaped section has a linear rise of the radius from R.sub.1 to R.sub.2. As a result, the position 9 of the transverse force C also advantageously remains nearly constant during the swiveling movement. In a half-extended position of the slider 3 according to FIG. 2, the position 9 of the transverse force C is at 20.8 mm in the example shown. In the case of a fully extended position of the slider 3 according to FIG. 3, the position 9 of the transverse force C is at 22.7 mm.

(19) In the preferred embodiment, over the entire range of the spiral-shaped section, a particularly central positioning of the transverse force C can thus be achieved, which enables a particularly stable guiding of the slider 3 in the linear guide 5.

(20) It is pointed out that the mentioned parameter variables for the position 9 of the transverse force C and for the axial offset D.sub.1 are merely intended to illustrate exemplary preferred embodiments of the invention. There is no limitation due to the parameters. The person skilled in the art knows that other parameters for the axial offset or the difference between R1 and R2 can be selected, which also lead to advantageous solutions.

(21) FIG. 4 shows an additional embodiment of the cam mechanism, wherein the rotation axis of the cam disk 17 and the rotation axis of the cam follower 15 coincide with the central axis 13. I.e., in contrast to the embodiment of the cam mechanism according to FIG. 1-3, there is no axial offset in this embodiment of the invention. The shape of the margin of the cam disk 1 and, in particular, of the spiral-shaped section is identical to the embodiment of FIG. 1-3. Due to the linear increase of 0.053 mm/ in the spiral-shaped section, the cam follower 7 exerts a radial force A onto the cam disk 1. Said radial force forms an angle with the axial force B, so that the slider 3 is exposed to a vertically downward transverse force C at the position 9. In this embodiment without axial offset as well, the slider 3 is thus advantageously pressed into the contact surface by a transverse force C. In the example, the position of the transverse force C is 10 mm. In contrast to the embodiment according to FIG. 1-3, the transverse force C is positioned less centrally. The embodiment according to FIG. 4 is suitable according to the invention; however, in comparison to the embodiment according to FIG. 1-3, it has a lower degree of tolerance with respect to deviations in the manufacturing. Due to the asymmetric positioning of the transverse force C with respect to the center of the sliding surface 11, this embodiment for the parameters shown is more susceptible to tilting movements of the slider 3.

(22) FIG. 5 shows a diagrammatic representation of another preferred embodiment of the cam mechanism, wherein said cam mechanism is characterized by a doubled axial offset between the central axis 13, the rotation axis of the cam disk 17 and the rotation axis of the cam follower 15. In the embodiment, the rotation axis of the cam disk 17 is shifted vertically upward by the vertical offset D.sub.2 with respect to the central axis 13, i.e., the force exertion axis for the axial force B. In addition, the rotation axis of the cam follower 15 is offset vertically upward by the distance D.sub.3 with respect to the rotation axis of the cam disk 17. The shape of the circumference of the cam disk 1 and in particular of the spiral-shaped section is identical to the embodiment according to FIG. 1-3. By means of the doubled axial offset, it is also possible to achieve advantageously a transverse force C onto the slider 3, which presses said slider vertically and at the center into the contact surface of the linear guide 12. For the example shown, D.sub.2 is 1 mm and D.sub.3 is 0.8 mm. For these parameter values, this results in a position 9 of the transverse force C at 23.3 mm.

(23) A doubled axial offset can thus also advantageously achieve a particularly central positioning of the transverse force C in the sliding surface 11.

(24) FIG. 6 shows a diagrammatic representation of a preferred embodiment of the cam mechanism, wherein the slope of the radius in the spiral-shaped section is increased in comparison to the embodiment according to FIG. 1-3. In the example shown, by means of a linear increase of the radius of the cam disk 1 in the spiral-shaped section of 0.1055 mm/, a stroke of 30 mm is implemented. Analogously to FIG. 1-3, the rotation axis of the cam disk 17 and the central axis 13 are located on a line, wherein the rotation axis of the cam follower 15 is offset vertically upward by a distance D.sub.1. In the example shown, D.sub.1 is 0.6 mm. This results in a transverse force C which is in a position 9 at 14.1 mm. Due to the increased linear increase in comparison to the embodiment of FIG. 1-3, the transverse force C has thus moved in a direction towards the front end of the sliding surface 11. While this embodiment is suitable for a stable guiding of the slider 3, it can be preferable to also increase the axial distance D.sub.1 for the increased linear increase of the radius in the spiral-shaped section. This leads to a shift of the position 9 of the transverse force C towards the end of the sliding surface 11. For example, in the case of an axial offset D.sub.1 of 1.5 mm and otherwise unchanged parameters, the position 9 of the transverse force C would be 22.5 mm.

(25) FIG. 1-6 illustrate several different embodiments of the cam mechanism according to the invention, wherein it can be particularly preferable to select the arrangement of the components in such a manner that the slider 3 is exposed to a transverse force C which presses said slider into the contact surface of the linear guide 5.

(26) FIG. 7 shows a three-dimensional diagrammatic representation of a preferred embodiment of the cam mechanism, whereby the advantageous v-shaped contact surface of the linear guide 12 is illustrated. The cam disk 1 can be set in a swiveling movement by a drive-side shaft 27 in order to drive a piston pump. For this purpose, a cam follower 7 is present at a front end of a slider 3 which can perform a translation in a linear guide 5. In accordance with the shape of the circumference of the cam disk 1, due to the swiveling movement, an oscillating axial movement of the slider 3, which is in contact with a piston, is brought about. Reference numeral 29 marks the contact surface for the piston. As illustrated in FIG. 1-6, for example, it is preferable that the arrangement of the components of the cam mechanism occurs in such a manner that a vertical force acts onto the slider 3 downward into the contact surface 12 of the linear guide. Due to the v-shaped design of the contact surface 12 of the linear guide and to the matchingly shaped sliding surface 11, a particularly stable guiding of the slider 3 is possible. Thus, the v-shaped contact surface 12 prevents lateral movements of the slider 3 and ensures a nearly play-free guiding of the slider 3 in the linear guide 5. In addition, tolerances, for example, by a lateral asymmetric exertion of the forces due to manufacturing defects, can be compensated particularly effectively. The particularly play-free embodiment allows a reduction of wear, in addition to an extremely stable and disturbance-free movement flow of the slider 3.

(27) It is pointed out that different alternatives to the described embodiments of the invention can be used in order to carry out the invention and reach a solution according to the invention. The cam mechanism according to the invention, the piston pump according to the invention as well as the use thereof in the described method are thus not limited in their designs to the above preferred embodiments. Instead, numerous design variants are conceivable, which can deviate from the solution represented. The aim of the claims is to define the scope of protection of the invention. The scope of protection of the claims aims to cover the cam mechanism according to the invention, the piston pump according to the invention and the preferred method for the use thereof as well as equivalent embodiments thereof.

LIST OF REFERENCE NUMERALS

(28) 1 Cam disk

(29) 3 Slider

(30) 5 Linear guide

(31) 7 Cam follower

(32) 9 Position of the transverse force C, i.e., distance from the transverse force C to the start of the sliding surface

(33) 11 Sliding surface

(34) 12 Contact surface of the linear guide

(35) 13 Central axis (or force exertion axis)

(36) 15 Rotation axis of the cam follower

(37) 17 Rotation axis of the cam disk

(38) 19 Start of the spiral-shaped section

(39) 21 End of the spiral-shaped section

(40) 23 Opening angle of the spiral-shaped section

(41) 25 Movement position of the slider

(42) 27 Drive-side shaft

(43) 29 Contact surface for a piston

(44) R.sub.1 Radius of the cam disk at the start of the spiral-shaped section

(45) R.sub.2 Radius of the cam disk at the start of the spiral-shaped section

(46) A Radial force

(47) B Axial force

(48) C Transverse force

(49) D.sub.1 Axial offset between the rotation axis of the cam follower and the rotation axis of the cam disk or central axis

(50) D.sub.2 Axial offset between the central axis and the rotation axis of the cam disk

(51) D.sub.3 Axial offset between the rotation axis of the cam disk and the rotation axis of the cam follower