Motion conversion device

Abstract

An apparatus for converting between motion in one direction and motion in another direction is disclosed, the apparatus comprising: a magnetic protrusion or patch attached to a first movable element and having a surface; and a track attached to a further movable element and having a predetermined magnetic property, the track defining a path along which the magnetic protrusion or patch is attracted by a magnetic force, the magnetic force being: The movable element is constrained from movement and the magnetic protrusions or patches are adapted to move in a direction along the magnetic track in response to relative movement between the first element and the further element.

Description

[Technical field]

[0001] The field of the invention relates to devices that convert motion in one direction into motion in another direction. [Background technology]

[0002] Mechanisms that convert motion in one direction to motion in another direction are known, such as the Scotch Yoke, which converts rotary and linear motion. These mechanisms have a pin extending from a wheel into a linear slot that runs perpendicular to the rod. Rotation of the wheel moves the pin up and down in the slot, pushing the slot back and forth, resulting in reciprocating linear motion of the rod. Shortcomings of such mechanisms result from friction and wear between relatively moving parts, such as the pin and slot of a Scotch Yoke. Summary of the Invention [Means for solving the problem]

[0003] One aspect provides an apparatus for converting between motion in one direction and motion in another direction, the apparatus comprising a magnetic protrusion or patch attached to a first movable element and having a surface, and a track attached to a further movable element and having predetermined magnetic properties, the track defining a path along which the magnetic protrusion or patch is attracted by a magnetic force that constrains the movable element from moving, the magnetic protrusion or patch being adapted to move in a direction along the magnetic track in response to relative movement between the first element and the further element, the surface of the magnetic protrusion or patch having a shape having a width dimension aligned with and differing from a width of the track by less than 30%, and a length dimension perpendicular to the width dimension that is substantially shorter than a length dimension of the track and is less than 30% of the length dimension of the track.

[0004] Devices that convert between different directions of motion, especially linear and rotary motion, are very important in many industrial sectors. These devices suffer from wear and friction where surfaces come into contact with each other. This not only leads to damage and failure of the device, but also to inefficiencies in operation. The present invention seeks to address these issues by using magnetic forces rather than mechanical forces to constrain movement, thereby reducing friction and wear. Thus, what was previously an arrangement of slots and pins is replaced by magnetic protrusions or patches and tracks with predetermined magnetic properties that act to attract the magnetic protrusions or patches. The predetermined magnetic properties can be magnets of opposite polarity or magnetic materials with a higher magnetic permeability compared to the surrounding material.

[0005] In some embodiments, the patch or protrusion has a dimension similar to the width of the track such that it is retained within the track and moves from one end to the other, and the length of the track is a multiple of its width.

[0006] In some embodiments, the surface of the magnetic protrusion or patch is flat, the track is straight, and the surface of the patch or protrusion facing the track lies in a plane parallel to the plane of the surface of the track.

[0007] In some embodiments, the surface of the magnetic patch or protrusion is substantially circular, and the width and length of the magnetic patch or protrusion are the diameter of the circle.

[0008] In some embodiments, the widths and lengths of said surface of said magnetic patches or protrusions are substantially similar, within 30%, preferably within 20%, of each other.

[0009] In some embodiments the width of the patch or protrusion is within 10% of the width of the track.

[0010] In some embodiments, the motion in one direction comprises a rotational motion and the motion in the other direction comprises a translational motion.

[0011] In some embodiments, said movement of said further movable element comprises a reciprocating motion.

[0012] In some embodiments, one of the movable elements is configured to be externally driven.

[0013] In some embodiments, the magnetic protrusions or patches may have a single magnetic pole, while in other embodiments, the magnetic protrusions or patches comprise at least two magnetic poles facing the track.

[0014] When the magnetic protrusion or patch has at least two magnetic poles facing the track, the magnetic field extending from the magnetic protrusion or patch may preferentially be within the track, the magnetic field extending into the track and returning to the other magnetic pole of the magnet, thereby being confined to a certain extent and reducing inefficiencies that may arise due to eddy currents and magnetic hysteresis losses that may arise if the magnetic field were not so confined.

[0015] In some embodiments, the magnetic protrusions or patches have an axis perpendicular to the surface, the magnetic protrusions or patches being mounted such that they are symmetrical about the axis or rotatable about the axis.

[0016] In order for the magnetic patch or protrusion to move along the track and maintain the magnetic fields aligned when there are multiple magnetic poles, the magnetic patch or protrusion may be symmetrical about an axis perpendicular to the surface of the magnetic patch or protrusion, and in some cases may be rotationally symmetric, or the magnetic protrusion or patch may be attached to a rotary joint so that the alignment can be maintained.

[0017] In some embodiments, the magnetic protrusion or patch comprises a horseshoe magnet that extends in a direction perpendicular to the surface and is mounted such that it is configured to rotate about an axis between the two magnetic poles.

[0018] As mentioned above, if the magnetic patch or protrusion is not symmetrical about an axis, a rotational mounting of the magnet can be utilized to maintain alignment during differential relative motion between the magnet and the track.

[0019] In some embodiments, the track comprises at least two tracks such that each pole of the at least two-pole magnet faces a respective track.

[0020] If the magnet patch or protrusion is a multi-pole magnet, it may be advantageous to have multiple tracks with a track facing each pole.

[0021] In some embodiments, the magnetic patch or protrusion comprises a permanent magnet, while in other embodiments, the magnetic patch or protrusion comprises at least one electromagnet or at least one permanent electromagnet.

[0022] Permanent magnets can be used, permanent electromagnets can be used whose magnetic properties can be turned on and off by the use of an electric current, or electromagnets can be used as the magnetic protrusions.

[0023] Both permanent magnets and electromagnets have the advantage of being controllable, but the disadvantage of requiring electrical circuitry and possibly associated control circuitry. Thus, the choice of magnet type will depend on the application.

[0024] In some embodiments, the apparatus comprises a plurality of electromagnets or permanent electromagnets mounted at different positions on the first movable element, the apparatus comprising a control circuit configured to activate one of the plurality of electromagnets or permanent electromagnets at any one time, the selection of which one of the plurality of electromagnets to activate defines a trajectory of one of the movable elements.

[0025] One advantageous use of electromagnets or permanent electromagnets is that they can provide a flexible device that offers different trajectory possibilities depending on which magnet is activated at any one time.

[0026] In some embodiments, the first movable element includes a rotating disk, and the plurality of electromagnets or permanent electromagnets are mounted at different radial positions on the rotating disk.

[0027] If the first moving element is a rotating disk, then by mounting different electromagnets at different radial positions, the translation length undergone by the further moving element can be varied.

[0028] In some embodiments, the at least one track having a predetermined magnetic property is formed by lithographic patterning of a material of high magnetic permeability on a substrate of low magnetic permeability.

[0029] Providing tracks with predetermined magnetic properties can be done using lithographic printing of high permeability material onto a low permeability substrate, providing a low cost device in which track shape and length can be easily customized as required.

[0030] Furthermore, the low permeability substrate can be a circuit board, and if there are multiple intersecting tracks, the switching and control elements can be mounted in parallel to the high permeability tracks. In the course of its movement along a given travel direction, the patch or protrusion will approach various intersections of said multiple tracks. The high permeability track material at any exit point can be driven into saturation by a control circuit mounted next to it. If all exits except one are saturated, the patch or protrusion will be directed to the non-saturated exit as the most energetically favorable option. Switching can be used to control the saturation of the tracks, allowing switching between paths based on the saturation of the tracks, which can be controlled by a control circuit with conductive switching.

[0031] In some embodiments, the at least one track having predetermined magnetic properties has a thickness of less than 3 mm.

[0032] Thin tracks can be cheaper to manufacture and provide suitable properties, for example thin tracks with suitable properties can be easily achieved when lithographically printing the tracks.

[0033] In some embodiments, the device comprises a slip joint, in some embodiments a cam follower, and in other embodiments a scotch yoke.

[0034] In some embodiments, the apparatus comprises an additional moving element corresponding to the first moving element, the additional moving element including a magnetic patch or protrusion corresponding to the magnetic patch or protrusion of the first moving element, the additional moving element being attached on an opposite side of the further moving element relative to the first moving element.

[0035] In some cases it may be advantageous to have a movable element corresponding to the first movable element and mounted opposite the further movable element, so that the further movable element is not only attracted towards the first movable element but also has a corresponding force attracting it in the opposite direction, such that the two forces substantially cancel each other out and there is no or minimal force acting perpendicular to the direction of movement along the track.

[0036] In some embodiments, the apparatus further comprises an airtight seal between the first element and the additional element.

[0037] One advantage of having a non-contact joint is that a hermetic seal can be placed between two elements, which in certain applications can be particularly advantageous. For example, when the device is used in an environment with a pressure differential, such as in a vacuum pump application, or when handling hazardous materials. A non-contact joint allows two elements that may interact with different parts of the system to be isolated from each other through the use of a hermetic seal placed between them.

[0038] A further aspect includes a cryocooler in which the rotational motion from the motor is converted to reciprocating motion by the apparatus according to one aspect. In some embodiments, the reciprocating motion drives a piston in a Gifford-McMahon type cycle process. In some embodiments, the cryocooler forms part of a cryopump.

[0039] Further particular and preferred aspects are set out in the accompanying independent and dependent claims. Features of the dependent claims may be combined with features of the independent claims as appropriate and in combinations other than those explicitly set out in the claims.

[0040] It should be understood that when features of an apparatus are described as operable to provide a certain function, this includes features of the apparatus that provide that function or that are adapted or configured to provide that function.

[0041] Embodiments of the present invention will now be further described with reference to the accompanying drawings. [Brief description of the drawings]

[0042] [Figure 1] 1 illustrates a scotch yoke according to one embodiment. [Diagram 2] 2 shows a top view of the Scotch yoke of FIG. 1. [Diagram 3] 1 shows a schematic of the magnetic field generated by a magnet with a pole at the opposite end of the magnet facing a pole piece. [Figure 4] Schematic diagram of the magnetic field generated by a magnet with two poles at the same end. [Figure 5A] Schematic showing the magnetic field generated by a horseshoe magnet facing a single track pole piece [Figure 5B] Schematic showing the magnetic field generated by a horseshoe magnet facing a dual track pole piece. [Figure 6] 1 shows a Scotch yoke according to another embodiment. [Figure 7] 13 illustrates additional machinery suitable for adaptation to form devices according to embodiments. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0043] Before describing the embodiments in more detail, an overview will first be provided.

[0044] Ever since James Watt's invention, efficient conversion between rotary and linear motion has been an important area of ​​industrial development. There have naturally been many inventions and developments on such an important topic, but the simple Scotch yoke remains a commonly chosen solution due to its simplicity and robustness, and is indeed used as the main element of some refrigerator vacuum pumps. A conventional Scotch yoke drives a suitably shaped sliding joint whose contact point is attached to a rotating drive wheel. In particular, the path of motion taken by the slider can be adjusted by modification of the slot; this can be used, for example, to adjust the dwell time at either end of the sliding motion.

[0045] While such conventional Scotch yokes have many advantages, they also have disadvantages due to wear and friction. The embodiments seek to use magnetic forces as the force used to convert motion, thereby reducing or eliminating friction between contacting moving parts. Utilizing strong interactions between magnetic poles instead of direct mechanical contact significantly reduces friction and wear and is more robust against damage.

[0046] The embodiments provide a contactless magnetoresistance-based mechanism for efficient conversion between rotary and linear motion.

[0047] Figure 1 shows an embodiment of a Scotch yoke in which a rod 10 reciprocates as a wheel 20 rotates. The wheel 20 has a permanent magnet "pin" 12. The rod 10 has a high permeability pole piece 22 that corresponds to the "slot" of a conventional Scotch yoke. In this case, due to the high permeability of the pole piece 22, it is energetically favorable for the magnet pin 12 to remain centered over the pole piece 22, and movement along the long axis of the pole piece is energetically neutral until the magnet reaches either end.

[0048] Any losses in such non-contact joints may take the form of eddy current dissipation or magnetic hysteresis losses. Fortunately, there are well-known ways to mitigate such effects. Since the power lost due to eddy current generation varies proportionally with the resistivity of the material in which the currents are generated, it may be advantageous to make the parts of the device where eddy currents are a problem out of a highly resistive material. If high permeability and high resistance are required, a material such as highly resistive silicon-iron can be selected. Further reduction in eddy current losses can be achieved by moving to one of the many high permeability sintered powders developed for transformers. It is also possible to reduce eddy currents by forming the core from a stack of thin, highly permeable layers, as is done in transformers.

[0049] Magnetic hysteresis losses occur when the local orientation of the magnetic field generated by the individual domains of a magnet changes. Such losses are large in magnetically "hard" materials, whose domains are less likely to change, and small in magnetically "soft" materials. For this reason, transformer cores usually use "soft" materials to minimize such losses, and non-contact joints should do the same. Note also that losses are generally worse when the magnetic field direction completely reverses, as in a transformer. In a magnetic sliding joint, the external magnetic field applied to a particular point on the slider never completely reverses, but simply rises to a peak value and then falls as the magnetic "pin" moves across it.

[0050] It is therefore effective and simple to incorporate such a magnetic sliding joint directly into a Scotch yoke. At the midpoint of the yoke's rotation, the force from the rotating member is transferred to the slider by the natural tendency of the pole pieces to center over the permanent magnet "pins". At either end of the yoke's rotation, the pins 12 can move easily along the length of the slider 22 because as long as the pins are completely covered by the pole pieces, the stored magnetic energy is minimized. At any point in between, there is the combination of force transfer in the linear direction and free sliding in the vertical direction as found in a conventional Scotch yoke, except with reduced friction and no contact.

[0051] Figure 2 is a top view of the Scotch yoke of Figure 1 and shows that there is a gap between the pin 12 and the slider 22. This gap allows an airtight seal (not shown) to be placed between the two moving elements. There are applications where it is highly desirable to be able to separate both parts of the joint, and having a non-contact joint means that there is a gap between the two elements to provide space for an airtight seal.

[0052] One potential problem with this design, shown diagrammatically in Figure 3, arises from the lack of a clearly defined way in which the magnetic field is routed to the opposite pole after crossing the high permeability track. Excessive stray magnetic fields can create eddy current losses in nearby metal parts, causing interference as other parts change. Also, poor routing of such a magnetic circuit reduces the effective connection force between the "pin" and the "slider".

[0053] An embodiment seeks to address this by using coaxially split poles instead of a single pole, as shown in Figure 4. This provides a circularly symmetric closed path for the magnetic flux, and stray fields are nearly eliminated or at least reduced. Circular symmetry is essential in this case, because for a fixed "pin" point, every revolution of the drive wheel would result in one revolution of the relative orientation of the pin with respect to the slider.

[0054] Another possible variation is to use a "horseshoe" magnet with both north and south poles facing the high permeability slider, see Figure 5A. This has the advantage of completing the overall magnetic circuit directly, thus minimizing or at least reducing the stray magnetic fields emanating from the mechanism, but requires the magnetic pin to be housed in a free-swivel joint such as provided by a ball bearing.

[0055] In the magnetic field generated by such a horseshoe magnet, the receiving pole can also be divided into multiple tracks or equivalent receiving "teeth" (see FIG. 5B). This alternating arrangement of high and low magnetic field regions creates a large connection force between the pin and the slider, since any lateral displacement of the pin relative to the slider will result in a larger energy loss than in the case of a single pole. This multiple-tooth or multiple-track scenario can be extended to many more than two teeth or tracks using a layered stack of multi-pole pins and sliders.

[0056] Another interesting feature of the Scotch Yoke is that the relative stroke length can be varied by adjusting the radial position of the pins. Normally this involves some mechanical complexity to dial the position of the pins in or out. This feature can be very easily incorporated into a non-contact magnetic Scotch Yoke.

[0057] The simplest option is to replace the permanent magnet with an electromagnet and incorporate other electromagnets at different distances along the same radius. Then, when the yoke is at the midpoint, the driving electromagnet can be switched off and a coil at a different radius can be energized to take over driving the slider. Compared to the simple permanent magnet solution, this variant requires the incorporation of several electromagnets or permanently electric magnets in the drive wheel, as well as drive circuits and associated rotary electrical connections. However, it is much simpler than a mechanically variable Scotch yoke and can be switched more quickly, even during one revolution of the drive wheel.

[0058] 6 shows an alternative embodiment of the Scotch yoke in which there is an additional wheel 24 corresponding to wheel 20 and having a corresponding magnetic pin. Wheel 24 serves to reduce the resulting normal force on slider 22 resulting from the magnetic attraction between the magnetic protrusions of wheel 22 and the slider by exerting its own force in the opposite direction. Wheel 20 may be a driving wheel and additional wheel 24 may be a driven wheel.

[0059] Figure 7 shows some conventional devices with mechanical slip joints, where the pins can be replaced with magnetic patches or protrusions and the slots can be replaced with high permeability tracks to produce devices according to embodiments. Thus, Figure 7A shows a Geneva wheel mechanism that acts as a kind of gear to convert continuous rotary motion to intermittent rotary motion in the opposite direction. Figures 7B and 7C show a 6-bar slide mechanism and a 5-bar slot mechanism, respectively, and Figure 7D shows a cam follower.

[0060] Although exemplary embodiments of the present invention have been disclosed in detail herein with reference to the accompanying drawings, it is understood that the present invention is not limited to the precise embodiments, and various changes and modifications can be made by those skilled in the art without departing from the concept of the present invention as defined by the appended claims and their equivalents. [Explanation of symbols]

[0061] 10 Rod or further moving element 20 Wheel or first movable element 12 Magnetic patches or protrusions 22 Track or slider 30 Swivel joint 24 Extra Wheels

Claims

1. 1. A device for converting between one direction of motion and another direction of motion, comprising: a magnetic protrusion or patch attached to the first movable element and having a surface; a track attached to the further movable element and having predetermined magnetic properties; Equipped with said track defining a path along which said magnetic protrusions or patches are attracted by a magnetic force, said magnetic force constraining said movable element from moving, said magnetic protrusions or patches being adapted to move in a direction along said magnetic track in response to relative movement between said first movable element and said further movable element; The surface of the magnetic protrusions or patches has a shape having a width dimension that is aligned with and differs from a width of the track by less than 30%, and a length dimension perpendicular to the width dimension that is substantially shorter than a length dimension of the track and is less than 30% of the length dimension of the track.

2. The apparatus of claim 1 , wherein the motion in one direction comprises a rotational motion and the motion in the other direction comprises a translational motion.

3. 3. The apparatus of claim 1 or 2, wherein the magnetic protrusions or patches comprise magnets having at least two magnetic poles facing the track.

4. 4. The device according to claim 1, wherein the magnetic protrusions or patches have an axis perpendicular to the surface, the magnetic protrusions or patches being mounted such that they are symmetrical about the axis or rotatable about the axis.

5. 5. The apparatus of claim 3 or 4, wherein the magnetic protrusion or patch comprises a horseshoe magnet mounted so as to extend perpendicular to the surface of the horseshoe magnet facing the track and configured to rotate about an axis between the two magnetic poles.

6. 6. An apparatus according to claim 3, wherein the track comprises at least two tracks, such that each pole of the at least two pole magnet faces a respective track.

7. 7. The device of claim 1, wherein the magnetic protrusions or patches comprise permanent magnets.

8. The device according to claim 1 , wherein the magnetic protrusion comprises at least one electromagnet or at least one permanent electromagnet.

9. 9. The apparatus of claim 8, wherein the apparatus comprises a plurality of electromagnets or permanent electromagnets mounted at different positions on the first movable element, the apparatus comprising a control circuit configured to activate one of the plurality of electromagnets or permanent electromagnets at any one time, and wherein the selection of one of the plurality of electromagnets to be activated defines a trajectory of one of the movable elements.

10. 10. The apparatus of claim 9, wherein the first movable element comprises a rotating disk, and the plurality of electromagnets or permanent electromagnets are mounted at different radial positions on the rotating disk.

11. 11. Apparatus according to any one of claims 1 to 10, wherein the at least one track having a predetermined magnetic property is formed by lithographic printing of a material of high magnetic permeability on a substrate of low magnetic permeability.

12. 12. Apparatus according to any one of claims 1 to 11, wherein the at least one track having predetermined magnetic properties has a thickness of less than 3 mm.

13. 13. Apparatus according to any one of the preceding claims, wherein the further moveable element comprises a plurality of tracks, the plurality of tracks defining different relative trajectories between the moveable elements.

14. 14. Apparatus according to any one of claims 1 to 13, wherein the apparatus comprises one of a cam follower or a scotch yoke.

15. 15. The apparatus of claim 1, further comprising an additional moving element corresponding to the first moving element, the additional moving element including magnetic protrusions or patches corresponding to the magnetic protrusions or patches of the first moving element, the additional moving element being mounted on an opposite side of the further moving element relative to the first moving element.

16. 16. Apparatus according to any one of claims 1 to 15, wherein the apparatus further comprises an airtight seal between the first element and the further element.

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