Simple, center-less universal joint

[0001] This application claims the benefit of PPA Ser. No. 60/936,350, Return Receipt Nr. 7006 2760 0003 6446 5318, filed Jun. 21, 2007 by Thomas Hermann Schroeder, which is incorporated by reference.

[0002] 1. Field of Invention

[0003] The present invention relates to a universal joint.

[0004] 2. Prior Art

[0005] Universal joints are commonly used to transmit rotational motion between two shafts, both being coplanar; they commonly consist of two shafts, each having a yoke, mounted rotatably and perpendicularly to a centerpiece. The universal joint thus uses two connections, each being a hinge joint.

[0006] Gimbal joints are commonly used to allow certain degrees of motion freedom, having one side stationary and the other movable; they commonly consist of 3 concentric rings of different diameter, mounted rotatably and perpendicularly. The intermediate ring functions as the centerpiece being connected to the inner and outer ring. Thus the gimbal joint also uses two connections, each being a hinge joint.

[0007] Both, the universal joint and gimbal joint, are closely related, such that the improvements of this patent are relevant for both structures. The use of the term universal joint from hereon should be viewed as inclusive in regard to the gimbal joint.

[0008] The universal joint commonly uses bearings such as pin bearings, roller bearings, ball bearings, or friction bearings to facilitate rotation. All these can be made using different degrees of tolerance. However, greater precision usually requires greater expense. The number of connections in a complex joint is negatively correlated to the degree of precision, each connection reducing precision. A center-less universal joint would reduce the number of connections to a single one, a direct interface between the two yokes.

[0009] U.S. Pat. No. 7,084,337 to Schroeder (2003) uses a universal joint to allow motion of a musical instrument while restricting rotation of such instrument around its longitudinal axis. The degree of precision while moving the instrument is highly important and it would thus be beneficial to have a universal joint of ultra tight tolerance, yet simple enough to allow inexpensive manufacturing.

[0010] Since the musical instrument interfaces with a support, this being a single connection, it would be of advantage to have a two part universal joint that can be easily engaged and disengaged, wherein one part would be attached to the support and the other to the instrument. Engaging the instrument-support interface would engage the universal joint interface. This engagement process should be easy; the instrument should align itself with the support such that the rotational axes of the universal joint are aligned perpendicularly. In the same manner the disengagement should be made simple allowing the player to easily release the instrument from the support. A further requirement of the joint in combination with a musical instrument would be safety; all protruding parts should have smooth surfaces. This is especially important if the player is a child. The weight of the instrument in addition to the forces applied by the player further require the joint to be durable.

[0011] U.S. Pat. No. 4,968,173 to Fujita (1990) shows a universal joint that can be disengaged as well as engaged by sliding a first yoke onto a spherical center piece connected to a second yoke. Fitting the spherical section on the yoke to the spherical center piece requires high precision to achieve smooth operation. This solution would thus not combine ultra tight tolerance and low cost.

[0012] The parts of most universal joints are not easily assembled or disassembled; thus these joints are often used as modules fitted with additional connectors to serve applications which require an easy interface for rapid connection and release.

[0013] Awnings use universal joints to allow the user to operate the crank shaft from different angles. The interface between crank and awning is often quite difficult to establish having to align the crank shaft to be collinear with the shaft of the awning's universal joint; in addition the rotational orientation of the crank shaft has to match that of the universal joint to allow the usual snap-in connection. A more usable system would be preferable.

[0014] Screwdrivers are usually used applying force against a screw while rotating the screw with the screw driver. Both screw and driver are designed to be used with collinear rotational axes. Universal joint modules can be used to allow non collinear operation, but they add to the instability of the system due to the increased number of non-weld connections. It would be beneficial to have an improved interface between screw and screwdriver that integrates the functionality of a universal joint. While wobble hex bits allow non-collinear operation, the design of the interface between driver and screw is biased towards collinear operation; thus this design is not a universal joint.

[0015] Accordingly, several objects and advantages of the present invention are to provide a universal joint:

• • [0016] (a) that is of simple design
  • [0017] (b) that is of durable construction
  • [0018] (c) that is inexpensive to manufacture
  • [0019] (d) that has ultra tight tolerance
  • [0020] (e) that is center-less
  • [0021] (f) that has an easily engaging interface
  • [0022] (g) that has an easily disengaging interface
  • [0023] (h) that is self aligning in two ways during the engagement process, having rotational axes perpendicular as well as having shafts coplanar
  • [0024] (i) that is user friendly and safe
    Further objects and advantages will be made clear by the following description and drawings.

[0025] A simple, center-less universal joint of ultra tight tolerance comprising two yokes, each having two facing, distinctly round interface surface areas; both yokes being easily engaged (a self aligning process) and disengaged.

• [0048] 1. first embodiment of the simple, center-less universal joint
• [0049] 2. first structure of first embodiment 1
• [0050] 3. first yoke of first structure 2
• [0051] 4. first shaft of first structure 2
• [0052] 5. first two ball knobs
• [0053] 6. rotational first primary axis
• [0054] 7. rotational first secondary axis
• [0055] 8. second structure of first embodiment 1
• [0056] 9. second yoke of second structure 8
• [0057] 10. second shaft of second structure 8
• [0058] 11. second two ball knobs
• [0059] 12. rotational second primary axis
• [0060] 13. rotational second secondary axis
• [0061] 14. two bores of first ball knobs 5
• [0062] 15. linear Bézier curve
• [0063] 16. non-linear Bézier curve
• [0064] 17. circle
• [0065] 18. rotational axis for sweep
• [0066] 19. first sweep surface area
• [0067] 20. second sweep surface area
• [0068] 21. first structure of second embodiment of the simple, center-less universal joint
• [0069] 22. third embodiment of the simple, center-less universal joint
• [0070] 23. first structure of third embodiment 22
• [0071] 24. second structure of third embodiment 22
• [0072] 25. track
• [0073] 26. first surface area of track 25
• [0074] 27. second surface area of track 25
• [0075] 28. centerline of track 25
• [0076] 29. shaft of second structure 24
• [0077] 30. yoke of second structure 24
• [0078] 31. two ball knobs of second structure 24
• [0079] 32. fourth embodiment of the simple, center-less universal joint
• [0080] 33. first yoked shaft of fourth embodiment 32
• [0081] 34. second yoked shaft of fourth embodiment 32
• [0082] 35. first two ball segments of first shaft 33
• [0083] 36. second two ball segments of second shaft 34
• [0084] 37. fifth embodiment of the simple, center-less universal joint
• [0085] 38. first structure of fifth embodiment 37
• [0086] 39. second structure of fifth embodiment 37
• [0087] 40. musical instrument
• [0088] 41. two ball knobs connected to musical instrument 40
• [0089] 42. double cone of first structure 38
• [0090] 43. support rod of first structure 38
• [0091] 44. stool
• [0092] 45. rotational first axis of fifth embodiment 37
• [0093] 46. rotational second axis fifth embodiment 37
• [0094] 47. two facing surface areas of double cone 42
• [0095] 48. sixth embodiment of the simple, center-less universal joint
• [0096] 49. first structure of sixth embodiment 48
• [0097] 50. shaft of first structure 49
• [0098] 51. ring of first structure 49
• [0099] 52. first two facing surface areas of ring 51
• [0100] 53. second structure of sixth embodiment 48
• [0101] 54. shaft of second structure 53
• [0102] 55. hook of second structure 53
• [0103] 56. second two facing surface areas of hook 55
• [0104] 57. seventh embodiment of the simple, center-less universal joint
• [0105] 58. first structure of seventh embodiment 57, screw
• [0106] 59. thread of first structure 58
• [0107] 60. first head of first structure 58
• [0108] 61. slot in first head 60
• [0109] 62. first two facing spherical surfaces of first head 60
• [0110] 63. second structure of seventh embodiment 57, screwdriver
• [0111] 64. handle of second structure 63
• [0112] 65. shaft of second structure 63
• [0113] 66. second head of second structure 63
• [0114] 67. second two facing spherical surfaces of second head 66
• [0115] 68. eighth embodiment of the simple, center-less universal joint
• [0116] 69. first structure of eighth embodiment 68
• [0117] 70. first yoke of first structure 68
• [0118] 71. first two protrusions of first yoke 70
• [0119] 72. first two spherical segments of first yoke 70
• [0120] 73. two slots of spherical segments 72
• [0121] 74. first two facing spherical surfaces of spherical segments 72
• [0122] 75. second structure of eighth embodiment 68
• [0123] 76. second yoke of second structure 75
• [0124] 77. second two protrusions of second yoke 76
• [0125] 78. second two spherical segments of second yoke 76
• [0126] 79. second two facing spherical surfaces of spherical segments 78
• [0127] 80. rotational chain system
• [0128] 81. first unit of rotational chain system 80
• [0129] 82. second unit of rotational chain system 80
• [0130] 83. third unit of rotational chain system 80
• [0131] 84. pipe

[0132] FIGS. 1-4 show a first embodiment 1 of the simple, center-less universal joint, having a first structure 2 and a second structure 8, both being identical. First structure 2 comprises a first shaft 4 attached to a first yoke 3 having first two ball knobs 5 securely mounted to it; second structure 8 comprises a second shaft 10 attached to a second yoke 9 having second two ball knobs 11 securely mounted to it. FIG. 2 in particular shows two bores 14 of first two ball knobs 5 for mounting onto first yoke 3; second two ball knobs 11 are mounted similarly onto second yoke 9.

[0133] FIG. 1 illustrates a rotational first primary axis 6 defined by the centers of the first two ball knobs 5; a rotational first secondary axis 7 is identical to the rotational axis of first shaft 4; both, rotational first primary axis 6 and rotational first secondary axis 7 are perpendicular. FIG. 1 also illustrates a rotational second primary axis 12 defined by the centers of second two ball knobs 11; a rotational second secondary axis 13 is identical to the rotational axis of second shaft 10; both, rotational second primary axis 12 and rotational second secondary axis 13 are perpendicular but not coplanar.

[0134] First structure 2 is interfaced by means of force, for example gravity, with second structure 8 such that first two ball knobs 5 touch second two ball knobs 11. FIGS. 3 and 4 illustrate the interface between first two ball knobs 5 and second two ball knobs 11. Each of first two ball knobs 5 touches each of second two ball knobs 11 in one point; each of second two ball knobs 11 touches each of first two ball knobs 5 in one point. Thus there are exactly 4 points of contact.

[0135] The process of engaging the interface between first structure 2 and second structure 8 is self aligning in that rotational first primary axis 6 and rotational second primary axis 12 are perpendicular; this process is further self aligning in that rotational first secondary axis 7 and rotational second secondary axis 13 are coplanar and in the illustrated base position even collinear. Keeping the interface between first structure 2 and second structure 8 engaged, the following rotations can be performed:

[0136] Both first structure 2 and second structure 8 can rotate around both rotational first primary axis 6 and rotational second primary axis 12, using the gliding surfaces of the first two ball knobs 5 and second two ball knobs 11.

[0137] Rotation of first structure 2 around rotational first secondary axis 7 results in rotation of second structure 8 around rotational second secondary axis 13; rotational first secondary axis 7 and rotational second secondary axis 13 can be non-collinear during transmission of rotational motion; thus the functionality of a traditional universal joint is being described.

[0138] In case second structure 8 is stationary, the freedom of motion of first structure 2 is restricted to rotation around both rotational first primary axis 6 and rotational second primary axis 12, but not around rotational first secondary axis 7; thus the functionality of a traditional gimbal joint is being described.

[0139] There is no center piece: First structure 2 interfaces directly with second structure 8; the interface can be engaged and disengaged easily, because it is non-permanently connected by force only. Furthermore, this interface has an ultra tight tolerance being based on exactly four points of contact, which are being established by force only.

[0140] While the diameter of all ball knobs (first two ball knobs 5 and second two ball knobs 11) is shown as being identical, is not a necessity. For example, the rotational first primary axis 6, being defined by the centers of first two ball knobs 5, would retain the same functionality when using different diameters. Similarly, the distance between first two ball knobs 5 and the distance between second two ball knobs 11 is shown as being identical. Again, this is not a necessity. Limitations to these measurements are obvious from the illustrations.

[0141] All, first two ball knobs 5 and second two ball knobs 11, have a low friction surface for smooth interface operation.

[0142] The simple, center-less universal joint derives its functionality from the shape of the interface surfaces, their relative positions and orientations. The following embodiments will further define the requirements of these interface surfaces and illustrate different applications benefitting from the use of this simple, center-less universal joint.

[0143] Bézier curves are used to describe smooth curves: They can describe straight lines (linear Bézier curves), arcs (curves of constant radius), as well as curves of changing radius.

[0144] FIG. 5 shows a rotational axis 18, a linear Bézier curve 15 and a non-linear Bézier curve 16, both curves being tangent to a circle 17, all four objects being coplanar. Rotational axis 18 is used for a 180 degree arc angle sweep of linear Bézier curve 15 and non-linear Bézier curve 16 creating a first sweep surface area 19 and a second sweep surface area 20 respectively, as illustrated in FIGS. 6 and 7.

[0145] Linear Bézier curve 15 and non-linear Bézier curve 16 are designed to ‘cradle’ circle 17 such that the described sweep creates two facing surface areas, first sweep surface area 19 and second sweep surface area 20, both surface areas functioning as the interface surface areas of first structure 21 of the second embodiment of the simple, center-less universal joint.

[0146] While the first sweep surface 19 is conical, the second sweep surface 20 is round but not spherical. It is obvious that there are many different ways of creating functional facing interface surface areas using different Bézier curves. In FIG. 1 for example, the interface surface areas of the first structure 2, being the spherical outer surfaces of first ball knobs 5, can be viewed as having been created by a sweep of two identical arcs around rotational first primary axis 6, the sweep having a 360 degree are angle, the arcs' radius being that of first ball knobs 5.

[0147] It is further obvious that only specific areas of the spherical outer surfaces of ball knobs 5 are essential for the interface between first structure 2 and second structure 8, here referred to as facing areas.

[0148] FIG. 9 shows a third embodiment 22 of the simple, center-less universal joint. A first structure 23 serves as a stationary base having track 25, consisting of a first surface area 26 and a second surface area 27, both connected at centerline 28. A second structure 24, having a shaft 29, a yoke 30, and two ball knobs 31, interfaces with first structure 23, in particular having the two ball knobs 31 interfacing with track 25. The first surface area 26 and second surface area 27, forming track 25, can be viewed as being created by sweeps of arcs, the radius of such arcs identical to those of the two ball knobs 31. Thus this third embodiment 22 illustrates an extreme interpretation of the simple, center-less universal joint; first structure 23 interfaces with second structure 24 in more than 4 points of contact: The contact area between one of the two ball knobs 31 and track 25 is an arc.

[0149] This third embodiment 22 could be used, for example, as a stand for a double bass, having shaft 29 connected to the double bass; the stand would thus prohibit rotation of the double bass around its longitudinal axis, such axis by design being identical to shaft 29. When compared to a traditional gimbal joint, this third embodiment 22 further illustrates the simplicity of the present invention: The elimination of both centerpiece, or center ring, and bearings creates a system that is durable yet inexpensive to manufacture.

[0150] FIG. 10 shows a fourth embodiment 32 of the simple, center-less universal joint having a first yoked shaft 33, having first two ball segments 35, interfacing with a second yoked shaft 34, having second two ball segments 36. This fourth embodiment 32, while closely resembling the traditional universal joint in appearance, operates without a center piece utilizing the spherical surface areas of both first two ball segments 35 and second two ball segments 36, thus retaining the rotational functions of a traditional universal joint. First yoked shaft 33 and second yoked shaft 34 can be easily engaged, a self aligning process, and disengaged.

[0151] While first two ball segments 35 are shown as parts connected to first yoked shaft 33, they could be manufactured, molded for example, as a single unit; accordingly second two ball segments 36 and second yoked shaft 34 could be molded as a single unit. Both described single units being identical, manufacturing could be simplified to producing a single mold, no assembly required.

[0152] FIGS. 11 and 12 show a fifth embodiment 37 of the simple, center-less universal joint. A first structure 38 having a support rod 43 and a double cone 42 is connected to a stool 44. A second structure 39, a musical instrument 40 having two ball knobs 41 connected to it, is interfacing with first structure 38, in particular having the two ball knobs 41 supported by two facing areas 47 of double cone 42.

[0153] Motion of musical instrument 40 is thus restricted to rotation around both rotational first axis 45 and rotational second axis 46. Musical instrument 40 can be easily engaged with its support, being second structure 39 connected to stool 44, as well as disengaged.

[0154] The two facing surface areas 47 of double cone 42 can be viewed as being created by a sweep of two linear Bézier curves around rotational first axis 45.

[0155] The two ball knobs 41 could alternatively be integrated at different sections of musical instrument 40, even mounted adjustably.

[0156] FIGS. 13-15 show a sixth embodiment 48 of the simple, center-less universal joint, having a first structure 49 and a second structure 53. FIG. 14 more detailed shows first structure 49 having a shaft 50 connected to a ring 51 having first two facing surface areas 52; FIG. 5 more detailed shows second structure 53 having a shaft 54 connected to a hook 55 having second two facing surface areas 56. First structure 49 can interface with second structure 53 utilizing first two facing surface areas 52 and second two facing surface areas 56.

[0157] This sixth embodiment 48 could be used in connection with an awning, particularly operation of its crank.

[0158] FIGS. 16-18 show a seventh embodiment 57 of the simple, center-less universal joint. A first structure 58, being a screw having a first head 60 and thread 59, interfaces with a second structure 63, being a screw driver having a shaft 65 connected to a handle 64 and a second head 66. First head 60 has a slot 61 exposing first two facing spherical surfaces 62, shown in FIG. 17, for interfacing with second two facing spherical surfaces 67 of second head 66.

[0159] FIG. 18 shows second structure 63 interfacing with first structure 58, the longitudinal axes of both shaft 65 and thread 59 being non collinear, while transmitting rotational motion from second structure 63 to first structure 58. This interface can be easily engaged (a self aligning process) and disengaged, because it is non-permanently connected by force only; it provides ultra tight tolerance being based on exactly four points of contact, which are established by force only.

[0160] There is no need for a traditional universal joint module to be inserted between second head 66 and shaft 65, thus retaining the stability provided by using only a single interface connection; this seventh embodiment 57 adds the benefits of a universal joint module while maintaining ultra tight tolerance.

[0161] FIGS. 19-21 show an eighth embodiment 68 of the simple, center-less universal joint as well as application examples. A first structure 69 has a first yoke 70 with first two protrusions 71 for connecting to first two spherical segments 72 via two slots 73; accordingly, a second structure 75 has a second yoke 76 with second two protrusions 77 for connecting to second two spherical segments 78. First structure 69 can interface with second structure 75 using first two spherical segments 74 and second two spherical segments 79.

[0162] FIG. 19 also suggests a permanent connection between first structure 69 and second structure 75 forming a single unit with two yoked ends. As shown in FIG. 20, such a unit can be used to form a rotational chain system 80 having a first unit 81, second unit 82, and third unit 83 interfacing. FIG. 21 shows the rotational chain system operating within a pipe 84.

[0163] Such rotational chain systems, using any number of units, could be used, particularly due to the self-aligning interfaces, to create universal joint connections in places that are not easily accessible. Such systems would further be of ultra tight tolerance.

[0164] While the above description contains many specificities, these should not be construed as limitations on the scope of the invention, but as exemplifications of the presently preferred embodiments thereof. Many other ramifications and variations are possible within the teachings of the invention. For example, the simple, center-less universal joint

• • [0165] (a) can be made of different materials
  • [0166] (b) can be made of different sizes
  • [0167] (c) can have additional parts attached to it
  • [0168] (d) can be integrated into other structures
  • [0169] (e) can use many variations of interface surface areas
  • [0170] (f) can be used in connection with all kinds of bolts and screws
  • [0171] (g) can be used in connection with other applications
  • [0172] (h) can be used for other musical instruments
    Thus the scope of the invention should be determined by the appended claims and their legal equivalent, and not by the examples given.