Continuously variable transmission with twisted strings

Abstract

The present invention relates to an active continuously variable transmission based on a twisted string actuator, comprising: a linear motion unit for outputting substantial linear motion; a power transmission unit for transmitting power; and at least two strings for connecting the linear motion unit and the power transmission unit, wherein a transmission ratio is set through the ratio of the individual twists of each string and the overlapping twists of the plurality of strings, and linear motion is adjusted within a range in which the individual twists and the overlapping twists are not excessive.

Description

Line twist continuously variable transmission

[0001] The present invention relates to a continuously variable transmission, and more particularly, to an active continuously variable transmission utilizing the twisting of a plurality of strings.

[0002] Robots are widely used in diverse applications, including industrial, surgical, and military applications. Actuators are essential components for implementing these robot movements, and among various actuators, motors are the most widely used. Motors are primarily used to power the wheels of mobile robots, which move by rotating their wheels, or to move the joints of manipulators. However, if these actuators are simply driven by motors and gears without a dedicated mechanism, the motor torque and speed are fixed, making it difficult for most users to achieve the desired robot performance. When the actuator's inherent performance cannot address these issues, specialized mechanisms are required to meet the performance requirements for each application and robot's intended use.

[0003] As an example of a special mechanism, a twisted string actuator mechanism that can generate a large linear driving force even with a small torque has been proposed. In particular, in the inventor's previous study, “Development of a twisted string actuator-based exoskeleton for hip joint assistance in lifting tasks,” a small and lightweight twisted string actuator (TSA)-based hip joint assistance device utilizing a monotonically decreasing nonlinear power transmission ratio (TR) was proposed.

[0004] Meanwhile, in the case of TSA presented in the aforementioned study, despite its many advantages, there were limitations in its application to systems requiring the opposite TR profile, which requires high speed in the initial contraction region and high force at the end of the contraction region.

[0005] As a solution to the unique characteristics of TSA and the demand for a TR profile that is opposite to them, the proposals in “Dual-mode twisting actuation mechanism with an active clutch for active mode-change and simple relaxation process,” “Designing anthropomorphic robot hand with active dual-mode twisted string actuation mechanism and tinytension sensors,” and “A 2-speed small transmission mechanism based on twisted string actuation and a dog clutch,” can also be applied. These systems exploit the difference in the contraction speed of the TSA according to the radius of the object in the middle of the string, and since placing a cylinder between the strings reduces the TR of the TSA, the system can change the input and output TR of the system in a binary manner by twisting the string with or without a cylinder.

[0006] However, these TSA systems still have limitations in that they cannot cover the entire ideal traction hyperbolic region due to the limitations in the speed and torque range caused by binary TR conversion, and there are problems in that the conversion takes a long time and the life of the TSA is shortened due to friction between the string and the cylinder.

[0007] The present invention is designed to solve such problems, and provides a string-twisted continuously variable transmission capable of compensating for a nonlinear gear ratio through continuous conversion of the gear ratio and increasing the operating range.

[0008] In addition, it is an object of the present invention to provide a string twist continuously variable transmission capable of stepless speed change based on a string twist mechanism.

[0009] In addition, it is an object of the present invention to provide a string twist continuously variable transmission capable of implementing a transmission ratio by adjusting the rotation ratio of individual twists and overlapping twists.

[0010] In addition, it is an object of the present invention to provide a string twist continuously variable transmission capable of implementing various actuating operations by adjusting the rotation radius of individual twists and overlapping twists and the diameter of the string.

[0011] According to one embodiment of the present invention for solving the above problem, a string twisted continuously variable transmission comprises: a linear motion unit that outputs linear motion; a power transmission unit that transmits power; and at least two strings connecting the linear motion unit and the power transmission unit, and sets a transmission ratio of power transmission by adjusting the ratio of individual twist of each string and overlapping twist between the plurality of strings, and is characterized in that the linear motion is adjusted within a range where the individual twist and overlapping twist do not become excessively twisted.

[0012] Additionally, force can be transmitted to the linear motion unit by contraction of the strings due to individual twisting of each string and overlapping twisting between the plurality of strings.

[0013] In addition, the power transmission unit can implement a first twisting operation in which the individual twists are set by adjusting the individual rotation angles of the strings to contract the entire string, and a second twisting operation in which the overlapping twists are set by adjusting the rotation angles between the strings to contract the entire string.

[0014] In addition, the power transmission unit is configured to include a first power transmission unit that implements a first twisting motion and a second power transmission unit that implements a second twisting motion.

[0015] In addition, the power transmission unit includes a ring gear, a sun gear, and a plurality of planetary gears corresponding to each of the strings, and the first twisting operation and the second twisting operation can be implemented by controlling the rotational speeds of the ring gear and the sun gear, respectively.

[0016] In addition, one end of each string is connected to the center of each planetary gear, the other end of each string is connected to the linear motion unit, the sun gear is externally engaged with each planetary gear, the ring gear is internally engaged with each planetary gear, and the sun gear and the ring gear can form a rotation axis on the same axis.

[0017] Additionally, each of the above strings can be gathered and combined at one point on the linear motion unit.

[0018] In addition, the ring gear and the sun gear may form a rotation axis on the same axis, but form a separate rotation axis, and the power transmission unit may include a first power unit that controls the rotation speed of the ring gear and a second power unit that controls the rotation speed of the sun gear.

[0019] Additionally, the linear motion unit may further include a linear rail in the same direction as the rotation axis of the string.

[0020] Additionally, the first power transmission unit implementing the first twisting motion and the eccentric rotation shaft configured to be eccentrically connected to the string may be further included.

[0021] In addition, the position of the eccentric rotation shaft can be controlled by controlling the first power transmission unit, thereby adjusting the rotation radius of the second twisting motion.

[0022] Additionally, multiple strings can be connected to the first power transmission unit that implements the first twisting motion to implement a multi-stage twisting motion.

[0023] Additionally, the thickness of the string connected to the first power transmission unit can be adjusted to different degrees to implement a pivot motion in the linear motion unit.

[0024] In addition, a method for controlling a twisted-string continuously variable transmission for controlling a twisted-string continuously variable transmission comprises: a contraction step of twisting and contracting a plurality of strings through a power transmission unit to transmit power to a driving unit; and a relaxation step of twisting and relaxing the plurality of strings in the opposite direction through the power transmission unit after the contraction step; wherein the contraction step includes a first twisting operation for implementing individual twisting by adjusting individual rotation angles of the strings and a second twisting operation for implementing overlapping twisting by adjusting rotation angles between the plurality of strings, wherein linear motion is controlled within a range where the individual twisting and the overlapping twisting do not become excessively twisted.

[0025] In addition, the above-described contraction step can implement the first twisting motion and the second twisting motion by controlling the rotational speed ratio of the sun gear and the ring gear, and the rotational speed of the planetary gear to which the string is directly connected and the rotational speed centered on the rotational axis of the sun gear.

[0026] Additionally, the relaxation step may include a first releasing operation for releasing individual twists by adjusting individual rotation angles of the strings and a second releasing operation for releasing overlapping twists by adjusting rotation angles between the plurality of strings.

[0027] Additionally, the relaxation step may perform the first releasing operation after the overlapping twist is completely released through the second releasing operation.

[0028] In addition, the relaxation step can implement the first release operation and the second release operation by controlling the rotational speed ratio of the sun gear and the ring gear, and the rotational speed of the planetary gear and the rotational speed centered on the rotational axis of the sun gear.

[0029] The string twisted continuously variable transmission according to the present invention has the advantage of being able to continuously vary the transmission ratio and increase the operating range while maintaining a high contraction speed.

[0030] In addition, the string twisted continuously variable transmission according to the present invention has the advantage of being easily implemented without performance degradation compared to existing variable transmissions.

[0031] FIG. 1 is a conceptual diagram for explaining the operating mechanism of a string twisted continuously variable transmission according to one embodiment of the present invention.

[0032] FIG. 2 is a conceptual diagram for explaining the geometric characteristics of a twisted-string continuously variable transmission according to one embodiment of the present invention.

[0033] FIG. 3 is a conceptual diagram for explaining a twist range for operation of a twisted continuously variable transmission according to one embodiment of the present invention.

[0034] Figure 4 is a perspective view illustrating another embodiment of the present invention using a planetary gear.

[0035] Fig. 5 shows a cross-section of a planetary gear according to another embodiment of the present invention.

[0036] FIG. 6 is a plan view of a string twisted continuously variable transmission according to another embodiment of the present invention.

[0037] Fig. 7 is a graph showing the contraction and relaxation process according to the gear ratio of a string twisted continuously variable transmission according to one embodiment of the present invention.

[0038] FIG. 8 is a conceptual diagram illustrating a string twisted continuously variable transmission according to another embodiment of the present invention.

[0039] Fig. 9 is a conceptual diagram for explaining the change in the radius of rotation of the overlapping twist according to the position of the eccentric rotation axis in Fig. 8.

[0040] FIG. 10 is a conceptual diagram illustrating a twisted-string continuously variable transmission according to another modified example of the present invention.

[0041] Hereinafter, the technical idea of ​​the present invention will be described in more detail using the attached drawings. Prior to this, it should be noted that the terms and words used in this specification and claims should not be interpreted as having conventional or dictionary meanings, and should be interpreted with meanings and concepts that are consistent with the technical idea of ​​the present invention, based on the principle that the inventor can appropriately define the concept of the term to best explain his or her own invention. Therefore, the embodiments described in this specification and the configurations illustrated in the drawings are only the most preferred embodiments of the present invention and do not represent all of the technical idea of ​​the present invention. Therefore, it should be understood that various modified examples that can replace them may exist at the time of filing this application.

[0042] FIG. 1 is a conceptual diagram for explaining the operating mechanism of a twisted-string continuously variable transmission according to an embodiment of the present invention. Referring to FIG. 1, the twisted-string continuously variable transmission according to the present invention is configured to include a linear motion unit (100), a first power transmission unit (201), a second power transmission unit (202), and a string (300) as illustrated.

[0043] To explain in more detail, the linear motion unit (100) is connected to one end of the plurality of strings (300) and can output power through the force transmitted from the strings (300). For example, the linear motion unit (100) can be mounted on a fixed shaft with respect to a specific device and output power by moving in the axial direction by the strings (300).

[0044] The first power transmission unit (201) is connected to the other end of the plurality of strings (300) to transmit rotational force, and the second power transmission unit (202) rotates the plurality of first power transmission units (201). At this time, the first power transmission unit (201) can contract the plurality of strings (300) by twisting them through the rotational force, and transmit power to the linear motion unit (100) through the difference in contraction displacement.

[0045] The above string (300) connects the linear motion unit (100) and the first power transmission unit (201), and can form at least two or more strings. The string (300) can adjust the transmission ratio by implementing individual twists and overlapping twists by the first power transmission unit (201) and the second power transmission unit (202). That is, the first power transmission unit (201) and the second power transmission unit (202) implement individual twists that twist each string (300) and overlapping twists that generate twists between the plurality of strings (300), and the transmission ratio can be set through the twist ratios of the individual twists and the overlapping twists.

[0046] FIG. 1(a) illustrates a first twisting operation in which the first power transmission unit (201) sets an individual twist by adjusting the individual rotation angle of the string (300), and FIG. 1(b) illustrates a second twisting operation in which the second power transmission unit (202) sets an overlapping twist by rotation.

[0047] Figure 2 is for explaining the geometric characteristics of the string twisted continuously variable transmission according to the present invention.

[0048] First, the d value corresponding to the string clearance shown affects the shrinkage length in the overlapping twist, but this effect is minimal and can be ignored. The shrinkage lengths due to individual twists and overlapping twists are each based on [Equation 1], and the shrinkage lengths due to both individual twists and overlapping twists follow [Equation 2].

[0049] [Formula 1]

[0050] [Formula 2]

[0051] (Here, Is The individual twist angle corresponding to Is The corresponding overlap twist angle, is the individual twist radius, is the overlap twist radius, is the total contraction length)

[0052]

[0053] Accordingly, in the string twisted continuously variable transmission according to the present invention is as follows.

[0054] [Formula 3]

[0055] According to [Equation 3], the total contraction length Is When this increases, it increases. At this time, each of the individual twists and overlapping twists will be affected. Additionally, the contraction speed follows the following formula:

[0056] [Formula 4]

[0057] So the contraction speed is the angular velocity of the ring gear is proportional to . At this time, the influence of each individual twist and overlap twist is It can be adjusted by, and as a result, it induces a change in the gear ratio.

[0058] At this time, if at least one of the individual twists and the overlapping twists exceeds the geometric prediction range, the string loses its function as a string twist actuator, so it is necessary to control the string so that the overlapping twists do not occur by adjusting the ratio of the individual twists and the overlapping twists.

[0059] Figure 3 is a conceptual diagram illustrating the range of twists within which a continuously variable transmission with a twisted string operates according to an embodiment of the present invention. Typically, overtwisting occurs when the displacement of linear motion reaches 30% of the total string length. However, in the present invention, the limit displacement for overtwisting can be adjusted by adjusting the ratio of individual twists to overlapping twists.

[0060] FIG. 4 is a perspective view for explaining another embodiment of the present invention using a planetary gear. Referring to FIG. 4, a power transmission unit (200) for implementing individual twisting and overlapping twisting may include a ring gear (210), a sun gear (220), and a plurality of planetary gears (230) to which each of the strings (300) is coupled.

[0061] The above planetary gear module may include a planetary gear (230), a sun gear (220), and a ring gear (210) as illustrated. One end of each string (300) may be connected to the center of each planetary gear (230). That is, the string (300) may implement a first twisting operation and a second twisting operation by the planetary gear (230). The individual twisting of the string (300) may be implemented by the rotation of the planetary gear (230), and the overlapping twisting of the string (300) may be implemented by the revolution of the planetary gear (230). For this purpose, the other end of each string (300) may be fixed to the linear motion unit (100). In addition, the above-mentioned sun gear (220) may be configured to externally mesh with each of the above-mentioned planetary gears (230) and internally mesh with each of the above-mentioned planetary gears (230) through the inner surface of the above-mentioned ring gear (210).

[0062] At this time, the sun gear (220) and the ring gear (210) form a rotation axis on the same axis, but the rotation axis can be separated so that the rotation speed can be individually controlled. As illustrated, in the present embodiment, the first power unit (250) and the second power unit (260) are individually positioned, and the sun gear (220) and the ring gear (210) can be individually operated. That is, by individually controlling the rotation speeds of the sun gear (220) and the ring gear (210), the rotation speed and revolution speed of the planetary gear (230) can be controlled, thereby controlling the individual twist and overlapping twist ratio of the string (300).

[0063] At this time, as illustrated, each string (300) may be gathered and combined at one point on the linear motion unit. This is to ensure driving stability by gradually twisting from one side when overlapping twisting occurs between the strings (300).

[0064] In addition, as illustrated, the linear motion unit (100) may further include a linear rail (110) in the same direction as the rotation axis of the string (300). This is to convert the contractile force due to the twisting of the string (300) into linear motion, and the linear motion unit (100) may be coupled with the linear rail (110) to move along at least two or more rails so as to be able to move in one direction without rotating.

[0065] FIG. 5 is a cross-sectional view of a planetary gear according to another embodiment of the present invention. Referring to FIG. 5, the planetary gear module includes a planetary gear (230), a sun gear (220), and a ring gear (210), and may include a carrier (240) connecting the planetary gear (230). The rotation angles of the planetary gear (230) and the carrier (240) may vary depending on the rotation angles of the sun gear (220) and the ring gear (210). That is, the following equation is followed.

[0066] [Formula 5]

[0067] [Formula 6]

[0068] (Here,

[0069] , , , are the rotation angles of the carrier, ring gear, sun gear and planetary gear, respectively.

[0070] , , , are the rotational radii of the carrier, ring gear, sun gear and planetary gear, respectively)

[0071] In the above equation class Due to the independence of the planetary gear (230), the angular velocity of the planetary gear (230) is inversely proportional to the angular velocity of the sun gear (220) when the rotational speed of the ring gear (210) is constant. Conversely, the angular velocity of the carrier (240) decreases linearly under the same conditions. That is, the carrier (240) has a rotational ratio corresponding to the rotational ratio of the sun gear (220) and the ring gear (210). go If the value is the same as , it is fixed. In other words, the planetary gear (230) is fixed with respect to the rotation axis of the sun gear (220) or ring gear (210) under the conditions described above. The string twisted continuously variable transmission according to the present invention is based on the rotation characteristics described above.

[0072] FIG. 6 is a plan view of a string-twisted continuously variable transmission according to another embodiment of the present invention. Referring to FIG. 6, a linear rail (110) in the same direction as the rotation axis of the string (300) may be further included. This is to convert the contraction force due to the twisting of the string (300) into linear motion, and the driving unit (100) may be coupled with the linear rail (110) to move along at least two or more rails so as to be able to move in one direction without rotating.

[0073] Figure 7 is a graph showing the contraction and relaxation process according to the gear ratio of a string twisted continuously variable transmission according to an embodiment of the present invention, and the rotation ratio of the sun gear and the ring gear. When the rotation of the ring gear is changed, it shows a continuous change in the contraction speed. Referring to Fig. 7, As increases, the slope of the contraction length decreases. This means that, than the speed when it is constant It indicates that the contraction rate is slower when increasing. Also, As decreases, the slope of the contraction length decrease is increasing. This means that, than the speed when it is constant This means that the contraction speed is faster when the pressure decreases.

[0074] one side, The state where is 0 is the first release operation, The state of -3 represents the second release operation. That is, In the first release operation where the value is 0, the rotation of the sun gear stops and the process of releasing the overlapping twist is implemented. In the second release operation of -3, the sun gear and ring gear can rotate together to implement the process of releasing individual twists.

[0075] As shown, After reaching the maximum contraction by implementing both individual twist and overlapping twist at -1.5, Set to 0 to completely disable the overlapping twist, and then By setting to -3, the individual twists can be completely released. That is, the two-step release operation, which implements the first release operation to release the overlapping twists and the second release operation to release the individual twists, can most efficiently implement complete relaxation of the string without delay in the gear ratio change.

[0076] FIGS. 8 and 9 are conceptual diagrams for explaining a string twisted continuously variable transmission according to another embodiment of the present invention. Referring to FIG. 8, a string (300) can be connected to a first power transmission unit (201) via an eccentric rotation shaft (203). In this case, the position at which the string (300) is connected to the first power transmission unit (201) varies depending on the position of the eccentric rotation shaft (203), and accordingly, the radius of the overlapping twist varies.

[0077] FIG. 9 is a conceptual diagram for explaining the change in the radius of rotation of the overlapping twist according to the position of the eccentric rotation axis (203). The radius of each twist is constant at r0, but when the eccentric rotation axis (203) is located at the outermost side as in (a), the maximum overlapping twist radius (r1) can be implemented, when the eccentric rotation axis (203) is located at the innermost side as in (b), the minimum overlapping twist radius (r2) can be implemented, and when the eccentric rotation axis (203) is located at an arbitrary position as in (c), the corresponding overlapping twist radius (r3) can be implemented.

[0078] FIG. 10 is a conceptual diagram for explaining a string twisting continuously variable transmission according to another modified example of the present invention, in which a plurality of strings are connected to a first power transmission unit that implements a first twisting operation, thereby enabling a multi-stage twisting operation to be implemented.

[0079] Additionally, the thickness of the string connected to the first power transmission unit can be adjusted differently, or the first power transmission unit can be individually controlled to implement a pivot motion in the linear motion unit.

[0080] Based on the above-described experiment, the string twisted continuously variable transmission control method according to the present invention may include a contraction step of twisting and contracting a plurality of strings through a power transmission unit to transmit power to a driving unit.

[0081] At this time, the contraction step may include a first twisting operation that implements individual twisting by adjusting the individual rotation angles of the strings, and a second twisting operation that implements overlapping twisting by adjusting the rotation angles between a plurality of strings. The first twisting operation and the second twisting operation may be implemented through the rotational speed ratio of the sun gear and the ring gear, thereby adjusting the rotational speed of the planetary gear to which the strings are directly connected, and the rotational speed ratio centered on the rotational axis of the sun gear. For example, the first twisting operation may be implemented by rotating the sun gear and the ring gear in opposite directions and fixing the rotational speed ratio to a specific value to stop the revolution of the planetary gear about the rotational axis of the sun gear but only maintain the rotation, and the second twisting operation may be implemented by fixing the rotational speed ratio of the sun gear and the ring gear to another specific value to only maintain the revolution. Here, it goes without saying that the control method according to the present invention can implement the first twisting operation and the second twisting operation in a complex manner by controlling the rotational speed of the sun gear and the ring gear.

[0082] After the above contraction step, a relaxation step may be included for relaxing the plurality of strings by twisting them in the opposite direction through the power transmission unit. The relaxation step may include a first relaxation operation for releasing individual twists by adjusting individual rotation angles of the strings, and a second relaxation operation for releasing overlapping twists by adjusting rotation angles between the plurality of strings. Similar to the above contraction step, the relaxation step may implement the first relaxation operation and the second relaxation operation by adjusting the rotational speed ratio of the sun gear and the ring gear, thereby adjusting the rotational speed of the planetary gear and the revolution speed centered on the rotational axis of the sun gear. For example, the first releasing operation can be implemented by rotating the sun gear and the ring gear in opposite directions and fixing the rotational speed ratio to a specific value to stop the revolution of the planetary gear about the rotational axis of the sun gear but maintain only the rotation, and the second releasing operation can be implemented by fixing the rotational speed ratio of the sun gear and the ring gear to another specific value to maintain only the revolution. Here, the control method according to the present invention can implement the first releasing operation and the second releasing operation in a complex manner by adjusting the rotational speed of the sun gear and the ring gear, but the control method according to the present invention can consider the efficiency of the releasing step as described in FIG. 7 described above, and the releasing step can include a process of performing the first releasing operation after the overlapping twist is completely released through the second releasing operation.

[0083] [Explanation of symbols]

[0084] 100: Linear motion unit 110: Linear rail

[0085] 200: Power transmission

[0086] 201: First power transmission unit 202: Second power transmission unit

[0087] 203: Eccentric rotation axis

[0088] 210: Ring gear 220: Sun gear

[0089] 230: Planetary Gear 240: Carrier

[0090] 250: 1st power unit 260: 2nd power unit

[0091] 300: String

[0092] 301: First string 302: Second string

[0093] The present invention relates to a twisted-string continuously variable transmission capable of compensating for a nonlinear gear ratio and increasing an operating range through continuous conversion of the gear ratio, and has industrial applicability.

Claims

1. Linear motion section where linear motion is output; A power transmission unit that transmits power; and It includes at least two strings connecting the linear motion unit and the power transmission unit, The gear ratio is set through the ratio of the individual twist of each string and the overlapping twist between the plurality of strings. Controlling linear motion within a range where the above individual twists and overlapping twists do not become excessive twists, Line twist continuously variable transmission.

2. In paragraph 1, A string twisted continuously variable transmission characterized in that power is transmitted to the linear motion unit by contraction of the strings due to individual twisting of each string and overlapping twisting between the plurality of strings.

3. In paragraph 2, The above power transmission unit sets individual twists by adjusting the individual rotation angles of the strings, thereby contracting the entire string, and A string twisting continuously variable transmission characterized in that it implements a second twisting operation that contracts the entire string by setting an overlapping twist by adjusting the rotation angle between the strings.

4. In paragraph 3, A string twisting continuously variable transmission characterized in that the power transmission unit comprises a first power transmission unit that implements a first twisting operation and a second power transmission unit that implements a second twisting operation.

5. In paragraph 3, The above power transmission unit includes a ring gear, a sun gear, and a plurality of planetary gears corresponding to each of the above strings, A string twisting continuously variable transmission characterized in that the first twisting operation and the second twisting operation are implemented by controlling the respective rotational speeds of the ring gear and the sun gear.

6. In paragraph 5, One end of each of the above strings is connected to the center of each of the above planetary gears, The other end of each of the above strings is connected to the linear motion unit, The above-mentioned sun gear externally meshes with each of the above-mentioned planetary gears, The above ring gear is internally engaged with each of the above planetary gears, A twisted-string continuously variable transmission characterized in that the above-mentioned sun gear and the above-mentioned ring gear form a rotation axis on the same axis.

7. In paragraph 4 or 5, A string twisted continuously variable transmission, characterized in that the linear motion unit further includes a linear rail in the same direction as the rotation axis of the string.

8. In paragraph 4, A string twisting continuously variable transmission characterized in that it further includes a first power transmission unit that implements a first twisting operation and an eccentric rotation shaft configured to be eccentrically connected to the string.

9. In paragraph 4, A string twist continuously variable transmission characterized in that a plurality of strings are connected to a first power transmission unit that implements a first twisting operation.

10. In paragraph 10, A string-twisted continuously variable transmission characterized by implementing a pivotal motion in a linear motion section by differently adjusting the thickness of a string connected to a first power transmission section.

Images