TRANSMISSION

Technical Field

The invention is related to a continuously variable transmission system.

The invention is particularly related to the usage of a power transmission method named as the continuously variable transmission system in the human-robot interfaces. The power transmission can be changed not in a stable ratio but within a theoretically predetermined limit in a non-staged manner together with said systems. It is used for arranging the bilateral physical interaction between the human and the robot. Continuously variable transmission systems are used in many different fields such as automotive, robotic, aviation and machine fields. The target field is the systems which includes physical human-robot interaction. In general, these types of robots are named as the collaborative robots.

State of the Art

In the design of this unique continuously variable transmission (CVT) system; criteria such as back driving, working field, impedance interval, independent control of the position and stiffness, and damping ability in sudden physical crashes are taken into consideration. Transmission is performed by means of a wheel in typical CVT systems. However, since the wheel cannot perform a holonomic motion, it is impossible to provide stage change by means of the wheel without rotating the conical variators. For this reason, instead of a wheel, a sphere is used in our invention of unique CVT design.

In the present state of the art, CVT mechanisms formed by using operating principles of the planet gear systems are encountered in the literature ¹ - ³ . These systems have the potential to change the output torque without applying any control algorithm, with the help of the mechanical design, in a non-staged manner. A constant input torque shall be given as an input to the system. In addition to these, when the output resistance is changed, the system has the ability to adapt itself to said resistance, mechanically. Although the mechanism has a simple structure in terms of kinematic view, the output torque and the output position cannot be controlled in an independent manner. Also, since the inertias of the gear systems are high, it is disadvantageous to be used in human-robot interactions taking into account the back driving criterion.

In spherical CVT systems, a point contact is established on the sphere at 4 different points. The output speed is adjusted by changing the rotational axis of the sphere by means of two input variators and two output variators ⁴ .

Another CVT system is a robot which is named as“cobot” in the literature and designed for haptic application ^{5 6} . In the literature, for this system, a patent is encountered ⁷ . In said system, the transmission is accomplished with the help of dry friction in between the CVT wheels and the contact cylinder. Each wheel, which is located around the cylinder, is coupled to the end point by means of a fastener. The contact angle with the cylinder is changed by means of directing the wheel with an engine and the linear output stiffness is adjusted. The disadvantages of this system is that the system has a complex mechanical structure and when the wheels are adjusted at zero degree (low stiffness values) condition, wheels lose the contact with the cylinder.

The operating principle of the general CVT systems is formed by means of locating two conical shaped variators parallel but in opposite directions. The input torque is given through the input variator and stage change is performed by means of a separate actuation system. The transmission between the variators is enabled by means of a belt, chain or dry friction ⁸ . Since contact points of the conical variators are changed during stage change, the outlet torque and speed are also changed. This type of systems is used in the transmission of the automobiles. However, their usage in human-robot interfaces is not common in the literature. The reason for this is that, these systems used in the automobiles are operated in a unidirectional manner ⁹ . Another reason is that, the mechanism required to be designed for enabling the stage change has a complex structure ⁴ . In addition to these, when we consider the joint designs, which are aimed to be used in the human-robot interfaces, the main criteria shall be back driving, controlling the position and stiffness in an independent manner, damping feature in case of sudden collisions and lightness etc. ¹⁰ . In said general CVT systems, the position and stiffness cannot be controlled in an independent manner.

The determined technical problems of the present state of the art are as follows; a. possible sudden robot link collisions may not be damped by the joint in a mechanical manner, b. transmission ratio may not be changed when the output position of the joint is kept constant, c. a unidirectional transmission is enabled. By means of a unidirectional transmission, the robot can drive the human back but the human cannot drive the robot back.

In the current designs, power transmission is provided by means of the planet gear systems and the variators. The gear systems exhibit poor performance when damping the sudden physical forces as a result of a collision. The second sphere is added to the system in a manner such that it contacts beneath the variators within our invention in order to provide a solution to the unidirectional transmission problem encountered in the literature.

Again, patent document No CA1043132 (A) included in the present state of the art is related to a continuously variable drive system which comprises a drive and a shaft which is driven in the control spheres that move together with the coaxial rotating friction surfaces which is in coaxial arrangement and in rotating surfaces form. A control element is combined with each control unit by means of the spherical bearings, all control elements abut on a common adjusting ring. Each control element is formed by means of a central, a circular abutment surface which coincides with the center of the sphere and each control element has a part which is joined with a recess in the adjusting ring, shifting the adjusting ring in an axial manner leads to continuous change in the transmission.

Again, Patent document No US201811981 1 (A1) is related to the devices and methods used in power transmission in motor vehicles. The torque is divided into two or more torque path and thus the power is transmitted in a smoother and effective manner. Here, it has a variators assembly which comprises a rotatable power source and a first traction ring assembly. Again it comprises a variable assembly which has a second traction ring in contact with a plurality of spheres. There is a variator of this assembly that includes an operable rotatable shaft. Here, each sphere of a plurality of spheres has an inclinable rotational axis. The variator assembly is coaxial with the rotational shaft and also comprises and a first axial thrust bearing coupled to a rotatable shaft and a first traction ring assembly and a second axial thrust bearing coupled to a rotatable shaft and a second traction ring assembly. Again, the patent document No US2018119810 (A1) is related to a non-staged variable transmission having a sphere type continuously variable transmission. A main shaft; a power transmission which comprises a variator that has a plurality of first sphere is disclosed. Each sphere is equipped with a rotatable rotation axis. Said each sphere is in contact with a first traction ring assembly and a second traction ring assembly and each sphere is connected operationally to the first carrier assembly. A first planet gear set having the first ring gear comprises a first planet bearer which supports a plurality of planet gear coupled to the first ring gear and a first sun gear set which is coupled to the first plurality of the first gear tooth; and a second planet gear set having a second ring gear, a second planet bearer which supports a plurality of planet gear coupled to the second ring gear and a second sun gear set coupled to the second plurality of the second planet gears.

Again in document No KR20170010608 (A), a continuously variable transmission device for the robot is disclosed. Said invention is related to a continuously variable transmission device for a robot and particularly is related to a continuously variable transmission device for a robot which allows the transmission process of a robot which has a simple and compact structure and is movable.

Aim of the Invention

One aim of the invention is to protect both the user and the actuator from excessive loads by means of creating a natural force limit in the joint when transmitting force via friction in order to eliminate the disadvantages included in the present state of the art.

Another aim of the invention is to change the output position and transmission ratio independent from each other by means of the designed carrier mechanism.

Another aim of the invention is to provide the stage change in a faster and easier manner by making holonomic movement by means of the spheres.

In order to fulfil the abovementioned aims, the invention is a continuously variable transmission collaborative robot joint which consists of the following; a carrying structure which can be moved in a forward and backward manner by means of activating the linear motion mechanism (e.g. ball-screw) on a linear slide that is located between fixed apparatus that bears the carrier mechanism along two conical variators for changing the transmission ratio, two spheres which compress onto two conical variators in the carrying structure housings from the top and lower portions, spherical bearings used for mounting the spheres on the carrying structure in a manner such that minimum friction force is created, compression springs which are coupled by means of a connecting piece that supports pins located in the sphere bearing that enables the spheres to create equal normal force on the conical variators with equal compression force, an adjusting screw which is used for changing the force created by means of the compression springs, conical variators on which friction surface is formed in order to perform the transmission, fixed apparatuses on which conics are supported between bearings in the rotation axes of the variators.

Description of Figures

Figure 1 is an assembly perspective view of the invention,

Figure 2 is a disassembly perspective view of the invention,

Figure 3 is a disassembled perspective view of the carrier mechanism of the invention, Figure 4 is a front view of the spring forces in the proposed solution, Figure 5 is a side view showing the normal forces between the sphere and the conical variators in the proposed solution,

Figure 6 is the drawing in which a clockwise transmission is performed,

Figure 7 is the drawing in which the counter-clockwise transmission is performed,

Description of Reference Numbers

Detailed Description of the Invention

The invention is the usage of a power transmission technique named as continuously variable transmission system in the human-robot interfaces. The invention is a collaborative robot joint with continuously variable transmission. In Figure 1 , an assembly perspective view of the invention is shown. Inlet/outlet conical variators (10) are located in an axial direction on the fixed apparatus where conical variators are supported between bearings (12). The lower sphere (1) and the upper sphere (2) mounted on the carrying mechanism (15) facilitate the forward-backward movement of the carrying mechanism (15) in a manner such that they contact to the both of the input/output conical variators (10). The forward-backward movement of the carrying mechanism (15) can be performed by means of any linear actuator.

In Figure 2 the assembly of the linear actuator system formed by means of the ball-screw (11) and the linear slides (9) is shown. A Fixed apparatus where conical variators are supported between bearings (12) and a fixed apparatus where the carrying structure is supported between bearings (13) are connected on the fixed plate (14). The linear slides (9) and the ball-screw (11) are connected between the fixed apparatuses where the carrying structure is supported between bearings (13). The carrying mechanism (15) is supported on the linear slide (9) between bearings, and connected to the linear slides (9) and the ball- screw (11) in order to make linear movement by means of the activation of the ball-screw (1 1).

According to the invention drawing in terms of the assembly given in Figure 1 , by changing the contact points of the spheres (1 , 2) on the input/output conical variators (10), the transmission ratio can also be changed. The transmission between the input/output conical variators (10) is performed by means of the rotation of the spheres (1 , 2) around the linear actuator axis. During the forward-backward movement of the spheres (1 , 2) by means of the linear actuator, the spheres roll in a perpendicular axis to the direction of progress. Therefore, the required rotational axis of the sphere for changing the transmission stage is perpendicular to the required rotational axis of the sphere for the transmission. As a result, without changing the angular locations of the input/output conical variators (10), the transmission ratio is provided to be changed. In the present state of the art, the wheel which is used in place of the sphere (1 , 2) cannot change the transmission ratio without changing the angular locations of the input/output conical variators (10). The main reason for this is that during the transmission stage change, the wheel does not rotate around the axis of the linear actuator and it is required to be shifted by means of friction. In order to minimize the frictional effects, during transmission stage change, the wheel is rotated around its own axis and in this case the angular locations of the conical variators are changed simultaneously during transmission stage change.

Using only the upper sphere (2) in the system is shown in Figures 6 and 7. As it is shown in Figure 6, since the friction forces (P1 , P2) are in the lower direction which is formed during the clockwise (SY) rotation of the input/output conical variators (10), the transmission process is guaranteed by means of increasing the normal forces (N1 , N2) on the friction surface formed between the conical variators (10) and the sphere (2). However, as it is shown in Figure 7, since the friction forces (P1 , P2) are in the upper direction which is formed during the counter-clockwise (SYT) rotation of the input/output conical variators (10), the transmission process cannot be guaranteed by means of decreasing the normal forces (N1 , N2) on the friction surface formed between the conical variators (10) and the sphere (2).

In order to solve this problem, the solution with two spheres (1 , 2) shown in Figure 5 forms the basis of this invention. In this case, when the input/output conical variators (10) rotate clockwise, on one hand the normal forces (N1 , N2) formed between the upper sphere (2) and the input/output conical variators (10) increase, on the other hand the normal forces (N3, N4) formed between the lower sphere (1) and the input/output conical variators (10) decrease. On the contrary; when the input/output conical variators (10) rotate counter clockwise, on one hand the normal forces (N1 , N2) formed between the upper sphere (2) and the input/output conical variators (10) decrease, on the other hand the normal forces (N3, N4) formed between the lower sphere (1) and the input/output conical variators (10) increase. Therefore, an equal transmission can be obtained in both directions. Another main aspect of the invention is to transmit the torques with upper values which are equal in both directions.

In order to limit transmitted torque, the normal forces on the friction surface formed between the input/output conical variators (10) and the spheres (1 , 2) are required to be adjustable. As it is given in Figure 4, the compression forces (F1 , F2) on the spheres and the normal forces formed on the friction surface can be adjustable. Therefore, the input/output torque which exceeds the threshold value is not transmitted to the other conical variator. This condition can be used for taking safety measure during a high level impact in the human- robot interfaces.

In Figure 3, the assembly of the carrying mechanism in which the input/output torque threshold can be adjusted in shown. After the sphere bearings (3) which will form the compression forces (F1 , F2) by means of a point contact on the spheres, (1 , 2) are fitted to the slots on the carrying structure (8), then the pins (4) are fitted to the inner rings (31) of the spherical bearings (3). The spherical bearings (3) contact to the spheres (1 , 2) over their outer rings (32). By means of this contact type, the spheres (1 , 2) can perform the rotation in two directions in order to provide transmission and to change the transmission ratio in a manner such that it is only subject to a minimum resistance. The supportive connecting pieces (5) are mounted on the pins (4) which can move within the slot in the forward- backward directions. The compression springs (6) are located on the supportive connecting pieces (5) in order to exert pressure on the pins. In order to adjust the compression forces applied by means of the compression springs (6), the required compression process is performed by means of adjusting screws (7). The assembly of the spheres (1 , 2) on the housings (81) on the carrying structure (8) is made subsequent to the assembly of the abovementioned spherical bearing (3). By means of the compression forces applied by the sphere bearing (3) assembly, the spheres (1 , 2) are caged in the housing (81). The third important aspect of the invention is that; the compression forces (F1 , F2) are adjusted by means of the adjusting screws and thus, the maximum torque transmission levels according to application requirements, which is equal in both directions, are determined.