Patent Application
20160025150
The present invention relates to a torque transmission device having variably adjustable stiffness, to an actuator having said torque transmission device and to a robot.
Robots are being used more and more in direct contact with humans whether in patient care or in industry. Common to these applications is that an increased demand is made on the safety of robots. Thus, a human being injured by a robot if he is accidentally struck by a moving robot part has to be ruled out. In the event of faults, above all in the area of wearable robotics, a human joint being acted upon with too much force and as a result being injured also has to be ruled out. A known approach to this problem is the use of actuators with variable stiffness.
A high degree of mechanical stiffness is desired for achieving high levels of positioning accuracy. However, if a robot part is to be moved rapidly, or if the movement of a human joint is to be matched, a flexible mechanism and consequently a low degree of stiffness is desirable for achieving a high level of safety. Two approaches are known for realizing actuators with variable stiffness (VSA in short for variable stiffness actuator).
On the one hand, actuators with a high degree of stiffness are supplemented by a force or torque sensor. By means of a suitable controller, this makes it possible to simulate a stiffness which is below the mechanical one. The force sensor, in this case, measures the force existing at the actuator or the existing torque. In dependence on the torque, the excursion is adjusted such that a mechanical spring is simulated.
The excursion is adjusted in proportion to the existing torque, the proportionality factor corresponding to the virtual stiffness. A disadvantage of the approach is the lack of intrinsic safety as in the event of a fault, for example failure of the force sensor or the control means, the intrinsic high degree of stiffness of the actuator comes into play.
The second approach is the structure of actuators, the stiffness of which is realized so as to be modifiable in a purely mechanical manner. In this case, lever system with a variable force application are used. An actuator is connected for this purpose, for example by means of an additional mechanical element which includes a spring as a central mechanism. In order to vary the stiffness of the spring, the lever arm of the force application is adjustable, for example, by means of an electric motor. A disadvantage of said approach is the relatively large amount of space required for the structure.
The object underlying the present invention is to eliminate said disadvantages and to provide an improved actuator with variable stiffness.
Said object is achieved with a torque transmission device according to claim 1, an actuator according to claim 10 and a robot according to claim 11. Advantageous further developments of the invention are described in the sub-claims and in the description.
The torque transmission device according to the invention is provided with an inner ring, an outer ring which is arranged so as to be rotatable relative to the inner ring from a neutral position in a positive direction of rotation or negative direction of rotation, at least one pair of receiving bellows, including a positive receiving bellows and a negative receiving bellows, at least one gas pressure spring and an adjusting unit which is connected to the at least one gas pressure spring. The receiving bellows are arranged between the outer ring and the inner ring in such a manner that the positive receiving bellows is compressible when the inner ring is rotated in the positive direction of rotation and the negative receiving bellows is compressible when the inner ring is rotated in the negative direction of rotation. The receiving bellows are additionally connected to the at least one gas pressure spring so as to conduct fluid. In a preferred manner, in this case, a hydraulic fluid is used as fluid.
In an advantageous manner, the torque transmission device according to the invention comprises very compact dimensions and, with the almost incompressible hydraulic fluid, is capable of providing very high degrees of stiffness. The hydraulic force transmission also comprises a high level of self-damping, the natural vibrations of the system are strongly over-damped and only appear in the event of high frequencies. Consequently the frequency response of the system is linear up to high frequencies, which means the torque transmission device according to the invention has good controllability.
In an advantageous development of the torque transmission device according to the invention, the at least one gas pressure spring comprises a hermetically sealed gas pressure chamber and a transmission bellows which projects into the gas pressure chamber and an adjusting bellows which projects into the gas pressure chamber. The receiving bellows, in this case, are connected to the transmission bellows so as to conduct fluid and the adjusting unit is connected to the adjusting bellows so as to conduct fluid.
An adjustable, compact and more durable gas pressure spring is realized in this manner.
In a further advantageous development of the torque transmission device according to the invention, the adjusting unit includes a reservoir and a pump. The pump, in this case, is in particular a piezo-pump. The piezo-pumps can be additionally provided with a non-return valve which is designed to be self-opening in the event of a fault (normally open).
With the reservoir and the pump, a hydraulic adjusting unit with simple and cost-efficient components is provided. In an advantageous manner, the piezo-pump requires a small installation space and operates in an effective manner. In the event of a fault, for example if the power supply or the control signal fails, the stiffness of the transmission torque device is automatically reduced to the minimum by way of the non-return valve, which provides the safe state of the system: the system is consequently intrinsically safe.
In a further advantageous development of the torque transmission device according to the invention, the torque transmission device comprises two gas pressure springs which are connected to the adjusting unit. In this case, the at least one positive receiving bellows is connected to one of the two gas pressure springs so as to conduct fluid and the at least one negative receiving bellows is connected to the other of the two gas pressure springs so as to conduct fluid.
Consequently, the receiving bellows have one gas pressure spring available in each case both for the compression movement and for the expansion movement. In an advantageous manner, both compression phases and tension phases of the receiving bellows are able to be influenced.
In a further advantageous development of the torque transmission device according to the invention, the adjusting unit includes a separate pump per gas pressure spring.
The gas pressure springs can consequently be adjusted independently of one another. In an advantageous manner, the stiffness of the torque transmission device is consequently designable and modifiable in a different manner in dependence on the direction. The compression phases are able to be designed differently to the tension phases. In a further advantageous development of the torque transmission device according to the invention, the torque transmission device includes two pairs of receiving bellows.
Consequently, the introduction of force can be distributed in a better manner. The individual receiving bellows are consequently exposed to smaller loads. In addition, the guiding of the inner ring is improved without additional supporting elements.
In a further advantageous development of the torque transmission device according to the invention, at least one of the bellows is a metal bellows.
Metal bellows are extremely sturdy, even at high temperatures and under the influence of aggressive environmental conditions. This lends durability and safety to the torque transmission device.
In a further advantageous development of the torque transmission device according to the invention, the torque transmission device comprises substantially the form of a cylinder with a circular surface area.
Consequently, the torque transmission device is provided with a shape which can easily be added to the shape of a usual servomotor. The servomotor and the torque transmission device together only take up a little more space than the servomotor on its own.
Thus, in a preferred manner, the torque transmission device according to the invention is integrated in all its developments into an actuator which comprises a servomotor along with the torque transmission device. The servomotor includes a rotor and a stator. According to the invention, the stator of the servomotor is non-rotatably connected to the outer ring or the inner ring of the torque transmission device.
Consequently, an actuator with variable stiffness is provided in an advantageous manner. The advantages of the torque transmission device according to the invention are seen with the actuator as a module. In a preferred manner, the actuator according to the invention is integrated in a robot. The actuator, in this case, is connected to the mechanical unit so as to transmit force or so as to transmit torque.
The mechanical unit of the robot can be operated with different levels of stiffness on account of the actuator according to the invention. Consequently, the robot provides a high level of safety precisely in direct contact with humans.
Exemplary embodiments of the invention are explained in more detail by way of drawings and the following description, in which:
A sketch of the robot 26 according to the invention is shown in
A sketch of the actuator 1 according to the invention is shown as an example in
The actuator 1 comprises a servomotor 2 and a torque transmission device 3. The servomotor 2 includes a rotor 21 and a stator 22. The rotor 21 is mounted on a rotational axis 23 so as to rotate in relation to the stator 22. The stator 22 can be arranged around the rotor 21, it is shown in this manner in
According to the invention, the torque transmission device 3 includes an inner ring 5 and an outer ring 4 which is arranged around the inner ring 5. The outer ring 4 and the inner ring 5 are arranged concentrically with respect to the rotational axis 23. The outer ring 4 is rotatable about a certain torsional angle on the rotational axis 23 in relation to the inner ring 5. In the example shown in
Different realization variants of the torque transmission device 3 are sketched as an example in
In
The outer ring 4 comprises at least two moldings 24. Each molding 24 projects into a recess 7 of the inner ring 5. At least one driver 6 is situated in each case at the moldings 24. At each recess 7, the inner ring 5 comprises a support 8 at a region that is positioned opposite the driver 6. In each case one of the receiving bellows 9, 10 is arranged between the support 8 of the inner ring 5 and the driver 6 of the outer ring 4. The receiving bellows 9, 10 are fastened in each case at least to the support 8. In terms of the present invention, a bellows can also be a hydraulic cylinder or the like, the bellows is in particular produced from metal.
The at least one pair of receiving bellows 9, 10 includes a positive receiving bellows 9 and a negative receiving bellows 10. In terms of the present invention, the positive receiving bellows 9 is arranged in such a manner that it is compressed when the inner ring 5 is modified 5 in the positive direction of rotation 17 from the neutral position 2. The negative receiving bellows 10 is arranged according to the invention in such a manner that it is compressed when the inner ring 5 is modified in the negative direction of rotation 18 from the neutral position.
The receiving bellows 9, 10 are provided according to the invention with a fluid, in particular with a hydraulic fluid, such as, for example, silicone oil or glycerin. The receiving bellows 9, 10 are connected to the at least one gas pressure spring 13 so as to conduct fluid by means of the fluid lines 16.
According to the invention, the at least one gas pressure spring 13 comprises a hermetically sealed gas pressure chamber 28 which is filled with a fluid. The fluid is in particular a gas and can be at an overpressure of between 2 bar and 10 bar. Two bellows 14, 15 which are positioned in particular opposite one another, are arranged projecting into the gas pressure chamber 28—a transmission bellows 14 and a receiving bellows 15. The transmission bellows 14 is connected to the adjusting unit so as to conduct fluid by means of fluid lines 16. The adjusting bellows 15 is connected to the adjusting unit so as to conduct fluid by means of fluid lines 16.
According to the invention, the adjusting unit comprises at least one pump 12, in particular a piezo-pump 12, and a reservoir 11 in which a fluid, in particular a hydraulic fluid, can be held.
When the inner ring 5 is rotated in the positive direction of rotation 17 in relation to the outer ring 4, the pressure in the positive receiving bellows 9 is increased and a hydraulic fluid that is situated in the positive receiving bellows 9 is conducted through the fluid line 16 into the transmission bellows 14 of the at least one gas pressure spring 13. The transmission bellows 14 attempts to expand. According to the invention, the torque necessary for rotation in the positive direction of rotation 17 is adjustable in a variable manner by the pressure in the gas pressure chamber 28.
When the inner ring 5 is rotated in the negative direction of rotation 18 in relation to the outer ring 4, the pressure in the negative receiving bellows 10 is increased and a hydraulic fluid located in the negative receiving bellows 10 is conducted through the fluid line 16 into the transmission bellows 14 of the at least one gas pressure spring 13. The transmission bellows 14 attempts to expand. According to the invention, the torque necessary for rotation in the negative direction of rotation 18 is adjustable in a variable manner by the pressure in the gas pressure chamber 28.
The pressure in the gas pressure chamber 28 of the gas pressure spring 13 acts on the transmission bellows 14 and the adjusting bellows 15. The adjusting bellow 15 is realized in such a manner that the gas volume in the gas pressure spring 13 is compressible. By means of the pump 12 of the adjusting unit, a fluid, in particular a hydraulic fluid, is pumpable out of the reservoir 11 into the adjusting bellows 15—or out of the adjusting bellows 15. In this way, the stiffness of the gas pressure spring 13 is able to be adjusted within a broad range.
If the adjusting bellows 15 is completely emptied, the gas in the gas pressure chamber 28 can take-in a high volume at a low pressure. The transmission bellows 14 can consequently expand without the pressure in the gas pressure chamber 28 increasing significantly, i.e. the gas pressure spring 13 has a small amount of stiffness in this position.
If the adjusting bellows 15, in contrast, is filled up to its end position, as is thus shown in
As the transmission bellows 14 transmits the pressure of the gas pressure chamber 28 of the gas pressure spring 13 to the receiving bellows 9, 10, and a torque is built up there, the variable stiffness of the gas pressure spring 13 therefore translates directly into a variable torsion spring characteristic. According to the invention, the volume of the adjusting bellows 15 is variable by means of the pump 12 and as a result the rotational stiffness of the torque transmission device 3 according to the invention is adjustable. This is effected within a few seconds or fractions of a second, depending on the design of the output of the pump 12.
The adjusting unit is controlled or regulated by a control unit which is not shown here in any detail and to which the adjusting unit is connected. In addition, sensors which detect states such as, for example, the pressure in at least one of the bellows, can be arranged in the torque transmission device 3.
The torque transmission device 3 can also comprise support elements. For example, rolling elements can be arranged between the outer ring 4 and the inner ring 5.
The realization variant of the torque transmission device 3 according to the invention sketched as an example in
The receiving bellows 9, 10 are fastened here in each case to the support 9 and rest loosely on the driver 6. The receiving bellows 9, 10 comprise in each case a stop 19 which prevents the receiving bellows 9, 10 expanding beyond the dimension available when the inner ring 5 is in the neutral position 25. Both receiving bellows 9, 10 comprise their maximum volume in the neutral position 25. When the inner ring 5 is rotated in relation to the outer ring 5 out of the neutral position, one of the receiving bellows 9, 10 is compressed, the other of the receiving bellows 10, 9 maintains its volume. During said compression, the above-described damping is performed by the gas pressure spring 13. The torque transmission device 3 has no stiffness when it is rotated in the opposite direction into the neutral position 25. Torque is able to work freely until the neutral position has been reached again.
Compared to the variant shown in
With two gas pressure springs 13, the number of gas pressure springs 13 corresponds to the possible directions of rotation 17, 18. The two gas pressure springs 13 are separately controllable. The adjusting unit includes two pumps 12 for this purpose. Consequently, the receiving bellows 9, 10 are able to be influenced in each case not only in a pressure phase but also in a tension phase. Whereas one of the gas pressure springs 13 accompanies the pressure phase of the one receiving bellows 9, 10, at the same time the other of the gas pressure springs 13 influences the tension phase of the other receiving bellows 10, 9.
The receiving bellows 9, 10 do not comprise a stop 19 in this case. The receiving bellows 9, 10 are fastened in each case both to the support 8 of the inner ring 5 and to the driver 6 of the outer ring 4. The positive receiving bellows 9 comprises its greatest volume with the inner ring 5 in the position in which the negative receiving bellows 10 comprises its smallest volume and vice versa. In particular, both pumps 12 can be operated in parallel in such a manner that the gas pressure springs 13 in each case comprise the same inner stiffness.
In addition to the realization variant shown in
Although the invention has been illustrated and described in detail by the preferred exemplary embodiment, the invention is not restricted by the disclosed examples and other variations can be derived herefrom by the person skilled in the art without departing from the scope of protection of the invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2013 204 588.3 | Mar 2013 | DE | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2014/050710 | 1/15/2014 | WO | 00 |
