Patent Application
20220355493
The invention relates to a robot joint comprising at least two elements rotatable about a common axis.
In horticulture, the scarcity of personnel for harvesting, sorting and packaging of fruit and vegetables is becoming an increasingly pressing problem. This scarcity is such that growers fear the continuity of their business, which also jeopardizes food supply. Automating processing in horticulture is technically feasible, but it has turned out that growers are reluctant to make the switch. This is on the one hand because the investment in robots is still very expensive.
Typically, ball bearings are used in robotic arms, which have friction, play and a shifting behavior over the lifetime. Typical robots in the market do have a good reproducibility in terms of positioning (often even a few hundredths of an inch), but in terms of absolute accuracy they are not good.
That is why a robot with a low cost is desired. This is achieved by providing the robot with an arm that cannot make more than the necessary movement, so that the joint only has to allow rotation through a limited angle. A low cost price is hereby possible by applying a robot joint with a working principle based on the properties of leaf springs. A disadvantage of such a robot joint is that the position of the elements relative to each other during rotation is not very accurate because the point of rotation moves during rotation.
An object of the invention is to provide a robot joint in which the elements can be rotated with high accuracy through a limited angle with respect to each other. To this end, the robot joint according to the invention is characterized in that the rotatable elements are diametrical opposite each other with respect to the joint axis, which joint axis is located in or near the center between the two elements, and which elements are connected to each other via at least two radially extending leaf springs crossing each other in or near the center, such that the elements are rotatable through a limited angle with respect to each other and upon rotation of the elements relative to each other about the common axis the elements bend the leaf springs, which robot joint further comprises measuring means which measure the angle through which the two elements rotate relative to each other, which measuring means are connected to the rotatable elements and are integrated at least partly in the rotatable elements. By measuring the rotation of the elements of the robot joint relative to each other and linking it back to the robot arm drive, the consequences of the inaccuracy in the joint can be compensated. By partially integrating the measuring means into the elements and connecting them to the elements, the cost price of the robot joint can be kept low. The inaccuracy as a result of the displacement of the point of rotation during the rotation can be corrected here because this displacement as a function of the angular rotation is always the same. The absolute position accuracy can be further improved by using a calibration routine. Any deviations in positioning that result from cost savings in the mechanical design of the robot joint can be automatically compensated for by controlling the drive, making use of sensors in the robot joint. The robot joint according to the invention makes it possible that the use of expensive mechanical joints can be avoided by using low-cost controlling and correcting electronics and controls with smart software algorithms. The leaf springs thus each extend in a flat plane, these planes intersect each other in a cutting line and each leaf spring extends on either side of the cutting line.
It is noted that from US2012/0210774A a viscosity meter is known which is provided with a joint with an operating principle based on the properties of leaf springs. Measuring means are also present in this case for measuring the angular rotation of the two elements rotatable relative to each other. However, there are no provisions to use the measuring means for controlling the rotation of the two elements relative to each other. Furthermore, each leaf spring extends in radial direction between the two tubes and is thereby located on one side of the cutting line. Therefore the leaf springs do not cross each other.
An embodiment of the robot joint according to the invention is characterized in that the elements are formed by two concentric cylinders, the inner cylinder of which is provided with openings through which the leaf springs protrude.
A further embodiment of the robot joint according to the invention is characterized in that the robot joint further comprises a further cylinder that is concentric to said two cylinders and in the axial direction is present adjacent one of these cylinders, wherein the other cylinder also extends in or over this further cylinder and is connected to this further cylinder via at least two further crossing radial leaf springs. This makes a larger angular rotation between the two outer cylinders possible. In the version with electric motors, the stator and the rotor must then be connected to the two outer cylinders.
A still further embodiment of the robot joint according to the invention is characterized in that the leaf springs cross one another without being stuck to each other, wherein in and near the center, the leaf springs are provided with holes and the parts between the holes of one of the leaf springs protrude through the holes in the other leaf spring and vice versa. The available axial length of the joint can be optimally utilized and a joint is obtained which is compact in the axial direction.
A further embodiment of the robot joint according to the invention is characterized in that the measuring means comprise markings and detection means for counting the number of markings that passes the detection means during rotation of the two cylinders relative to each other, which markings are uniformly distributed over at least a part of the circumference on or in the cylinder wall of one of the cylinders, and which detection means are connected to the other cylinder. As a result, the angular rotation of the cylinders relative to each other can be measured with simple and therefore inexpensive means. The markings are preferably formed by holes in the cylinder wall.
A still further embodiment of the robot joint according to the invention is characterized in that it further comprises interaction means comprising two parts that can be rotated relative to each other, one of the parts being connected with one of the elements is and the other part is connected to the other element. These interaction means can, for instance, be formed by a brake disc/brake drum and a brake caliper or brake pads to brake the rotatable parts relative to each other or to block them against rotation relative to each other. The interaction means can for instance also be formed by a spring, one end of which is connected to one of the elements and the other end to the other element. This spring can, for example, compensate for the force exerted by one cylinder on the other cylinder as a result of gravity.
The interaction means can also be formed by an electric motor, one of the parts being formed by a stator and the other part by a rotor. By integrating the motor for rotating the joint parts relative to each other in the robot joint, a further cost reduction can be achieved when the joint is used in a robot arm. In this case, an air gap is preferably present between the two elements in order to compensate for the shift of the axis about which the two elements rotate relative to each other during rotation, and a contactless direct drive motor is used as the electric motor so that during the entire lifetime there will be a high positional accuracy because no wear occurs.
The one part and/or the other part of the interaction means and the cylinder connected thereto are preferably manufactured in one piece, for example by 3D printing, so that the production costs can be limited. Preferably, the two cylinders with the at least two leaf springs are also manufactured in one piece.
The invention also relates to a robot arm provided with two arm parts which are connected to each other via a robot joint according to the invention, wherein one of the arm parts is connected to one of the elements and the other arm part is connected to the other element and wherein one of the arm parts is further connected to manipulation means for manipulating objects. Manipulation means can be a gripper for gripping objects.
The invention will be explained in more detail below with reference to exemplary embodiments of the robot joint according to the invention shown in the drawings. Hereby:
The inner cylinder 7 is connected via radially extending leaf springs 11 and 13 to the two outer cylinders 3 and 5. These leaf springs with an end 11a, 13a are each attached to the inside 7a of the inner cylinder 7 directly opposite one of the openings 9 and are secured with the other end 11b, 13b to the inside 3a of one of the outer cylinders 3 and 5, whereby they protrude through one of the openings 9. Each outer cylinder 3, 5 is connected to the inner cylinder 7 via three leaf springs 11, 13. These leaf springs are formed by a wide middle leaf spring 13 and two narrower outer leaf springs 11 which extend perpendicular to the wide leaf spring 13 and are located on either side of this wide leaf spring.
The outer cylinders 3 and 5 can be rotated with respect to the inner cylinder 7 over an angle, equal to the angle over which the openings 9 extend. As a result, the two outer cylinders can thus rotate relative to each other at a maximum over an angle that is twice the angle over which the openings extend. The two outer cylinders 3, 5, the inner cylinder 7 and the leaf springs 11, 13 are integrally formed by 3D printing.
One of the outer cylinders 3 is at the end 3b turned away from the other outer cylinders 5 provided with markings 15 formed by holes. These holes can be detected by a sensor 17 connected to the other outer cylinder 5. The sensor 17 is connected to an electronic unit 19 which counts the number of holes that passes the sensor during rotation of the two outer cylinders relative to each other.
The two outer cylinders 35 facing each other of the two robot joints 21, which are connected to the stators 27 of the electric motors 25, are connected via arms 38 to a first mounting element 39 and the other two outer cylinders 33, which are connected with the rotors 29 of the electric motors 25, are connected via further arms 41 to a second mounting element 43. Each mounting element 39, 43 is provided with a mounting surface 39a, 43a to which a part of a robot arm can be attached.
For clarification,
The leaf springs 53 and 55 are attached with one end to the inside of a first cylinder 61 and are attached to a cylinder part 63A with the other end. This cylinder part 63A is attached to cylinder 63 which is provided on the outside with markings 65 that can be detected by a sensor in order to be able to measure the rotation.
Although the present invention is elucidated above on the basis of the given drawings, it should be noted that this invention is not limited whatsoever to the embodiments shown in the drawings. The invention also extends to all embodiments deviating from the embodiments shown in the drawings within the scope of the invention defined by the appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| NL2022473 | Jan 2019 | NL | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/NL2020/050048 | 1/29/2020 | WO |
