DE202018000473U1 - Movement simulator for implants, prostheses and orthoses - Google Patents

Abstract

Movement simulator for implants, orthoses and prostheses, characterized in that the movements are performed by a parallel kinematic.

Description

An important aspect in the development of joint implants is their testing under the most realistic, physiological movements and forces. For this purpose, motion simulators are used as a test bench. Thereby, the mobility, the luxation behavior as well as the fatigue strength and the abrasion resistance of the components are to be determined. The implants may be artificial joints (endoprostheses) for knees, hips or shoulders, or even intervertebral disc prostheses. There may also be spacers (so-called spacers) for said joints, wherein in both cases, all other joints, such as. Foot, hand or elbow, of the human body should be included. But it can also be orthoses related to the joints mentioned or prostheses for foot, leg and arm.

Today, predominantly Cartesian-built, expensive kinematics of special machine construction are used for such testing purposes. These structures are serial kinematics. In addition, mostly differently configured test stands are used for knees, hips and intervertebral discs. Examples are the test rigs of the companies Advanced Mechanical Technology, Inc. (AMTI) - US, EndoLab GmbH - DE, MTS Systems Corporation - US. These or other available test rigs have a limited translational and / or rotational range of motion and low angular velocities or the loads to be applied are limited, in particular for worst-case scenarios.

Another possibility is relatively inexpensive industrial robots, e.g. Articulated robot. These have a large range of motion and can muster relatively high forces, but are too slow due to the serial arrangement of the axes and their consequent high mass. In addition, articulated robots are not stiff enough, so that the predetermined trajectories and motion cycles can not be met precisely.

It is the object of the present invention to provide a motion simulator for testing implants, prostheses and orthoses, which can perform spatial movements in all degrees of freedom quickly and accurately while applying very high forces.

This object is achieved by the motion simulator according to claim 1. According to the invention, the movements are performed by a parallel kinematic.

Compared to serial kinematics, machines with parallel kinematics, such as hexapods, tripods or delta robots, are better suited for the aforementioned test tasks. Parallel kinematics robots are based on a kinematics in which the moving platform (gripper platform) of three to six parallel arranged linear axes or articulated arms is guided, which are stored in a fixed base (base platform or base frame). Due to the parallel arrangement, the axes form a closed kinematic chain, which allows a higher repeatability and rigidity of the construction compared to vertical or horizontal articulated robots.

Depending on the number of axes, the term tripod robot for three-axis and hexapod robots is used for six-axis kinematics with parallel linear axes. The construction of hybrid robots is also possible, in which the moving platform is equipped with further serial hand axes. The hexapod's typical construction has six variable-length legs, allowing for flexibility in all six degrees of freedom (three translational and three rotational).

Advantages of the parallel kinematics are the low moving mass and consequent high dynamics. This results in high accelerations and final speeds and a correspondingly faster manipulation. In addition, the positioning accuracy is basically better, since position errors of the axes do not accumulate - as in the case of serial kinematics - but only partially contribute to the overall movement. In addition, parallel kinematics are characterized by a high degree of flexibility. The degree of freedom reaches almost spherical 5-sides, which is particularly advantageous for testing joint implants.

As previously stated, the arms of the robot kinematics are stored in a common base frame - the base platform - which is either suspended or placed on the ground. The three-dimensional movement of the moving platform in X / YZ Direction is via the coordinated control of all engines, whereby the platform can also tilt and rotate. For high forces, which are typically required in hexapod robots, the movement of the arms in the longitudinal direction z. B. generated by the use of spindle drives in the axes. It is also possible to use hydraulic or servohydraulic linear axes or directly driven linear motors, for example also tubular motors.

For delta robots with mostly 3 or even 4 arms, the drive motors for the upper arm are firmly mounted in the base frame and articulated to the non-powered forearms for quick handling, whereby the moving mass of the arms is reduced to a minimum.

Preferably, the motion simulator has a hexapod with linear axes. For this purpose, relatively inexpensive industrial components can be used. The smaller the moving platform is compared to the base platform of the hexapod, the higher are the possible tilting or rotation angles and angular speeds of the moving platform. It is advantageous if the approximate circle on which the suspension points of the joints of the moving platform are arranged in a ratio of 1: 3 to 1:10 is smaller than the approximate circle diameter of the suspension points of the joints of the base platform. In addition, the pivot point of the implant to be examined should be arranged as close as possible and centrally to the moving platform, because otherwise the translational movements become very large and the travel speeds increase. In such an embodiment, the hexapod covers an angular range ≥ ± 30 °, preferably ≥ ± 45 °, and more preferably ≥ ± 60 °. The angle range refers to rotations around the X or. Y - axis. In this case, angular velocities of more than 360 ° / s can be achieved. The rotation around the Z Axis reaches angular ranges ≥ ± 20 °, preferably ≥ ± 35 °, more preferably ≥ ± 70 °. In this way, all necessary angle ranges for flexion / extension, abduction / adduction and rotation for testing knee and hip implants as well as intervertebral disc prostheses can be covered. In addition, various anterior-posterior movements or translations of the rolling process can be programmed by the knee and readjusted precisely. In addition, the travels in X - and Y- Direction big enough to place multiple test stations or test chambers on a work platform. When using 25mm diameter threaded spindles for the linear axes, continuous forces of 5,000N can already be achieved, with short peak forces of about 15,000N. Of course, with such a structure and an adequate control almost any movement profiles such. B. walking, jogging or climbing stairs are simulated and programmed. Due to the very high accelerations and speeds that a hexapod allows, a dynamic control of the motion profiles can be achieved.

With the motion simulators according to the invention, the range of motion, the luxation behavior, the fatigue strength, the abrasion behavior and various worst-case scenarios of the components to be examined can be determined and tested. The motion simulators are also suitable for testing dental implants.

• 1 den Bewegungssimulator mit Hexapoden, und
• 2 eine Detailansicht aus 1 auf die bewegte Plattform und Arbeitsplattform.

Concrete embodiments and further preferred embodiments of the present invention are explained below with reference to the figures. Show it:

• 1 the motion simulator with hexapods, and
• 2 a detailed view 1 on the moving platform and working platform.

LIST OF REFERENCE NUMBERS

Arrow (1)

motion simulator

(2)

Base platform of hexapods (base frame)

(3, 3 ')

Joints of the hexapod

(4)

Linear axes (actuators, arms) of the hexapod

(5)

Moving platform of hexapods

(6)

test chamber

(7)

working platform

(8th)

Force and / or torque sensor

(9)

Frame of the motion simulator

(10)

Femoral Head

(11)

acetabulum

Arrow (100)

Hexapod

The 1 shows a motion simulator ( arrow 1 ) preferably with a hexapod ( arrow 100 ) as a test bench for testing implants for joints. The hexapod is executed with six linear axes 4 , The hexapod is in an overhead position on the frame 9 the testing machine 1 mounted: The linear axes 4 are each on one side hanging over joints 3 with the base platform 2 attached. The other side of the linear axes is again via joints 3 ' with the moving platform 5 connected. Below the moving platform 5 is the working platform 7 that's back to the frame 9 is mounted. On the work platform 7 is the sensor 8th , a single or multi-axis force and / or torque sensor attached. On the sensor 8th is the test chamber 6 ,

2 shows a section on the lower part of the hexapod 100 and the work platform 7 out 1 , In 2 the test chamber is off 1 opened, so that the configuration, here exemplified, of the hip joint is visible. At the moving platform 5 central is the one side of the hip joint, the femoral head 10 attached to the work platform 7 of the frame 9 is the other side of the hip joint, the acetabulum 11 , assembled. The test chamber is shaped so that the implant, in particular the articulating surfaces of the implant or the joint, can be immersed in a test liquid. In an alternative embodiment, the sensor can also be mounted between the moving platform and the upper side of the implant to be examined, in 2 this would be the femoral head.

The Hexapoden receiving frame can also be executed cuboid with four legs instead of three or in other, other forms. Also advantageous is a height-adjustable work platform, so that the working space on the traverse path of the hexapod in Z Direction can be extended and larger or different sized components can be integrated. Another variant of the structure of the motion simulator is that the base platform at an angle to the XY Level is mounted on the frame. As a result, for example, the tilt angle range of the moving platform can be adjusted from +/- 45 ° to + 25 ° / -70 ° relative to the work platform, which is advantageous for testing knee endoprostheses or knee spacers. In addition, the force in Z Direction can be initiated via an infeed axis, which is mounted on the work platform. This could further increase the dynamics for controlling force / movement progressions.

Claims (6)

Movement simulator for implants, orthoses and prostheses, characterized in that the movements are performed by a parallel kinematic. Motion simulator after Claim 1 , characterized in that the Parailelkinematik allows mobility in all six degrees of freedom, three translational and three rotational. Motion simulator after Claim 1 or 2 , characterized in that the parallel kinematic is a delta robot or preferably a hexapod and more preferably a hexapod with legs of variable length. Motion simulator after Claim 1 to 3 , characterized in that the motion simulator is designed for testing implants for joint areas. Motion simulator after Claim 1 to 4 , characterized in that the moving plate of the hexapod covering a Kippwinkelbereich around the X or Y-axis of greater than ± 30 °, preferably greater than ± 45 °, and more preferably greater than ± 60 °. Motion simulator after Claim 1 to 5 , characterized in that the moving plate of the hexapod can rotate about the Z-axis more than ± 20 °, preferably more than ± 35 °, and more preferably more than ± 70 °.

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