NL1040702A

NL1040702A - Cryo hexapod positioning system.

Info

Publication number: NL1040702A
Application number: NL1040702A
Authority: NL
Inventors: Hubertus Leonardus Mathias Marie Janssen Ir; Bartholomeus Catharina Thomas Van Bree Ir; Maurice Anton Jacques Teuwen Ir
Original assignee: Janssen Prec Eng; Hubertus Leonardus Mathias Marie Janssen Ir
Priority date: 2014-03-04
Filing date: 2014-03-04
Publication date: 2015-10-14
Also published as: NL1040702B1

Description

Crvo hexapod positioning system

The invention concerns an actuated positioning device for positioning a sample in six degrees of freedom in a cryogenic environment.

Especially in the field of scientific research for instance with quantum physics, experiments are done under cryogenic environment close to the absolute zero point in temperature. In these experiments alignments and linear displacements need to be realized over millimetre strokes and with nanometre accuracy. Especially high position stability is required.

Typically combined positioning in three linear axes and three rotations is done by stacking multiple positioning devices each being able to manipulate at least one degree of freedom. Due to the fact that each positioning device has its own guiding with limited stiffness and certain mass, the total stack of devices that is used for the manipulation of the sample is relatively heavy and the connection to the base is relatively weak, resulting in poor modal behaviour and hysteresis in the motion. Moreover a feature of typical devices that are used in this kind of applications is that they are based on standard stages, with modified rollers and guidings for cryo compatibility. Disadvantages lie in the uncontrollable preload due to different thermal shrinkage of the various materials. The effect of this uncontrollable preload is the unpredictable translation force or, even worse, the unwanted play both leading to inaccurate positioning or even malfunction of the device.

The invention concerns the use of a hexapod configuration in which all manipulation actions are done in parallel in order to overcome these issues.

The positioning table is supported by 6 parallel acting, f r i c t i ο η 1 e s s , hysteresis free and play free guiding elements based on elastic deformation of flexures which are each individually driven by an actuator.

The actuators to be used in a hexapod configuration can be based on numerous different principles like: hydraulic actuators, spindle drives, piezoelectric actuators, used as direct drive but also in combination with stroke enhancement methods like flexures or stepping, and electromagnetic principles but for cryogenic high stiffness, high resolution and high stability demands a piezo driven spindle actuator is an obvious choice.

The exact nature of this invention, as well as its objectives becomes clear in the accompanying drawings wherein:

Fig.l Is a schematic drawing of the invention

Fig.2 Is a schematic drawing of a single guiding element with spring and sensor

In figure 1, the system is depicted. On top of the rigid base 1, six identical guiding elements 4 are placed. The topside of each element is coupled to the rigid table 6. Each element has the capacity to output a linear motion, exemplary shown by the arrow 5. Controlling the in total six output motions of the elements allows position control of table 6 with respect to base 1 in six degrees of freedom.

Each guiding element 4 is a monolithic machined block with integrated flexures to allow relative motion between the stationary frame 1 and the table 6. The combined frictionless, hysteresis free and play free flexures 10, 11, 12, 13 and 14 allow the exemplary motion 5 to be transferred with high stiffness to the rigid table 6 of the system while the other degrees of freedom remain unconstrained and have a relative low sti ffness .

Each of the controllable output motions 5 has its own actuator 2. Between the actuator 2 and the guiding element 4 a piezo stack is placed which can generate displacements with high force, high stiffness, high resolution and high frequency in the direction of motion of the guiding element. A pretension spring 9 ensures a proper contact between the actuator, the piezo stack and the guiding element to ensure a stiff and play free contact.

Each of the controllable output motions 5 has a position measurement system 7.

Each guiding element has a defined internal mechanical end-stop 8 which can be used to define a reference position of the table 6.

Claims

1. The invention relates to a device characterized in that: A hexapod-like system is realized to position a table in six degrees of freedom with high accuracy, stability and stiffness relative to a base over a range of a few millimeters, by applying six identical modules between the base and table, the module being capable of internally passing one relative movement relative to its stationary part and transmitting this movement to the table; each module is manufactured from a single part, the so-called monolithic part, which includes, among other things, all the required deformations based on elastic deformation in order to pass through one play relative relative to the base with high rigidity, without play and without friction. the connection between the base and each module is realized by a linear actuator capable of realizing positional changes in the drive direction of the module relative to the base; each linear actuator is based on a rotating screw spindle in a nut connected to the base so that it retains its position in self-braking condition with high positional stability, holding force and rigidity; each module is provided with a piezo stack that is capable of realizing a displacement in the drive direction relative to the position already forced by the actuator, so that displacements with very high resolution and high frequency can be realized within a limited extent; the position of each module, in the location, relative to the base, is measured with a position or displacement sensor; a bias over the contact between module and actuator is realized by applying springs which are not connected to the table but are integrated in the module or are connected to the base; the system is provided with one or more reference positions by delineating the module in one or more places by defined reproducing mechanical end positions.

A device according to any one of the preceding claims, characterized in that the modules are not provided with a piezo stack.

A device as claimed in any one of the preceding claims, characterized in that the linear actuator is not designed as a clamp 1 and a nut connected to the base, but can maintain its once-adjusted position in another manner unencumbered

A device as claimed in any one of the preceding claims, characterized in that the actuator does not retain its position in its condition, but that it is retained using a position or displacement sensor and a servo controller.

A device as claimed in any one of the preceding claims, characterized in that the patient is able to provide absolute patiently, so that no mechanical end positions are required for reference.

A device according to any one of the preceding claims, characterized in that no position or displacement sensor is applied in each individual module, but that the position information is obtained by one or more sensors which directly determine the position of the table, or a position connected thereto. object, measure.

A device according to any one of the preceding claims, characterized in that the bias over the contact between actuator and module is realized in a different way than by applying springs which are not connected to the table but are integrated in the module or are connected to the base.