CA2274049A1

CA2274049A1 - Position measuring device for detecting displacements with at least three degrees of freedom

Info

Publication number: CA2274049A1
Application number: CA002274049A
Authority: CA
Inventors: Martin Sundin
Original assignee: Individual
Current assignee: Sundin GmbH
Priority date: 1996-12-04
Filing date: 1997-12-02
Publication date: 1998-06-11
Also published as: JP2001505334A; US6593729B2; EP0941507A1; JP4587498B2; US20010045825A1; US6329812B1; WO1998025193A1; AU4962997A

Abstract

The invention comprises a fixed platform (1) and a displaceable platform (2) that are coupled by six tension springs (3) and an elastic spacing element (6), which forms with each platform, for instance, a ball-and-socket joint, so that the platforms can be displaced in a total of five to six degrees of freedom with respect to each other. Displacement is detected by measuring at the tension springs (3) or at the spacing element (6). This is preferably done by measuring the inductivity of the tension springs (3), thereby making it possible to easily determine the relative position of the platforms.

Description

''. I =ll ~p+N-IN THIS AMENpE~' ~E~f'TR~1NSL.ATlQ9~

LEAST THREE DEGREES OF FREEDOM
CROSS REFERENCE TO RELATED APPLICATIONS
This application claims the priority of Swiss patent application 2983/96, filed December 12, 1996, the dis-closure of which is incorporated herein by reference in its entirety.
TECHNICAL FIELD
The invention relates to a position-measuring de-vice according to the preamble of the independent claims.
Devices of this type are especially used as input or operating apparatus, e.g. for operating screen graphics (e. g. for CAD systems) and computer animations, for control-ling robots, for moving parts of tool and measurement ma-chines (spindle boxes and measuring heads), as sensors or for controlling remote controlled probes and surgical instru ments.
STATE OF THE ART
In conventional devices, where displacements with three or even five to six degrees of freedom are measured, complicated measuring electronics are required, which makes the devices more expensive and unwieldy, or simpler measuring electronics are used, which, however, lead to unsatisfactory ergonomic properties. Examples of such devices are given in US 4 811 608, EP 244 497, EP 240 023 and EP 235 779. In all these devices, optical, mechanical or electrical sensors are required, which must additionally be housed in the device and lead to a correspondingly complicated setup.
SLTNIMARY OF THE INVENTION
Hence, it is an object of the invention to pro-vide a device of the type mentioned above that avoids these disadvantages. This object is met by the device of claim 1.
Hence, parameters of the elastic coupler are measured directly, such as forces, electrical properties, etc. In this way, separate sensors can be dispensed with or be designed in very compact manner, since the coupling device itself forms at least a part of the sensors.
In a preferred embodiment several inductivities of the coupler, or of parts of the coupler are measured.
Thus, for instance, the inductivity of springs of the coupler depending on the dilatation is measured.
Further electric parameters that can be measured are the electric resistance or the capacity of parts of the coupler.
Since three or more parameters must be measured for detecting the position or orientation with three or more degrees of freedom, these parameters are preferably measured sequentially, such that the individual measurements cause no mutual interferences and the apparatus remains simple.
The coupling device preferably comprises several spring members, in particular springs, which movably hold the two reference members at a distance from each other with the desired number of degrees of freedom. In a simple and there-fore preferred embodiment, several extension springs and a spacer member are e.g. provided. The spacer member is con-nected in articulated manner to one or both reference mem-bers, e.g. via ball-and-socket joints. Depending on the num-ber of the desired degrees of freedom, the spacer member can be compressible along its length.
The device is preferably designed such that the possible mutual displacement of the reference members upon an actuation by hand is perceived to be comparatively large, i.e. that it is as least 1 centimeter or 20° in each degree of freedom. Such displacements are distinctly perceived by a human user and allow a secure operation of the device.
The device according to the invention is espe-cially suited as an input device for computers, a control de-vice or a measuring device.
BRIEF DESCRIPTION OF THE DRAWINGS
Further advantages and applications of the inven-tion result from the now following description making refer-ence to the annexed drawings, wherein:
Fig. 1 is a first embodiment of the invention, Fig. 2 is a detailed view of the spacer member of the embodiment of Fig. 1, Fig. 3 is a block diagram of a circuit for meas-uring the spring inductivity, Fig. 4 is a spring with metal core, Fig. 5 is a spring with metal shell, Fig. 6 is a spring with a capacitive measuring arrangement, Fig. 7 is a spring with force sensor, Fig. 8 is a second embodiment of the invention, Fig. 9 is a side view onto a capacitive measuring arrangement for the embodiment of Fig. 8, Fig. 10 is a top view onto the device of Fig. 9, Fig. 11 is a third embodiment with only five de-grees of freedom, Fig. 12 is a fourth embodiment of the invention, Fig. 13 is a fifth embodiment of the invention with extension springs, Fig. 14 is a sixth embodiment of the invention with pressure springs, Fig. 15 is a further embodiment of the invention with a total of nine springs, Fig. 16 is an alternative to the embodiment of Fig. 15 with covering bellow from above, wherein only the right half of the figure is shown, Fig. 17 is a vertical section along line XVII-XVII of Fig. 16, and Fig. 18 is the attachment of the springs of the embodiment of Fig. 15.
METHODS FOR CARRYING OUT THE INVENTION
A first embodiment of the device according to the invention is shown in Fig. 1. Here, only those parts are shown that are of significance for the suspension and the ac-tual measurement. Provided with a handle the device can e.g.
be used as computer mouse with up to six degrees of freedom, i.e. as a hand sized apparatus, the displacements of which are generated by one hand and are measured and transferred to a target system. Further applications are listed at the end of the description.
The device comprises to platforms 1, 2, which act as the reference members, the mutual position of which is de-termined. Platform 1 is in the following called the fixed platform, platform 2 the movable platform. However, platform 2 could also be fixed and platform 1 movable, or both plat-forms can be arranged in movable manner.
Six schematically shown extension springs 3 are arranged between the two platforms, preferably coil springs made of steel or copper alloys. The extension springs 3 are not parallel to each other, nor are they parallel to a single plane. The extend from three lower points 4 of fixed platform 1 to three upper points 5 of movable platform 2. The lower and upper points are preferably approximately on the corners of a equilateral triangle, wherein the triangle of the lower points 4 is rotated about 60° in respect to the one of the upper points 5. Two extension springs 3 extend from each lower point 4, one to each of the neighboring upper points 4.
It is also possible to arrange the extension springs in an-other manner between the platforms, wherein they are, in this embodiment, preferably not parallel and chosen such that the relative position of the two platforms can be calculated from their lengths.
A spacer member 6, as shown in Fig. 2, is located between platforms 1, 2 and in the center of the extension springs 3. It comprises a lower ball 7 and an upper ball 8, which lie in corresponding holes 9 and 10 of the platforms 1, 2 and form two ball-and-socket joints with the same. Lower ball 7 is rigidly connected to a rod 11, to which upper ball 8 is mounted in axially displaceable manner. A (schematically shown) pressure spring 12 designed as a coil spring extends between balls 7 and 8. In mounted state as shown in Fig. 1, pressure spring 12 is biased and urges upper ball 8 and therefore upper platform 2 upwards. Hence, pressure spring 12 acts against the force of the extension springs 3.
In the embodiment of Fig. 1, upper platform 2 can be moved in respect to lower platform 1 in all three transla-tional and all three rotative degrees of freedom because the spring elastic coupler consisting of spacer member 6 and the extension springs 3 allow displacements in all rotative and translational directions.
In an application as input device for computers, the lower, fixed platform 1 can rest on a table, while the user actuates a handle arranged on the upper, movable plat-form 2. The displacements (i.e. the rotations as well as the translations) of the movable platform 2 can be detected by differing methods as explained in the following.
In a preferred embodiment of the invention, the displacement or motion of the upper platform is calculated by measuring the inductivity of the tension springs 3. For this purpose, the relation is used that the inductivity LF of a coil shaped spring is approximately proportional to z~W/g, wherein z is the number of windings, W the winding surface and g the distance between windings. The inductivity LF is therefore approximately proportional to the reciprocal length 1F (cf. Fig. 1) of the spring body. Therefore, by measuring the inductivity of all tension springs 3, their lengths 1F
can be determined. From these six lengths 1F and from the stored configuration information of the device (i.e. the sizes of the two triangles formed by the lower points 4 and the upper points 5 or the relative positions of the spring suspension points on the corresponding platforms) the rela-tive position of the two platforms 1, 2 can then be calcu-lated.
Fig. 3 shows a circuit for determining the induc-tivity of the tension springs 3. Here, each tension spring 3 forms the inductivity LF of a LC-oscillator 20. For this pur-pose, the ends of the springs are connected with feed wires, which are not shown in Fig. 1.
The frequency of each LC-oscillator 20 is given in known manner by the inductivity LF and its parallel capac-ity. From the frequency and the given value of the capacity, the value of the inductivity LF can therefore be calculated.
Each oscillator 20 possesses a control input, by means of which it can be switched on and off. In switched off state, the oscillator is not oscillating and its output is on high impedance. When the oscillator is switched on, it is os-cillating and generates an output signal. The outputs of the oscillators 20 are connected to each other and are led to a frequency counter 22.
In operation, control 21 operates the oscillators in sequential phases of measurement one after the other.
In each phase, only one oscillator 20 is in operation and its frequency is measured by frequency counter 22 and then fed to a computer (not shown). In this way, the inductivities L of 15 all tension springs 3 can be determined one after the other in six measuring phases. This sequential operation avoids that the measurements of the individual springs interfere with each other. Furthermore, only a single frequency counter 22 is required.
20 In the present embodiment, springs with a diame-ter of 5 mm, a number of coils of 70 and, depending on exten-sion, a distance between windings between approximately 0.5 and 1.0 mm are used, i.e. the inductivity LF is in the order of some ~H. The oscillators are dimensioned such that their frequencies are in the range of several megahertz. In this way, an accurate measurement or frequency count can e.g. be carried out within a millisecond.
In order to make the effect of the change of in ductivity of the springs stronger, each tension spring 3 can be provided with a core 30 or shell 31 of high magnetic per meability, as it is shown in Figs. 4 and 5. The core 30 or shell 31 can e.g. be attached at one end to a coil of the spring, such that it maintains its vertical position.
_ 7 _ Instead of the inductivity, other electric pa-rameter of the coupler 3, 6 can be measured as well. Since the specific electric resistance of spring steel increases upon deformation, the lengths 1F of the tension springs 3 (and/or the pressure spring 12) can e.g. also be determined from their electric resistance RF. Also this measurement is again carried out sequentially such that the complexity of the circuit is reduced.
Finally, electric capacities of the coupler 3, 6 could be measured as well. In this case, an arrangement ac-cording to Figs. 4 or 5 could be used, too, wherein the core 30 or the shell 31 are insulated against spring 3 and are used as one electrode of a capacitor. The second electrode of the capacitor is then formed by the spring. The capacity CF
of the capacitor formed in this way depends on how many of the coils are located in the area of core 30 or shell 31, re-spectively. The capacity measurement is again preferably car-ried out in sequential manner.
A further arrangement for a capacitive measure-ment is shown in Fig. 6. Here, the spring 3 is surrounded by two shells 31a, 31b, which are inserted telescopically into each other and electrically insulated from each other. One shell 31a is attached to the upper and the other shell 31b to the lower end of the spring. The capacity of the capacitor formed by the two shells 31a, b depends in linear manner from the length of the spring. The telescopic arrangement of Fig.
6 does not necessarily have to be arranged around a spring.
In the embodiment of Fig. 6, the spring 3 can also be dispensed with. In this case, the shells 31a, 31b are connected to the platforms 1, 2 and are in frictional contact with each other. A device with a coupler of this kind is not self-restoring, i.e. when platform 2 is moved and then re-leased, it will remain in its moved position.
_ g Non-electric properties of the coupler 3, 6 can be measured as well in order to determine its state of defor-mation. In particular, forces in the coupler can e.g. be measured for this purpose. The extension springs 3 can e.g.
be provided with a force sensor 32, such as it is shown in Fig. 6. This sensor generates a signal that is proportional to the pulling force FF of spring 3, from which the length of the spring can be determined as well. A further example for such a device with force measurement is described further be-low.
A mechanical Eigenfrequency or resonance fre-quency fF of one or more of the springs 3 can be determined as well. Since the Eigenfrequencies of the springs depend on their state of extension, the length of the spring can also be determined by means of such a measurement.
The above methods of measurement can, of course, also be combined. Furthermore, measurements can also be car-ried out in the area of the spacer member 6 and, in particu-lar, on its spring 12.
In the following, some further, preferred embodi ments of the device according to the invention are discussed.
Fig. 8 shows an embodiment of the device with only three tension springs 3 and a spacer member 6. The spacer member 6 is again located in the center of forces of the tension springs 3 and acts against their pulling force.
The tension springs 3 are attached at their lower ends on three tongues 35. Flexion and torsion sensors 36 are arranged on the tongues. The tongues 35 are of a spring steel that is comparatively hard compared to the springs and are only slightly deformed by the pulling forces of the springs.
The sensors 36 are designed such that they can not only de-termine the absolute value but also the direction of the in-dividual force FF. From this quantity, the length and direc-tion of the corresponding tension spring and therefrom the position of the movable platform 2 can be calculated. Pref-erably, three values are measured, from which the exact di-rection and magnitude of the pulling force FF can be calcu-fated completely. It is, however, also possible to carry out e.g. two measurements only, such that only two components or degrees of freedom of the pulling force are determined for each spring.
Figs. 9 and 10 show an alternative, capacitive measurement of the state of the springs of the embodiment of Fig. 8. Here, the tongues are arranged close above a printed circuit 50. Two or three measurement electrodes 51 are ar-ranged on printed circuit 50 below each tongue 35, the capac-ity of which in respect to the corresponding tongue 35 is de-termined. For achieving a measurement that is as linear as possible, an insulating ring 32 and an annular auxiliary electrode 53 are arranged around each measuring electrode 51, wherein the potential of the auxiliary electrode tracks the one of the measuring electrode such that the field of the measuring electrode becomes as homogeneous as possible. By measuring the capacity of two measuring electrodes 51 in re-spect to each tongue 35, the torsion and flexion of the same can be determined. By using a third measuring electrode in position 54, the derivative of the flexion and thereby the end point of the spring can also be determined. It is also possible to measure the torsion only on the fixed platform 1 and to measure the flexion on the movable platform 2. This is done preferably without part 55, which generates a torque, i.e. the spring 3 is attached directly to tongue 35, such that the individual components of spring 3 can be measured immediately.
Therefore, in the device of Fig. 8, several com-plementary values are measured, such that the total number of springs can also be smaller than six, while still all the translational and rotative coordinates of the movable plat-form can be determined.
In the embodiments of the invention described so far, movable platform 2 has a total of six degrees of free-dom. This number can, however, also be reduced.
Thus, Fig. 11 shows a device with only five de-grees of freedom. This is achieved by using a spacer member 6a with constant length. Just as the variable spacer member of Fig. 2, it comprises two balls 7, 8, both of which are, however, rigidly connected to rod 11. Hence, the allowed sur-face of displacement of movable platform 2 is restricted to the calotte of a sphere.
In Fig. 12, a further embodiment is shown, where upper platform 2 has only three degrees of freedom in respect to lower platform 1. This is achieved by rigidly connecting spacer member 6c with lower platform 1, while it forms a ball-and-socket joint 8 with upper platform 2 only.
As indicated in Fig. 12, this device can also be provided with a further level. For this purpose, platform 1 is e.g. placed on a socket 38, into which a conventional com-puter mouse displaceable in two dimensions is integrated.
Socket 38 rests on the surface of a table 39. Hence, the sur-face of the table 39 can be considered to be a third refer-ence member of the device, in respect to which the second reference member can be displaced in two dimensions. Coupling between the first and third reference member can also be im-plemented in an other manner, such that e.g. displacements in three translational degrees of freedom are possible as well.
Fig. 13 schematically shows an embodiment of the invention that uses tension springs only. Here, fixed plat-form 1 is e.g. designed as a cup with a bottom 41 and a cy-lindrical side wall 42, in which movable platform 2 is sus-pended on a total of nine tension springs 43. Two tension springs 43 extend from each corner of the movable platform to the upper rim of side wall 42 and one to floor 41. Also in this arrangement, the lengths springs can e.g. be measured with the means mentioned above. The application of nine springs has the advantage that even large displacements still can be calculated robustly by means of balancing calcula-tions.
Fig. 14 schematically shows an embodiment of the invention where only pressure springs 12a are used for con-necting fixed platform 1 with movable platform 2. Here, too, the deformation of the springs can be determined with the methods mentioned above, such that the displacements of the joy stick type handle can be determined in two or three de-grees of freedom. Preferably, for this purpose, the degrees of freedom of the handle are limited to two or three, respec-tively.
Fig. 15 shows a further embodiment of the inven-tion. In this embodiment, platform 2 is designed to be a hol-low half sphere and can be used as a handle. The coupler be-tween platform 1 and platform 2 comprises nine coil springs 60, 61. Six coil springs 60 arranged horizontally are used as measuring elements by determining their inductivity in the manner described above. Each of the horizontal springs 60 is connected at one end with a pin 62, which is rigidly anchored in platform 1. On its other end, it is connected via a flexi-ble connection member, i.e. a string or a wire 63, with plat-form 2. Each spring or wire 63 is deviated by a hook 64 mounted to platform 1, such that the springs 60 can extend horizontally while the strings or wires 63 are deviated from the plane of the springs 60. In this way, more room is avail-able for the springs 60. In addition to this, it is possible to house the springs in a housing (not shown), for suppress-ing interfering signals.
Between platform 1 and 2 the strings or wires 63 extend in the same geometry as the springs 3 of the embodi-ment of Fig. 1, such that the relative position of the two platforms 1, 2 can be calculated from the variations of lengths in simple and numerically stable manner.
It is also possible to anchor the springs 60 at one end in the points 64 and at their other end in platform 2 such that they take the place of the strings or wires 63. The strings or wires can also be dispensed with and hooks for de-viation are not necessary anymore.
The coupler of Fig. 15 further comprises three vertical springs 61. They are anchored at one end in platform 1. At their other end, they are each connected via a wire or string 66 to platform 2. The wires or strings 66 are deviated by three hooks 67. The hooks are located at the corners of a triangular plate 68, which is resting on a column 69. Column 69 is rigidly connected to platform 1. The purpose of the parts 61, 66 - 69 lies primarily in receiving the weight of platform 2 and in acting against the pulling force of the springs 60, i.e. they serve as a spacer member between both platforms.
Depending on the frictional losses in the hooks 64 and 67, the arrangement of Fig. 15 can be self-restoring or not. If no automatic restoration is desired, frictional losses are chosen to be large. If the frictional losses are small, platform 2 automatically goes back into its equilib-rium position after a displacement.
The deviation for the springs 61 or their wires or strings 66 can be dispensed with as well if the springs extend directly between the points 67 and the lower rim of platform 2.

Six vertical rods 71 are arranged along the pe-riphery of platform 1. At the upper end of each rod 71, a safety string 72 is attached, which is connected to platform 2. Rods 71 and strings 72 limit the range of displacements of platform 2 in respect to platform 1.
It is also possible to provide e.g. a cylindrical wall instead of the rods 71, extending along the periphery of platform 1. The strings 71 then extend from the upper rim of the cylindrical wall to the lower rim of platform 2. In place of individual strings, a bellow can be used as well, such as it is illustrated in Figs. 16 and 17. Here, 80 designates the cylindrical wall, to the upper rim of which the bellow 81 is attached. Bellow 81 seals the device on its upper side. It consists of an annular, foil-like, flexible material, which is dimensioned such that it hangs loosely if the platform 2 is in its center position. Furthermore, radial ribs 82 are formed in the bellow 81, which are more tension proof than the remaining bellow. They take the place of the strings 72 and limit the range of displacement of platform 2. The ribs 82 can be worked into the bellow or e.g. extend below the bellow.
Fig. 18 shows a vertical cross section through a spring 60, as it e.g. is used in the embodiment of Fig. 15.
For simplifying the set-up, platform 1 is designed as a printed circuit, onto which the measuring electronics are placed. The springs 60 are made of material that can be sol-dered, preferably beryllium bronze. At their outer ends they end in a straight wire section 85. This wire section 85 is led through a hole in one of the pins 62 and from there to a soldering point 86 on platform 1. Behind pin 62, wire section 85 is bent such that the axial pulling force of spring 60 is received by pin 62, i.e. pin 62 is used as an anchor. In this way, soldering point 86, which is connected to the evaluating circuitry, remains force free. Corresponding anchors of the springs can also be used for the other embodiments of the in-vention shown here, at one end or a both ends.
In general, all the principles of measurement discussed here can also be used for input devices or joy sticks with only two or three degrees of freedom, respec-tively.
As mentioned initially, the device according to the invention can be used as an input element for computers of the type of a computer mouse. Another application of the device relates to a measuring sensor, the displacements of which caused by contact with an object to be measured provide complete information about the position and orientation of the surface element that has been touched.
If the device is used as a computer mouse, two buttons in addition to the known ones are preferably pro-vided. These additional buttons can be used for switching the mouse on and off, such that the object moved by the mouse does not fall back into its central position after releasing the mouse.
The device can also be used as a measuring system for the continuous tracking of a robot, wherein one platform is mounted to the fixed and the other to the moved part (e. g.
a gripper hand) of the robot.
A further application relates to the control of vehicles, wherein the vehicle driver can control all possible displacements of the vehicle with the device according to the invention instead of using the conventional separate control devices (steering wheel, gas and brake pedals, stick etc.).
The device can also be used for controlling cranes and robots.

The displacement of the movable platform can also be caused by other parts of the human body but a hand, such as with one or both feet.
In the present embodiments spring members of metal, in particular a well conducting material that can be soldered are used, such as beryllium bronze. It is, however, possible to use elastic elements of another material, in par-ticular plastic.
While in the present application preferred em-bodiments of the invention are shown, it is to be distinctly understood that the invention is not limited thereto but can also be carried out in other manner within the scope of the following claims.

Claims

CLAIMS AS ANNEXED TO THE PRELIMINARY EXAMINATION REPORT

1. Position measurement device, preferably input device or operator control device, with a first and a second reference member (1, 2), which are connected to each other via at least one spring elastic coupler (3, 6; 60, 61) in such a way that the second reference member (2) is displaceable in respect to the first reference member (1) with at least three, preferably five or six, degrees of freedom, wherein measuring means (20 - 22) for determining the relative position of the reference members are provided, characterized in by means of the measuring means at least one length-dependent inductivity (L F) of a coil spring (3) in the coupling device (3, 6; 60, 61) can be determined.

2. Position measurement device of claim 1, characterized in that a metallic core (30) and/or shell (31) is arranged in the region of the coil spring (3).

3. Position measurement device of one of the preceding claims, characterized in that the inductivity (L F) of several current paths in the coupler (3, 6; 60, 61) can be determined, wherein each current path is part of an oscillator (20), and wherein means (22) for measuring the Eigenfrequency of each oscillator (20) are provided.

4. Position measurement device of one of the preceding claims characterized in that by means of the measuring means at least one electric capacity (C F) in the coupler (3, 6) can be measured.

5. Position measurement device of claim 4, characterized in that the coupler comprises at least one spring (3), which comprises a core (30) and/or shell (31) insulated from the same, wherein the capacity (C F) between the core (30) or shell (31), respectively, and the spring (32) can be determined, and/or that at least two electrodes (31a, 31b) telescopically inserted into each other are provided, the mutual position of which depends on the mutual position of the reference members (1, 2), and that with the measuring means the capacity between the two electrodes (31a, 31b) telescopically inserted into each other can be measured.

6. Position measurement device of one of the preceding claims characterized in that by means of the measuring means at least one electric resistance (R F) of a spring member (3, 12) of the coupler can be measured.

7. Position measurement device of one of the preceding claims characterized in that with the measuring means at least one mechanical resonance frequency (f F) of at least a part of the coupler (3, 6; 60, 61) can be measured.

8. Position measurement device of one of the preceding claims characterized in that the measurement means comprises a control (21) for sequentially measuring at least a part of the deformation dependent parameters one after the other.

9. Position measurement device of one of the preceding claims characterized in that the coupler (3, 6; 60, 61) comprises several spring members (3, 6), the extension or compression of which can be measured by means of the measuring means (20 - 22).

10. Position measurement device of claim 9 characterized in that at least one of the spring members (3, 6;
60, 61) is connected to a force sensor (32, 36), by means of which a force (F F) in the spring member can be measured.

11. Position measurement device of claim 10, characterized in that by means of the force sensor (36) the direction of the force (F F) in the spring member in at least two components or degrees of freedom can be measured, for which purpose preferably the at least one of the spring members is arranged on a spring plate (35), the flexion and/or torsion of which can be determined by means of the force sensor (36).

12. Position measurement device of claim 11, characterized in that it comprises at least one stationary measuring electrode (51), preferably arranged on a printed circuit board (50), a capacity of which in respect to the spring plate (35) can be determined.

13. Position measurement device of one of the preceding claims characterized in that it comprises six non-parallel, spring elastic connections (3; 63), which connect the first reference member to the second reference member and changes of the lengths of which can be measured.

14. Position measurement device of one of the preceding claims characterized by several spring members, which connect as extension springs (3) or elastic pulling members (60, 63) the first with the second reference member, and by a spacer member (6; 61, 66), which is arranged between the first and the second reference member and counteracts the force of the extension springs or pulling members, wherein the spacer member (6; 61, 66) is movably connected to the first and/or second reference member, and wherein the spacer member (6; 61, 66) is preferably arranged in the center of the tension springs (3) or the pulling members (60, 63).

15. Position measurement device of claim 14 characterized in that the spacer member (6) is connected by means of ball-and-socket joints with the first and/or second reference member.

16. Position measurement device of claim 15 characterized in that the spacer member (6; 61, 66) is elastically deformable, in particular elastically compressible in its longitudinal direction, such that the reference members (1, 2) can be mutually displaced in six degrees of freedom.

17. Position measurement device of one of the claims 14 - 16 characterized in that the spacer member comprises several extension springs (61), which are connected by means of string or wire like pulling strings (66), wherein the pulling string (66) are deviated at an anchor member (67, 68) connected to one of the reference members.

18. Position measurement device of claim 15 characterized in that the spacer member (6) has a substantially fixed length, such that the reference members (1, 2) can be mutually displaced in five degrees of freedom.

19. Position measurement device of claim 15 characterized in that the spacer member (6) is connected by means of a ball-and-socket joint with one reference member and rigidly with the other reference member, such that the reference members (1, 2) can be mutually displaced in three degrees of freedom.

20. Position measurement device of one of the preceding claims characterized in that it comprises a third reference member (39), wherein the second reference member (2) is displaceable in respect to the first (1) reference member in three degrees of freedom, preferably in three rotative degrees of freedom, and the second (2) is displaceable in respect to the third (39) reference member in at least two, preferably two translational degrees of freedom.

21. Position measurement device of one of the preceding claims characterized in that the second reference member (2) forms a handle, which is displaceable in translational degrees of freedom by at least approximately 1 cm and in rotative degrees of freedom by at least 20 degrees.

22. Position measurement device of one of the preceding claims characterized in that the second reference member (2) can be displaced in respect to the first reference members (1) in only two degrees of freedom.

23. Position measurement device of one of the preceding claims characterized in that the coupler comprises several pulling members (60, 63; 61, 66), wherein each pulling member (60, 63; 61, 66) comprises a spring (60, 61) and a wire- or string-like flexible connecting member (63, 66).

24. Position measurement device of claim 23, characterized by means (64, 67) for deviating the connecting members (63, 66).

25. Position measurement device of one of the claims 24 or 25, characterized in that several of the springs (60) extend substantially parallel to a plane and their connecting members (63) do not extend parallel to said plane.

26. Position measurement device of one of the preceding claims characterized in that the coupler (3, 6; 60, 61) comprises several extension springs (3, 60, 61), wherein each extension spring comprises and attachment means for attaching the corresponding spring to one of the two reference members, and that the attaching means comprises an anchor means (62) for receiving the force of the spring, wherein a wire is led from the spring to the anchor means (62) and is soldered to the corresponding reference member only after the anchor means.

27. Position measurement device, preferably input device or operator control device, in particular of one of the preceding claims, with a first and a second reference member (1, 2), which are connected to each other via at least one coupler (3, 6; 60, 61) in such a way that the second reference member (2) is displaceable in respect to the first reference member (1) with at least three, preferably five or six, degrees of freedom, wherein measuring means (20 - 22) for determining the relative position of the reference members are provided, characterized in that by means of the measuring means at least one length-dependent inductivity (L F) of a coil spring (3) in the coupling device (3, 6; 60, 61) can be determined.

28. Position measurement device of one of the preceding claims, characterized in that the coupler comprises several elastic pulling means (3, 6; 43; 60, 61), which act between the first and the second platform in such a way that the second platform can be extended from an equilibrium position in six degrees of freedom.

29. Position measurement device of claim 28, characterized in that at least a part of the pulling means are extension springs, which in particular extend between the first and the second platform.