DE102007026827A1 - Single-axis force-torque-sensor for robot-supported manipulation and assembling processes, has extension measuring structure for detecting deformation, realized as part of metal lamination of printed circuit board in deformable area - Google Patents

Abstract

The sensor has an electrical printed circuit board (3) exhibiting bending resistance (6) and a deformable area (2) deformed under force- and/or torque effect. An extension measuring structure (5) for detecting the deformation is realized as a part of a metal lamination of the circuit board in the deformable area. The extension measuring structure is realized in the deformable area so that a force, a transverse force or an effective torque are measured. A wiring is realized on the printed circuit board for a part of an electrical circuit. The circuit board is reinforced by aluminum layers.

Description

It becomes a device for measuring mechanical forces and moments suggested.

to Measurement of mechanical forces and moments are different Devices known. In connection with the here proposed is in particular the transformation of the acting forces and Moments in corresponding expansions of a special deformation body, in the following also called "carrier", and whose Detection via strain gauge relevant. These usually consist of a on a film carrier applied meandering wire, his electrical resistance changes during stretching. For measurement of forces or moments is usually a metallic one Carrier used, the force introduced into a measurable Deformation transforms and a defined relationship between having introduced force and resulting deformation. In suitable places be by means of an adhesive joint strain gauges such applied to them due to the deformation of the carrier either stretched or compressed. To temperature dependence and variations in the base resistance of the strain gauges reduce strain gauges are usually in a bridge arrangement operated. To improve the sensitivity of the pickup, In this case, the strain gauges are arranged such that their electrical resistance changes in the opposite direction due to the deformation. On the basis of this procedure are different transducers for Forces and moments are known, for example, in weighing, find application in general mechanical engineering as well as in robotics. In all known from the prior art transducers are the strain gauges as a separate component on the carrier applied.

DE 34 04 936 A1 proposes an electromechanical load cell for measuring a uniaxial mechanical force, in which the load-dependent deformation of a metal body is detected via an array of strain gauges. The connected in bridge arrangement strain gauges are realized on a common film which is applied to the carrier. A passive electrical arrangement of resistors for temperature compensation, which is realized on a further film is also part of the load cell.

An arrangement for combined force and torque measurement is for example off DE 100 13 059 C2 known. Here, a force-moment transducer is described, which consists of a metallic support structure, which is such that forces and moments of the respective major axes cause a characteristic deformation of the carrier. The deformation is detected by discrete strain gauges, which are applied to different areas in different levels of the carrier and which are each contacted via individual lines. The evaluation of the electrical resistance changes takes place away from the carrier.

DE 102 17 017 C1 proposes a combined force-moment transducer, which is designed so that the determination of all moments and forces by a strain measurement in only one plane is possible. Again, conventional strain gages are used for the determination of the carrier strain. However, they are connected directly to a foil conductor, which also contains the evaluation electronics.

The described embodiments of the prior art have in common that they have several discrete strain gauges insert in a separate process on the support structure must be applied and wired. The application The strain gauge is currently mostly manual, as well the wiring. This results in a high failure rate and leads due to positioning inaccuracies of the gauges to sensitivity scattering of the individual measuring axes, which must be corrected in complex calibration processes. This makes the production of today's force-moment sensors very expensive and thus the end product expensive. A machine assembly for improvement The economic efficiency is due to the difficult gluing process hardly possible at different points of the support structure.

task The invention is a transducer for single and multi-axis To suggest measurement of mechanical forces and moments in the due to its novel structure the subsequent Applying strain gauges deleted, this by is fully machinable and at the same time has lower scattering of the measuring axes. In addition, should It may be possible to use the transducer particularly economically to produce in a batch process.

These Objective is achieved by a device having the features of claim 1, hereinafter "transducer" called, reached. Advantageous developments and refinements the device are the subject of the respective dependent Claims.

In contrast to the prior art, where a deformation body is manufactured separately and then equipped with discrete strain gauges, the transducer according to the invention is characterized according to the preamble of claim 1, characterized in that as a deformation body from the Elektrotech nik known conventional circuit board is used on the same time the measuring structures for detecting the resulting due to external force or momentary strain and the necessary interconnection are made for example by photo-structuring. This eliminates the manual assembly with discrete strain gauges and their complex wiring. The required electronics for signal conditioning and evaluation can also be realized directly on the circuit board, resulting in a monolithic constructed, compact force-torque transducer with integrated signal conditioning. In this case, the transducer according to the invention can be designed so that it can measure both a single force and / or a moment as well as forces and moments in several axes. The manufacturing processes used for the production of printed circuit boards are known from the electronics manufacturing and are now very well controlled technically. Thus, the deformation of the body together with the necessary strain gauges, the necessary interconnection and the associated signal conditioning electronics can be made very economically in a batch process in one operation. Here, it is particularly advantageous that the materials used and manufacturing methods for the force-moment transducer are compatible with those of the production of conventional assembled assemblies. As a result, electronic components can be soldered directly to the previously structured deformation body without additional conditioning.

Possible Embodiments of a pickup according to the preamble of claim 1 are shown in the drawings and are in described in more detail below. Show it

1 : Single-Axial Force / Moment Transducer With Meander-shaped Strain Measurement Structure ( 5 ) and signal conditioning ( 4 ) on the same circuit board ( 3 )

2 : Layer structure of the uniaxial force-moment transducer 1 , on the outer layers is the structure for measuring the bending strain ( 5 . 8th ), on the inner layer are two structures for measuring the transverse strain ( 7 ) arranged side by side.

3 : Layer structure of a uniaxial force-moment transducer with additional layers ( 10 . 12 . 13 ) to improve the sensitivity. Shown here as a sectional drawing.

4 : Bridge interconnection of the layers after 3 , The resistance designations are based on the layer designation (eg measuring structure on the lowest layer ( 8th ) corresponds to R8).

5 : Stiffening of the bending area by applying an additional functional layer to the actual circuit board on both sides, shown here as a sectional drawing.

6 : Six-axis force-moment transducer as a combination of three single-axis transducers 1 ,

An embodiment of the transducer according to the invention for detecting mechanical forces and torques is in 1 shown. He is able to detect a normal force (F) and a transverse force (Q) or torsional component (M) in each spatial direction and consists of a conventional electrical circuit board ( 3 ), as used for the construction of electrical circuits. A printed circuit board (also referred to as "circuit board") referred to here generally comprises at least one insulating carrier layer (base material) on which at least one conductive and structured layer is applied and used to this end, an electrical function, for example the interconnection of electrical components In a multilayer board, a plurality of layers of the insulating substrate and patterned conductive layers are alternately stacked to obtain a plurality of wiring levels, and the base material is preferably an FR4 type epoxy glass fiber substrate because of its mechanical properties The base material acts as a bending or torsion beam whose deformation is in a defined relationship with the acting forces F, Q and the moments M. The beam is preferably designed so that the outer Bela distribute the resulting mechanical stresses as evenly as possible. This can be achieved, for example, by means of a suitable outer contour ( 2 ) of the beam or by a change in thickness over its length or by a Unterhöhlung in the region of the Dehnmeßstrukturen done. The circuit board is designed as a multilayer board, on the like in 2 illustrated in different superimposed planes at least one Dehnmeßstruktur for measuring the elongation in the longitudinal direction ( 5 . 8th ) as well as at least one strain gauge structure for measuring transverse or torsional strain ( 7 . 12 ) is realized. In order to obtain a maximum lift of the output signal in the case of a bridge connection of the strain gauges, two strain gauges for detecting the normal stresses of the base material are preferably applied to those of the neutral fiber ( 1 ) of the arrangement of farthest and opposite planes ( 5 . 8th ) realized. Preferably close to the neutral fiber at least two layers are preferably each with two juxtaposed Dehnmeßstrukturen ( 7a . 7b such as 12a . 12b ) for the detection of mechani realized transverse voltages. Due to their arrangement on or near the neutral fiber ( 1 ) reduces the sensitivity to longitudinal mechanical stresses. However, an arrangement outside the neutral fiber is also conceivable. The preferably used strain-measuring structures are, for example, meander-shaped conductive structures, as known from strain gauges. They are made directly from the copper cladding via photo-structuring, as is customary in printed circuit board production, and are therefore made of copper. However, other materials with a higher electrical resistivity and better thermal properties may be used, such as nickel-copper alloys (Konstantan Cu ₅₅ Ni ₄₅ , Manganin Cu ₈₆ Mn ₁₂ Ni ₂ or Isotan Cu ₅₅ Ni ₄₄ Mn ₁ ) or tungsten , For measuring the transverse stresses, the strain gauges ( 7a . 7b . 12a . 12b ) compared to those for longitudinal voltage measurement ( 5 . 8th ) at an angle of preferably rotated by ± 45 ° from each other. It is also sufficient to rotate only the conductors relevant to the measurement of the elongation so as to obtain a strain gauge structure shifted in a parallelogram manner. The strain gauges are operated in a bridge circuit, preferably a full-bridge circuit, in order to minimize the temperature dependence and interference caused by production-related tolerances of the base resistances of the strain gauges. Half and quarter bridge circuits are also conceivable for reducing the circuit complexity. Depending on the interconnection of the individual bridge resistors with one another, the arrangement for measuring the transverse force can be sensitive either to torsional moments or to purely transverse forces. With a half-bridge arrangement, sensitivity for both components is also possible. Further balancing and compensation resistors, as known from weighing technology, can likewise be realized directly on the printed circuit board.

In order to improve the sensitivity of the device as measured in resistance change by elongation, a plurality of strain gauges as shown in FIG 3 represented, for the same mechanical stress in layers stacked and electrically to a full bridge according to 4 be switched. It is on the upper layer ( 9 ) realized the Dehnmeßstruktur for measuring the bending load F. The same structure is also applied to the first inner layer ( 10 ) produced. The same applies to the lowest layer ( 13 ) as well as for the fourth inner layer ( 14 ). On the second ( 11 ) and third ( 12 ) Inner layer is realized according to the Dehnmeßstruktur for the torsional load M. In order to further increase the internal resistance of the full bridges and thus the achievable resolution of the force measurement, additional pairs of layers can be realized with preferably identical strain gauges. These are connected in series with the Dehnmeßstrukturen same load direction in series and then in turn combined in a Meßbrückenschaltung. As a result, the internal resistance of the measuring bridge increases proportionally with the number of additional layers.

Also, the electronic circuit required for evaluating the change in resistance of the strain-measuring structures, essentially a differential amplifier (preferably implemented as an integrated circuit) (US Pat. 4 ), can on the same circuit board ( 3 ), on which the strain gauges ( 5 ) are arranged can be realized. For this purpose, a mechanical substructure ( 6 ) stiffened the board part of the evaluation electronics and thus mechanically decoupled from the deforming part on which the Dehnmeßstrukturen are arranged. The stiffener preferably consists of an additional layer of the base material, which is applied during the board production. The mechanical decoupling between Dehnmeßteil and electronic part on the circuit board can also be done by notching the PCB at appropriate locations or by a targeted weakening of the PCB material, for example by a Niveaufräsung or by removing pockets.

To improve the drift and hysteresis behavior of a pickup according to the invention, the region in which the measuring structures are arranged and whose mechanical properties are thus essentially responsible for the drift and hysteresis of the pickup is significantly increased by an additional layer whose elasticity and flexural modulus than that of the base material of the circuit board is stiffened. For this purpose, an aluminum layer is preferably used, as used in the art for heat dissipation in power electronics. It is applied over the entire surface of the circuit board, so that it forms a stable and durable bond with the circuit board. This can be done, for example, via a prepreg layer ( 16 ), with which the layer is hot laminated to directly on the circuit board. The additional layer can be either one-sided or as in 5 shown, applied to both sides of the board carrier. Also, the board carrier can be built around this extra layer around. Depending on the desired measuring range, other materials are conceivable, for example, an additional FR4 layer, steel, titanium, etc. By this method, higher measuring ranges can be realized than would be possible with pure FR4 carriers.

For measuring forces and moments in a plurality of axes, the transducer according to the invention is expanded accordingly by measuring structures. Such multi-axis transducers are example wise in handling technology or for robot-assisted joining processes used to register the process forces occurring. With multiaxial transducers here are meant transducers that can detect mechanical forces and / or torques in or around different spatial axes. So can with the in 6 shown transducer mechanical forces in all three spatial directions and torques are measured around the associated three spatial axes. For this purpose, at least three of the force-moment transducers already described above for measuring at least one force and at least one transverse force 1 combined together. The individual transducers are arranged centrally and preferably at an equal angle to each other. The carrier for the individual sensors is a single contiguous printed circuit board ( 3 ). The signal processing electronics ( 4 ) is realized on the inner part of the circuit board. A stiffening ( 6 ) prevents deformation of this area and at the same time serves to mount the sensor on a supporting structure. The force application points are transmitted via a ring ( 17 ), which may also be part of the circuit board, mechanically interconnected. This is preferably carried out stiffened so that there is no unwanted deformation in this area. The stiffening can also be part of the housing. The forces to be measured as well as torques are introduced via this outer ring. Depending on the design and the outer ring can be fixed and the forces and moments are coupled via the inner part of the transducer structure. The determination of the acting forces and torques is done mathematically from the measured components.

In order to capture the acting moments and forces in several levels, as in 7 represented as a carrier a printed circuit board ( 3 ) with flexible areas ( 18 ) are used, in which the printed circuit board is bent, so that this on a metallic support structure ( 19 ) can be applied. The individual rigid areas here again correspond to a transducer 1 , Particularly suitable for this purpose are circuit boards which comprise an additional flexible core, preferably made of polyimide ( 20 ) in certain areas of the surrounding rigid base material ( 21 ), preferably FR4. Although such a pick-up requires an additional supporting structure that acts as a deformation body and holds the board in place, it can also be made in a batch process and easily assembled. The necessary interconnection of the strain gauge structures as well as the signal conditioning electronics for detecting the strain-based resistance change is also realized on the board.

Around To obtain an intelligent measuring module, the inventive Transducer in another version to an integrated digital evaluation of the measured values extended. It will the digitization of the measured values preferably directly on the circuit board performed on the also the measuring structures are formed. On another board, over an electrical contact, preferably via connectors, can be fixed directly above the first board a microcomputer, which detects the measured values and from them the force components of the forces acting on the transducer certainly. Depending on the degree of miniaturization, the microcomputer can also be arranged on the circuit board, on which also the measuring structures are located. For communication of the invention Transducers via various interfaces according to industry-relevant Standards.

current Force-moment transducer consist of a metallic support structure, the deformed under force or moment effect. This deformation is detected by applied strain gauges. These are applied manually and individually wired, thereby the production is very costly. An automated production current force-moment transducer is due to the complex Carrier structure not possible.

It is proposed a sensor for detecting forces and moments, which can be produced economically in a batch process due to its structure. In this case, the deformation body ( 1 ) from a conventional printed circuit board ( 3 ), which are in a rigid ( 6 ) and a deformable region ( 2 ) and on the Kupferkaschierung the strain gauges ( 5 ) are realized directly. The required wiring of the strain gauges and the necessary electronic signal conditioning electronics ( 4 ) are realized on the same circuit board.

Of the new transducer is preferably suitable for use in robot-assisted Handling and joining processes, where the forces acting and moments must be registered and limited.

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• - DE 3404936 A1 [0003]
• - DE 10013059 C2 [0004]
• - DE 10217017 C1 [0005]

Claims (12)

Sensor for measuring forces and moments, characterized in that it consists of a printed circuit board having at least one rigid and at least one under force or moment action deformable region, wherein in the deformable region at least one Dehnmeßstruktur for detecting the deformation as part of Metallkaschierung the circuit board is realized. Device according to claim 1, characterized in that that in the deformable region at least two strain gauges realized for detecting the deformation, so that at least an externally acting force and at least one lateral force or at least an acting torque can be measured. Device according to one of the preceding claims, characterized in that on the circuit board, the wiring for at least part of the evaluation necessary electrical wiring is realized. Device according to one of the preceding claims, characterized in that on the rigid part of Printed circuit board at least part of the required signal conditioning electronics is realized. Device according to one of the preceding claims, characterized in that a plurality of transducers for measuring one power and one moment on a single circuit board are arranged so that multiaxial forces and Moments can be measured. Device according to one of the preceding claims, characterized in that the sensors for each measurement a force and a moment circular and preferably are arranged at equal angles to each other and by a rigid structure connected on both sides of the deformable area are. Device according to one of the preceding claims, characterized in that the contiguous PCB contains at least one flexible area, in which it can easily be bent and thus also forces and moments in different levels can be detected. Device according to claim 7, characterized in that that for local invariant positioning of the individual rigid Subareas of the circuit board another support structure is used. Device according to one of the preceding claims, characterized in that a multilayer printed circuit board Use finds, in which on different layers structures for Strain measurement are realized and these interconnected so can be an improvement in the Sensitivity of the arrangement results. Device according to one of the preceding claims, characterized in that the strain gauges for measuring longitudinal and transverse stress on different Layers of the board are arranged one above the other. Device according to one of the preceding claims, characterized in that this completely in a conventional manufacturing process for printed circuit boards can be made. Device according to one of the preceding claims, characterized in that the circuit board at least in the field of strain gauge structures by one or more additional layers, preferably made of aluminum reinforced becomes.