CN112611497B - Multi-dimensional force sensor structure of parallel rod system - Google Patents

Multi-dimensional force sensor structure of parallel rod system Download PDF

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CN112611497B
CN112611497B CN201910882361.6A CN201910882361A CN112611497B CN 112611497 B CN112611497 B CN 112611497B CN 201910882361 A CN201910882361 A CN 201910882361A CN 112611497 B CN112611497 B CN 112611497B
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coordinate system
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strain
strain beam
displacement
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CN112611497A (en
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马洪文
邢宇卓
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
    • G01L5/00—Apparatus for, or methods of, measuring force, work, mechanical power, or torque, specially adapted for specific purposes
    • G01L5/16—Apparatus for, or methods of, measuring force, work, mechanical power, or torque, specially adapted for specific purposes for measuring several components of force
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
    • G01L1/00—Measuring force or stress, in general
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
    • G01L1/00—Measuring force or stress, in general
    • G01L1/16—Measuring force or stress, in general using properties of piezoelectric devices
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
    • G01L1/00—Measuring force or stress, in general
    • G01L1/20—Measuring force or stress, in general by measuring variations in ohmic resistance of solid materials or of electrically-conductive fluids; by making use of electrokinetic cells, i.e. liquid-containing cells wherein an electrical potential is produced or varied upon the application of stress
    • G01L1/22—Measuring force or stress, in general by measuring variations in ohmic resistance of solid materials or of electrically-conductive fluids; by making use of electrokinetic cells, i.e. liquid-containing cells wherein an electrical potential is produced or varied upon the application of stress using resistance strain gauges
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
    • G01L5/00—Apparatus for, or methods of, measuring force, work, mechanical power, or torque, specially adapted for specific purposes
    • G01L5/16—Apparatus for, or methods of, measuring force, work, mechanical power, or torque, specially adapted for specific purposes for measuring several components of force
    • G01L5/165—Apparatus for, or methods of, measuring force, work, mechanical power, or torque, specially adapted for specific purposes for measuring several components of force using variations in capacitance
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
    • G01L5/00—Apparatus for, or methods of, measuring force, work, mechanical power, or torque, specially adapted for specific purposes
    • G01L5/16—Apparatus for, or methods of, measuring force, work, mechanical power, or torque, specially adapted for specific purposes for measuring several components of force
    • G01L5/167—Apparatus for, or methods of, measuring force, work, mechanical power, or torque, specially adapted for specific purposes for measuring several components of force using piezoelectric means

Abstract

A multi-dimensional force sensor structure of a parallel rod system relates to the field of sensor measurement. The invention aims to solve the problem that the accuracy of acquiring the multi-dimensional force is low due to the structure of the existing multi-dimensional force sensor. The invention relates to a multi-dimensional force sensor structure of a parallel rod system, which comprises a supporting platform and a load platform, wherein the load platform is connected with the supporting platform through the parallel rod system, and external force borne by the load platform is completely transmitted to the supporting platform through the parallel rod system; a micro-displacement sensor for measuring micro-displacement between the supporting platform and the load platform is arranged between the supporting platform and the load platform, and/or a strain sheet is arranged on a strain beam of the parallel rod system, and/or a piezoelectric crystal is adopted as the strain beam. The method is mainly used for the multi-dimensional force sensor of the parallel rod system.

Description

Multi-dimensional force sensor structure of parallel rod system
Technical Field
The invention belongs to the field of sensor measurement, and relates to a multi-dimensional force sensor structure.
Background
The multi-dimensional force sensor can detect the information of the force acting in space, wherein a typical six-dimensional force sensor can acquire 3 component forces and 3 moment forces formed by the acting force in a space coordinate system. In the fields of aerospace, robots and the like, the six-dimensional force sensor plays an important role, and the accuracy of the obtained six-dimensional force directly influences the working and control precision of the system.
The six-dimensional force sensor mainly comprises an integral elastic structural formula, a Stewart parallel structural formula, a piezoelectric crystal formula, a friction-free guide rail type (air flotation, magnetic suspension), a flexible structural formula and the like according to structural analysis of the six-dimensional force sensor, wherein the integral elastic structural formula is mainly adopted in the fields of commercial small six-dimensional force sensors and MEMS, the integral elastic structural formula is mainly adopted in the fields of large six-dimensional force sensors, the piezoelectric crystal formula is mainly used in the field of high-frequency dynamic measurement, the friction-free guide rail type is extremely small in application due to large structural size, the flexible structural formula is mainly used for grabbing of a mechanical finger end, and the precision is low.
The whole elastic structural formula generally adopts a flexible hinge or a flexible flat plate structure to replace a physical hinge, the precision is slightly high, but the structural rigidity is very small, and the precision is generally not more than 2% due to the coupling influence of a flexible body part. The Stewart parallel connection structure has higher rigidity, but has higher friction influence and lower precision due to the adoption of a physical hinge. The piezoelectric crystal type generally adopts a planar multi-group arrangement, each group comprises three wafers for respectively measuring three axial forces, the torque is calculated by a plurality of groups of force measurement, the force measurement frequency response is high, but the force measurement precision is low, and the static measurement is not suitable due to charge drift.
The existing six-dimensional force sensor has low precision and low rigidity, so that the large-scale commercial application is difficult to carry out in the commercial field except the conditions of low sensor precision required by grinding, polishing, clamping, automobile crash tests and the like, and the application occasions of grinding, polishing, clamping and the like can be easily replaced by pneumatic, elastic and other components, so that the application is not many. Taking a cooperative force-controlled robot requiring high-precision force measurement as an example, a real commercialized force-controlled robot is almost replaced by a single-axis force sensor, but because each axis of the robot needs to adopt a single-axis force sensor, the robot is extremely complex in structure and high in cost, and the inertial force is extremely difficult to resolve during high-speed motion. In the case of medical surgical robots requiring high-precision force measurement, almost all operating doctors consider that force feedback during surgery has a great influence on the operator, but all actual commercial surgical robots abandon the use of six-dimensional force sensors and only use image sensors because the precision of the existing six-dimensional force sensors is too low.
Due to the problems of the traditional multi-dimensional force sensor resolving method, the structural design of the traditional multi-dimensional force sensor is imperfect, large inter-dimensional coupling exists, the inter-dimensional coupling is generally larger than 2%, and basically the problem of low precision is mainly caused by the inter-dimensional coupling. The multi-dimensional force sensor structure provided by the invention can be basically regarded as an ideal linear elastomer, and the coupling between dimensions is less than 1 per thousand.
The current major application areas of multi-dimensional force sensors are: a force-controlled robot; the system comprises a minimally invasive surgery mechanical arm, medical auxiliary exercise equipment, a walking robot, a space mechanical arm and a space butt joint force measuring device; a wind tunnel balance, an automobile collision sensor, a hub force measuring device, a jet engine force measuring device, a propeller thrust force measuring device and a deep sea butt joint force measuring device; and (4) machining the force measuring device.
Disclosure of Invention
The invention aims to solve the problem that the accuracy of acquiring the multi-dimensional force is low due to the structure of the existing multi-dimensional force sensor. Further provides a multi-dimensional force sensor structure of parallel linkage.
The multi-dimensional force sensor structure of the parallel rod system comprises a supporting platform and a load platform, wherein the load platform is connected with the supporting platform through the parallel rod system, and external force borne by the load platform is completely transmitted to the supporting platform through the parallel rod system;
a micro-displacement sensor for measuring micro-displacement between the supporting platform and the load platform is arranged between the supporting platform and the load platform, and/or a strain sheet is arranged on a strain beam of the parallel rod system, and/or a piezoelectric crystal is adopted as the strain beam.
Further, the multi-dimensional force sensor structure includes an integral type, a welding and mechanical connection type, an embedded type, a press-fitting type and a suspension wire type.
Further, the multi-dimensional force sensor structure acquires a multi-dimensional force by:
the global coordinate system is a coordinate system attached to the supporting platform;
the local coordinate system of the strain beam is a coordinate system attached to the strain beam;
the local coordinate system of the micro displacement sensor is a coordinate system attached to the micro displacement sensor;
establishing a vector transformation relation matrix between a local coordinate system and a global coordinate system according to a space vector transformation rule, wherein the vector transformation relation matrix comprises a generalized force transformation relation, a generalized deformation displacement transformation relation and a displacement sensor transformation relation;
the generalized force comprises force and moment, and the generalized deformation displacement comprises linear displacement and corner displacement;
when the multi-dimensional force is six-dimensional force, the generalized force comprises 3 forces and 3 moments, and the generalized deformation displacement comprises 3 linear displacements and 3 corner displacements; when the multi-dimensional force is a planar three-dimensional force, the generalized force comprises 2 forces and 1 moment, and the generalized deformation displacement comprises 2 linear displacements and 1 corner displacement;
establishing a relation matrix of deformation and stress of the strain beam, the supporting platform and the loading platform under a local coordinate system according to theoretical mechanics, material mechanics and elastic mechanics, namely a local rigidity matrix and a local flexibility matrix;
according to a strain gauge adhered to the strain beam, or/and a piezoelectric crystal serving as the strain beam, or/and a displacement sensor arranged between the load platform and the support platform, obtaining local deformation displacement of a coincident point of the load platform and a corresponding local coordinate system origin along/around a measurement axis under a local coordinate system, and obtaining observability;
calculating the deformation displacement of the load platform under the global coordinate system according to the local deformation displacement of the coincident point of the load platform and the origin of the corresponding local coordinate system along/around the measuring axis in the local coordinate system, wherein the deformation displacement comprises three linear displacements and three corner displacements;
calculating all local deformation displacements of the corresponding local coordinate origin of each strain beam in the local coordinate system according to the deformation displacement of the load platform in the global coordinate system, wherein the local deformation displacements comprise three linear displacements and three corner displacements;
calculating local generalized force of each strain beam under a local coordinate system according to local deformation displacement of each strain beam under the local coordinate system, wherein the local generalized force comprises three forces and three torques;
and translating the local generalized force of all the strain beams in the local coordinate system to the origin of the global coordinate system according to the vector transformation relation between the local coordinate system and the global coordinate system, and summing to obtain the multi-dimensional force of the multi-dimensional force sensor.
The multi-dimensional force sensor structure obtains the multi-dimensional force through the following steps:
establishing a global coordinate system oxyz attached to a supporting platform;
the load platform generates displacement under the action of external force under the action of the global coordinate system oxyz
Figure GDA0002247839590000031
Wherein the content of the first and second substances,
Figure GDA0002247839590000032
as a local coordinate system oixiyiziLinear displacement of the lower part;
Figure GDA0002247839590000033
as a local coordinate system oixiyiziDisplacement of a lower corner;
respectively establishing local coordinate systems o attached to the strain beamsixiyizi(ii) a i represents the serial number of the strain beam;
the center of the contact surface of the strain beam and the supporting platform is taken as the origin of a local coordinate system
Figure GDA0002247839590000034
Respectively establishing local coordinate systems of the supporting platforms
Figure GDA0002247839590000035
The strain beam in the local coordinate system generates deformation displacement under the action of force,
Figure GDA0002247839590000036
wherein
Figure GDA0002247839590000037
As a local coordinate system oixiyiziLinear displacement of the lower part;
Figure GDA0002247839590000038
as a local coordinate system oixiyiziDisplacement of a lower corner;
according to a strain gauge adhered to the strain beam, or/and a piezoelectric crystal serving as the strain beam, or/and a displacement sensor arranged between the load platform and the support platform, obtaining local deformation displacement of a coincident point of the load platform and a corresponding local coordinate system origin along a measurement axis under a local coordinate system, and obtaining observable measurement; according to the space vector transformation, the local displacement, namely the observable quantity, of the load platform under the partial local coordinate system can be utilized to calculate the displacement of the load platform under the global coordinate system oxyz
Figure GDA0002247839590000039
Further calculating the local displacement of all the strain beams under the local coordinate system
Figure GDA00022478395900000310
According to said obtained all strain beams
Figure GDA00022478395900000311
The local generalized force of all the strain beams can be obtained
Figure GDA00022478395900000312
Wherein
Figure GDA00022478395900000313
As a local coordinate system oixiyiziThe force to be exerted is,
Figure GDA00022478395900000314
as a local coordinate system oixiyiziA lower moment;
defining the strain beam at a local origin of coordinates oiHas a compliance matrix of
Figure GDA00022478395900000315
Methods or test methods using finite element analysisObtaining the local coordinate origin o of the strain beamiCompliance matrix of
Figure GDA00022478395900000316
Or, aiming at the equal-section straight-bar strain beam, determining a flexibility matrix according to the stress deformation relation of the strain beam by adopting Euler, Timoshenko or high-order modern beam theory
Figure GDA0002247839590000041
Regarding the load platform and the support platform, the load platform and the support platform are regarded as semi-elastic spaces; defining the load platform at a local origin of coordinates oiHas a compliance matrix of
Figure GDA0002247839590000042
Defining a local coordinate origin of the supporting platform on the supporting platform
Figure GDA0002247839590000043
Has a compliance matrix of
Figure GDA0002247839590000044
Obtaining compliance matrix by finite element analysis method or test method
Figure GDA0002247839590000045
And
Figure GDA0002247839590000046
or, the flexible matrix is deduced by adopting Boussinesq, Mindlin or modern high-order semielastic space theory
Figure GDA0002247839590000047
And
Figure GDA0002247839590000048
an approximation of (d);
compliance matrix corresponding to support platform
Figure GDA0002247839590000049
Move to point oiAt local coordinate oiThe sum of the flexibility matrixes of the elastic deformation parts of the load platform and the support platform and the strain beam is as follows:
Figure GDA00022478395900000410
representing from a local coordinate system
Figure GDA00022478395900000411
To a local coordinate system oixiyiziThe space vector transformation matrix of (2); thereby obtaining the inverse of the compliance sum matrix, i.e. its stiffness matrix
Figure GDA00022478395900000412
Converting the local coordinate system into the global coordinate to obtain the stiffness matrix under the global coordinate
Figure GDA00022478395900000413
Representing the secondary coordinate system oiA space vector transformation matrix to the coordinate system o;
the sum of the stiffness matrices of all the strain beams, the load platforms and the support platforms at the origin under the global coordinate system is
Figure GDA00022478395900000414
The load platform bears the external generalized force of
Figure GDA00022478395900000415
The generalized displacement of the load platform under the global coordinate system when the load platform bears external force is
Figure GDA00022478395900000416
The relationship between generalized force, generalized displacement and rigidity under the global coordinate system is as follows:
Figure GDA00022478395900000417
the relationship between the generalized force under the global coordinate system and the local generalized force under the local coordinate system of the strain beam is as follows:
Figure GDA00022478395900000418
wherein
Figure GDA00022478395900000419
Representing the secondary coordinate system oiA space vector transformation matrix to the coordinate system o;
obtainable as described above
Figure GDA00022478395900000420
And
Figure GDA00022478395900000421
using a formula
Figure GDA00022478395900000422
Calculating six-dimensional forces
Figure GDA00022478395900000423
Can also be obtained according to the above
Figure GDA00022478395900000424
Using a formula
Figure GDA00022478395900000425
Calculating six-dimensional forces
Figure GDA00022478395900000426
The invention has the beneficial effects that:
the method can greatly improve the measurement precision of the micro-displacement of the load platform of the multi-dimensional force sensor, can greatly expand the installation method and means of the measurement sensitive element for measuring the micro-displacement of the load platform, finally improve the measurement precision of the multi-dimensional force sensor, and can effectively improve the structural rigidity of the multi-dimensional force sensor through a parallel connection rod system mode.
Drawings
FIG. 1 is a schematic diagram of a multi-dimensional force (six-dimensional force) sensor configuration;
FIG. 2 is a schematic view of a local coordinate system;
FIG. 3 is a schematic diagram of a relationship determination process between each local coordinate system and the global coordinate system;
FIG. 4 is a schematic diagram of deformation of a strain beam under force in a local coordinate system;
FIG. 5 is a schematic view of a strain beam that may be any shape;
FIG. 6 is a schematic view of a resilient semi-dimensional rigid planar force;
FIG. 7 is a schematic view of the contact surface partially broken away during a force applied to the bolted joint;
FIG. 8 is a plane-symmetric 8-strain beam multi-dimensional force sensor;
FIG. 9 is an exemplary strain gage processing circuit;
FIG. 10 is a schematic view of some classic planar three-dimensional force sensor configurations;
FIG. 11 is a schematic diagram of an exemplary spatial six-dimensional force sensor configuration;
FIG. 12 is a schematic diagram of some exemplary monolithic spatial six-dimensional force sensor configurations and processing sequences;
FIG. 13 is a schematic diagram of some exemplary integrated spatial six-dimensional force sensor configurations;
FIG. 14 is a schematic diagram of some exemplary welded and mechanically coupled six-dimensional force sensor configurations;
FIG. 15 is a schematic diagram of some exemplary flat embedded connection methods;
FIG. 16 is a schematic diagram of some exemplary embedded spatial six-dimensional force sensor configurations;
fig. 17 is an example of a press-fitting method of the press-fitting type structure and a mounting position of the sensor;
FIG. 18 shows a press block strain beam embedded press mounting configuration with an integral housing;
FIG. 19 shows a press block strain beam embedded press mounting configuration with split housing;
FIG. 20 illustrates a method of using a pull strain beam in combination with a press fit configuration;
FIG. 21 is a method of measuring relative displacement of a load platform and a support platform using capacitive sensors in a press-fit configuration;
FIG. 22 is a schematic diagram of a typical press-fit spatial six-dimensional force sensor configuration;
FIG. 23 is a schematic view of the connection of the upper and lower support platforms in a press-fit configuration;
FIG. 24 is a schematic view of an 8-beam and 12-beam press-fit structural load platform, respectively;
fig. 25 shows a multidimensional force sensor with three types of suspension wire structures.
The English corresponding Chinese meaning in all the figures is as follows:
loading platform: load platform, Supporting platform: support platform, Strain gauge: strain gauge, Fixed on supporting platform: fixed to the support platform, Initial state: initial state, Rotation about x/y/z: rotation around the x/y/z axis, Transformation angle x/y/z: moving along the x/y/z axis, Connection with loading platform: connected to the load platform, Displacement of loading platform: displacement of load platform, Displacement of o in global coordinate system: the o point is displaced in the global coordinate system, Displacement of oi in global coordinate system: oiDisplacement of a point in the global coordinate system, Displacement of oil in local coordinate system: oiDisplacement of points in a local coordinate system, bundling deformation by F: bending deformation by F, Shear deformation by F: shear deformation by F, View a: view A, Elastic half-space: elastic half-space, raised plane: rigid plane, Capacitive sensor: capacitive sensor, Piezoelectric crystal: piezoelectric crystals, Sufficient gap for deformation of the beam, Head of the beam Head, of the Head into the hole, of the Maintenance hole, of the suspension wire;
Detailed Description
The first embodiment is as follows:
the embodiment is a multi-dimensional force sensor structure of a parallel rod system, which comprises a supporting platform and a load platform, wherein the load platform is connected with the supporting platform through the parallel rod system, each rod of the parallel rod system is arranged between the load platform and the supporting platform as an independent strain beam, and external force borne by the load platform is completely transmitted to the supporting platform through the parallel rod system; the parallel rod system can be composed of one strain beam or a plurality of strain beams;
a micro-displacement sensor for measuring micro-displacement between the supporting platform and the load platform is arranged between the supporting platform and the load platform, and/or a strain sheet is arranged on a strain beam of the parallel rod system, and/or a piezoelectric crystal is adopted as the strain beam.
The multi-dimensional force borne by the load platform can be calculated through the deformation of the strain beam or the micro-displacement between the load platform and the supporting platform;
by way of strain beam deformation: and a strain sheet is adhered to the strain beam or a piezoelectric crystal is adopted as the strain beam, the strain beam deformation of the strain beam in a local coordinate system is obtained through strain measured by the strain sheet or charge change measured by the capping crystal, and the deformation can be further used for calculating the deformation displacement of the load platform so as to obtain the multidimensional force.
By means of micro-displacements between the load platform and the support platform: and a micro-displacement sensor for measuring the displacement between the load platform and the supporting platform is arranged between the load platform and the supporting platform, and the deformation displacement of the load platform is calculated according to the measurement quantity of the micro-displacement sensor in a local coordinate system of the micro-displacement sensor, so that the multi-dimensional force is obtained.
The adopted multidimensional force calculation method is that micro-displacement of a corresponding micro-displacement sensor and a strain beam under a local coordinate system of the strain beam is obtained through the micro-displacement sensor, a strain gauge and a piezoelectric crystal, the micro-displacement is called observable, a coordination relation equation set of the micro-displacement of a load platform and the micro-displacement of the local coordinate system is obtained through a space vector transformation mode, a load platform micro-displacement solving equation set is established through a mode of extracting a specific equation in the coordination relation equation set, the load platform micro-displacement solving equation set is solved through the obtained observable, and finally the micro-displacement of the load platform in a global coordinate system is obtained; and further solving all local micro-displacements of each strain beam by utilizing the micro-displacement of the load platform, further solving the local force of each strain beam, and finally obtaining the multi-dimensional force applied to the multi-dimensional force sensor in a mode of summation after force transformation.
The multi-dimensional force sensor structure comprises an integral type, a welding and mechanical connection type, an embedded type, a press-fitting type, a suspension wire type and the like;
(1) the integral type is as follows: the load platform, the supporting platform and the strain beam are of an integrated structure, namely, the load platform, the supporting platform and the strain beam are manufactured and finished in a machining mode (such as routing and the like) through an integral material, and force between the load platform and the supporting platform is transferred in the integral material; the stress-free stress type stress-free stress combined support is used, the rigidity of all parts on a stress-free stress combined stress-free stress-free stress-free stress-.
(2) The welding and mechanical connection mode is as follows: the strain beam is respectively connected with the load platform and the supporting platform by adopting a welding or mechanical connecting structure, the force transmission between the load platform and the supporting platform is transmitted by welding or other mechanical connecting structures, and the welding part and other contact parts are basically kept in contact in the stress process; the aim is that when the supporting platform is stressed and the strain beam deforms, the contact rigidity of the contact surface between the strain beam and the load platform and between the strain beam and the supporting platform is basically kept unchanged.
(3) The embedded type is as follows: the roof beam that meets an emergency adopts embedded structure to be connected with load platform and supporting platform respectively, the power transmission between load platform and the supporting platform will be transmitted through embedded structure, adopt the pressure assembly method to impress the built-in end corresponding embedding hole when connecting, perhaps the built-in end passes through other medium with the embedding hole and is connected, all produce the prestressing force between the contact surface that makes all, and still keep certain prestressing force at all contact surfaces of atress in-process, and then guarantee that all contact surfaces can not break away from, promptly: an embedded pre-tightening structure is adopted to avoid the separation of the strain beam and the contact surface of the platform in the stress process of the sensor; the aim is that when the load platform is stressed and the strain beam deforms, the contact rigidity of the contact surface between the strain beam and the load platform and between the strain beam and the support platform is kept unchanged.
(4) The press-fitting mode is as follows: the strain beam is respectively connected with the load platform and the support platform by adopting a press-fitting structure, and the force transmission between the load platform and the support platform needs to be carried out through the press-fitting structure; the pressure equipment formula structure indicate that make the roof beam both ends of meeting an emergency and load platform and supporting platform contact surface all keep certain pre-compressive stress through pressure assembly mode, and all contact surfaces still keep certain pre-compressive stress at the atress in-process, and then guarantee that the contact surface can not break away from at the atress in-process, promptly: the separation of the strain beam from the contact surface of the platform in the stress process of the sensor is avoided by adopting a press-fitting structure; (ii) a The aim is that when the supporting platform is stressed and the strain beam deforms, the contact rigidity of the contact surface between the strain beam and the load platform and between the strain beam and the supporting platform is kept unchanged.
(5) The suspension wire type is as follows: each strain beam is a thin suspension wire and is respectively connected with the load platform and the support platform, all the suspension wire strain beams apply certain pre-tensioning stress and keep the tensile stress all the time in the stress process; the method aims to keep the rigidity of each part including the suspension line strain beam part unchanged when the load platform is stressed and the suspension line strain beam deforms.
The resolving mode of the multi-dimensional force sensor is as follows:
first, the representation of the space vector symbol is explained, for example
Figure GDA0002247839590000071
The entirety of each parameter is illustrated as one form:
the body of the symbol represents a space vector, Q represents a generalized force including a force and a moment, F represents a force, and M represents a moment; Δ represents a generalized deformation displacement including a linear displacement and a rotational displacement, Δ D represents a linear deformation displacement, and Δ θ represents a rotational deformation displacement; r represents the distance between the origin of the local coordinate system and the origin of the global coordinate system under the global coordinate system, and beta represents the rotation angle of the local coordinate system around three axes of the global coordinate system;
the upper corner of the upper left corner represents the coordinate system, and the upper corner of the upper left corner represents the corresponding parameter under the global coordinate system oxyzThe parameters of (1); the upper corner of the upper left corner is marked with i to indicate that the corresponding parameter is a local coordinate system o of the strain beamixiyiziThe following parameters; the upper corner of the upper left corner is marked with j, and the corresponding parameter is a local coordinate system o of the displacement sensorjxjyjzjThe following parameters;
the lower corner of the lower left corner represents a point of vector action, and the lower corner of the lower left corner is marked as o to represent the origin o of the corresponding vector action in the global coordinate system oxyz; the lower corner of the lower left corner is marked oi/ojRespectively representing the corresponding vector acting on the local coordinate system o of the strain beam/displacement sensorixiyizi/ojxjyjzjOrigin o ofi/oj；
The upper corner of the upper right corner is marked as i/j, and the applicator is the ith strain beam or the jth sensor respectively; g or blank, expressed as a global quantity, i.e. the applicator is an external force on the load platform;
the lower corner of the right lower corner is marked with x to indicate the direction of the vector, the lower corner of the right lower corner is marked with y to indicate the direction of the vector, the lower corner of the right lower corner is marked with z to indicate the direction of the vector, the lower corner of the right lower corner is marked with F and M to indicate that the variable is caused by force or moment, no finger is caused by the combined action of force and moment, and the lower corner of the right lower corner is marked with blank to indicate the vector formed by the xyz axes.
For example,
Figure GDA0002247839590000081
representing the ith beam, acting on o under the global coordinate system oxyz (i.e., g)iPoint, force F in the x-direction of the global coordinate system;
Figure GDA0002247839590000082
representing the ith beam in a local coordinate system i (i.e. o)ixiyizi) Under the action ofiPoints induced by the torque M along the local coordinate system ziLinear displacement of direction Δ D.
Because the micro-displacement measurement method of the load platform of the multi-dimensional force sensor is the basis of the multi-dimensional force acquisition method, the multi-dimensional force acquisition method of the multi-dimensional force sensor adopting the parallel rod system is explained first;
the load platform and the support platform are regarded as pseudo rigid bodies, all the deformation parts under external force and all the deformation parts of each connecting strain beam can be isolated on the load platform, and all the deformation parts under support force and all the deformation parts of each connecting strain beam can be isolated on the support platform; the deformation displacement and stress of each strain beam are related to the displacement and stress of a load platform serving as a pseudo rigid body through a beam theory of elastic mechanics and a force space transformation theory of theoretical mechanics, and the external force borne by the load platform is obtained through the strain or piezoelectric change of the strain beams or the micro-displacement change between the load platform and a supporting platform, wherein the calculation method comprises the following steps:
firstly, establishing each coordinate system:
and establishing a global coordinate system attached to the supporting platform, namely, the coordinate system is fixedly connected to the supporting platform and does not move, but for the convenience of display, generally placing the origin of the coordinate system at the center o of the stressed part of the loading platform. As shown in fig. 1, the global coordinate system is oxyz, abbreviated as xyz; the y-axis is perpendicular to the x-axis, and the z-axis is perpendicular to the plane y-x;
establishing a local coordinate system for expressing local deformation of the strain beam, wherein the local coordinate system in the graph is oixiyiziAbbreviated as xiyiziWherein i represents the ith beam; the center of the contact surface of the strain beam and the load platform is taken as the origin o of a local coordinate systemi(ii) a As shown in fig. 2, the center line of the strain beam is used as a local coordinate system xiAxis, yiAxis and xiThe axis is vertical, and yiThe axis being in the end face of the strain beam, ziAxis and plane yi-xiAnd vertically, the local coordinate system is regarded as being fixed in the global coordinate system after being established and does not change along with the deformation of the strain beam, and the specific establishment mode is as follows:
each relationship between the local coordinate system and the global coordinate system can be represented by three rotation angles and three translation distances, which are recorded as
Figure GDA0002247839590000091
And
Figure GDA0002247839590000092
as shown in fig. 3, fig. 3 shows a process of determining a relationship between each local coordinate system and the global coordinate system, that is, a manner of establishing the beam local coordinate system; namely: in the initial state, a local coordinate system is coincident with a global coordinate system, and the strain beam rotates along x relative to the initial position
Figure GDA0002247839590000093
Then rotate along y
Figure GDA0002247839590000094
Then rotate along z
Figure GDA0002247839590000095
Then respectively translated along xyz coordinate axes
Figure GDA0002247839590000096
Then connecting two ends of the strain beam to the load platform and the supporting platform respectively; when the load platform is stressed to generate displacement, a coincident point of the load platform and the origin of the global coordinate system moves from o to o'; origin o of local coordinate system on strain beamiTo the coincidence point of oi' we refer to this way of establishing a local Coordinate system as Coordinate Ma;
the deformation schematic diagram of the strain beam in the local coordinate system under the action of force is shown in fig. 4; when an Euler beam is adopted (a Timoshenko beam or other high-order beams can also be adopted), according to the stress relation of the strain beam, the following conditions are known:
Figure GDA0002247839590000097
Figure GDA0002247839590000098
Figure GDA0002247839590000099
Figure GDA00022478395900000910
Figure GDA00022478395900000911
Figure GDA00022478395900000912
e is the elastic modulus, G is the shear modulus; liIs the strain beam length; a. theiIs the cross-sectional area of the strain beam;
Figure GDA00022478395900000913
is wound around yiThe moment of inertia of the shaft;
Figure GDA0002247839590000101
is wound around ziThe moment of inertia of the shaft;
Figure GDA0002247839590000102
(in fact, it is
Figure GDA0002247839590000103
Is generally written as
Figure GDA0002247839590000104
) Is wound around xiThe moment of inertia of the shaft, also known as the polar moment of inertia;
Figure GDA0002247839590000105
as with the above representation of space vector symbols, the lower corner of the right hand corner labeled as the direction of the vector, the lower corner of the right hand corner labeled as x represents along the x-axis, and the lower corner of the right hand corner labeled as y represents along the x-axisy-axis, the lower corner of the lower right corner being labeled z to indicate along the z-axis; the presence of other parameters in the lower corner of the right indicates the amount of the corresponding parameter on the corresponding axis, e.g. the lower corner of the right, labeled Mz, indicates the amount in z due to M.
The strain beam is at the local origin oiThe compliance matrix of (2) is defined as:
Figure GDA0002247839590000106
the strain beam may be any shape of strain beam as shown in fig. 5. For the strain beam with any shape, the local coordinate origin o of the strain beam can be obtained by adopting a finite element method or a test methodiA compliance matrix of (c); for the equal-section straight-bar strain beam, a flexibility matrix (which can also be obtained according to the Timoshenko beam theory and other modern beam theories) can be written as follows according to the stress-deformation relationship of the strain beam and further according to the Euler-Bernoulli beam theory:
Figure GDA0002247839590000107
the stress schematic diagram of the rigid plane of the elastic half-space is shown in fig. 6, for the load platform and the support platform, the load platform and the support platform can be regarded as the elastic half-space, and the flexibility matrix at the joint of the elastic half-space and the strain beam can be obtained through the stress displacement deformation relation of the rigid plane on the elastic half-space;
load platform at local origin of coordinates oiThe compliance matrix of (2) is defined as:
Figure GDA0002247839590000111
the center of the contact surface of the strain beam and the supporting platform is taken as the origin of a local coordinate system
Figure GDA0002247839590000112
Establishing a local coordinate system (and establishing strain) of a support platformThe local coordinate system of the center of the beam and load platform interface is similar); the supporting platform is arranged at the local coordinate origin of the supporting platform
Figure GDA0002247839590000113
The compliance matrix of (2) is defined as:
Figure GDA0002247839590000114
the flexibility matrix can be obtained by adopting finite element or test method
Figure GDA0002247839590000115
And
Figure GDA0002247839590000116
the flexible matrix approximation can also be derived using the semielastic space theory of Boussinesq and Mindlin, etc.:
Figure GDA0002247839590000117
in the formula: e-modulus of elasticity; μ -poisson's ratio; a-rigid planar area; i isp-polar moment of inertia of the rigid plane about the x-axis; r isp-polar radius of inertia of the rigid plane about the x-axis; s-the length of the rigid plane along the z-axis; w-the length of the rigid plane along the y-axis;
compliance matrix corresponding to strain beam
Figure GDA0002247839590000118
Compliance matrix corresponding to load platform
Figure GDA0002247839590000119
Compliance matrix corresponding to supporting platform
Figure GDA00022478395900001110
Are all required at point oiProcessing and summing the above; so as to support the corresponding flexibility matrix of the platform
Figure GDA00022478395900001111
Move to point oi；
For the convenience of the following description, a general transformation matrix is defined as:
Figure GDA0002247839590000121
a spatial transformation matrix from coordinate system p to coordinate system q, where op,xp,yp,zpRepresenting the origin, x, y and z, o axes, respectively, of a coordinate system pq,xq,yq,zqDenotes the coordinate origin, x, y and z axes of the coordinate system q, respectively, [ γ ═ γ [ [ γ ]x,γy,γz]TIs the spatial angle of coordinate system p and coordinate system q around x, y, z in coordinate system q, d ═ dx,dy,dz]TThe distance between coordinate system p and coordinate system q along x, y and z in coordinate system q is defined as follows:
Rot(γ)＝Rot(z，γz)Rot(y，γy)Rot(x，γx) (13)
rot () refers to a spatial rotation transform; the inverse transformation is as follows:
RotT(γ)＝RotT(x,γ)RotT(y,γ)RotT(z,γ) (14)
Figure GDA0002247839590000122
representative vector d ═ dx，dy，dz]TA corresponding antisymmetric operator; the operator can also be regarded as a cross product operator, i.e. the force and moment arm cross product is converted into moment, and the rotating speed (micro-corner or corner difference) and the rotating radius cross product is converted into linear speed (micro-displacement or displacement difference);
in particular application
Figure GDA0002247839590000123
When the coordinate system is used, p and q are replaced by a specific coordinate system, γ is replaced by a specific included angle between the two coordinate systems, and d is replaced by a specific distance between the origins of the two coordinate systems, for example, as described later
Figure GDA0002247839590000124
I.e. the coordinate system at the intersection of the secondary beam and the support platform
Figure GDA0002247839590000125
Spatial transformation to coordinate system i at the intersection of the beam and the load platform, Ti gI.e. the spatial transformation from the coordinate system i where the beam intersects the load platform to the global coordinate system g.
At local coordinate oiCompliance and matrix of
Figure GDA0002247839590000126
Figure GDA0002247839590000127
Representing from a local coordinate system
Figure GDA0002247839590000128
To a local coordinate system oiThe spatial transformation matrix of (a);
Figure GDA0002247839590000129
for two local coordinate systems oixiyiziAnd
Figure GDA00022478395900001210
the included angle of the coordinate axes of the two-dimensional,
Figure GDA00022478395900001211
for two local coordinate systems oixiyiziAnd
Figure GDA00022478395900001212
the distance between the origins;
when the strain beam is a straight beam,
Figure GDA00022478395900001213
Figure GDA0002247839590000131
representative vector l ═ lx，ly，lz]TA corresponding antisymmetric operator;
wherein l ═ lx，ly，lz]TRepresenting two local coordinate systems oixiyiziAnd
Figure GDA0002247839590000132
origin in local coordinate system oixiyiziThe distance of (1);
for each strain beam i, the flexibility matrix at the origin of the local coordinate system of each strain beam i can be obtained by adopting the method;
single strain beam and the inverse matrix of the flexibility and matrix at the joint with the load platform and the support platform respectively, namely the rigidity matrix
Figure GDA0002247839590000133
The conversion formula of the rigidity matrix under the conversion of the local coordinate system to the global coordinate is as follows:
Figure GDA0002247839590000134
Figure GDA0002247839590000135
Ti grepresenting the secondary coordinate system oixiyizi(i) Spatial transformation matrix to coordinate system oxyz (g), between coordinate system i and coordinate system gAngle of inclusion of betaiDistance between origins being ri；
Taking the six-dimensional force sensor shown in FIG. 1 as an example, the sum of the stiffness matrixes of all the strain beams, the load platforms and the support platforms at the origin point under the global coordinate system is
Figure GDA0002247839590000136
The spatial six-dimensional force sensor shown in fig. 1 is fully consistent therewith;
the total external force borne by the load platform under the global coordinate system is
Figure GDA0002247839590000137
The displacement of the load platform under the global coordinate system when the load platform bears external force is
Figure GDA0002247839590000138
The relationship between force and displacement, stiffness can be written as:
Figure GDA0002247839590000139
during actual measurement of the multi-dimensional force sensor, because the rigidity matrix is only related to an actual structure, all structural parameters are obtained in advance, and the magnitude of six components of the external load force can be obtained as long as micro displacement of the load platform in six directions under the action of external force is measured, namely: the multidimensional force sensor can obtain multidimensional forces including three-dimensional forces, six-dimensional forces and other dimensional forces by measuring the micro-displacement in six directions of the load platform under the action of external force by using the micro-displacement measuring sensor arranged between the supporting platform and the load platform and/or the strain gauge adhered to the strain beam and/or adopting the piezoelectric crystal as the strain beam.
This calculation method is referred to as principal Ma in the present invention.
The current multidimensional force sensor solving method is that the six-dimensional force is considered to be in a linear relation with the strain of certain weak parts of a structural body directly, cross coupling in all internal transmission processes is omitted, or the structural body is considered to be a pure rigid body, and all structural body deformation and friction are omitted through frictionless hinge connection, so that the structural body is either too complex, has a large number of parallel-serial structural bodies, or is too simple, and all forces are decoupled by adopting a hinge structure. The multi-dimensional force sensor structure in the invention can not be solved by the traditional solving method.
For the above reasons, the structure of the present invention is also embodied in other fields, but the existing multidimensional force sensor does not adopt the structure of the present invention, and does not think of using the structure of the present invention, because the prior art does not have a solution corresponding to the structure of the present invention, and naturally the prior art does not think of the corresponding structure of the present invention.
Examples
The sensor needs to obtain high measurement precision, and needs to ensure that in the measurement process, multidimensional force is transmitted from a load platform to a support platform through a strain beam, the structural rigidity of all parts on the whole force transmission path needs to be basically unchanged, and the contact surface of two parts in the common structures of welding, bolt connection and the like is easy to have the phenomenon that the local contact surface is separated from contact in the whole stress process, so that the contact rigidity of the contact surface is mutated, and the precision of the multidimensional force measurement result is reduced.
The multidimensional mechanical sensor can be divided into a 2-dimensional force (a plane 2-dimensional force or a 1-dimensional force plus a one-dimensional moment) 3-dimensional force (a plane 2-dimensional force plus a plane internal moment, or a three-dimensional force along 3 coordinate axes, or a moment around 3 coordinate axes), a 4-dimensional force, a 5-dimensional force and a 6-dimensional force sensor. The planar 3-dimensional force (planar 2-dimensional force plus in-plane torque) and the three-dimensional 6-dimensional force sensor are the most common sensors, and other sensors can be obtained by neglecting some dimensional force (torque) on the basis.
The multi-dimensional force sensor is composed of a plurality of strain beams in parallel connection structure, and can be divided into an integral structure, a welding machine and mechanical connection structure, an embedded structure and a press-mounting structure.
The multi-dimensional mechanics sensor structure of the invention is explained by combining the attached drawings, and each structure has two forms of plane three-dimensional force and three-dimensional six-dimensional force.
As shown in fig. 7(a) and 7(b), the strain beam and the base platform (the load platform and the support platform) are connected together by bolts, under the condition that the strain beam is acted by force, the contact surface of the strain beam and the base platform is deformed, and when the deformation is large, the original contact surface is partially separated from contact, so that the contact rigidity is suddenly changed, the displacement transmission of the strain near the contact surface is also suddenly changed, and finally the result of the calculated multidimensional force is inaccurate; this result is to be avoided in the design of the multi-dimensional force sensor structure; not only is such a bolted structure subject to local stiffness changes during stress, but similar problems occur in other kinds of structures, and therefore all of the following structures focus on solving such problems.
The beneficial result of this kind of limited is to avoid the emergence of some position rigidity sudden change phenomenon on the power transmission route, and then guarantee load platform micrometric displacement calculation accuracy effectively, guarantee multidimensional force sensor accuracy finally.
One-piece and integral structure
The monolithic structure means that the entire sensor (mainly including the strain beam, the load platform and the support platform) is machined from a single piece of work-piece except for the auxiliary parts (the housing, the external adapter, etc.). The structure has the advantages that the strain beam is a uniform and continuous whole at the joint of the strain beam and the supporting platform and the load platform, the sudden change of rigidity cannot be generated, and the measurement precision is high. The structure is particularly suitable for small and medium-sized, miniature and MEMS structure multi-dimensional force sensors with the load of hundreds of kilograms or less, and is applied to a force control robot, a cooperation robot, an endoscope minimally invasive surgery robot, a bionic mechanical arm and other small and medium-sized multi-dimensional force measuring devices.
1. Planar three-dimensional force sensor structure
The planar three-dimensional force sensor means that the load platform, the supporting platform and the beam structure are all arranged in a plane or a plurality of planes parallel to each other, the structural relationship of the load platform, the supporting platform and the beam structure can be projected in a plane, and the force which can be represented comprises two forces and a moment in the projection plane, as shown in fig. 8.
Taking the central position of the strain foil stuck on four surfaces of the strain beam as an example, the strain foil can be used for measuring the strain beam along the axial direction x of the strain beamiAverage tensile/compressive strain (stress).
In fig. 9(a) and 9(b), E is an applied reference voltage, and E is a measurement voltage. The strain of the strain gauge may also be measured by a frequency method or the like. The strain gauges can adopt a universal differential bridge measurement, or can directly measure the strain amount of each strain gauge and then perform processing through a digital circuit, so that the strain sum of the strain gauges 1 and 3 or the sum of the strain gauges 2 and 4 or the sum of all 4 strain gauges 1, 2, 3 and 4 is measured. Therefore, bending stress can be ignored, only tensile/compressive stress of the strain beam is obtained, and the strain beam is further obtained along the axial direction xiThe tension/pressure of.
Fig. 10(a) to 10(f) are typical monolithic planar three-dimensional force sensors, respectively, and the strain beams include constant-section strain beams and variable-section strain beams.
2. Three-dimensional six-dimensional force sensor structure
The three-dimensional six-dimensional force sensor is arranged in a space three-dimensional structure of a load platform, a supporting platform and a beam structure, and the force which can be represented comprises three forces and three moments; as shown in fig. 11(a) and 11 (b);
fig. 12(a) and 12(b) show the processing procedure of the integrated three-dimensional six-dimensional force sensor structure, respectively.
The integrated structure includes, but is not limited to, the structure shown in fig. 11(a) and 11(b), and may be another structure such as the structure shown in fig. 13(a) to 13 (h).
Welding and mechanical connecting structure
As shown in fig. 14(a) to 14(b), the welding and mechanical connection structure is formed by separately processing the support platform, the load platform, and the strain beam, and then assembling the three together to complete the entire sensor body structure. The welding and mechanical connecting structure includes, but is not limited to, the structure shown in fig. 14(a) and 14(b), and may be other structures shown in fig. 14(c) to 13 (d).
The sensor is characterized by more convenient processing and manufacturing, and is particularly convenient for manufacturing large-scale heavy-load sensors. It should be noted that the structural dimensions of the welded or bolted joints are larger than the cross-sectional dimensions of the strain beam to ensure that the structural stiffness of the welded or bolted joints is greater than the structural stiffness of the strain beam. The pretightening force of the bolt connection is large enough to ensure that the contact surface is not locally separated in the stress process.
Three, embedded structure
The embedded structure is characterized in that a strain beam material with lower rigidity and a supporting platform and a load platform structure with higher rigidity can be adopted, for example, the supporting platform and the load platform are made of steel, titanium alloy and the like, the strain beam is made of rubber, bakelite, plastic and the like, and therefore, the strain beam can be ensured to deform greatly under the condition of smaller stress, and the embedded structure is more suitable for micro-force measurement.
1. Planar three-dimensional force sensor structure
Planar three-dimensional force sensor structures include, but are not limited to, the structure shown in fig. 15 (a).
In this embodiment, an embedded type pretensioning mode is adopted, as shown in fig. 15(b), relatively large heads are made at two ends of the strain beam, corresponding embedding holes are made in the load platform and the support platform, the size of each hole is slightly smaller than that of the strain beam head, and the strain beam head is respectively squeezed into the embedding holes in the load platform and the support platform by adopting a mechanical squeezing mode. The purpose is to create a pre-stress on the contact surface between the head and the platform, so that the contact surface does not partially come out of contact during the measurement process, and the contact stiffness does not change.
The embedding can also adopt other forms, such as wedge pre-tightening mode shown in fig. 15 (c).
The top of the wedge pretensioning means may be pretensioned with a pressure plate as shown in fig. 15(d), but this may or may not be the case. The pressing plate pre-tightening is not only suitable for a wedge block pre-tightening type, but also suitable for other extrusion type equal pre-tightening modes;
the embedded type can also adopt other forms, such as an injection type connection mode shown in fig. 15(e), namely, a mode of injecting solidifiable liquid, such as liquid metal, resin and the like.
Of course, it is also possible to use a method of first connecting by pressing and then welding, as shown in fig. 15 (f).
Alternatively, the embedded end may be bolted, i.e., the embedded end is pressed or tightened with a bolt, as shown in fig. 15(g) and 15 (h). The connection mode is convenient to broker, but the problems of low contact rigidity and partial separation of contact surfaces easily occur, the size of the load force needs to be considered carefully, and the diameter of the bolt is increased properly.
All embedded structure interfaces should preferably also ensure that no local detachment should occur during the application of force.
2. Three-dimensional six-dimensional force sensor structure
The three-dimensional six-dimensional force sensor structure is embedded in the same manner, but has a three-dimensional structure as shown in fig. 16(a) to 16 (c). The present invention includes, but is not limited to, these several forms.
Four, press mounting type structure
The press-fitting type structure is characterized in that the thin elastic beams are press-fitted between the load platform and the supporting platform through pretightening force, all the elastic beams are not in the same plane at the same time, the pretightening force is applied during the assembly, the elastic beams generate the pressed pretightening force, the pressed pretightening force is kept in a Chinese type in the measuring process, and the elastic beams are prevented from being separated from the load platform and the supporting platform. The strain beam can adopt piezoelectric crystal to measure by piezoelectric effect, or can adopt other materials to measure by pasting a strain gauge on the strain beam or installing a micro-displacement sensor on the strain beam, or installing the micro-displacement sensor between the load platform and the supporting platform.
As shown in fig. 17(a) to 17(c), in which fig. 17(a) is a view for directly disposing a strain beam between a load platform and a support platform, fig. 17(b) is a view for disposing a strain beam inside a member between a load platform and a support platform, and fig. 17(c) is a view for disposing capacitive sensors at upper and lower ends of the strain beam.
1. Planar three-dimensional force sensor structure
Integral pre-tightening type:
as shown in fig. 18, the overall pre-tightening planar three-dimensional force sensor is that the supporting platform and the load platform are both of an integral structure, when the strain beam is installed, external force is applied through a press machine and the like to prop the platform open, then the strain beam is placed into the platform (located at four corners in fig. 18), and after the external force is removed, the platform rebounds, so that the strain beam is pre-tightened. The present invention includes, but is not limited to, the integrally preloaded planar three-dimensional force sensor shown in fig. 18.
The three-dimensional six-dimensional force sensor can also be pre-tightened in the same way.
Supporting platform pretension formula:
as shown in fig. 19, the supporting platform pre-tightening type planar three-dimensional force sensor is characterized in that the supporting platform is divided into separate structures, and different parts of the supporting platform are connected into a whole by bolts or welding or other connection methods in the assembling process, so that the elastic beam is subjected to compressive pre-tightening force.
Beam pretension formula:
as shown in fig. 20(a) and 20(b), the beam pre-tightening type planar three-dimensional force sensor is configured to pre-tighten a thin-walled elastic beam (generally, a non-metallic beam) with a pre-tightening beam (generally, a metallic beam) capable of being tensioned, where the pre-tightening beam may be disposed outside the thin-walled elastic beam (fig. 20(a)) or disposed in the middle of the thin-walled elastic beam (fig. 20 (b)). The structure is characterized in that the stress of the pre-tightening beam is also considered in calculation in the measuring process of the sensor.
The stress calculation of the multi-dimensional force sensor can adopt a stress mode of measuring the elastic beam, and can also adopt a micro-displacement mode of measuring the load platform and the supporting platform.
The micro-displacement between the load platform and the support platform can be measured by using a plurality of micro-displacement sensors (capacitance, inductance, eddy current, triangle light, confocal light, astigmatism, etc.), and the capacitance sensors in the figure can be arranged outside the elastic beam or on the elastic beam, as shown in fig. 21(a) and 21 (b).
When the strain beam is a piezoelectric crystal, the charge quantity change generated by the stress of the piezoelectric crystal can be directly utilized for calculation.
Strain gauges (electrical and optical) can be arranged on the thin-wall strain beam and the pre-tightening beam, and calculation is carried out by measuring strain.
1. Three-dimensional six-dimensional force sensor structure
The arrangement mode of the three-dimensional six-dimensional force is basically similar to a plane mode, all the elastic beams are not arranged in the same plane at the same time, two modes of platform pre-tightening and pre-tightening of the pre-tightening beams can be adopted, and the measuring method can adopt three modes of measuring micro displacement between a load platform and a supporting platform, measuring piezoelectric crystals and arranging strain gauges.
Fig. 22 is a schematic diagram of arrangement and pre-tightening of piezoelectric crystals, in which the piezoelectric crystals can be regarded as strain beams, and when the piezoelectric crystals are used, six-dimensional force can be directly calculated according to charge variation of the piezoelectric crystals; the piezoelectric crystal in the figure can be replaced by other materials, a micro-displacement sensor is required to be arranged between the load platform and the supporting platform, and six-dimensional force is calculated according to the variation of the micro-displacement sensor; the supporting platform in the figure is divided into an upper part and a lower part, and the specific structure needs to be connected into a whole;
fig. 23 is a schematic view of a split structure and a connection manner of the supporting platform. For the upper and lower supporting platforms in fig. 22, the upper and lower supporting platforms can be connected into a whole by using the structure in the figure, and meanwhile, pre-tightening force is applied to the strain beam.
Fig. 24(a) and 24(b) are schematic views of load platform structures of 8 press-fit strain beams and 12 press-fit strain beams, respectively, in which only the load platform and the strain beam structures are shown, and the corresponding support platform structure can refer to fig. 22 above.
Five, suspension wire type structure
Fig. 25 is a multi-dimensional force sensor with three types of suspension wire structures, fig. 25(a) is a plane structure, all suspension wires are tensioned by a clamping and pre-tightening structure, fig. 25(b) is a plane structure with an embedded structure, the suspension wires and embedded blocks at two ends are integrated, the suspension wires are fixed and pre-tightened by the embedded structure, fig. 25(c) is a three-dimensional structure, a supporting platform is divided into an upper supporting platform and a lower supporting platform, and the two supporting platforms need to be connected by a fixing structure and apply pre-tightening force to the suspension wires. The advantage of this kind of structure is that suspension line formula strain beam can be very thin, and then can regard supporting platform and load platform as the pseudo rigid body that extremely approaches ideal rigid body, and its structure bearing capacity is less, but multidimension force measurement accuracy is high.
The present invention, including but not limited to the multi-dimensional force sensor structures shown in fig. 8-25, may be in the form of a combination of all the structures in embodiments of the present invention or in other forms.

Claims (5)

1. The multi-dimensional force sensor structure of the parallel rod system is characterized by comprising a supporting platform and a load platform, wherein the load platform is connected with the supporting platform through the parallel rod system, and external force borne by the load platform is completely transmitted to the supporting platform through the parallel rod system;
a micro-displacement sensor for measuring micro-displacement between the supporting platform and the load platform is arranged between the supporting platform and the load platform, and/or a strain sheet is arranged on a strain beam of the parallel rod system, and/or a piezoelectric crystal is adopted as the strain beam;
the multi-dimensional force sensor structure acquires a multi-dimensional force by:
the global coordinate system is a coordinate system attached to the supporting platform;
the local coordinate system of the strain beam is a coordinate system attached to the strain beam;
the local coordinate system of the micro displacement sensor is a coordinate system attached to the micro displacement sensor;
establishing a vector transformation relation matrix between a local coordinate system and a global coordinate system according to a space vector transformation rule, wherein the vector transformation relation matrix comprises a generalized force transformation relation, a generalized deformation displacement transformation relation and a displacement sensor transformation relation;
the generalized force comprises force and moment, and the generalized deformation displacement comprises linear displacement and corner displacement;
establishing a relation matrix of deformation and stress of the strain beam, the supporting platform and the loading platform under a local coordinate system according to theoretical mechanics, material mechanics and elastic mechanics, namely a local rigidity matrix and a local flexibility matrix;
according to a strain gauge adhered to the strain beam, or/and a piezoelectric crystal serving as the strain beam, or/and a displacement sensor arranged between the load platform and the support platform, obtaining local deformation displacement of a coincident point of the load platform and a corresponding local coordinate system origin along/around a measurement axis under a local coordinate system, and obtaining observability;
calculating the deformation displacement of the load platform under the global coordinate system according to the local deformation displacement of the coincident point of the load platform and the origin of the corresponding local coordinate system along/around the measuring axis in the local coordinate system;
calculating all local deformation displacements of the corresponding local coordinate origin of each strain beam in the local coordinate system according to the deformation displacement of the load platform in the global coordinate system;
calculating the local generalized force of each strain beam under the local coordinate system according to the local deformation displacement of each strain beam under the local coordinate system;
and translating the local generalized force of all the strain beams in the local coordinate system to the origin of the global coordinate system according to the vector transformation relation between the local coordinate system and the global coordinate system, and summing to obtain the multi-dimensional force of the multi-dimensional force sensor.
2. The multi-dimensional force sensor structure of claim 1, wherein the multi-dimensional force sensor structure comprises one-piece, welded and mechanically connected, embedded, press-fit, and catenary types;
the integral type is as follows: the load platform, the supporting platform and the strain beam are of an integrated structure, namely, the load platform, the supporting platform and the strain beam are processed by a whole continuous material;
the welding and mechanical connection mode is as follows: the strain beam is respectively connected with the load platform and the supporting platform by adopting a welding or mechanical connecting structure;
the embedded type is as follows: the strain beam is connected with the load platform and the supporting platform respectively by adopting an embedded structure;
the press-fitting mode is as follows: the strain beam is connected with the load platform and the supporting platform respectively by adopting a press-fitting structure;
the suspension wire type is as follows: each strain beam is a suspension wire and is respectively connected with the load platform and the supporting platform, all the suspension wire strain beams apply certain pre-tensioning stress, and the tensile stress is kept all the time in the stress process.
3. The multi-dimensional force sensor structure of claim 2, wherein the embedded form comprises an extrusion pre-tightening mode, a wedge pre-tightening mode, an injection connection mode, a first extrusion and then welding mode, and an embedded end bolt connection mode.
4. The multi-dimensional force sensor structure of claim 2, wherein the press-fit type comprises an integral pre-tightening mode, a support platform pre-tightening mode, and a beam pre-tightening mode.
5. The multi-dimensional force transducer structure of claim 1, wherein the strain beam is in constant contact with the contact surfaces of the load platform and the support platform when the multi-dimensional force transducer is subjected to a force.
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