CN110788874B

CN110788874B - Manipulator for controlling clamping force to measure distance between clamping points

Info

Publication number: CN110788874B
Application number: CN201911001461.XA
Authority: CN
Inventors: 鲁阳; 胡惠君; 倪嘉昊; 沈建; 李昕
Original assignee: China Academy of Art
Current assignee: China Academy of Art
Priority date: 2019-10-21
Filing date: 2019-10-21
Publication date: 2021-06-01
Anticipated expiration: 2039-10-21
Also published as: CN110788874A

Abstract

The invention discloses a manipulator for controlling clamping force to measure the distance between clamping points, which is used for an industrial robot. The device consists of a clamping arm, an encoding screw rod, a rack, a driver and a digital controller. The clamp arm includes a movable arm and a fixed arm having force and deformation sensing functions. The coding screw rod consists of a micrometer screw rod and a three-state coder, and the three-state coder comprises a fluted disc and a cantilever beam sensor. The clamping arm and the coding screw rod form a force-deformation-displacement composite sensing mechanism which is arranged on the frame. The digital controller controls the clamping arms to clamp objects through the driver and the coding screw rod, the composite sensing mechanism and the digital controller interactively transmit measurement and control signals, and the digital controller controls the clamping force and provides the distance between the clamping points.

Description

Manipulator for controlling clamping force to measure distance between clamping points

Technical Field

The design is a manipulator for controlling clamping force to measure the distance between clamping points, and the manipulator is used for an industrial robot.

Background

The manipulator is a front-end operation mechanism of various robots, is generally arranged on a mechanical arm of the robot, and has the basic functions of taking and placing, namely grabbing, transferring and releasing objects. In the process of taking and placing, the clamping force of the manipulator to the object needs to be controlled. The robot is provided with a manipulator for a large number of robots including automatic production, processing and detection equipment in the industrial field, and has the functions of taking and placing as well as other functions such as measurement, identification, assembly, adjustment and the like according to different operation tasks. In the machine industry, length-based dimension measurement is the most common measurement, however, up to now, there is no mechanical arm with dimension measurement capability. The design of the mechanical arm solves the key problems that: how to realize the clamping force can be effectively controlled, and the size data can be conveniently and quickly measured to achieve enough precision.

Disclosure of Invention

The purpose of the design is to provide a manipulator for controlling the clamping force to measure the distance between the clamping points for an industrial robot, which is used for taking and placing objects such as mechanical parts and the like, controlling the clamping force, tracking and measuring the distance between the clamping points, and obtaining size data such as the length, the thickness, the diameter and the like of the objects and other data such as deformation and the like from the distance between the clamping points. The manipulator consists of a guide rail seat, a sliding rack, a transmission shaft, a coding screw rod, a driver, a clamping arm and a digital controller.

The guide rail seat structure comprises a rectangular thick plate, a parallel male guide rail and a coupler. The parallel male guide rails are positioned on the front side and the rear side above the thick plate and are used for being matched with the sliding rack. The coupling is fixed below the thick plate and used for connecting the arm of the robot.

The structure of the sliding rack comprises a rectangular bottom plate, parallel female guide rails positioned on the front side and the rear side edges below the bottom plate, a boss positioned on the left lower side of the bottom plate and provided with a threaded through hole, a left bearing support plate positioned on the left side above the bottom plate, a right bearing support plate positioned above the bottom plate and close to the right side edge, and a U-shaped guide limiting groove between the two bearing support plates on the upper surface of the bottom plate. The left bearing support plate is embedded with a left bearing, the right bearing support plate is embedded with a right bearing, and the left bearing support plate and the right bearing are in a coaxial position. The axis of the threaded through hole on the boss, the axis of the guide limiting groove and the axes of the two bearings are all positioned in the longitudinal symmetrical plane of the parallel female guide rail and are parallel to the axis of the parallel female guide rail. The sliding frame and the guide rail seat are installed together through the matching of the male guide rail and the female guide rail.

The structure of transmission shaft includes threaded rod and the left connecting axle of threaded rod, and the threaded rod is installed on the slip frame through the cooperation with the screw through-hole on the lug boss, and the connecting axle stretches to the left side of lug boss outward.

The coding screw rod consists of a micrometer screw rod and a three-state coder. The micrometer screw rod is a step shaft with screw threads, the structure of the micrometer screw rod is divided into three sections I-II, II-III and III-IV from left to right, the sections I-II and III-IV are optical axes, the section II-III is a screw thread shaft, and the external diameter of the screw threads is larger than the diameters of the optical axes of the sections I-II and III-IV. The micrometer screw rod is arranged on the sliding frame through the matching of the section I-II optical axis and the left bearing and the matching of the section III-IV optical axis and the right bearing, the section II-III threaded shaft is positioned between the left bearing support plate and the right bearing support plate, the section I-II optical axis extends to the left side of the left bearing support plate, and the section III-IV optical axis extends to the right side of the right bearing support plate. The left end face and the right end face of the section II-III threaded shaft are respectively matched with the right end face of the left bearing and the left end face of the right bearing, and the two matching pairs prevent the micrometer screw rod from moving left and right.The tri-state encoder is composed of a sensor support, a fluted disc, an upper left cantilever beam sensor, an upper right cantilever beam sensor, a lower left cantilever beam sensor and a lower right cantilever beam sensor. The sensor support is generally a rectangular frame and is fixed at the upper right side of the bottom plate of the sliding rack, the fluted disc is enclosed in the middle, and a rectangular through hole with the axis parallel to the plane of the frame and perpendicular to the side of the frame and a threaded hole vertically communicated with the rectangular through hole are processed at the position, close to the corner of one side, of the four sides of the frame in sequence. The fluted disc is an equal-thickness disc with circular arc teeth distributed on the periphery, and is coaxially fixed on the III-IV section optical axis of the micrometer screw rod. The number of circular arc teeth is an integral multiple of 4, such as 180, 500. The four cantilever beam sensors are the same in shape and size, the elastic bodies are uniform-section elastic beams or variable-section elastic beams, the roots of the elastic bodies are respectively matched with the four rectangular through holes of the sensor support, and the elastic bodies are fixed on the upper inner wall, the right inner wall, the left inner wall and the lower inner wall of the sensor support through fastening screws. The four elastic beams are respectively provided with a left triangular ridge, an upper triangular ridge, a right triangular ridge and a lower triangular ridge at the positions close to the free ends and facing the side of the fluted disc, and single-axis resistance strain gauges [ R ] are respectively attached at the positions close to the roots along the axial direction of the beams₅,R₆]、[R₇,R₈]、[R₉,R₁₀]And [ R ]₁₁,R₁₂]. The four elastic beams are all pre-deformed by a certain amount, the tops of the four triangular convex edges are respectively kept in contact with the circular arc teeth on the periphery of the fluted disc by elastic pressure generated by pre-deformation, and the specific positions of contact points are determined according to the following conditions:

a. the longitudinal symmetry line of the fluted disc is just through the centers of the arc teeth right above and the arc teeth right below, and the horizontal symmetry line of the fluted disc is just through the centers of the arc teeth at the leftmost end and the arc teeth at the rightmost end.

b. At the moment, the left triangular ridge is positioned on the horizontal symmetry line of the fluted disc and is contacted with the vertex of the leftmost circular arc tooth. The right triangular ridge is positioned on the horizontal symmetry line of the fluted disc and the upper side of the rightmost circular arc tooth and is aligned with the valley bottom between two adjacent circular arc teeth. The upper triangular ridge and the lower triangular ridge are both positioned on the right side of the longitudinal symmetry line of the fluted disc and are respectively connected with the right side of the right-above circular arc toothAnd contacts the right side of the arc teeth right below. H is used for distance from left triangular ridge to longitudinal symmetric line of fluted disc_maxThe distance from the right triangular ridge to the longitudinal symmetry line of the fluted disc is represented by h_minThe distance from the contact point of the upper triangular ridge and the right upper arc tooth to the horizontal symmetry line of the fluted disc is equal to the distance from the contact point of the lower triangular ridge and the right lower arc tooth to the horizontal symmetry line of the fluted disc, and the distances are both expressed by h_midAnd (4) showing. h is_midAnd h_minAnd h_maxThere is a relationship represented by formula (1):

h_min、h_midand h_maxCollectively called the characteristic height, where h_minIs the minimum feature height, h_midIs the average feature height, h_maxIs the maximum feature height.

The driver comprises a first driver and a second driver, and both can adopt a stepping motor with a coupling. The first driver is arranged at the left upper part of the guide rail seat and is fixedly connected with the connecting shaft of the transmission shaft through a coupler. The second driver is arranged on the left side of the left bearing support plate and is fixedly connected with the optical axis of the section I-II of the micrometer screw rod through a coupler.

The clamping arm consists of a movable arm and a fixed arm, both of which are cantilever type elastic beam sensors with clamps, and the elastic beams used by the two sensors are the same in material, shape and size. The elastic beam of the movable arm is fixedly connected with a shaft sleeve to form an integral structure, the middle part of the shaft sleeve is embedded with a transmission nut, and the bottom part of the shaft sleeve is embedded with a limiting guide rod. The movable arm is arranged on the sliding rack through the matching of the transmission nut and the micrometer screw rod and the matching of the limiting guide rod and the U-shaped guiding limiting groove. The movable arm can not rotate around the axis of the micrometer screw rod due to the matching of the limiting guide rod and the U-shaped guiding limiting groove, and the movable arm is driven to move along the axis direction of the micrometer screw rod when the micrometer screw rod rotates. The transmission nut and the micrometer screw rod are matched with a pair, and a clearance removing measure needs to be adopted, so that two requirements are met: first, it can be theoretically considered that the micrometer screw rod changes rotationWhen the direction is in, the driving nut can be driven to move reversely without lag; secondly, the rotational freedom of the axis of the transmission nut in the x-y plane is zero. The elastic beam of the fixed arm is fixedly connected with the right bearing support plate to form an integral structure. The movable arm and the fixed arm are vertically upward and are in symmetrical positions. A single-axis resistance strain gauge R is adhered to the left side and the right side of the elastic beam of the movable arm at the b-c section along the axial direction of the beam₂And R₁The elastic beam of the fixed arm is pasted with a single-axis resistance strain gauge R along the beam axis direction at the left side and the right side of the b-c section₃And R₄Resistance strain gauge R₁、R₂、R₃、R₄Forming a full bridge measurement circuit. The elastic beam of the clamping arm has the following two basic structural forms:

a) the fishhook-shaped folding beam structurally comprises a long arm a-c section, a folding joint a-d section and a short arm d-e section, wherein the cross sections of the three sections are all rectangular, and the section c is a fixed end of the folding beam. The cross-sectional dimensions of the sections a-d are much larger than those of the sections a-c and d-e, and the sections can be regarded as rigid nodes of the folded beam. The structure of the long arm a-c section is divided into a-b section and a b-c section from top to bottom, the height H of the a-b section is greater than the height H of the b-c section₁. The section d-e of the short arm is generally a beam with equal section.

b) The structure of the straight beam is divided into a section a-b and a section b-c from top to bottom, the height H of the section a-b is larger than the height H of the section b-c, the cross sections of the section a-b and the section b-c are both rectangular, the section c is a fixed end of the beam, and the section a is a free end of the beam.

The clamp holder of the clamping arm has three types of surface contact, line contact and point contact, and is selected according to the use requirement. The gripper of the fishhook-shaped folding beam is arranged at the section e of the section d-e of the short arm, for example the left gripping surface on the movable arm and the right gripping surface on the fixed arm in fig. 1, which constitute a pair of surface contact type grippers. The distance between the two clamping surfaces is denoted by s. The grippers of the straight beam are arranged at the left and right sides of the free end a, such as a first gripping thimble and a second gripping thimble in fig. 4(a), which form a pair of point contact type grippers; the third clamping thimble and the fourth clamping thimble form a pair of point contact type clamping devices which are supported outwards. The fishhook-shaped folding beam can be designed according to the zero-corner condition of the holder. The conditions are as follows: when the clamping force acts on the lineWhen the intersection line of the longitudinal symmetry plane of the beam and the cross section e is coincident, the corner of the cross section e and the holder in the longitudinal symmetry plane is zero. For example, the width of each segment of the folded beam is equal, and is denoted by b in fig. 1. The sections b-c are of equal height to the sections d-e, i.e. h₁＝h₂H. The height H of the section a-b is more than or equal to 5H, so that the section can be regarded as a rigid body. The length L of the a-c segment is the length L of the b-c segment₁5 times of (i), i.e. L is 5L₁. According to the bending theory, under the condition of small linear elastic deformation, the relation formula can be obtained:

in the formula (2), l₂Is the length of the d-e segment. As long as L, l₁And l₂Satisfying equation (2), the clamper can maintain a zero rotation angle.

The digital controller is a microcomputer measurement and control system with a strain signal acquisition-conditioning circuit, a driver control circuit and measurement software, and is generally integrated with a control system of a robot. Resistance strain gauge R₁、R₂、R₃、R₄The formed full-bridge measuring circuit is connected with the strain signal acquisition-conditioning circuit. Resistance strain gauge [ R ]₅,R₆]、[R₇,R₈]、[R₉,R₁₀]、[R₁₁,R₁₂]The strain signal acquisition-conditioning circuits are respectively connected in a half-bridge mode, and the strain readings of the four half-bridge measurement circuits measured by the digital controller are respectively used

And (4) showing. The first driver and the second driver are respectively connected to the driver control circuit.

In the design, the code screw rod is a relatively independent part with relatively independent functions and is used for tracking and measuring the displacement of the movable arm.

The coding screw rod works in the following way:

1) adjusting the zero position of a measuring circuit of the tri-state encoder: the digital controller controls the second driver to rotate, the micrometer screw rod and the fluted disc rotate along with the second driver, and the strain reading is carried out

The change period is represented by T, and T also represents the tooth crest distance of two adjacent circular arc teeth on the fluted disc. Strain readings for each tooth rotated by the toothed disc, i.e. one period T

Respectively completing one cycle. Tracking observations

When changing over to

To a minimum value epsilon_rminWhen the gear disc stops rotating, the resistance strain gauge R on the digital controller is adjusted₅,R₆]The balance circuit of the bridge being in a balanced state, i.e.

Repeating the above operations in sequence

Take the minimum value epsilon_rminTime, adjust the resistance strain gauge [ R ]₇,R₈]、[R₉,R₁₀]And [ R ]₁₁,R₁₂]The balance circuit of the bridge is arranged so that

After the zero adjustment of the four half-bridge measuring circuits is completed according to the method, the fluted disc is rotated, and then the strain reading is carried out

Are all at a minimum value of 0 and a maximum value of epsilon_rmaxWith a minimum value of 0 corresponding to the left triangular ridge or the upper triangular ridge or the right triangleThe angular convex edge or the lower triangular convex edge is positioned at the position opposite to the valley bottom between two adjacent circular arc teeth, namely corresponding to the minimum characteristic height h_minMaximum value epsilon_rmaxCorresponding to one of the four triangular ridges being in point contact with the tip of the circular arc, i.e. corresponding to the maximum feature height h_max. The method for adjusting the zero position of the measuring circuit of the tri-state encoder is called a zero position four-step adjusting method.

2) And determining the relation between the strain reading and the rotation state of the fluted disc: after the zero adjustment of the measuring circuit of the three-state encoder is completed, the

numbers

1, 0 and 1/2 are respectively used for representing strain reading

Maximum value of (e)_rmaxMinimum 0 and mean 0.5 epsilon_rmax. Number 1 and maximum feature height h_maxCorrespondingly, a full value is defined. Number 0 and minimum feature height h_minAnd correspondingly, a value of zero is defined. Number 1/2 and average feature height h_midCorrespondingly, the median value is defined. The full value, the zero value and the middle value are defined as tri-state encoding values of the strain reading, and are referred to as tri-state values for short. When the fluted disc rotates, the three state values 0, 1/2 and 1 change circularly according to the period T. The cyclic variation of the three-state values is used for determining the rotation state of the fluted disc, namely the rotation direction and the rotation angle of the fluted disc. There are a total of four different combinations of tristate values, as shown in table 1:

TABLE 1 Strain readings

Tri-state value combination of

TABLE 2 Change of tri-state values 0, 1/2, 1 during clockwise rotation of the toothed disc during each cycle T.

"↓" in the table means an increase in the three-state value, and "↓" means a decrease in the three-state value

TABLE 3 change of tri-state values 0, 1/2, 1 during counterclockwise rotation of the toothed disc during each period T.

Any one of the three-state value combinations shown in table 1 is selected as a starting point for determining the rotation state of the toothed disc, and for the sake of clarity, three-state value combination 1 is selected, so that the toothed disc rotates clockwise by one tooth, and the three-state values complete a cycle of a period T as shown in table 2. The tri-state values complete a cycle of one period T as shown in table 3 for every tooth rotated by the gear plate in the counter-clockwise direction. In tables 2 and 3, the period T is divided into four 1/4 sub-periods, with four strain readings during each 1/4 sub-period

The three-state values 0, 1/2, and 1 are changed in different ascending and descending ways. The eight rows of data numbered from (i) to (b), which are different from each other in pairs, are unique, wherein each row of data uniquely represents a specific rotation state of the toothed disc. For example, the row of data numbered c represents and only represents the rotation of the toothed disc in the clockwise direction through the third 1/4 cycles within one cycle T, i.e., 0.5T to 0.75T. The row of data numbered fifthly represents and represents that the fluted disc is rotated counterclockwise through only the first 1/4 cycles within one cycle T, i.e., 0 to 0.25T. The continuously changing strain reading is matched with the tri-state value to monitor the rotation state of the fluted disc.

3) Measurement of displacement amount of movable arm: the numerical controller controls the micrometer screw rod to rotate, the movable arm is adjusted to a certain designated position or any position on the micrometer screw rod, the position is recorded as the displacement original point of the movable arm, and the position of the fluted disc at the moment is recorded as the fluted disc zero position. The fluted disc is rotated from the fluted disc zero position, and the movable arm is displaced from the displacement original point along with the rotation of the fluted disc. The displacement amount of the movable arm with respect to the displacement origin is represented by S, which is called origin-dependent displacement, and S is calculated by equation (3):

in the formula (3), t represents the lead of the micrometer screw (3), N_cIndicating the number of teeth of the toothed disc, n_z,sRepresenting the cumulative number of teeth, n, rotated clockwise by the toothed disc from its zero position_z,nRepresenting the cumulative number of teeth, n, rotated by the toothed disc counterclockwise from its zero position_z,sAnd n_z,nTaking a constant positive value. n is_zRepresents n_z,sAnd n_z,nThe difference is defined as the number of active rotating teeth. n is_z,s、n_z,nAnd n_zAlso known as the tooth disc rotation parameter. n is_zAnd S is the number of generations. When the fluted disc rotates clockwise, the movable arm moves rightwards, n_zAnd the symbols of S are "-". When the fluted disc rotates anticlockwise, the movable arm moves leftwards, n_zAnd S are all "+".

The use method of the manipulator comprises the following steps:

1) the measuring line is connected. Resistance strain gauge R₁、R₂、R₃、R₄The formed full-bridge measuring circuit is connected with a digital controller, and the circuit is used for sensing and measuring the clamping force F and the clamping point spacing s. For measuring F, the strain reading measured by the digital controller is epsilon_rfRepresents; for measuring s, the strain reading measured by the digital controller is epsilon_rdAnd (4) showing.

2) And (5) calibrating the force measuring system. A standard load sensor or a standard force measuring ring is generally adopted as a force value standard device, and a clamp holder on a clamping arm is used for clamping the force value standard device to calibrate a force measuring system. Taking the surface contact type clamp shown in FIG. 1 as an example, when calibrating, a standard load sensor or a standard force measuring ring is clamped by a left clamp surface on the left side of the movable arm and a right clamp surface on the fixed arm, the movable arm is controlled by the numerical controller to move, and the movable arm and the fixed arm are clamped by the right clamp surface on the fixed armThe arm exerting a set of standard forces F₁，F₂，…，F_N，(F₁＜F₂＜…，＜F_NN is a positive integer not less than 2, the value range is determined according to the requirement, for example, 2 is more than or equal to N is less than or equal to 10), and the value range is recorded by a digital controller and F₁，F₂，…，F_NCorresponding strain reading

Then is provided with

For calibration, force F and strain reading ε_rfThe force F is calculated by equation (4):

in the formula (4), A₁And B₁Is a constant, calculated according to equations (5) and (6), respectively:

in the formulae (5) and (6), N represents the ordinal number of the standard force, F_iForce values representing different ordinal standard forces,

representation and force F_iCorresponding strain readings, i.e. calibration numbers

In calibration, the spring beam is at a standard force F_NMaximum stress generated under the action of the stressBeyond the limit of the proportions of the materials used.

3) And (5) calibrating a length measuring system. And (4) calibrating a system for measuring the length (the distance between the clamping points), wherein an appropriate length standard is selected according to the type of the clamp, and a standard diameter gauge and a standard thickness gauge are the most commonly used length standards. The standard diameter gauge is a group of standard cylinders with different diameters and is used for a line contact type clamp and a surface contact type clamp; the standard thickness gauge is a group of standard thickness block gauges with different thicknesses, is mainly used for point contact type clampers, and can also be used for line contact type clampers and surface contact type clampers. The thickness value of each standard cylinder or standard block gauge is sequentially expressed by d₀，d₁，d₂…，d_nIs represented by d₀＜d₁＜d₂,…,＜d_nAnd n represents the number of standard cylinders or standard block gauges, and is generally 2 ≦ n ≦ 10 (e.g., n ≦ 7). d₀，d₁，d₂，…，d_nAnd is also used to denote a corresponding standard cylinder or standard block gauge. Here, the calibration method will be described by taking a point contact type clamper shown in fig. 4(a) as an example. The standard thickness gauge is adopted as a standard device, and the thickness value of the standard block gauge meets the condition: when the elastic beam of the clamping arm has the deflection lambda (d) at the section e_n-d₀The maximum stress value of the beam does not exceed the proportional limit of the materials used. The calibration is carried out in four steps: first, read for strain_rdPresetting an initial value

Generally, values are taken within the range of 5 mu epsilon to 20 mu epsilon, e.g.

Second, get the standard block gauge₀The movable arm is controlled by a digital controller to move, and a first clamping thimble and a second clamping thimble clamp d₀Strain reading measured by digital controller

When the movable arm stops moving, recording the current position of the movable arm as a displacement original point, and recording the current position of the fluted disc as a fluted disc zero position; thirdly, using a standard block gauge d₁，d₂…，d_nBy replacing d in turn₀Repeating the second operation and recording the corresponding strain reading

The fourth step is to

For calibration, reading e according to the length s and strain_rdIs equation (7), s is calculated:

in the formula (7), A₂And B₂Is a constant, calculated using equations (8) and (9), respectively:

in the formulae (8) and (9), n represents the number of gauge blocks, d_iRepresenting thickness values of different thickness standard thickness gauges,

is represented by_iCorresponding strain readings, i.e. calibration numbers

Both the formula (4) and the formula (9) are derived by a linear fitting method.

4) And (5) clamping and measuring. In the surface contact type as shown in FIG. 1The gripper is taken as an example to explain the operation process. For simplicity, the object is assumed to be a rigid body and the position is fixed. The operation procedure can be divided into five steps: firstly, adjusting the position of a manipulator and the distance s between two clamping surfaces by a digital controller to ensure that s is greater than the length m of an object, and the object enters between the two clamping surfaces; secondly, controlling the first driver to rotate to enable the fixed arm to move leftwards along with the sliding rack, enabling the right clamping surface to be in contact with an object, and reading when the strain is read

When the first driver is rotated, stopping the rotation of the first driver; thirdly, controlling the second driver to rotate, enabling the movable arm to move rightwards, enabling the right clamping surface to be in contact with the object, and reading when the strain is read

When the second driver is rotated, stopping the rotation of the second driver; fourthly, controlling the two drivers to rotate simultaneously to enable the movable arm and the fixed arm to move synchronously and oppositely, and reading the strain epsilon_rdObtaining

Any value of the range epsilon_rdxWhen it is, record_rdxCorresponding to epsilon_rdxStrain reading of_rfAnd a dependent origin displacement S; the fifth step is to convert epsilon_rfSubstituted by formula (4) with_rdxAnd S into equation (10):

equation (4) gives the clamping force F to which the object is subjected, and equation (10) gives the length m of the object.

Based on the measurement of the nip point distance s, the deformation of a deformed object such as a spring, rubber, or the like can be measured. Taking a compression spring as an example, the measurement procedure is divided into three steps: first, a strain reading is set

As a measurement starting point; second, the digital controller controls the clamper to clamp the bulletSpring, enabling strain reading

Take notes of

And the origin-dependent point shift S corresponding thereto^*(ii) a Thirdly, increasing the clamping force F, tracking and recording F and strain reading epsilon_rdAnd depending on the original point displacement S, calculating the deformation v of the spring according to the formula (11):

by using the measurement software, a force-deformation relation curve, namely an F-v curve, can be drawn.

Compared with the existing manipulator, the design has the following characteristics:

1. and (4) controlling the clamping force by using a clamping arm and coding screw rod combined mechanism, and measuring the distance between the clamping points. The mechanical arm has the core part of a force-deformation-displacement composite sensing mechanism consisting of a clamping arm and a coding screw rod, and the force-deformation-displacement composite sensing mechanism is matched with a driver and a digital controller to realize closed-loop control and measurement of clamping force F and clamping point distance s. The measured F value is directly indicative of the force to which the object is subjected. The measured s value directly represents the length-like sizes of the rigid object or structure, such as thickness, outer diameter, inner diameter, hole distance, space and the like; for elastic elements such as springs and the like and deformable objects such as rubber, plant fruits and the like, the deformation amount required to be measured can be calculated by s, and a relation curve of force and deformation is given by software.

2. The grip has flexible properties. The design clamps objects by the elastic force of the clamping arms, and the digital controller controls the change of the clamping force, so that the clamping mode is flexible.

3. The measurement has flexible properties. When the manipulator clamps a rigid object, if the fluted disc is controlled to rotate at a small angle, the strain reading epsilon is realized_rdContinuously changing, it can be seen that although ε_rdAnd the origin-dependent displacement S are all varied, but the length given by equation (10)The value m remains unchanged. The phenomenon is called 'flexible equal differential output', is a characteristic property of a force-deformation-displacement composite sensing mechanism consisting of the clamping arm and the coding screw rod, and is a principle basis for measuring the distance between the clamping points in the design. Varying epsilon within a certain range_rdThe measured length m remains constant and is different by_rdThe values correspond to different clamping forces. Therefore, the algorithm design of the measurement software can utilize the output property of the flexibility equal difference according to different operation objects and measurement requirements.

4. The design range of the clamping force and the measurement and control precision thereof is wider. The value range of the clamping force and the measurement resolution of the clamping force of the mechanical arm are mainly determined by the structural form, the size and the material property of the elastic beam used by the clamping arm, the design flexibility is high, the clamping arm with the force value range of 0-10N and the resolution smaller than 0.1N can be designed, and the clamping arm with the force value range of 0-5000N and the resolution smaller than 1N can also be designed.

5. The design range of the adjustment of the distance between the clamping points is wider. The adjusting range of the clamping point distance of the manipulator mainly depends on the moving distance of the movable arm, and the minimum distance is zero theoretically. Therefore, the micrometer screw rod with proper length is selected for the clamping arm-coding screw rod combined mechanism, and the required adjustment range of the distance between the clamping points can be obtained, such as 0-20 mm, 0-100 mm and 200-500 mm.

6. The resolution of the nip point spacing measurement can reach a moderate level of length measurement in the mechanical industry. The manipulator of this design, its grip point interval measurement resolution is decided by two aspects of factor in centre gripping arm and code lead screw. The displacement resolution of the clamping arm is basically the same as that of the coding screw rod in the design range of 0.1-10 microns.

Drawings

FIG. 1 is a front view of a schematic construction of the device of the present design;

FIG. 2 is a right side view of the schematic of the device construction;

FIG. 3 is a schematic diagram of a full bridge measurement circuit of the double cantilever beam sensor;

FIG. 4 is a measurement circuit of a tristate encoder, in which (a) a resistorStrain gauge [ R ]₅,R₆]Half-bridge diagram, (b) resistance strain gauge [ R ]₇,R₈]Half-bridge diagram, (c) resistance strain gauge [ R ]₉,R₁₀]Half-bridge diagram, (d) resistance strain gauge [ R ]₁₁,R₁₂]A half-bridge diagram;

FIG. 5 is a schematic diagram of a tri-state encoder architecture;

FIG. 6 is a schematic view of a clamp arm in the form of a straight beam;

in the figure: 1. guide rail seat, 2, coupler, 3, male guide rail, 4, transmission shaft, 5, boss, 6, first driver, 7, second driver, 8, left bearing support plate, 9, micrometer screw rod, 10, left bearing, 11, U-shaped guide limit groove, 12, transmission nut, 13, limit guide rod, 14, right bearing, 15, right bearing support plate, 16, movable arm, 17, fixed arm, 18, left clamping surface, 19, right clamping surface, 20, sensor support, 21, right upper cantilever beam sensor, 22, fluted disc, 23, arc tooth, 24, left lower cantilever beam sensor, 25, right lower cantilever beam sensor, 26, sliding frame, 27, female guide rail, 28, left upper cantilever beam sensor, 29, left triangular ridge, 30, upper triangular ridge, 31, right triangular ridge, 32, lower triangular ridge, 33, rectangular through hole, 34, threaded hole, 35, set screw, 36. the three-state encoder comprises a first clamping thimble, 37, a second clamping thimble, 38, a third clamping thimble, 39, a fourth clamping thimble, 40, a first clamping blade block, 41, a second clamping blade block, 42, a third clamping blade block, 43, a fourth clamping blade block, TE., a three-state encoder and a W object.

Detailed Description

The design is further explained below with reference to the drawings.

Referring to fig. 1-6, the present design is a robot that controls the clamping force to measure the distance between the clamping points. The manipulator consists of a guide rail seat 1, a sliding rack 26, a transmission shaft 4, a coding screw rod, a driver, a clamping arm and a digital controller.

The structure of the guide rail seat 1 comprises a rectangular thick base plate, a coupler 2 and a parallel male guide rail 3. The coupler 2 is fixed below the thick substrate and used for connecting the arm of the robot. The parallel male guides 3 are located on both front and rear sides of the upper surface of the thick base plate.

The structure of the sliding frame 26 comprises a rectangular bottom plate, parallel female guide rails 27 positioned at the front and rear side edges below the bottom plate, a boss 5 with a threaded through hole positioned at the left lower part of the bottom plate, a left bearing support plate 8 positioned at the left side above the bottom plate, a right bearing support plate 15 positioned above the bottom plate and close to the right side edge, and a U-shaped guide limiting groove 11 positioned on the upper surface of the bottom plate. The left bearing support plate 8 is embedded with a left bearing 10, and the right bearing support plate 15 is embedded with a right bearing 14. The left bearing 10 is in a coaxial position with the right bearing 14. The axial line of the threaded through hole on the boss 5, the axial line of the guide limiting groove 11 and the axial lines of the left bearing 10 and the right bearing 14 are all positioned in the longitudinal symmetrical plane of the parallel female guide rail 27 and are parallel to the axial line of the parallel female guide rail 27. The sliding frame 26 and the guide rail base 1 are installed together through the matching of the male guide rail 3 and the female guide rail 27.

The transmission shaft 4 comprises a threaded rod and a connecting shaft on the left side of the threaded rod, the threaded rod is installed on the sliding rack 26 through matching with a threaded through hole in the boss 5, and the connecting shaft extends out of the left side of the boss 5.

The coding screw rod consists of a micrometer screw rod 9 and a three-state coder TE.

The micrometer screw rod 9 is a step shaft with screw threads, the structure of the micrometer screw rod is divided into three sections I-II, II-III and III-IV from left to right, the sections I-II and III-IV are optical axes, the section II-III is a screw thread shaft, and the external diameter of the screw thread is larger than the diameters of the optical axes of the sections I-II and III-IV. The micrometer screw rod 9 is arranged on the sliding frame 26 through the matching of the section I-II optical axis and the left bearing 10 and the matching of the section III-IV optical axis and the right bearing 14, the section II-III threaded shaft is positioned between the left bearing support plate 8 and the right bearing support plate 15, the section I-II optical axis extends to the left side of the left bearing support plate 8, and the section III-IV optical axis extends to the right side of the right bearing support plate 15. The left end face and the right end face of the section II-III threaded shaft are respectively matched with the right end face of the left bearing 10 and the left end face of the right bearing 14, and the two matching pairs prevent the micrometer screw rod 9 from moving left and right.

The tri-state encoder TE is composed of a sensor support 20, a fluted disc 22, an upper left cantilever beam sensor 28, an upper right cantilever beam sensor 21, a lower left cantilever beam sensor 24, and a lower right cantilever beam sensor 25. The sensor holder 20 may be a rectangular frame, and four sides of the frame are sequentially provided with a rectangular portion having an axis parallel to the plane of the frame and perpendicular to the side near the corner of one sideA through hole 33 and a threaded hole 34 communicating perpendicularly with the rectangular through hole 33. The fluted disc 22 is a disk with equal thickness and the periphery of which is uniformly distributed with arc teeth 23, and the arc teeth 23 can be made in a way of embedding steel balls or by a cutting process. The number of circular arc teeth 23 is an integer multiple of 4, for example 180, 500. The four cantilever beam sensors have the same shape and size, the elastic bodies are uniform-section elastic beams or variable-section elastic beams, the roots of the four elastic beams are respectively matched with the four rectangular through holes 33 of the sensor support 20, and the four elastic beams are fixed on the upper inner wall, the right inner wall, the left inner wall and the lower inner wall of the sensor support 20 by utilizing pressing force generated by screwing the set screws 35 into the threaded holes 34. Four elastic beams are respectively stuck with a single-axis resistance strain gauge R along the axial direction of the beams at the positions close to the roots₅,R₆]、[R₉,R₁₀]、[R₁₁,R₁₂]And [ R ]₇,R₈]. The four elastic beams are respectively provided with a left triangular ridge 29, an upper triangular ridge 30, a lower triangular ridge 32 and a right triangular ridge 31 at the side close to the free end and facing the fluted disc 22. The four elastic beams are all pre-deformed by a certain amount, the tops of the four triangular convex edges are respectively kept in contact with the circular arc teeth 23 by elastic pressure generated by pre-deformation, and the specific positions of contact points are determined according to the following conditions:

a. it is assumed that the longitudinal symmetry line of the toothed disc 22 passes through the centers of the right-upper circular arc teeth and the right-lower circular arc teeth, and the horizontal symmetry line of the toothed disc 22 passes through the centers of the leftmost circular arc teeth and the rightmost circular arc teeth.

b. At this time, the left triangular ridge 29 is located on the horizontal symmetry line of the toothed disc 23 and contacts the apex of the leftmost circular tooth. The right triangular ridge 31 is located on the horizontal symmetry line of the fluted disc 22 and the upper side of the rightmost circular arc tooth and is opposite to the valley bottom between two adjacent circular arc teeth 23. The upper triangular ridge 30 and the lower triangular ridge 32 are both located on the right side of the longitudinal symmetry line of the fluted disc 23 and are respectively in contact with the right side of the right upper circular arc tooth and the right side of the right lower circular arc tooth. The distance h from the left triangular ridge 29 to the longitudinal symmetry line of the toothed disc 22_maxThe distance h from the right triangular ridge 31 to the longitudinal symmetry line of the toothed disc 23 is shown_minIndicating that the contact point of the upper triangular ridge 30 and the right upper circular arc tooth is connected to the fluted discThe distance between the horizontal symmetry line of the fluted disc 22 and the contact point of the lower triangular convex edge 32 and the circular arc teeth right below is equal to the distance between the horizontal symmetry line of the fluted disc 22 and the contact point of the lower triangular convex edge 32 and the circular arc teeth right below, and the distances are both h_midAnd (4) showing. h is_midAnd h_minAnd h_maxThere is a relationship represented by formula (1):

The fluted disc 22 is coaxially fixed on the III-IV section optical axis of the micrometer screw rod 9. The sensor carrier 20 is fixed to the upper right of the base plate of the carriage 26 and encloses the toothed disc 22 in the middle.

The driver includes a first driver 6 and a second driver 7, both of which may employ a stepping motor. The first driver 6 is arranged at the upper left part of the guide rail seat 1 and is fixedly connected with the connecting shaft of the transmission shaft 4. The second driver 7 is arranged on the left side of the left bearing support plate 8 and is fixedly connected with the optical axis of the section I-II of the micrometer screw 9.

The clamping arm consists of a movable arm 16 and a fixed arm 17, both of which are cantilever type elastic beam sensors with clamps, and the two pairs of elastic beams of the sensors are the same in material, shape and size. The elastic beam of the movable arm 16 is fixedly connected with a shaft sleeve to form an integral structure, the middle part of the shaft sleeve is embedded with a transmission nut 12, and the bottom part of the shaft sleeve is embedded with a limiting guide rod 13. The movable arm 16 is arranged on the sliding frame 26 through the matching of the transmission nut 12 and the micrometer screw 9 and the matching of the limiting guide rod 13 and the U-shaped guiding limiting groove 11. The limiting guide rod 13 is matched with the U-shaped guiding limiting groove 11, so that the movable arm 16 cannot rotate around the axis of the micrometer screw 9, and when the micrometer screw 9 rotates, the movable arm 16 is driven to move along the axis direction of the micrometer screw 9. The transmission nut 12 and the micrometer screw 9 are matched with each other, and a clearance eliminating measure is adopted to meet two requirements: firstly, theoretically, the micrometer screw rod 9 can drive the transmission nut 12 to move reversely without lag when changing the rotating direction; secondly, the rotational freedom of the axis of the drive nut 12 in the x-y plane is zero. The elastic beam of the fixed arm 17 is fixedly connected with the right bearing support plate 15 to form an integral structure. The elastic beam of the movable arm 16 and the elastic beam of the fixed arm 17 are vertically upward, and are in symmetrical positions. The elastic beam of the clamping arm has two basic structural forms:

a) the fishhook-shaped folding beam structurally comprises a long arm a-c section, a folding joint a-d section and a short arm d-e section, wherein the cross sections of the three sections are all rectangular, and the section c is a fixed end of the folding beam; the cross-sectional dimension of the sections a-d is much larger than the cross-sectional dimensions of the sections a-c and d-e, so that the sections can be regarded as rigid nodes of the folded beam. The structure of the long arm a-c section is divided into a-b section and a b-c section from top to bottom, the height H of the a-b section is greater than the height H of the b-c section₁. The section d-e of the short arm is a beam with equal section. The heights of the sections a-c of the long arm, the sections a-d of the turning joint and the sections d-e of the short arm can be equal or unequal.

A single-axis resistance strain gauge R is attached to the left and right sides of the elastic beam of the movable arm 16 along the beam axis direction at the b-c section₂And R₁The elastic beam of the fixed arm 17 is pasted with a single-shaft resistance strain gauge R along the beam axis direction at the left side and the right side of the b-c section₃And R₄Resistance strain gauge R₁、R₂、R₃、R₄Forming a full bridge measurement circuit.

The clamp holder of the clamping arm has three types of surface contact, line contact and point contact, and is selected according to the use requirement. The gripper of the fishhook-shaped folding beam is arranged at the section e of the section d-e of the short arm, for example the left gripping surface 18 on the movable arm 16 and the right gripping surface 19 on the fixed arm 17 in fig. 1, which constitute a pair of surface contact type grippers. The distance between the left clamping surface 18 and the right clamping surface 19 is indicated by s. Holders for the straight beam are provided on both left and right sides of the free end a, such as a first holding pin 36 on the movable arm 16 and a second holding pin 37 on the fixed arm 17 in fig. 6(a), which constitute a pair of point contact type holders; third clamping thimble 38 on movable arm 16 and fixed armThe fourth gripping pin 39 on 17 constitutes a pair of point contact type grippers supported outwardly. When the line of action of the clamping force of the fishhook-shaped folding beam coincides with the intersection of the longitudinal symmetry plane of the beam (x-y plane in fig. 1) and the cross section e, the zero angle of rotation of the clamp can be maintained by coordinating the structural dimensions of the beam parts so that the angle of rotation of the cross section e is equal to zero. For example, the widths b of the sections of the folded beam are equal, as shown in fig. 1; the sections b-c are of equal height to the sections d-e, i.e. h₁＝h₂H; the height H of the section a-b is more than or equal to 5H, so the section can be regarded as a rigid body. The length L of the a-c segment is the length L of the b-c segment₁5 times of (i), i.e. L is 5L₁. According to the bending theory, under the condition of small linear elastic deformation, the relation formula can be obtained:

in the formula (2), l₂Is the length of the d-e segment. As long as L, l₁And l₂Satisfying equation (2), the angle of rotation of cross-section e is equal to zero, and the left clamping surface 18 and the right clamping surface 19 in fig. 1 can maintain the zero angle of rotation.

The digital controller (not shown in the figure) is a microcomputer system with a strain signal acquisition-conditioning circuit, a driver control circuit and measurement software, and the measurement software is written according to the following method. Resistance strain gauge R₁、R₂、R₃、R₄The formed full-bridge measuring circuit is connected with the strain signal acquisition-conditioning circuit. Resistance strain gauge [ R ]₅,R₆]、[R₇,R₈]、[R₉,R₁₀]、[R₁₁,R₁₂]The strain signal acquisition-conditioning circuits are respectively connected in a half-bridge mode, and the strain readings of the four half-bridge measurement circuits measured by the digital controller are respectively used

And (4) showing. The first driver 6 and the second driver 7 are respectively connected to the driver control circuit. The digital controller is generally integrated with the control system of the robot, and can also be arranged separately.

In the present design, the encoder screw is a component with independent function, which can track and measure the displacement of the movable arm 16.

The coding screw rod works in the following way:

1) adjusting the zero position of a measuring circuit of the tri-state encoder: the digital controller controls the second driver 7 to drive the coding screw rod to rotate, and the strain reading is carried out

A continuous periodic variation occurs, the period of variation being denoted by T. The toothed disc 22 rotates one tooth at a time, i.e. one period T,

respectively completing one cycle. Tracking observations

When changing over to

To a minimum value epsilon_rminWhen the rotation of the fluted disc 22 is stopped, the resistance strain gauge R in the digital controller is adjusted₅,R₆]The balance circuit of the bridge is arranged so that

Repeating the above operations in sequence

After the zero adjustment of the four half-bridge circuits is completed, the fluted disc 22 is rotated again, and then

Are all at a minimum value of 0 and a maximum value of epsilon_rmaxBetweenCyclically, the minimum value 0 corresponds to the position of the left triangular ridge 29 or the upper triangular ridge 30 or the right triangular ridge 31 or the lower triangular ridge 32 opposite to the valley bottom between two adjacent circular-arc teeth 23, i.e. corresponds to the minimum characteristic height h_minMaximum value epsilon_rmaxCorresponding to one of the four triangular ridges in contact with the apex of the circular-arc tooth 23, i.e. corresponding to the maximum characteristic height h_max. The method for adjusting the zero position of the TE measuring circuit of the tri-state encoder is called a zero position four-step adjusting method.

2) And determining the relation between the strain reading and the rotation state of the fluted disc: after the zero adjustment of the TE measuring circuit of the three-state encoder is completed, the

numbers

1, 0 and 1/2 are respectively used for representing strain reading

Maximum value of (e)_rmaxMinimum 0 and mean 0.5 epsilon_rmax. Number 1 and maximum feature height h_maxCorrespondingly, a full value is defined. Number 0 and minimum feature height h_minAnd correspondingly, a value of zero is defined. Number 1/2 and average feature height h_midCorrespondingly, the median value is defined. Full, zero, and median values are collectively defined as strain readings

The tri-state encoded value of (1) is referred to as a tri-state value for short. Three state values 0, 1/2, 1 cyclically change with a period T as the toothed disc 22 rotates. The cyclical variation of the three-state values is used to determine the rotational state of the toothed disc 22, i.e. the rotational direction and the rotational angle of the toothed disc 22. There are a total of four different combinations of tristate values, as shown in table 1:

TABLE 1 Strain readings

Tri-state value combination of

TABLE 2 Change of tri-state values 0, 1/2, 1 during clockwise rotation of the toothed disc 22 during each cycle T.

TABLE 3 Change of tri-state values 0, 1/2, 1 during counterclockwise rotation of the toothed disc 22 during each cycle T.

The three-state values 0, 1/2, and 1 are changed in different ascending and descending ways. The eight rows of data numbered from (i) to (b), which are different from each other in pairs, are unique, wherein each row of data uniquely represents a specific rotation state of the toothed disc. For example, the row of data numbered c represents and only represents the rotation of the toothed disc in the clockwise direction through the third 1/4 cycles within one cycle T, i.e., 0.5T to 0.75T. One line of data of number five represents and only represents fluted disc edgeThe first 1/4 cycles within one cycle T, i.e., 0 to 0.25T, is rotated counterclockwise. The continuously changing strain reading is matched with the tri-state value to monitor the rotation state of the fluted disc.

3) Measurement of displacement amount of movable arm: the micrometer screw rod 9 is controlled by the numerical controller to rotate, the movable arm 16 is adjusted to a certain designated position or any position on the micrometer screw rod 9, the position is recorded as the displacement original point of the movable arm 16, and the position of the fluted disc 22 at the moment is recorded as the fluted disc zero position. The toothed disc 22 is rotated from its zero position and the movable arm 16 is displaced from the origin of displacement. The amount of displacement of the movable arm 16 with respect to the origin of displacement is represented by S, which is defined as the origin-dependent displacement, and S is calculated by equation (3):

in the formula (3), t represents the lead of the micrometer screw 9, N_cRepresenting the number of teeth, n, of the toothed disc 22_z,sRepresenting the cumulative number of teeth turned clockwise by the toothed disc 22 from its zero position, n_z,nRepresenting the cumulative number of teeth turned counterclockwise by the toothed disc 22 from its zero position, n_z,sAnd n_z,nTaking a constant positive value. n is_zRepresents n_z,sAnd n_z,nThe difference is defined as the number of active rotating teeth. n is_z,s、n_z,nAnd n_zAlso known as the tooth disc rotation parameter. n is_zAnd S is the number of generations. When the gear plate 22 rotates clockwise, the movable arm 16 moves rightward, n_zAnd the symbols of S are "-". When the gear plate 22 rotates counterclockwise, the movable arm 16 moves leftward, n_zAnd S are all "+".

The use method of the manipulator of the design is as follows:

1) the measuring line is connected. Resistance strain gauge R₁、R₂、R₃、R₄The formed full-bridge measuring circuit is connected with a digital controller, and the circuit is used for sensing and measuring force and length. For measuring force, the strain reading measured by the digital controller is epsilon_rfRepresents; for measuring length, the strain reading measured by the digital controller is epsilon_rdTo represent。

2) And (5) calibrating the force measuring system. A standard load sensor or a standard force measuring ring is generally adopted as a force value standard device, and a clamp holder on a clamping arm is used for clamping the force value standard device to calibrate a force measuring system. Taking the surface contact type clamp shown in fig. 1 as an example, in calibration, a standard load sensor or a standard force measuring ring is clamped by a left clamping surface 18 on a movable arm 16 and a right clamping surface 19 on a fixed arm 17, the movable arm 16 is controlled by a numerical controller to move, and a set of standard forces F are applied to the movable arm 16 and the fixed arm 17₁，F₂，…，F_N，(F₁＜F₂＜…，＜F_NN is a positive integer not less than 2, the value range is determined according to the requirement, for example, 2 is more than or equal to N is less than or equal to 10), and the value range is recorded by a digital controller and F₁，F₂，…，F_NCorresponding strain reading

Then is provided with

In calibration, the spring beam is at a standard force F_NThe maximum stress generated by the action must not exceed the limit of the proportion of the materials used.

3) And (5) calibrating a length measuring system. First, a length standard is selected according to the type of the holder, and a standard diameter gauge and a standard thickness gauge are commonly used length standards. The standard diameter gauge is a group of standard cylinders with different diameters and is used for a line contact type holder and a surface contact type holder. The standard thickness gauge is a group of standard thickness block gauges with different thicknesses, and is used for point contact type clampers, and also can be used for line contact type clampers and surface contact type clampers. The thickness value of each standard cylinder or standard block gauge is sequentially expressed by d₀，d₁，d₂…，d_nIs represented by d₀＜d₁＜d₂,...,＜d_nAnd n represents the number of standard cylinders or standard block gauges, and is generally 2 ≦ n ≦ 10 (e.g., n ≦ 7). d₀，d₁，d₂，…，d_nAlso denoted the corresponding standard cylinder or standard block gauge. The calibration method will be described by taking the point contact type clamper shown in fig. 6(a) as an example. The standard thickness gauge is adopted as a standard device, and the thickness value of the standard block gauge meets the condition that: when the elastic beam of the clamping arm has the deflection lambda (d) at the section e_n-d₀The maximum stress of the beam does not exceed the proportional limit of the materials used. The calibration is carried out in four steps: first, read for strain_rdPresetting an initial value

Second, get the standard block gauge₀The digital controller controls the movable arm 16 to move, and the first and second holding pins 36 and 37 hold the movable arm d₀When reading strain

When the movable arm 16 stops moving, the current position of the movable arm 16 is recorded as the original displacement point, and the current position of the fluted disc 22 is recorded as the fluted disc zero position; thirdly, using a standard block gauge d₁，d₂…，d_nBy replacing d in turn₀Repeating the second step to record corresponding strain readings

The fourth step is to

For calibration, reading e according to the length s and strain_rdThe length s is calculated by equation (7):

is represented by_iCorresponding strain readings, i.e. calibration numbers

Both the above formula (4) and formula (9) are derived by linear fitting. When the force measuring system calibration and the length measuring system calibration are carried out, a force value standard device positioning device and a length standard device positioning device can be designed so as to be convenient for correctly installing the two standard devices.

4) And (5) clamping and measuring. The manipulator is connected with the robot through a coupler 2, and clamping measurement operation is carried out under the control of a digital controller. The operation will be described by taking the surface contact type clamper shown in fig. 1 as an example. For simplicity, the object W is assumed to be a rigid body and fixed in position. The operation process comprises five steps: firstly, adjusting the position of a manipulator and the distance s between two clamping surfaces to ensure that s is greater than the length m of an object W, and the object W enters between the two clamping surfaces; in the second step, the first driver 6 is controlled to rotate, so that the fixed arm 17 moves leftwards along with the sliding frame 26, the right clamping surface 19 contacts with the object W, and when the strain reading is carried out

When the rotation of the first driver 6 is stopped; thirdly, controlling the second driver 7 to rotate, so that the movable arm 16 moves rightwards, the right clamping face 19 is contacted with the object W, and when the strain reading is carried out

When the rotation of the second driver 7 is stopped; fourthly, controlling the first driver 6 and the second driver 7 to rotate simultaneously, so that the movable arm 16 and the fixed arm 17 synchronously move towards each other, and when the strain reading epsilon is_rdObtaining

Any value of the range epsilon_rdxWhen it is, record_rdxCorresponding to epsilon_rdxStrain reading of_rfAnd a dependent origin shift S; the fifth step is to convert epsilon_rfSubstituted by formula (4) with_rdxAnd S into equation (10):

equation (4) gives the clamping force F to which the object W is subjected, and equation (10) gives the length m of the object W.

For a deformed object such as a spring, rubber, or the like, the amount of deformation can be measured. Taking a compression spring as an example, a surface contact type clamper is used. The measuring procedure is divided into three steps: first, a strain reading is set

For example provided with

As a measurement starting point; secondly, the digital controller controls the clamper to clamp the spring to read the strain

Take notes of

The indentation deformation can be measured for articles such as polymer material products, plant fruits, animal organs and the like. Assuming that the object W is a spherical body or a regular hexahedral body, the depth of pressing of the holding pin into the object W is measured using the holding pin shown in fig. 6 (a). First, a strain reading is set

For example provided with

As a measurement starting point. During measurement, the gripper is controlled to clamp the object W, and strain reading is firstly carried out

Take notes of

And the origin-dependent point shift S corresponding thereto^*Then increasing the clamping force F, tracking and recording F, epsilon_rdAnd calculating the penetration depth delta according to equation (12) based on the origin point displacement S:

using the measurement software, a force-indentation depth relationship curve, i.e., an F-delta curve, can be plotted. F. And v, delta and S can be used as control parameters, so that the manipulator can be controlled in different modes.

Claims

1. The manipulator is characterized by comprising a guide rail seat, a sliding rack, a transmission shaft, a coding screw rod, a driver, a clamping arm and a digital controller;

the guide rail seat structurally comprises a base plate, a parallel male guide rail positioned at the top of the base plate, and a coupler positioned below the base plate and used for connecting a robot arm;

the structure of the sliding rack comprises a bottom plate, a parallel female guide rail positioned below the bottom plate, a boss with a threaded through hole positioned at the left lower part of the bottom plate, a left bearing support plate and a right bearing support plate which are respectively embedded with bearings at the left side and the right side above the bottom plate, and a U-shaped guide limiting groove positioned on the upper surface of the bottom plate; the two bearings are in a coaxial position; the axial line of the threaded through hole on the boss, the axial line of the guide limiting groove and the axial lines of the two bearings are all positioned in the longitudinal symmetrical plane of the parallel female guide rail and are parallel to the axial line of the parallel female guide rail; the sliding frame and the guide rail seat are installed together through the matching of the male guide rail and the female guide rail;

the transmission shaft structurally comprises a threaded section and a connecting shaft on the left side of the threaded section, the connecting shaft is arranged on the sliding rack through the matching of the threaded section and a threaded through hole on the lug boss, and the connecting shaft extends to the left side of the lug boss;

the coding screw rod consists of a micrometer screw rod and a three-state coder;

the micrometer screw rod is a step shaft with a thread, the structure of the micrometer screw rod is divided into three sections I-II, II-III and III-IV from left to right, the sections I-II and III-IV are optical axes, the section II-III is a threaded shaft, and the outer diameter of the thread is larger than the diameters of the optical axes of the sections I-II and III-IV; the micrometer screw rod is arranged on the sliding frame through the matching of the section I-II optical axis and the section III-IV optical axis with the bearings on the two bearing support plates, the section II-III threaded shaft is positioned between the two bearing support plates, the section I-II optical axis extends to the left side of the left bearing support plate, and the section III-IV optical axis extends to the right side of the right bearing support plate;

the tri-state encoder consists of a fluted disc, a sensor bracket and four cantilever beam sensors; the fluted disc is a disc with arc teeth uniformly distributed on the periphery, and is coaxially fixed on the optical axis of the III-IV section of the micrometer screw rod, and the number of teeth of the fluted disc is an integral multiple of 4; the sensor bracket is a rectangular frame, is fixed at the upper right of the bottom plate of the sliding rack and surrounds the fluted disc in the middle; the four cantilever beam sensors are respectively provided with a left triangular ridge, an upper triangular ridge, a right triangular ridge and a lower triangular ridge at the positions close to the free ends and towards one side of the fluted disc, and resistance strain gauges R are respectively attached at the positions close to the beam roots and along the axial direction of the beam₅,R₆、R₇,R₈、R₉,R₁₀And R₁₁,R₁₂(ii) a The four cantilever beam sensors are respectively fixed on the inner walls of four sides of the sensor support and have a certain amount of pre-deformation, the elastic pressure generated by the pre-deformation enables the tops of the four triangular convex edges to respectively keep contact with the circular arc teeth on the periphery of the fluted disc, and the specific positions of the contact points are determined according to the following conditions:

a. the longitudinal symmetry line of the fluted disc passes through the centers of the arc teeth right above and the arc teeth right below, and the horizontal symmetry line of the fluted disc passes through the centers of the arc teeth at the leftmost end and the arc teeth at the rightmost end;

b. at this time, the left triangular ridge is located on the toothThe top point of the circular arc tooth at the leftmost end is contacted with the horizontal symmetrical line of the disk; the right triangular ridge is positioned on the horizontal symmetry line of the fluted disc and the upper side of the rightmost circular arc tooth and is opposite to the valley bottom between the two adjacent circular arc teeth; the upper triangular ridge and the lower triangular ridge are both positioned on the right side of the longitudinal symmetry line of the fluted disc and are respectively contacted with the right side of the right upper arc tooth and the right side of the right lower arc tooth; h is used for distance from left triangular ridge to longitudinal symmetric line of fluted disc_maxThe distance from the right triangular ridge to the longitudinal symmetry line of the fluted disc is represented by h_minThe distance from the contact point of the upper triangular ridge and the right upper arc tooth to the horizontal symmetry line of the fluted disc and the distance from the contact point of the lower triangular ridge and the right lower arc tooth to the horizontal symmetry line of the fluted disc are all represented by h_midRepresents; h is_midAnd h_minAnd h_maxThere is a relationship represented by formula (1):

h_min、h_midand h_maxCollectively called the characteristic height, where h_minIs the minimum feature height, h_midIs the average feature height, h_maxIs the maximum feature height;

the driver comprises a first driver and a second driver; the first driver is arranged at the upper left part of the guide rail seat and is connected with the connecting shaft of the transmission shaft; the second driver is arranged on the left side of the left bearing support plate and is connected with the optical axis of the section I-II of the micrometer screw rod;

the clamping arm consists of a movable arm and a fixed arm, and both the movable arm and the fixed arm are cantilever type elastic beam sensors with clamps; the elastic beam of the movable arm is fixedly connected with a shaft sleeve to form an integral structure, the middle part of the shaft sleeve is embedded with a transmission nut, and the bottom part of the shaft sleeve is embedded with a limiting guide rod; the movable arm is arranged on the sliding rack through the matching of the transmission nut and the micrometer screw rod and the matching of the limiting guide rod and the U-shaped guiding limiting groove; the movable arm cannot rotate around the axis of the micrometer screw rod, and when the micrometer screw rod rotates, the movable arm is driven to move along the axis direction of the micrometer screw rod; the elastic beam of the fixed arm is fixed with the right bearing support plateAre connected into an integral structure; the movable arm and the fixed arm are vertically upward and are in symmetrical positions; resistance strain gauges R are respectively adhered to the left side and the right side of the elastic beam of the movable arm close to the root part along the axis direction of the beam₂And R₁The elastic beam of the fixed arm is respectively stuck with a resistance strain gauge R along the beam axis direction at the left side and the right side close to the root part₃And R₄Resistance strain gauge R₁、R₂、R₃、R₄Forming a full-bridge measuring circuit; the elastic beam of the clamping arm has the following two basic structural forms:

a) the fishhook-shaped folding beam structurally comprises a long arm a-c section, a folding joint a-d section and a short arm d-e section, wherein the cross sections of the three sections are all rectangular, the section c is a fixed end of the folding beam, the a-d section is a rigid joint of the folding beam, and the section d is a fixed end of the short arm d-e section; the structure of the long arm a-c section is divided into a-b section and a b-c section from top to bottom, the height H of the a-b section is greater than the height H of the b-c section₁(ii) a The section d-e of the short arm is a beam with equal section;

b) the structure of the straight beam is divided into a section a-b and a section b-c from top to bottom, the height H of the section a-b is greater than the height H of the section b-c, the section c is a fixed end of the beam, and the section a is a free end of the beam;

the clamp holder of the clamping arm is in surface contact, line contact and point contact; the holder of the fishhook-shaped folding beam is arranged on the section e of the section d-e of the short arm and meets the zero-turning angle condition; the zero rotation angle condition means that: when the action line of the clamping force is superposed with the intersecting line of the longitudinal symmetrical surface of the folded beam and the cross section e, the corner of the cross section e and the corner of the clamp are both zero; the clamp holders of the straight beam are arranged on the left side and the right side of the free end a;

the digital controller is a microcomputer measurement and control system with a strain signal acquisition-conditioning circuit, a driver control circuit and measurement software;

the coding screw rod is used for measuring the displacement of the movable arm, and the measuring mode is as follows:

1) adjusting the zero position of the circuit: the digital controller controls the second driver to rotate, the micrometer screw rod and the fluted disc rotate along with the second driver, and the digital controller measures the strain readings of the four half-bridge measuring circuits of the tri-state encoder

The continuous periodic change is generated, and the change period is represented by T; each time the toothed disc rotates by one tooth, i.e. one period T,

respectively completing a cycle; tracking observations

When changing over to

To a minimum value epsilon_rminWhen the gear disc stops rotating, the resistance strain gauge R on the digital controller is adjusted₅,R₆The balance circuit of the bridge being in a balanced state, i.e.

Repeating the above operations in sequence

Take the minimum value epsilon_rminWhile, the resistance strain gauge R is adjusted₇,R₈、R₉,R₁₀And R₁₁,R₁₂The balance circuit of the bridge is arranged so that

After the zero adjustment of the four half-bridge measuring circuits is completed according to the method, the fluted disc is rotated, and then

Are all at a minimum value of 0 and a maximum value of epsilon_rmaxCyclically change between; the minimum value 0 corresponds to the position of the triangular ridge opposite to the valley bottom between two adjacent circular arc teeth, namely the minimum valueHeight h of characteristic_min(ii) a Maximum value epsilon_rmaxCorresponding to the triangular ridge at the point of contact with the tip of the circular arc, i.e. to the maximum feature height h_max(ii) a The method for adjusting the zero position of the measuring circuit of the tri-state encoder is called a zero position four-step adjusting method;

2) and determining the relation between the strain reading and the rotation state of the fluted disc: after the zero adjustment of the measuring circuit of the three-state encoder is completed, the numbers 1, 0 and 1/2 are respectively used for representing strain reading

Maximum value of (e)_rmaxMinimum 0 and mean 0.5 epsilon_rmax(ii) a Number 1 and maximum feature height h_maxCorrespondingly, defining as a full value; number 0 and minimum feature height h_minCorrespondingly, a value of zero is defined; number 1/2 and average feature height h_midCorrespondingly, defining the median value; full, zero, and median values are collectively defined as strain readings

The tri-state encoding value of (1) is called tri-state value for short; when the fluted disc rotates, the three-state values 0, 1/2 and 1 change circularly according to the period T; the cyclic change of the three-state values is used for determining the rotation state of the fluted disc, namely the rotation direction and the rotation angle of the fluted disc;

3) measurement of displacement amount of movable arm: adjusting the movable arm to a certain designated position or any position on the micrometer screw rod by using a digital controller, recording the position as the displacement original point of the movable arm, and recording the position of the fluted disc at the moment as the fluted disc zero position; the fluted disc is enabled to start to rotate from the fluted disc zero position, and the movable arm is displaced from the displacement original point; the amount of displacement of the movable arm with respect to the origin of displacement is represented by S, and defined as origin-dependent displacement, and S is calculated by equation (3):

in the formula (3), t represents the lead of the micrometer screw, N_cIndicating the number of teeth of the toothed disc, n_z,sRepresenting the cumulative number of teeth, n, rotated clockwise by the toothed disc from its zero position_z,nRepresenting the cumulative number of teeth, n, rotated by the toothed disc counterclockwise from its zero position_z,sAnd n_z,nTaking a positive value constantly; n is_zRepresents n_z,sAnd n_z,nThe difference, defined as the number of active rotating teeth; n is_z,s、n_z,nAnd n_zAlso known as the tooth disc rotation parameter; n is_zAnd S is the number of generations; when the fluted disc rotates clockwise, the movable arm moves rightwards, n_zAnd the symbols of S are both "-"; when the fluted disc rotates anticlockwise, the movable arm moves leftwards, n_zAnd the symbols of S are both "+";

the use method of the manipulator comprises the following steps:

1) measuring line connection; resistance strain gauge R₁、R₂、R₃、R₄The formed full-bridge measuring circuit is connected with a digital controller, and the circuit is used for sensing and measuring force and sensing and measuring the distance between clamping points; during measuring force, strain reading measured by digital controller is epsilon_rfRepresents; when the distance between the clamping points is measured, the strain reading measured by the digital controller is epsilon_rdRepresents;

2) calibrating a force measuring system; calibrating the force measuring system by adopting a force value standard; the numerical controller controls the clamping force value standard device of the clamping arm to apply a group of standard forces F to the clamping arm₁，F₂，…，F_N，(F₁＜F₂＜…，＜F_NN is a positive integer of not less than 2), and F₁，F₂，…，F_NCorresponding strain reading

To be provided with

For calibration, force F and strain reading ε_rfIs equation (4), calculates F:

3) Calibrating a length measuring system; calibrating the length measuring system by adopting a length standard device; the standard device comprises a standard diameter gauge and a standard thickness gauge, wherein the standard diameter gauge is a group of standard cylinders with different diameters, and the standard thickness gauge is a group of standard thickness block gauges with different thicknesses; the standard length values of the standard are sequentially used as d₀，d₁，d₂，…，d_nIs represented by d₀＜d₁＜d₂,...,＜d_nN represents the number of standard cylinders or standard block gauges; d₀，d₁，d₂，…，d_nAlso a standard cylinder or a standard block gauge; the calibration procedure is divided into four steps: first, read for strain_rdPresetting an initial value

Taking the value in the range of 5 mu epsilon-20 mu epsilon; second, take d from the standard₀Controlling the movable arm grip d₀When reading strain

When the movable arm stops moving, recording the current position of the movable arm as a displacement original point, and recording the current position of the fluted disc as a fluted disc zero position; third step, with d₁，d₂…，d_nBy replacing d in turn₀Repeating the second step and recording the corresponding strain reading

The fourth step is to

For the calibration number, the length is calculated according to (7), namely the clamping point spacing s:

in the formulae (8) and (9), n represents the number of standard cylinders or standard thickness gauge blocks, d_iWhich indicates a different value of the standard length,

is represented by_iCorresponding calibration number

4) Clamping and measuring; the length of the rigid object is measured, and the operation process comprises five steps: firstly, a digital controller controls a second driver to adjust the interval of the clampers and enables objects to enter a clamping space; secondly, controlling the first driver to rotate to enable the fixed arm to move leftwards along with the sliding rack to be in contact with the object, and when the strain is read

When the first driver is rotated, stopping the rotation of the first driver; thirdly, controlling the second driver to rotate, enabling the movable arm to move rightwards to contact with the object, and reading when the strain is read

When the second driver is rotated, stopping the rotation of the second driver; fourthly, controlling the first driver and the second driver to rotate simultaneously to enable the movable arm and the fixed arm to move oppositely, and when the strain reading epsilon is carried out_rdObtaining

Specified or any value epsilon of the range_rdxWhen it is, record_rdxCorresponding to epsilon_rdxStrain reading of_rfAnd a dependent origin displacement S; the fifth step is to convert epsilon_rfCalculating the clamping force F by substituting formula (4) to obtain_rdxAnd S-substituted equation (10) calculating the length m of the object:

and measuring the deformation of the deformed object by measuring the distance s between the clamping points.