CN112504957B - Method for testing friction characteristics of fingers on deterministic texture surface - Google Patents
Method for testing friction characteristics of fingers on deterministic texture surface Download PDFInfo
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- CN112504957B CN112504957B CN202011207019.5A CN202011207019A CN112504957B CN 112504957 B CN112504957 B CN 112504957B CN 202011207019 A CN202011207019 A CN 202011207019A CN 112504957 B CN112504957 B CN 112504957B
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Abstract
The invention relates to a method for testing friction characteristics of a finger on a deterministic texture surface, which comprises the following steps: screening the subject in accordance with the requirements, wherein the finger of the subject is in partial contact with the deterministic texture surface; calculating the real contact area of the fingertip skin and the deterministic texture surface, and analyzing the change rule of the adhesive friction force along with a normal load value, the distance between ridges, the width of the ridges and the radius of the index finger of the subject; determining test variables as normal load value, width and height of ridge; setting an aluminum finger clamp, and building a test system according to the aluminum finger clamp, the sample ridge size and test variables; loading the fingertip of the subject with a load, and acquiring the friction force and the contact force of the contact section and the position information of the sample; and acquiring friction force data of a contact surface in the contact process, acquiring a basis for analyzing the average fluctuation degree of the friction force in the touch process, and combining the basis with a change rule of the adhesive friction force to obtain an analysis test result of the friction force of the finger on the deterministic texture surface.
Description
Technical Field
The invention relates to the field of finger friction tests, in particular to a test method of friction characteristics of fingers on deterministic texture surfaces.
Background
The human fingertip consists of nails, dermis, subcutaneous tissue, phalanges and epidermis, and has mechanoreceptors with different functions and structures and a large amount of nerve tissues, the physiological structure is complex and changeable, and the touch perception effect of the human fingertip is closely related to the age, sex, occupation and the like of a subject. From the biomechanical aspect, when a finger contacts an external object and generates relative motion, the skin of the finger generates mechanical deformation such as compression, stretching and the like, and mechanoreceptors positioned in the deep layer of the skin are induced to generate corresponding action potentials, and the pulse signals containing the physical characteristics of the surface of the object are transmitted to the cerebral cortex of the brain through a nervous system, so that feel is generated to sense the physical geometrical characteristics such as hardness, geometric shape, surface texture and the like of the external world. The research of the finger friction touch sense perception mechanism can provide data support and theoretical basis for the design and preparation of bionic skin, bionic finger and disabled artificial limbs.
In fact, human touch is not a simple process of converting physical characteristics into electrical signals through skin, and due to the complex physiological structure of fingers, mechanical deformation such as inlaying, shearing, squeezing and collision is complex in the finger contact process, and in addition, the external environment and the change of physical parameters in the contact process lead to the characteristics of complexity, interdigitability and randomness in finger contact, and the finger friction sensing process is complicated and difficult to imitate.
Numerous researchers at home and abroad conduct comprehensive researches on finger contact, the researches try to clarify finger contact characteristics from the aspects of experiments and theories, but because of the random texture surfaces adopted by the current touch objects, the influence of the sizes of textures on the finger friction characteristics is difficult to quantitatively discuss, and the actions of exploring the textures of the finger movements are easy to be interfered by human factors because of the fact that the samples are usually not moved, so that the reliability and the repeatability of the experiments are low. In order to overcome the interference of human factors, some researches adopt simulated fingers to replace human fingers, so that the persuasion of data is weaker, and in addition, the accidental data cannot be avoided by a test result processing method. Therefore, the current experimental study still cannot well reveal the finger friction touch sensing mechanism, so that the humanoid robot has skin to obtain touch feeling, which is always a great challenge for the robot research and development work, particularly the research on friction characteristics, and has a plurality of barriers.
Disclosure of Invention
Aiming at the problems, the invention aims to provide a method for testing the friction characteristics of fingers on deterministic texture surfaces, which can effectively avoid the interference of human factors, enhance the reliability and repeatability of tests, avoid the accidental data, and provide more reliable test basis for the development of human-like robot skin and the touch simulation design of intelligent robots.
In order to achieve the above purpose, the present invention adopts the following technical scheme: a method of testing a deterministic texture surface friction characteristic of a finger, comprising the steps of:
1) Obtaining a value range of the radius of the index finger of the subject according to a pre-determined normal load value and the set distance and height of the sample ridges, and screening the subject meeting the requirements according to the value range, wherein the finger of the subject is in partial contact with the deterministic texture surface;
2) According to the influence factors of the adhesive friction force in the partial contact state, calculating the real contact area of the fingertip skin and the deterministic texture surface, and analyzing the change rule of the adhesive friction force along with the normal load value, the ridge spacing, the ridge width and the index finger radius of the subject according to the obtained real contact area result;
3) According to the influence factors of the adhesive friction force, determining the normal load value, the width and the height of the ridge as test variables, and determining whether a lubricating oil medium is added as the test variables;
4) According to the distance, the height and the width of the sample ridges, two groups of samples of W groups and N groups are processed by adopting 3D printing;
5) According to the radius of an index finger of a subject and the contact angle of a set fingertip and the surface of a sample being 30 degrees, setting an aluminum finger clamp according to the structural characteristics of an adapter of the UMT Tribolab testing machine, and building a test system according to the aluminum finger clamp, the size of a sample ridge and test variables;
6) Loading the fingertip of the subject, controlling the movement of the sample, enabling the fingertip skin to interact with the surface of the sample, and acquiring the friction force and the contact force of the contact section and the position information of the sample;
7) And acquiring friction force data of a contact surface in the whole contact process, acquiring and analyzing a basis of average fluctuation degree of friction force in the touch process according to the friction force data, and combining the basis with a change rule of adhesive friction force to obtain an analysis test result of the friction force of the finger on the deterministic texture surface.
Further, the change rule of the adhesion friction force is as follows: increasing the normal load increases the adhesion friction; the larger the width of the ridge, the greater the adhesion force; adding lubricating oil medium reduces the adhesive friction; increasing the pitch of the ridges reduces the adhesive friction.
Further, when the influence of the normal load on the friction perception of the subject is studied, a W group of samples are selected as a touch object, and the normal load is sequentially set to 0.5, 1, 1.5 and 2N to simulate the touch force of the finger contacting the object.
Further, when researching whether the influence of a lubricating oil medium on friction perception of a subject exists or not, selecting a W group sample as a touch object, coating lubricating oil on the surface of a finger for testing, collecting a friction force result in the test process, comparing and analyzing the friction force result with the friction force result obtained when the finger is not coated with the lubricating oil and other contact parameters are set to be the same, respectively taking peak-valley value, average value, variance, standard deviation and fluctuation period data of a curve of the friction force changing along with time, and comparing the difference of the two groups of data, thereby analyzing the influence of the lubricating oil on the friction force result; other contact parameters are other contact parameters F N The spacing λ and width ω of the sample ridges, and the radius R of the subject's finger.
Further, when researching the influence of the width of the sample surface ridge on the friction perception of a subject, selecting W groups of samples and N groups of samples as touch objects, wherein the width omega of the W groups of sample ridges is larger than N groups of samples, comparing friction force results obtained when the fingers are not smeared with lubricating oil and other contact parameters are set to be the same, respectively taking peak-valley value, average value, variance, standard deviation and fluctuation period data of a curve of the friction force changing along with time, and comparing the differences of the two groups of data, thereby analyzing the influence of the lubricating oil on the friction force results; other contact parameters are other contact parameters F N The spacing λ and width ω of the sample ridges, and the radius R of the subject's finger.
Further, the basis acquisition method of the average fluctuation degree of the friction force comprises the following steps: the peak value and the trough value of the curve change period caused by the ridges of the sample in the curve of the friction force data obtained by each test along with the time change are subjected to difference value, the difference values are ordered according to the size, the change period of the curve corresponding to the 5 difference values in the middle is taken, and the periodThe corresponding friction peak value is F X1 ，F X2 ,F X3 ,F X4 ,F X5 And a friction trough value of F X1 ’,F X2 ’,F X3 ’,F X4 ’,F X5 ' average value F of the difference between the peak value and the trough value XM1 The method comprises the steps of carrying out a first treatment on the surface of the The same test was repeated three times, and the average values obtained in the other two times were F XM1 ' and F XM1 ", the average value is taken again according to the times of the test to obtain the total average value F XM2 F is to F XM2 As a basis for analyzing the average fluctuation degree of friction force in the touch process.
Further, the analysis test result of the friction force of the finger on the deterministic texture surface is obtained by combining the change rule of the adhesive friction force with the basis: in the process of contact between fingertip skin and deterministic texture surface, friction force periodically fluctuates along with time, and the change of average fluctuation degree is consistent with the change rule of adhesive friction component, and at the moment, the adhesive friction component takes the dominant role; inconsistent, the average fluctuation degree of the friction force can be increased along with the increase of the distance, and the plow friction component plays a dominant role at the moment, so that the fluctuation degree of the total friction force is increased; when the finger skin slides over the rectangular ridge, friction force F is generated f Mainly by the adhesive friction component F a Plow friction component F p And the friction force reduction amount DeltaF generated by elastic energy recovery deformation: f (F) f ＝F a +F p ΔF, adhesive friction component F a As a main friction mechanism, the total friction force in the process of touching the deterministic texture by a finger can not be measured through a test, and the change of the adhesion friction component is deduced through theory, so as to infer the plow friction component F p And the change rule of the friction force reduction delta F corresponding to the friction force reduction delta F is adopted, and finally the friction mechanism of the finger and the deterministic texture surface is obtained.
Further, the UMT Tribolab tester comprises a tester body, a Z-axis, a test suspension, an elevating block, a three-dimensional force sensor, an adapter, an aluminum finger clamp, a sample and a linear motion module; the top of the tester main body is provided with the Z shaft which is driven by a motor to move up and down, and the end part of the Z shaft is provided with the test suspension; the heightening block is clamped at the bottom of the test suspension in a clamping way, the lower part of the heightening block is connected with the three-dimensional force sensor through a bolt, and the adapter is fixed on the three-dimensional force sensor through a bolt; the lower part of the adapter is clamped with the aluminum finger clamp through a bolt, the adapter is positioned below the aluminum finger clamp, the linear motion module is arranged on the ring seat of the main body of the testing machine, and the sample is arranged on the linear motion module.
Further, the aluminum finger clamp comprises a pre-clamp fastener, a clamp body, a finger pre-tightening bolt and a pre-tightening bolt adjusting groove; the middle part of the clamp body is provided with a sleeve which is used for accommodating fingers of a subject; the upper part of the fixture body is provided with the pre-fixture fastener which is clamped by the adapter and then is arranged on the UMT Tribolab tester; the side walls at two sides of the clamp body are respectively provided with the pre-tightening bolt adjusting grooves, the finger pre-tightening bolts are arranged in the pre-tightening bolt adjusting grooves and can move up and down in the pre-tightening bolt adjusting grooves to clamp fingers of a subject.
Further, the sample is stuck on the linear motion module through double faced adhesive tape; the sample is composed of a plurality of ridges which are arranged at intervals, and the cross section of each ridge is rectangular.
Due to the adoption of the technical scheme, the invention has the following advantages: 1. according to the invention, the height, the spacing and the loading range of the normal load of the force of the ridge on the sample are selected according to the friction mechanism of the fingertip, so that the contact state of the finger and the sample is partial contact. On the premise, the main friction mechanism, namely the influence factors of the adhesive friction force, are a normal load value, the width, the height and the spacing of the ridges, whether a lubricating oil medium is added to a friction interface or not, and the design of the width of the ridges on the sample and the design of test variables are further determined. 2. According to the invention, the normal load value, the width and the spacing of the ridges are substituted into a solving formula of the real contact area, so that the change rule of the adhesive friction force is obtained, and a theoretical basis is provided for the rule of the total friction force obtained by the test. 3. UMT-based Tribolab frictional wear healdThe testing machine establishes a friction force measuring system, and all subsystems of the Tribolab, including a driving device, an environment controller, a programming test system and a real-time monitoring control system are monitored and controlled by upper computer software, so that the contact force and the friction force of fingertip skin and the surface of a sample can be monitored in real time. 4. Compared with a self-made friction force measuring device, the invention saves time and is convenient, error and vibration can be reduced, and the reliability of data is ensured. 5. According to the invention, the linear motion module of UMT Tribolab is selected, and the mode of uniform linear motion of the sample is adopted, so that the interference of human factors can be reduced to a great extent. 6. The aluminum finger clamp adopted by the invention can ensure that the finger of each subject keeps the position and the angle in the experimental process, can greatly reduce the interference of human factors and ensures that the experiment has repeatability. 7. Because the physiological structure and the surface morphology of the index finger of each subject are not consistent, and although the interference of human factors is reduced by various designs, the interference is unavoidable, so that the accidental test result is easily caused by using the data analysis friction force change rule of two specific points of a single test of a single subject. The invention adopts the F XM2 As a basis for analyzing the average fluctuation degree of friction force in the touch process, each F XM2 All the 10 points of each test of six subjects are involved, so that the accidental test results can be avoided to a great extent, and the rule obtained by test analysis is more convincing.
Drawings
FIG. 1 is a schematic flow chart of a test study method of the invention.
FIG. 2 is a schematic view of the structure of the test stand of the present invention.
FIG. 3 is a schematic view of the structure of a test sample according to the present invention.
Fig. 4 is a schematic view of the structure of the aluminum finger grip of the present invention.
FIG. 5 is a schematic diagram of the composition of the test system of the present invention.
Fig. 6 is a typical plot of friction force versus time for the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention more clear, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. It will be apparent that the described embodiments are some, but not all, embodiments of the invention. All other embodiments, which are obtained by a person skilled in the art based on the described embodiments of the invention, fall within the scope of protection of the invention.
In the description of the present invention, it should be understood that the directions or positional relationships indicated by the terms "upper", "lower", "inner", "outer", etc. are based on the directions or positional relationships shown in the drawings, are merely for convenience of description and simplification of the description, and do not indicate or imply that the apparatus or element in question must have a specific orientation, be constructed and operated in a specific orientation, and thus should not be construed as limiting the present invention.
As shown in fig. 1, the present invention provides a method for testing the friction characteristics of a finger on a deterministic texture surface, in which the adhesion friction is the main friction mechanism of the finger contacting the deterministic texture surface, where the deterministic texture surface refers to a surface textured by ridges with rectangular cross sections, and the adhesion friction is positively correlated with the real contact area, and the contact state determines the solving formula of the real contact area of the finger and the sample surface, so that the contact state is determined first. The test method of the invention comprises the following steps:
1) Obtaining a value range of the radius of the index finger of the subject according to a pre-determined normal load value and the set distance and height of the sample ridges, and screening the subject meeting the requirements according to the value range, wherein the finger of the subject is in partial contact with the deterministic texture surface;
the method comprises the following steps: in order to simplify the problem, only the friction characteristics of the finger tip skin in a partial contact state with the deterministic texture surface are researched, normal load values applied to the finger are required to be determined to be 0.5N, 1.0N, 1.5N and 2.0N according to empirical values, the distances between ridges on the sample surface are respectively 4.8mm, 5.8mm, 6.8mm, 7.8mm and the heights of the ridges are respectively 0.8mm, the three terms are substituted into a contact state judgment formula, the value range of the radius of the index finger of a subject can be finally determined, six healthy people with ages of 24-26 years old are selected as the subject according to the range, and the radius of the index finger of the person is used for realizing the partial contact between the finger and the sample surface.
Wherein, the contact state judging formula is:
wherein D is the height of the ridge, E * Is an effective Young's modulus, a known amount; f (F) N For normal load values, R is the subject finger radius and λ is the sample ridge spacing.
When x is<1, the fingertip skin is in partial contact with the sample. From the above formula, x and normal load value F N The distance lambda between the ridges is positively correlated with the radius R of the finger of the subject, and the value of the distance lambda between the ridges and the radius R is negatively correlated with the radius R of the finger of the subject, and the value range of the distance lambda between the ridges and the radius R of the finger of the subject is substituted into the value of the distance lambda between the ridges and the radius R of the finger of the subject. For example: when the normal load is F N When the contact state is in a critical state, namely x=1, when the distance between the ridges is=0.5N and λ=4.8, the minimum index finger radius meeting the partial contact is 4.9564mm, at the moment, the index finger radius of a subject requiring to participate in the test is larger than 4.9564mm, when the normal load value or the sample changes, the value range of the index finger radius is also determined according to the method, and finally the intersection of the ranges is obtained, so that the value range of the index finger radius of the subject can be finally determined.
2) According to the influence factors of the adhesive friction force in the partial contact state, calculating the real contact area of the fingertip skin and the deterministic texture surface, and analyzing the change rule of the adhesive friction force along with the normal load value, the ridge spacing, the ridge width and the index finger radius of a subject according to the obtained real contact area result, so as to prepare for the change rule of the friction force obtained by an analysis test;
the calculation formula of the real contact area S is:
where ω is the width of the sample ridge; normal load value F during contact of finger with sample N The distance lambda and width omega of the sample ridges, and the radius R of the subject's finger are substituted into the formula, different contact parameters (F N λ, ω, R) sets the true contact area of the fingertip skin with the sample.
The change rule of the adhesive friction force is as follows: increasing the normal load increases the adhesion friction; the larger the width of the ridge, the greater the adhesion force; adding lubricating oil medium reduces the adhesive friction; increasing the ridge spacing reduces the adhesive friction;
wherein, the influencing factors of the adhesive friction force comprise a normal load value, the interval between ridges, the radius of an index finger of a subject and the width of the ridges; wherein the normal load value, the pitch of the ridges, and the radius of the index finger of the subject are determined, and the width of the ridges is determined to be 0.8mm and 1.6mm by empirical values, respectively.
3) According to the influence factors of the adhesive friction force, determining that the test variable is a normal load value, the width and the height of the ridge, and the radius of the index finger of the subject is not the test variable; since the addition of the lubricating oil medium directly affects the actual contact area, whether the lubricating oil medium is added or not is to be determined as a test variable.
4) According to the distance, the height and the width of the sample ridges, two groups of samples of W groups and N groups are processed by adopting 3D printing;
in this embodiment, as shown in fig. 3, the overall thickness h of the sample is 2mm, the overall length l of the sample is 100mm, and the overall width w of the sample is 35mm. In addition, the width omega of the sample ridges of the W group is 0.8mm, the width omega of the sample ridges of the N group is 1.6mm, each group of samples has 4, the spacing lambda is 4.8mm, 5.8mm, 6.8mm and 7.8mm respectively, the heights D of the two groups of sample ridges are 0.8mm, and the material is photosensitive resin.
5) According to the radius of the index finger of the subject and the contact angle of the set fingertip and the sample surface of 30 degrees, an aluminum finger clamp is arranged according to the structural characteristics of an adapter of the UMT Tribolab testing machine as shown in figure 4; building a test system according to the aluminum finger clamp, the sample ridge size and the test variable;
in this example, subjects were selected with index finger radii of 5.1579mm, 6.3667mm, 6.5867mm, 6.9576mm, 7.5374mm, and 7.9618mm.
6) Loading the fingertip of the subject, controlling the movement of the sample, enabling the fingertip skin to interact with the surface of the sample, and acquiring the friction force and the contact force of the contact section and the position information of the sample;
when researching the influence of normal load on friction perception of a subject, selecting a W group of samples as a touch object, and sequentially setting the normal load to be 0.5, 1, 1.5 and 2N to simulate the touch force of a finger contacting an object;
when researching the influence of lubricating oil medium on the friction perception of a subject, selecting a W group sample as a touch object, coating lubricating oil on the surface of a finger for test, collecting the friction force result in the test process, and obtaining various contact parameters (F N And lambda, omega and R) are set to be identical, namely respectively taking data such as peak-valley value, average value, variance, standard deviation, fluctuation period and the like of a curve of the friction force changing along with time, and comparing the difference of the two groups of data, thereby analyzing the influence of lubricating oil on the friction force result.
When researching the influence of the width of the sample surface ridge on the friction perception of a subject, selecting a W group of samples and a N group of samples as touch objects, wherein the width omega of the W group of sample ridges is larger than that of the N group of samples, setting the two groups of samples on the finger without lubricating oil and other contact parameters (F N And comparing the friction results obtained when lambda and R) are the same, namely respectively taking data such as peak-valley value, average value, variance, standard deviation, fluctuation period and the like of a curve of the friction force changing along with time, and comparing the difference of the two groups of data, thereby analyzing the influence of lubricating oil on the friction result.
The finger and the sample surface generate contact force, when the numerical value reaches a preset value, the finger is stopped by the aluminum finger clamp, after the finger is kept for 15 seconds, the sample starts to move linearly at the speed of 4mm/s, the finger and the sample surface generate friction force, when the stroke of the sample reaches 60mm, the sample stops moving, the finger is moved upwards by the aluminum finger clamp, the sample returns to the original test starting position, and the test is ended. Each subject was subjected to 3 replicates under the same test conditions, each run at 15min intervals.
7) Acquiring friction force data of a contact surface in the whole contact process, wherein the friction force data changes along with time, acquiring and analyzing a basis of average fluctuation degree of friction force in the touch process according to the friction force data, and combining the basis with a change rule of adhesive friction force to obtain an analysis test result of the friction force of a finger on a deterministic texture surface;
the friction force of the fingertip skin and the curve changing with time when the fingertip is scratched through the sample in the test process have obvious periodic change rule. Due to the existence of the ridges, the fingertip skin sequentially passes through repeated cycles of bulge-recess-bulge, and the contact area of the fingertip skin and the surface of the sample and the deformation degree of the fingertip are periodically fluctuated due to the complex mechanical property of the fingertip skin.
The curve changes irregularly when the sliding starts, because the speed suddenly changes from 0mm/s to 4mm/s when the sample starts to slide, a certain impact is caused on the skin of the fingertip, and the difference value of a single period is larger than that of other periods in the sliding process, which is caused by the fact that the protrusions caused by the cooling ridges are removed, and the surface of the sample has irregular fine textures caused by the manufacturing process.
As shown in fig. 6, which is a typical curve of friction force of fingertip skin and time variation when the fingertip is drawn through the sample, the average fluctuation degree of friction force is obtained based on the test result, and the obtaining method specifically comprises: the peak value and the trough value of the curve change period caused by the ridges of the samples in the curve obtained by each test are subjected to difference value, the difference values are ordered according to the size, the change period of the curve corresponding to the 5 difference values (the number of the ridges of all the samples is odd and is more than 5) in the middle is taken, the corresponding curve change period is 5 more uniform periods, and the friction force wave peak value corresponding to the period is F X1 ，F X2 ,F X3 ,F X4 ,F X5 And a friction trough value of F X1 ’,F X2 ’,F X3 ’,F X4 ’,F X5 ' average value F of the difference between the peak value and the trough value XM1 ：
Since the same test was repeated three times, the average values obtained in the other two times were F XM1 ' and F XM1 ", the average value is taken again according to the times of the test to obtain the total average value F XM2 ：
Will F XM2 As a basis for analyzing the average fluctuation degree of the friction force in the touch process, the test result of the friction force is analyzed by combining the change rule of the adhesive friction component: in the process of contact between fingertip skin and deterministic texture surface, friction force is basically periodically fluctuated along with time, and the change of average fluctuation degree is consistent with the change rule of adhesive friction component, and at the moment, the adhesive friction component takes the dominant role; the average degree of fluctuation of the friction force does not consistently increase with increasing pitch because increasing the pitch of the ridges results in a decrease in the sticking friction component and an increase in the plow friction component, where the plow friction component dominates and the degree of fluctuation of the total friction force increases. When the finger skin slides over the rectangular ridge, friction force F is generated f Mainly by the adhesive friction component F a Plow friction component F p And the friction force reduction amount DeltaF generated by elastic energy recovery deformation: f (F) f ＝F a +F p ΔF, adhesive friction component F a The main friction mechanism cannot be detected through experiments, while the total friction force in the process of touching the deterministic texture by a finger can be detected through experiments, but the friction mechanism is unknown, so the change of the adhesion friction component is deduced through theory, and the plow friction component F is further deduced p And the change rule of the friction force reduction delta F corresponding to the friction force reduction delta F is adopted, and finally the friction mechanism of the finger and the deterministic texture surface is obtained.
In the embodiment, the finger clamp made of aluminum ensures that the finger tip part of the index finger of the right hand of each subject is fixed at an angle of 30 degrees with the surface of the sample in the experimental process, and the finger is fixed.
In the steps, a test system comprises a UMT Tribolab tester and an upper computer system; and the UMT Tribolab tester performs information interaction with the upper computer system. As shown in fig. 2, the UMT Tribolab tester includes a tester main body 1, a Z-axis 2, a test suspension 3, a heightened block 4, a three-dimensional force sensor 5, an adapter 6, an aluminum finger grip 7, a sample 9, and a rectilinear motion module 10. The top of the tester main body 1 is provided with a Z-axis 2 which is driven by a motor to move up and down, and the end part of the Z-axis 2 is provided with a test suspension 3. The heightening block 4 is clamped at the bottom of the test suspension 3 in a clamping mode, the three-dimensional force sensor 5 is connected to the lower portion of the heightening block 4 through bolts, and the adapter 6 is fixed to the three-dimensional force sensor 5 through bolts. The lower part of the adapter 6 is clamped with an aluminum finger clamp 7 by bolts. A linear motion module 10 is arranged on the ring seat of the testing machine main body 1 and a sample 9 is arranged on the linear motion module 10 and is positioned below the aluminum finger clamp 7.
In the above embodiment, as shown in fig. 5, the UMT Tribolab tester further includes a driving device, a position encoder, and a data acquisition system. The driving device is controlled by the upper computer system to work, the driving device drives the motor to act, the driving device loads the finger tip, the movement of the sample is controlled, the interaction between the finger tip skin and the surface of the sample is caused, the friction force and the contact force of the contact section are detected through the three-dimensional force sensor, the position information of the sample is obtained through the position encoder arranged on the linear motion module 10, the friction force, the contact force and the position information of the sample are transmitted to the upper computer system through the data acquisition system, and the upper computer system can monitor and control the test process in real time.
In the above embodiments, as shown in fig. 4, the aluminum finger grip includes the pre-grip fastener 71, the grip body 72, the finger pre-tightening bolt 73, and the pre-tightening bolt adjustment groove 74. A sleeve is arranged in the middle of the clamp body 72, and is used for accommodating fingers of a subject; the upper part of the clamp body 72 is provided with a pre-clamp fastener 71, and the pre-clamp fastener 71 is clamped by the adapter 6 of the UMT Tribolab tester and is then mounted on the UMT Tribolab tester. The side walls of both sides of the clamp body 72 are respectively provided with a pre-tightening bolt adjusting groove 74, a finger pre-tightening bolt 73 is arranged in the pre-tightening bolt adjusting groove 74, and the finger pre-tightening bolt 73 can move up and down in the pre-tightening bolt adjusting groove 74 so as to clamp the finger of the subject.
In the above embodiment, the aluminum finger grip further includes a washer 75 and a nut 76, the nut 76 being provided on the pretension bolt 73 through the washer 75 for fixing the finger pretension bolt 73 in the pretension bolt adjustment groove 74.
When in use, the index finger of a subject is inserted into the sleeve of the clamp body 72, the lower part of the index finger is attached to the lower surface of the inner wall of the sleeve, the position of the pre-tightening bolt 73 is adjusted to compact the upper part of the index finger, and the position of the pre-tightening bolt 73 is fixed by the nut 76 and the gasket 75.
In the above embodiment, the clamp body 72 is screwed with the pre-clamp fastener 71.
In the above embodiment, the lower portion of the adapter 6 is fixedly connected to the pre-jig fastener 71 of the aluminum finger jig 7.
In the above embodiment, the three-dimensional force sensor 5 is a model DFM-1.0 three-dimensional force sensor with a measuring range of 10N.
In the above embodiment, the sample 9 is stuck to the linear motion module 10 by double-sided tape, as shown in fig. 3. The sample 9 is constituted by a number of spaced apart ridges, the cross section of which is rectangular.
In the above embodiment, the movement mode of the linear movement module 10 is unidirectional sliding, and the force loading mode is normal constant loading. Wherein:
the unidirectional sliding means that a sample with a deterministic texture surface moves at a constant speed of 60mm at a constant speed of 4mm/s, a five-phase stepping motor of the linear movement module 10 is connected with a built-in shaft position encoder, a ball screw is connected with the position encoder, an objective table is meshed with a screw, two parallel linear guide rails enable the objective table to move linearly, the linear guide rails are fixed on a base, the base is connected with a main body of the testing machine through a self-locking device, and the sample is glued on the objective table by double-sided glue.
The normal constant loading mode can be realized through the UMT Tribolab tester main body, the motor drives the Z shaft 2 to rotate, the test suspension 3 moves downwards, the heightening block 4 is connected with the test suspension 3, the three-dimensional force sensor 5 is connected with the heightening block 4 through a screw, the adapter 6 is connected with the three-dimensional force sensor 5 through a screw, the finger clamp 7 is connected with the adapter 6 through a double-end stud, the finger is fixed in a sleeve of the finger clamp 7, the contact force is finally generated between the finger and a sample, when the contact force reaches a target value, the test suspension 3 keeps the current position, and the finger is subjected to constant normal load.
In the embodiment, the test process is divided into two stages, namely, a static loading stage, a sample is fixed on an objective table by double faced adhesive tape, an upper computer system controls a test suspension to move downwards to apply a normal load to fingertips, a three-dimensional force sensor is arranged on the test suspension and is used for monitoring the pressure and friction values of a contact surface in real time and feeding back to the upper computer system, and the test suspension keeps the current position after the load is slowly loaded to a target value; and in the sliding friction stage, the upper computer system controls the five-phase stepping motor in the linear motion module 10 to drive the ball screw, so that a sample on the object stage of the linear motion module 10 slides along the linear guide rail at a constant speed in a direction away from a body, a built-in shaft position encoder of the motor records the relation between the position of the main shaft and the control force and the position of the sample and feeds the relation back to the upper computer system, when the target stroke is reached, the sample stops moving, the test suspension moves upwards, and the test is ended.
In the steps, the surface texture of the deterministic texture is selected to be a ridge with a rectangular cross section, and the positions of the finger and the texture surface are the abdomen parts of the finger skin.
In summary, the friction force measurement test system is built based on the UMT Tribolab multifunctional friction and wear comprehensive testing machine, a linear motion module is selected, the position and the angle of a finger are strictly controlled by adopting an aluminum finger clamp, the interference of human factors is avoided as much as possible, the reliability of the test is enhanced, the surface of a touch object is designed by taking the ridge with the rectangular cross section as a deterministic texture, the influence of the surface texture on the friction characteristics of finger skin can be explored by the changed ridge size, and the repeatability of the test is enhanced. The method avoids the accidental data, analyzes the friction characteristics of the fingertip skin by combining theory, and provides more reliable test basis for the development of the humanoid robot skin and the touch simulation design of the intelligent robot.
The foregoing embodiments are only illustrative of the present invention, and the structure, dimensions, placement and shape of the components may vary, and all modifications and equivalents of the individual components based on the teachings of the present invention should not be excluded from the scope of protection of the present invention.
Claims (6)
1. A method of testing the friction characteristics of a finger against a deterministic textured surface, comprising the steps of:
1) Obtaining a value range of the radius of the index finger of the subject according to a pre-determined normal load value and the set distance and height of the sample ridges, and screening the subject meeting the requirements according to the value range, wherein the finger of the subject is in partial contact with the deterministic texture surface;
2) According to the influence factors of the adhesive friction force in the partial contact state, calculating the real contact area of the fingertip skin and the deterministic texture surface, and analyzing the change rule of the adhesive friction force along with the normal load value, the ridge spacing, the ridge width and the index finger radius of the subject according to the obtained real contact area result;
3) According to the influence factors of the adhesive friction force, determining the normal load value, the width and the height of the ridge as test variables, and determining whether a lubricating oil medium is added as the test variables;
4) According to the distance, the height and the width of the sample ridges, two groups of samples of W groups and N groups are processed by adopting 3D printing;
5) According to the radius of an index finger of a subject and the contact angle of a set fingertip and the surface of a sample being 30 degrees, setting an aluminum finger clamp according to the structural characteristics of an adapter of the UMT Tribolab testing machine, and building a test system according to the aluminum finger clamp, the size of a sample ridge and test variables;
6) Loading the fingertip of the subject, controlling the movement of the sample, enabling the fingertip skin to interact with the surface of the sample, and acquiring the friction force and the contact force of the contact section and the position information of the sample;
7) Acquiring friction force data of a contact surface in the whole contact process, acquiring and analyzing a basis of average fluctuation degree of friction force in the touch process according to the friction force data, and combining the basis with a change rule of adhesive friction force to obtain an analysis test result of the friction force of the finger on the deterministic texture surface;
the change rule of the adhesive friction force is as follows: increasing the normal load increases the adhesion friction; the larger the width of the ridge, the greater the adhesion force; adding lubricating oil medium reduces the adhesive friction; increasing the ridge spacing reduces the adhesive friction;
the aluminum finger clamp comprises a pre-clamp fastener, a clamp body, a finger pre-tightening bolt and a pre-tightening bolt adjusting groove; the middle part of the clamp body is provided with a sleeve which is used for accommodating fingers of a subject; the upper part of the fixture body is provided with the pre-fixture fastener which is clamped by the adapter and then is arranged on the UMT Tribolab tester; the two side walls of the clamp body are respectively provided with the pre-tightening bolt adjusting grooves, the finger pre-tightening bolts are arranged in the pre-tightening bolt adjusting grooves, and can move up and down in the pre-tightening bolt adjusting grooves to clamp fingers of a subject;
the basis acquisition method of the average fluctuation degree of the friction force comprises the following steps: the peak value and the trough value of the curve change period caused by the ridges of the sample in the curve of the friction force data obtained by each test along with the time change are made to be different, the differences are ordered according to the size, the change period of the curve corresponding to the 5 differences in the middle is taken, and the friction force peak value corresponding to the period is F X1 ，F X2 ,F X3 ,F X4 ,F X5 And a friction trough value of F X1 ’,F X2 ’,F X3 ’,F X4 ’,F X5 ' average value F of the difference between the peak value and the trough value XM1 The method comprises the steps of carrying out a first treatment on the surface of the The same test was repeated three times, and the average values obtained in the other two times were F XM1 ' and F XM1 ' taking average again according to the number of tests to obtain total average value F XM2 F is to F XM2 As an analysis of touch oversThe basis of the average fluctuation degree of friction force in the process;
and combining the basis with the change rule of the adhesive friction force to obtain an analysis test result of the friction force of the finger on the deterministic texture surface: in the process of contact between fingertip skin and deterministic texture surface, friction force periodically fluctuates along with time, and the change of average fluctuation degree is consistent with the change rule of adhesive friction component, and at the moment, the adhesive friction component takes the dominant role; inconsistent, the average fluctuation degree of the friction force can be increased along with the increase of the distance, and the plow friction component plays a dominant role at the moment, so that the fluctuation degree of the total friction force is increased; when the finger skin slides over the rectangular ridge, friction force F is generated f Mainly by the adhesive friction component F a Plow friction component F p And the friction force reduction amount DeltaF generated by elastic energy recovery deformation:
component F of tack friction a As a main friction mechanism, the total friction force in the process of touching the deterministic texture by a finger cannot be measured through a test, and the change of the adhesion friction component is deduced through theory, so as to infer the plow friction component F p And the change rule of the friction force reduction delta F corresponding to the friction force reduction delta F is adopted, and finally the friction mechanism of the finger and the deterministic texture surface is obtained.
2. The test method of claim 1, wherein when studying the influence of the normal load on the friction perception of the subject, selecting the W group of samples as the touch object, the normal load is set to 0.5, 1, 1.5 and 2N in order to simulate the touch force of the finger touching the object.
3. The test method according to claim 1, wherein when the influence of the presence or absence of the lubricating oil medium on the friction perception of the subject is studied, selecting W groups of samples as touch objects, coating the lubricating oil on the surface of the finger for the test, collecting the friction results during the test, comparing and analyzing the friction results obtained when the finger is not coated with the lubricating oil and other contact parameter settings are the same, and taking the friction results respectivelyPeak-to-valley value, average value, variance, standard deviation and fluctuation period data of a curve of the friction force changing along with time are compared, and differences of the two groups of data are compared, so that the influence of lubricating oil on friction force results is analyzed; other contact parameters are normal load value F N Spacing of sample ridges
And width->
And a radius R of the subject's finger.
4. The test method of claim 1, wherein the method comprises selecting W groups and N groups of samples as touch objects while studying the effect of the width of the sample surface ridges on the subject's friction perception, wherein the width of the W groups of sample ridges
Comparing friction force results obtained when the two groups of samples are not smeared with lubricating oil on fingers and other contact parameters are set to be the same, respectively taking peak-valley value, average value, variance, standard deviation and fluctuation period data of a curve of friction force changing along with time, and comparing differences of the two groups of data, thereby analyzing the influence of the lubricating oil on the friction force results; other contact parameters are normal load value F N Distance between sample ridges->
And width->
And a radius R of the subject's finger.
5. The test method of claim 1, wherein the UMT Tribolab tester comprises a tester body, a Z-axis, a test suspension, a booster block, a three-dimensional force sensor, an adapter, an aluminum finger grip, a sample, and a linear motion module; the top of the tester main body is provided with the Z shaft which is driven by a motor to move up and down, and the end part of the Z shaft is provided with the test suspension; the heightening block is clamped at the bottom of the test suspension in a clamping way, the lower part of the heightening block is connected with the three-dimensional force sensor through a bolt, and the adapter is fixed on the three-dimensional force sensor through a bolt; the lower part of the adapter is clamped with the aluminum finger clamp through a bolt, the adapter is positioned below the aluminum finger clamp, the linear motion module is arranged on the ring seat of the main body of the testing machine, and the sample is arranged on the linear motion module.
6. The test method of claim 5, wherein the sample is affixed to the linear motion module by double sided tape; the sample is composed of a plurality of ridges which are arranged at intervals, and the cross section of each ridge is rectangular.
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