RU2659179C1 - Unit for determining friction coefficient - Google Patents

Abstract

FIELD: measuring equipment.

SUBSTANCE: invention relates to a measuring equipment for engineering, namely to units for determining parameters of friction of kinematic pairs. Unit for determining a friction coefficient comprises a carriage with a kinematic friction pair located on it. Investigated friction pair is represented by a removable horizontal plate, fixed on a fixed base. Moving element of the pair is a removable plate on the carriage, which is driven by an electric drive. Means for measuring the frictional force are installed on the carriage, output signal of which is the frequency. To transmit the measuring signal, a linear transformer is used. Moving windings of the transformer are fixed on the carriage, and fixed windings - on the unit base. Signal of the measuring means is processed by an electronic unit. Output information signal of the electronic unit is a rectangular pulse, with a duration equal to the frequency period of the frictional force converter. Unit allows to determine a friction coefficient for different combinations of materials with different combinations of the normal pressure force and the speed of the movable element of the friction pair under study.

EFFECT: technical result is increased reliability of the result of determining the friction coefficient.

7 cl, 5 dwg

Description

The invention relates to mechanical engineering, and in particular to installations for determining the friction parameters of kinematic pairs.

When designing experimental installations, the coefficient for studying friction is based on the concept of the coefficient of friction as the slope of the characteristic (function) of friction.

A known method of determining the coefficient of friction (patent RU 2343455, IPC G01N 19/02, publ. 10.01.2009), according to which the test sample is placed between two identical test surfaces, articulated on one side and compressible with equal force, with half the angle between the investigated surfaces when the sample stops will be the desired angle of friction. However, the reliability of the measurement result is low. The measurement result is influenced by the friction of the sample on the horizontal surface on which the experiment is performed. In addition, the sample will go to the final design position due to the kinetic energy accumulated during the movement.

Greater reliability of the measurement result is realized by the balancing principle, in which the primary parameter of the installation is the reaction of the rotational kinematic friction pair (patent RU 2461811, G01N 19/02, publ. September 20, 2012).

The friction coefficient is often determined after the time of movement of the moving element of the friction pair. In the device for determining the coefficient of friction (patent RU 2340886, IPC G01N 19/02, publ. 10.12.2008) measure the time of the fall of the load on the base site. A friction pair is formed by a sample and a cylinder on which a thread with a load is wound. A similar approach is implemented in the device for determining the coefficient of friction according to patent RU 2373518, publ. 11/20/2009.

Through fixing the time of movement of the movable element determine the coefficient of friction of planar pairs. According to the method for determining the coefficient of friction (patent RU 2362985, IPC G01N 19/02, publ. 07/27/2009), the experiment is carried out on an inclined plane, and the movement is specified by the drive, composed by a thread thrown through the block, while the load is fixed at the end of the thread. The above formula for calculating the coefficient of friction does not take into account the energy loss in the block. The movement of the movable element is uniformly accelerated, so it is impossible to say for what relative speed the coefficient of friction is determined. Does not take into account friction in the unit for determining the coefficient of rest friction force according to patent RU 2511615, publ. 04/10/2014.

Finding the coefficient of friction is given in special conditions, under the influence of external factors (patent RU 2349901, IPC G01N 19/02, publ. 20.03.2009).

The listed analogues have a common drawback - low reliability of the result of determining the coefficient of friction, since the desired coefficient is an indirect measurement.

As a prototype adopted the installation that implements the method of determining the coefficient of friction according to patent RU 2375700, IPC G01N 19/02, publ. 12/10/2009. The studied friction pair is represented by a fixed element (plane), fixed on the basis of the installation, and a movable element (sample). There is a drive for moving the movable element in the form of a thread thrown over the block and having a load at the end. There are means for measuring the primary parameters - two electric stopwatch - and communication means - sensors at the borders of two sections of the movement S1 and S2. Since the friction coefficient depends on the force of normal pressure, in this installation, this force can only be changed due to the mass of the movable element, and this in a real design involves some kind of fastener (let's call it a carriage), to which the drive thread is attached. Thus, in the installation under consideration, the coefficient of friction is determined indirectly, where the primary parameters are two time intervals of the movement of the carriage with the moving element of the friction pair in two sections of motion. The calculation formula given in the patent does not take into account the energy loss in the drive unit and the uneven speed of the moving element, which reduces the reliability of the result of determining the desired friction coefficient.

The technical result of the proposed solution is to increase the reliability of the result of determining the coefficient of friction.

The tasks are solved:

1. Development of the main technical solutions for the creation of a device for determining the coefficient of friction, which uses a direct measurement of the friction force at various values of the normal pressure force and the speed of the moving element of the studied friction pair.

2. The rationale for decisions.

The specified technical result is achieved in that the installation for determining the coefficient of friction, comprising a fixed flat element mounted on a horizontal base and a movable flat element of the kinematic friction pair under study, mounted on a carriage equipped with a drive and having two sections of movement, the installation comprising measuring and communication means for identification of primary parameters, it is equipped with an electronic unit that converts the signals of measuring instruments of primary parameters into an output information the signal, while the means of measuring the primary parameters are mounted on the carriage, and the means of communication connect the carriage and the base, while the means of measuring the primary parameters are based on the series-connected transducer of force to displacement, transducer of displacement to electric capacitance and transducer of electric capacitance to frequency signal, transducer forces in movement is made in the form of a membrane with a rigid center, to which a measured force is applied, while the membrane is fixed along the contour in the car In particular, the transducer of displacement into an electric capacitance is made in the form of a cylindrical capacitor, the movable lining of which is fixed on the rigid center of the membrane of the transducer of force into displacement, and the immovable lining is rigidly connected to the carriage, the converter of the electric capacitance to the frequency signal is made according to the oscillator circuit based on the field transistor with a channel n-type and with double winding transformer, the primary winding of the transformer is connected in parallel with the plates of the cylindrical capacitor a drive to the electric capacitance and is connected at one end to the drain of the transistor and the other to a feedback capacitor, the second terminal of which is connected to the gate of the transistor and the resistor connected to the common bus, the middle terminal of the primary winding forms a power bus, the source of the transistor is connected to the common bus through a resistor and a capacitor connected in parallel; the secondary winding of a transformer with a series-connected capacitor is a translator of the converter signal.

In the proposed installation, the carriage drive is made up of a cable and a DC motor with parallel excitation, on the shaft of which a pulley is installed, one end of the cable mounted on the cylindrical surface of the pulley, the other on the rigid center of the membrane of the force transducer into movement, and the cable section between the points fastening is located horizontally, the electronic unit contains a power supply that generates m constant voltage power supply of the drive motor and the voltage of the functional elements of the electric of the crown unit, a time channel consisting of a pulse generator, a toggle switch, a two-input conjunctor, a counter and a decoder having n output buses, an RS flip-flop, and a normally closed contact of the toggle switch connected to the voltage output of the functional elements of the electronic unit on the power supply and form a bus reset the electronic unit, the pulse generator is connected via a normally open contact of the toggle switch with the first input of the two-input conjunctor, and its second input is a single output RS -trigger, the installation input of the latter is connected to the reset bus of the electronic unit, and the reset input is connected to bus n of the decoder, the control channel contains an RS-interval trigger with input m-input disjunctors, a packet switch for m positions, each group of input contacts of which is connected to the bus 1 decoder, with tires of the decoder of the first and second interval of the carriage and with the corresponding output of the voltage of the electric motor on the power supply, the output contacts of the packet switch of the first interval of the caret the ki are connected to the inputs of the disjunctor of the RS-interval trigger installation, and the output contacts of the second interval are connected to the descends of the reset disjunctor, the output contacts corresponding to the voltage of the electric motor, bus 1 and the bus of the second interval on the decoder are connected to the electronic keys of the drive motor, the information channel contains a driver the primary information signal, the output of which is the counting input of the T-trigger, the reset input of the latter is connected to the reset bus of the electronic unit, a single output of the T-trigger is compatible It is possible that with a single output of the RS-trigger of the interval, the inputs of the conjunctor of the information channel form, the output of which is the information output of the electronic unit.

The installation device for determining the coefficient of friction is illustrated by drawings:

FIG. 1 - structural diagram of the installation;

FIG. 2 - the shape of the lining of a cylindrical capacitor;

FIG. 3 - connection diagram of a communication transformer;

FIG. 4 is an electrical schematic diagram of a self-oscillator (converter of electric capacitance to frequency);

FIG. 5 is a functional diagram of an electronic unit.

Accepted Designations

1. The basis

2. Screws of the movable element

3. Carriage

4. The movable element of the friction pair

5. Fixed element of friction pair

6. Fixed element screws

7. Electric motor drive

8. Electric motor pulley

9. Flexible cable

10. Fixed transformer windings

11. Winding frame 10

12. Screws securing the frame 11

13. The frame bracket 11

14. Transformer windings on the carriage

15. Winding frame 14

16. Frame mounting screws 15

17. Carriage housing

18. The screws of the membrane unit

19. Membrane

20. The rigid center of the membrane

21. The membrane ring

22. The movable lining of the cylindrical capacitor

23. The disk of the hard center of the membrane

24. Fixed capacitor plate

25. Fee of the oscillator (converter of electric capacity into a frequency signal)

26. Auto-generator

27. Bracket of the oscillator circuit board

28. Power supply circuit of the oscillator

29. Power supply unit of the oscillator

30. Carriage cover

31. Casing screws 30

32. Cargo

33. Eye bolt

34. The electronic unit

35. Power supply.

Time channel:

36. Pulse generator

37. Toggle switch

38. Cycle trigger

39. Counter conjunctor

40. Counter

41. Decoder.

Control channel:

42. Batch switch

43. Electronic keys

44. RS-interval trigger

45. Installation disjunctor

46. Reset Disjunctor

Information Channel:

47. The trigger of the frequency period fn

48. Shaper

49. The exit conjunctor.

The main elements of the installation are mounted on the base in the form of a table 1 with a horizontal tabletop. Screws 2 with countersunk head on the carriage 3 fixed the movable element 4 of the investigated kinematic friction pair. The fixed element of the friction pair is represented by a plate 5, which is fixed with screws 6 on the base.

The carriage drive is represented by a direct current electric motor with parallel excitation 7, on the shaft of which a pulley is fixed 8. The pulley is connected to the carriage by a flexible cable 9, while the cable section from the carriage to the cylindrical part of the pulley is horizontal.

The communication means is formed by a linear transformer having two fixed windings 10-a, 10-b, wound on a frame 11, which is fastened with screws 12 to the bracket 13, and the latter is connected with the base of the unit with screws. There are movable windings of the transformer 14-a, 14-b, which are wound on the frame 15, connected by screws 16 to the housing 17 of the carriage. The axial length of the windings 10, 14 is chosen so that the magnetic flux of the transformer remains at a sufficient level when moving the carriage during the experiment.

Measuring instruments for primary parameters are located on the carriage and are formed by series-connected transducers: a force to displacement transducer, a displacement transducer to an electric capacitance, and a transducer of electric capacitance to a frequency signal. The force-to-displacement transducer is structurally designed in the form of a membrane unit fixed to the carriage housing 17 by screws 18. The membrane 19 (can be flat or corrugated) has a rigid center 20 and ring 21. The membrane fastening with these elements is typical - rolling. In this transducer, under the action of a force applied to the rigid center of the membrane, the rigid center will be displaced in proportion to the force. The transducer to the electric capacitance is represented by a cylindrical capacitor. There is a movable lining 22, which is mounted through an insulating disk 23 on the rigid center 20 of the membrane. The fixed plate 24 is mounted coaxially movable and mounted on the card 25 of the carriage. Thus, if a force is applied to the rigid center of the membrane from the side of the carriage drive, this will lead to the displacement of the movable plate and the electric capacity of the cylindrical capacitor will decrease. The converter of the electric capacitance into a frequency signal is made according to the inductive three-point circuit and is a self-oscillator circuitry. The amplifying element is a field effect transistor VT1 with an n-type channel. The primary winding of the load transformer is connected parallel to the cylindrical capacitor C2 *. One end of the primary winding is connected to the drain of the transistor, and the second through a feedback capacitor C1 with the gate of the transistor, while the gate through a resistor R1 is connected to a common bus. The middle terminal of the primary winding is connected to the power bus E. The source of the transistor through a thermostabilizing target consisting of a parallel-connected resistor R2 and capacitor C3 is connected to a common bus. The output signal in the form of a sinusoidal voltage of frequency f _p , is transmitted by the secondary winding of the transformer through an isolation capacitor C4. The converter in question is structurally made by a separate assembly unit - the electronic circuit 26 is mounted on the board 25, the board is mounted on an arm 27, which is mounted on the carriage body. To power the oscillator, a secondary power supply 27 is mounted on the carriage (Fig. 4). The voltage of industrial frequency (50 Hz) is supplied from the power supply unit of the electronic unit through the transformer Tr of the communication means - windings. 10-a - 10-b to the rectifier on diodes VD1-VD4, then the filter is located as part of the inductor Dr and two capacitors C1-C2, then there is a stabilizer on a bipolar transistor VT with a Zener diode VD5 in the base circuit, the current of which is set by resistor R. B In general, the carriage is made by a separate assembly unit, its internal volume is closed by a U-shaped casing 30, which is fixed to the carriage housing 17 by screws 31. The upper horizontal surface of the casing is designed to install a load 32 that sets the normal pressure force of the friction pair under study. To connect the carriage to the drive, a screw 33 is provided in the form of an eye bolt screwed into the rigid center 20 of the membrane.

In the initial position, the drive motor 7 is turned off, the carriage is stationary, respectively, the membrane 19 is undeformed, the axial length of the overlap of the plates of the cylindrical capacitor is maximum. The capacitance of the capacitor is

where ε = ε ₀ ε is the absolute dielectric constant of the gap;

r ₂₄ , r ₂₅ - respectively, the inner radius of the lining 24 and the outer radius of the lining 25.

This capacity value corresponds to the frequency of the oscillator

where L ₁ is the inductance of the primary winding of the oscillator.

If you turn on the drive motor, then when sliding the movable element 4 along the stationary element 5 of the investigated friction pair, a friction force will appear, which will lead to the deflection of the membrane 19.

In the linear section of the characteristic, the relation for the deflection δ

- средний радиус мембраныwhere F _Tr is the force applied to the rigid center of the membrane, i.e. friction force;

- average radius of the membrane

R20, R21 - respectively, the inner and outer radius of the membrane (rolling radii);

- цилиндрическая жесткость мембраны;

- cylindrical rigidity of the membrane;

Em, μ, h _m , respectively, are the elastic modulus of the first kind, Poisson's ratio, and membrane thickness.

Formulas (2), (3) show that the capacity C * linearly depends on the friction force F _Tr

where the setup constant is

Substituting the value of the capacitance (4) in the formula (2), we obtain the transfer function of the force transducer

where the installation constant K2 through the primary parameters is

Thus, the friction force is uniquely determined by the frequency of the oscillator. An electrical signal of this frequency is output from the movable carriage through communication means - windings 10-b, 14-b.

The installation is completed with an electronic unit 34 for processing primary information. Functionally, it can be divided into: power supply, time channel, control channel and information channel.

The power supply generates m constant voltages (according to the number of test modes) of the power supply of the drive motor and the voltage of the functional elements of the electronic unit.

The time channel sets the timeline and duration of the test cycle. The channel consists of: a pulse generator 36, a toggle switch 37 having one normally open contact HP and one normally closed contact NC. The initial position of the toggle switch is “reset”, the operating position is “measurement”. There is an RS - trigger 38 of the cycle, a conjunctor 39 of the counter 40 and a decoder 41 having n output buses of the position code. In the initial position, the reset bus “c” holds a logical unit (supply voltage E of the microcircuit) through the normally closed contact of the toggle switch, while the counter 40 is in the zero state, and the zero (0) bus is excited at the output of the decoder 41. When the toggle switch 37 is moved to the “measurement” position, the pulses of the generator 36 begin to fill the counter 40 and logical units appear sequentially at the output of the decoder 41. For the filled counter, the decoder bus n is excited, the potential of which overturns the trigger 38 of the cycle and its output closes the connector 39, the arrival of the generator pulses to the counter stops.

The control channel is designed to switch the test mode (speed of the moving element, normal pressure force) and the formation of the interval of movement at which the speed is constant. The channel contains a packet switch 42 on m positions (according to the number of test modes). Input terminals of each switch group are connected with the tire decoder 41, which receive a logical one at time t _S1 passing the first portion of the carriage - S1, t _S2 at the moment of passage of the second section S2, and the corresponding output drive voltage for the motor power supply. The output contacts of the switch 42 transmit these signals to electronic keys 43, which energize the drive motor in the interval from the moment of switching on (decoder bus 1) to the moment t _S2 (end of carriage passage of the entire travel path S1 + S2.) The interval trigger 44 generates a pulse of duration equal to the time the carriage travels for interval S2. The equipment for connecting the input contacts of the switch is based on the following ratios.

In the first section S1 of carriage movement, uniformly accelerated movement takes place, and the second section S2 of the carriage runs at a constant speed V _S2

where ω ₇ is the frequency of rotation of the shaft of the electric motor 7,

R ₈ is the radius of the pulley 8 of the electric motor.

As a drive electric motor, a direct current electric motor with parallel excitation is adopted, which has linear speed and mechanical characteristics with a small slope, therefore, ω ₇ is determined only by the magnetic flux of the motor, i.e. supply voltage

The characteristics of the engine ensure the constancy of the rotation frequency as a function of the load (value of the friction force), i.e. ω ₇ does not depend on the total mass of the carriage, but is determined only by the supply voltage.

Carriage speed in the first section

Based on engine performance, you can take

Since the lengths of sections S1, S2 are constant, it is necessary to maintain the constancy of the products of speed and time

For clarity, in FIG. 5 for one switch position, the decoder output buses are named with the above notation.

The information channel is designed to generate a rectangular pulse with a duration equal to the period T of the signal ƒ _{p of the} oscillator

where ƒ _n - is expressed by formula (6).

The function of forming the duration (13) is performed by the counting trigger 47, which is set to its initial state by the reset bus "C" of the electronic unit. The control signal of this trigger is created by the driver 48, to the input of which the signal of the self-oscillator поступ _p is supplied _{. The} circuitry driver is built on the basis of the Schmidt trigger, and the output signal corresponds to the pulse front of the Schmidt trigger. The final element of the information channel is the conjunctor 49. The output signal of the conjunctor 49 is a rectangular pulse of duration T-formula (13), which is present in the interval of carriage movement t _S2 - t _Sl , where the carriage speed is constant.

The friction force will be found by formulas (6), (13), and the coefficient of friction for the adopted test mode is

where the force of normal pressure N is equal to the force of the weight P of the carriage together with the load 32.

Installation for determining the coefficient of friction works as follows. Pre-select the test mode:

- the moving speed of the movable element of the studied friction pair is set by the packet switch 42 (m options);

- the force N of normal pressure is the sum of the passport value of the weight of the carriage and the weight of the additional load 32.

After the toggle switch is moved to the "measurement" position, the pulses of the generator 36 through the conjunctor 39 begin to fill the counter 40, the decoder 41 translates the binary code of the counter into position. During the accumulation of pulses in the counter, a logical unit appears sequentially on the output buses of the decoder. The potential of the bus 1 through the electronic key 43 will ensure the inclusion of the motor 7 of the carriage drive, and the carriage will begin to move. At the end of the first section S1, the logical unit of the bus t _Sl through the dejunctor 45 will translate the interval trigger 44 into a single state. With further movement of the carriage, the generator pulses will accumulate on the counter, and the decoder bus t _S2 will receive a logical unit. The potential of this bus through the electronic key 43 will turn off the power to the engine 7, at the same time through the disjunctor 46, the trigger 44 will return to its original state. The operation of the counter 40 will stop when it is full, while the potential of the bus n of the decoder will overturn the trigger 38 of the cycle, which will close the connector 39.

In section S2, from the time t _Sl to t _S2 , the carriage speed is constant, therefore, the friction force F _{TP is} also constant. This force corresponds to a constant value of the movement of the rigid center 20 of the membrane 19, therefore, the movement of the movable plate 22 of the cylindrical capacitor and the constant value of the frequency ƒ _{n of the} oscillator will be constant. The period T of this signal will be generated by the trigger 47 and will be sent to the output of the conjunctor 49.

The initial coefficient of friction is determined by the formula (14).

Thus, the proposed installation for determining the coefficient of friction allows you to find the coefficient of friction for various combinations of area, normal pressure force and speed of the moving element of the investigated friction pair. The information received is reliable due to the exclusion of influencing factors. In the design of the installation, the principle of aggregation is applied, which increases its manufacturability, the electronic unit is made on standard elements of electronics.

Claims (7)

1. Installation for determining the coefficient of friction, comprising a stationary flat element mounted on a horizontal base and a movable flat element of the kinematic friction pair under study, mounted on a carriage equipped with a drive and having two motion sections, the installation comprising measuring and communication means for detecting primary parameters, characterized in that the installation is equipped with an electronic unit that converts the signals of the measuring instruments of the primary parameters into an output information signal, while primary measurement parameters CTBA mounted on the carriage and connection means connect the carriage and the base. 2. Installation for determining the coefficient of friction according to claim 1, characterized in that the means for measuring the primary parameters are based on a series-connected transducer of force into displacement, a transducer of displacement into an electric capacitance, and a transducer of electric capacitance into a frequency signal. 3. Installation for determining the coefficient of friction according to claim 2, characterized in that the force-to-displacement transducer is made in the form of a membrane with a rigid center, to which a measured force is applied, and the membrane is fixed along the office in the carriage. 4. Installation for determining the coefficient of friction according to claim 2, characterized in that the displacement transducer into an electric capacitance is made in the form of a cylindrical capacitor, the movable lining of which is fixed to the rigid center of the membrane of the force to displacement transducer, and the fixed lining is rigidly connected to the carriage. 5. Installation for determining the coefficient of friction according to claim 2, characterized in that the converter of the electric capacitance into a frequency signal is made according to a self-oscillator circuit based on a field-effect transistor with an n-type channel and with a double winding transformer, the primary winding of the transformer is connected in parallel with the plates of the cylindrical capacitor of the converter displacement into an electric capacitance and is connected to the drain of the transistor by one end and the feedback capacitor by the other, the second terminal of which is connected to the gate of the trans a source and a resistor connected to a common bus, the middle terminal of the primary winding forms a power bus, the source of the transistor is connected to the common bus through a parallel-connected resistor and capacitor, the secondary winding of a transformer with a series-connected capacitor is a translator of the converter signal. 6. Installation for determining the coefficient of friction according to claim 1, characterized in that the carriage drive is made up of a cable and a direct current electric motor with parallel excitation, on the shaft of which a pulley is mounted, while one end of the cable is mounted on the cylindrical surface of the pulley, the other on the rigid center of the membrane of the transducer of force into displacement, and the portion of the cable between the attachment points is horizontal. 7. Installation for determining the coefficient of friction according to claim 1, characterized in that the electronic unit contains a power supply unit that generates m constant power supply voltages of the drive motor and a supply voltage of functional elements of the electronic unit, a time channel consisting of a pulse generator, a toggle switch, and a two-input conjuncture connected in series , a counter and a decoder having n output buses, an RS flip-flop, and the normally-closed contact of the toggle switch is connected to the output of the supply voltage of the functional elements of the electric of the crown unit on the power supply unit and forms the reset bus of the electronic unit, the pulse generator is connected via the normally open contact of the toggle switch to the first input of the two-input conjunctor, and its second input is a single output of the RS-flip-flop, the installation input of the latter is connected to the reset bus of the electronic unit, and the reset input is with decoder bus n, the control channel contains an RS-trigger of the interval with the input of the electronic unit on the power supply and forms a reset bus of the electronic unit, the pulse generator is connected via noramal open contact of the toggle switch with the first input of the two-input conjunctor, and its second input is a single output of the RS-trigger, the installation input of the latter is connected to the reset bus of the electronic unit, and the reset input is connected to the decoder bus n, the control channel contains an RS-trigger interval with input m- input disjunctors, a batch switch for m positions, each group of input contacts of which is connected to the decoder bus 1, to the decoder buses of the first and second interval of carriage movement and with the corresponding voltage output the power supply of the electric motor on the power supply, the output contacts of the packet switch of the first interval of carriage movement are connected to the inputs of the disjunctor of the installation of the RS-trigger of the interval, and the output contacts of the second interval are connected to the outputs of the disjunctor of the reset, the output contacts corresponding to the voltage of the electric motor, bus 1 and bus of the second interval on the decoder, connected to the electronic keys of the electric motor of the drive, the information channel contains a signal shaper of primary information, the output of which is by the T-trigger input, the reset input of the latter is connected to the reset bus of the electronic unit, the single output of the T-trigger together with the single output of the RS-interval trigger form the inputs of the information channel, the output of which is the information output of the electronic unit.

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