rus
Issue #3-4/2023
D.S.Shakhov, V.P.Mikhailov, A.M.Bazinenkov, M.E.Zhukov
LINEAR PNEUMOHYDRAULIC DRIVE WITH ELECTRORHEOLOGICAL SPEED CONTROL
LINEAR PNEUMOHYDRAULIC DRIVE WITH ELECTRORHEOLOGICAL SPEED CONTROL
DOI: https://doi.org/10.22184/1993-8578.2023.16.3-4.232.238
A linear pneumohydraulic drive with electrorheological (ER) control is considered to ensure movement speed of objects according to a given law. The high accuracy of movement speed maintaining of is ensured by the use of a starch-based liquid as a working medium, capable of almost instantly changing rheological properties under the action of an electric field. Calculations of potential distribution in the ER valve is carried out, as well as calculation of the flow velocity of the ER fluid in the throttle and pipelines. It has been experimentally established that effective adjustment of drive rod movement speed is carried out at air pressure of 0.4 atm at the inlet to the pneumatic cylinder and a volume concentration of working fluid dispersed phase of 25%.
A linear pneumohydraulic drive with electrorheological (ER) control is considered to ensure movement speed of objects according to a given law. The high accuracy of movement speed maintaining of is ensured by the use of a starch-based liquid as a working medium, capable of almost instantly changing rheological properties under the action of an electric field. Calculations of potential distribution in the ER valve is carried out, as well as calculation of the flow velocity of the ER fluid in the throttle and pipelines. It has been experimentally established that effective adjustment of drive rod movement speed is carried out at air pressure of 0.4 atm at the inlet to the pneumatic cylinder and a volume concentration of working fluid dispersed phase of 25%.
Теги: electrorheological fluid pneumohydraulic drive speed adjustment viscosity вязкость пневмогидравлический привод регулировка скорости перемещения электрореологическая жидкость
INTRODUCTION
Linear drives are used in nanotechnology equipment both for loading and unloading workpieces and for moving workpieces and tools during the technological process. The machining requirements often require movement at a constant speed or according to a certain law and maintaining the required speed with high accuracy, e.g. when scanning coordinate tables during electronic, ion and laser machining. The most efficient speed control is performed in pneumatic and hydraulic actuators. In order to increase accuracy of pneumohydraulic actuator movements, an intelligent material, electro-rheological fluid (ERF), is used as a working fluid [4, 5]. ERF is a suspension of particles of polarizable materials distributed in dielectric fluid. In electric field is absent, ERFs behave like most conventional suspensions, exhibiting Newtonian flow properties. However, when electric field is applied to them, a sharp reversible increase in viscosity occurs almost instantaneously due to the formation of chain-like structures directed parallel to the electric field lines of force. In addition to viscosity, elasticity and plasticity of the fluid will change. When electric field is removed, ERF also quickly returns to its original state. Works on investigation of ERF are mainly focused on selection of disperse phase, which will provide maximum electro-rheological (ER) effect of suspension. The use of barium titanate as disperse phase gives a shear strain of 400 Pa at an electric field strength of 800 V/mm [1]. If a lithium salt suspension of polystyrene-block-polyisoprene copolymer is used as solid phase, a shear stress of 50 Pa at 560 V/mm is achieved [2]. If cerium dioxide is used as the filler, a shear stress of 4000 Pa at 3000 V/mm can be achieved [3]. Starch can be used as the solid phase of ERF. A picture of a linear experimental pneumohydraulic actuator with ER control is shown in Fig.1.
The main elements of the linear drive are a pneumatic cylinder 1 and a hydraulic cylinder 2, with the pistons connected by a common rod and an ER throttle 3. The drive works as follows. Compressed air is supplied from compressor into pneumatic cylinder 1, which moves piston of pneumatic cylinder in reciprocating motion and moves piston of hydraulic cylinder 2 rigidly connected to it. A diagram of hydraulic cylinder is shown in Fig.2. The hydraulic cylinder is filled with ERF and as the piston moves, it is pumped from one cylinder cavity to another through the ERF restrictor. The drive speed is managed by applying a control voltage to the ERF restrictor. This changes viscosity of the ERF and pressure drop of the fluid in the throttle, which causes the volume flow of the ERF through the throttle to change and, consequently, the rod speed.
CALCULATIONS OF DRIVE PARAMETERS
Calculations of drive parameters were performed: potential distribution in ERF-throttle, and also speed of flow of ERF-fluid in throttle and pipelines. Figure 3 shows the scheme of ERF-throttle and its basic elements: electrode 1, regulating plate 2, insulator 3, seal 4, washer 5, screw 6, and also a micro-gap between the electrodes. When there is no electric field in the micro-gap, when field strength E = 0, the particles of the disperse phase are uniformly distributed between the electrodes. When E field strength is created in the gap, the particles line up along the field lines and change the viscosity of ERF.
Figure 4 presents photo of ERF-throttle and its elements: aperture for pipe connection 1, electrodes 2 and insulator 3.
Figure 5 shows the results of electric field calculation in Comsol software environment for an ERF-throttle: axisymmetrical finite-element model (a) and potential distribution (b). Calculations showed that the field is uniformly distributed between the electrodes and there are practically no edge effects.
Calculation of speed of flow of ERF in throttle gap and tubing was also carried out, as speed of flow essentially influences efficiency of throttle control and, accordingly, actuator. On Fig.6 the scheme of a hydraulic cylinder and connection to it ERF throttle is shown: hydraulic cylinder 1, ERF throttle 2 and pipelines 3.
Figure 7 shows results of laminar flow velocity calculation in Comsol software for ERF liquid in throttle, Fig.8 presents flow velocity of ERF in cross-section of the pipeline at the outlet of ERF throttle.
The results of hydraulic calculation showed that ERF flow velocity in the throttle gap and in the pipeline cross section is distributed unevenly due to angular arrangement of pipelines, therefore such arrangement is not optimal. In future it is recommended to use straight-through throttle.
EXPERIMENTAL RESULTS
The purpose of the experiment was to determine efficiency of the pneumohydraulic actuator stem speed control. At different pressures in the pneumohydraulic cylinder and different stresses on the throttle settings the position of the rod was measured. The paper presents the results of a sample of ERF with a volume concentration of starch dispersion phase of 25 %. The dispersion medium is organosilicon liquid PMC-20, the activator is water.
The resulting coordinate values have been converted into a rod travel speed. As a result of experimental data processing the dependences of piston rod travel velocity on voltage on ERF-throttle windings were obtained. These graphs for pressures at pneumatic cylinder inlet 0.4 atm and 0.5 atm are shown in Fig.9 and 10, respectively.
It is shown that with increase of voltage on ERF shells there is decrease of speed of rod movement. For air inlet pressure 0.4 atm the change of speed is most pronounced in comparison with pressure 0.5 atm. This is explained by the fact that viscosity change effect in the gap is attenuated at higher ERF flow velocity in the throttle.
CONCLUSIONS
The change in actuator speed is due to the ERF effect occurring in the working gap of the ERF throttle. Formation of starch particle chain structures between the throttle electrodes provides a local increase in fluid viscosity in the gap, leading to reduction in the working fluid flow rate and reduction in the drive stem speed.
When air inlet pressure is about 0.5 atm, the fluid flow rate is relatively high, resulting in inefficient rod speed control. The chain structures do not have time to form and are quickly washed out by the high liquid flow.
The most effective piston rod speed control is observed at an air inlet pressure of 0.4 atm. As the voltage increases from zero to 2 kV, the piston rod speed decreases from 12 to 3 mm/s.
PEER REVIEW INFO
Editorial board thanks the anonymous reviewer(s) for their contribution to the peer review of this work. It is also grateful for their consent to publish papers on the journal’s website and SEL eLibrary eLIBRARY.RU.
Declaration of Competing Interest. The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Linear drives are used in nanotechnology equipment both for loading and unloading workpieces and for moving workpieces and tools during the technological process. The machining requirements often require movement at a constant speed or according to a certain law and maintaining the required speed with high accuracy, e.g. when scanning coordinate tables during electronic, ion and laser machining. The most efficient speed control is performed in pneumatic and hydraulic actuators. In order to increase accuracy of pneumohydraulic actuator movements, an intelligent material, electro-rheological fluid (ERF), is used as a working fluid [4, 5]. ERF is a suspension of particles of polarizable materials distributed in dielectric fluid. In electric field is absent, ERFs behave like most conventional suspensions, exhibiting Newtonian flow properties. However, when electric field is applied to them, a sharp reversible increase in viscosity occurs almost instantaneously due to the formation of chain-like structures directed parallel to the electric field lines of force. In addition to viscosity, elasticity and plasticity of the fluid will change. When electric field is removed, ERF also quickly returns to its original state. Works on investigation of ERF are mainly focused on selection of disperse phase, which will provide maximum electro-rheological (ER) effect of suspension. The use of barium titanate as disperse phase gives a shear strain of 400 Pa at an electric field strength of 800 V/mm [1]. If a lithium salt suspension of polystyrene-block-polyisoprene copolymer is used as solid phase, a shear stress of 50 Pa at 560 V/mm is achieved [2]. If cerium dioxide is used as the filler, a shear stress of 4000 Pa at 3000 V/mm can be achieved [3]. Starch can be used as the solid phase of ERF. A picture of a linear experimental pneumohydraulic actuator with ER control is shown in Fig.1.
The main elements of the linear drive are a pneumatic cylinder 1 and a hydraulic cylinder 2, with the pistons connected by a common rod and an ER throttle 3. The drive works as follows. Compressed air is supplied from compressor into pneumatic cylinder 1, which moves piston of pneumatic cylinder in reciprocating motion and moves piston of hydraulic cylinder 2 rigidly connected to it. A diagram of hydraulic cylinder is shown in Fig.2. The hydraulic cylinder is filled with ERF and as the piston moves, it is pumped from one cylinder cavity to another through the ERF restrictor. The drive speed is managed by applying a control voltage to the ERF restrictor. This changes viscosity of the ERF and pressure drop of the fluid in the throttle, which causes the volume flow of the ERF through the throttle to change and, consequently, the rod speed.
CALCULATIONS OF DRIVE PARAMETERS
Calculations of drive parameters were performed: potential distribution in ERF-throttle, and also speed of flow of ERF-fluid in throttle and pipelines. Figure 3 shows the scheme of ERF-throttle and its basic elements: electrode 1, regulating plate 2, insulator 3, seal 4, washer 5, screw 6, and also a micro-gap between the electrodes. When there is no electric field in the micro-gap, when field strength E = 0, the particles of the disperse phase are uniformly distributed between the electrodes. When E field strength is created in the gap, the particles line up along the field lines and change the viscosity of ERF.
Figure 4 presents photo of ERF-throttle and its elements: aperture for pipe connection 1, electrodes 2 and insulator 3.
Figure 5 shows the results of electric field calculation in Comsol software environment for an ERF-throttle: axisymmetrical finite-element model (a) and potential distribution (b). Calculations showed that the field is uniformly distributed between the electrodes and there are practically no edge effects.
Calculation of speed of flow of ERF in throttle gap and tubing was also carried out, as speed of flow essentially influences efficiency of throttle control and, accordingly, actuator. On Fig.6 the scheme of a hydraulic cylinder and connection to it ERF throttle is shown: hydraulic cylinder 1, ERF throttle 2 and pipelines 3.
Figure 7 shows results of laminar flow velocity calculation in Comsol software for ERF liquid in throttle, Fig.8 presents flow velocity of ERF in cross-section of the pipeline at the outlet of ERF throttle.
The results of hydraulic calculation showed that ERF flow velocity in the throttle gap and in the pipeline cross section is distributed unevenly due to angular arrangement of pipelines, therefore such arrangement is not optimal. In future it is recommended to use straight-through throttle.
EXPERIMENTAL RESULTS
The purpose of the experiment was to determine efficiency of the pneumohydraulic actuator stem speed control. At different pressures in the pneumohydraulic cylinder and different stresses on the throttle settings the position of the rod was measured. The paper presents the results of a sample of ERF with a volume concentration of starch dispersion phase of 25 %. The dispersion medium is organosilicon liquid PMC-20, the activator is water.
The resulting coordinate values have been converted into a rod travel speed. As a result of experimental data processing the dependences of piston rod travel velocity on voltage on ERF-throttle windings were obtained. These graphs for pressures at pneumatic cylinder inlet 0.4 atm and 0.5 atm are shown in Fig.9 and 10, respectively.
It is shown that with increase of voltage on ERF shells there is decrease of speed of rod movement. For air inlet pressure 0.4 atm the change of speed is most pronounced in comparison with pressure 0.5 atm. This is explained by the fact that viscosity change effect in the gap is attenuated at higher ERF flow velocity in the throttle.
CONCLUSIONS
The change in actuator speed is due to the ERF effect occurring in the working gap of the ERF throttle. Formation of starch particle chain structures between the throttle electrodes provides a local increase in fluid viscosity in the gap, leading to reduction in the working fluid flow rate and reduction in the drive stem speed.
When air inlet pressure is about 0.5 atm, the fluid flow rate is relatively high, resulting in inefficient rod speed control. The chain structures do not have time to form and are quickly washed out by the high liquid flow.
The most effective piston rod speed control is observed at an air inlet pressure of 0.4 atm. As the voltage increases from zero to 2 kV, the piston rod speed decreases from 12 to 3 mm/s.
PEER REVIEW INFO
Editorial board thanks the anonymous reviewer(s) for their contribution to the peer review of this work. It is also grateful for their consent to publish papers on the journal’s website and SEL eLibrary eLIBRARY.RU.
Declaration of Competing Interest. The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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