Pneumatic Control Research Articles

Pneumatic Pressure Control Using on‐off Valves with Pulse Width Modulation

AbstractServomotor‐controlled valves are widely used in industry for pressure control of pneumatic systems. However, as a first stage, they can cause significant hysteresis that can result in loss of pressure or flow control accuracy at the second stage level. To reduce this effect and improve accuracy, a possible solution relies on the use of on‐off switching valves controlled by Pulse Width Modulation (PWM). This approach is studied, firstly by analytically determining how the PWM parameters have to be tuned according to the on‐off valve characteristics, secondly by ensuring that these characteristics provide the desired behavior of the system, and finally by experimentally verifying whether the PWM control can successfully reduce hysteresis, without decreasing the application range.

Selection of the Optimal Parameters of a Pneumatic Three-line Direct-acting Pressure Reducing Valve

Reducing pneumatic valves, which are part of modern pneumatic control systems, are widely used in the automation of production and technological processes in various fields of technology. The efficiency of using pressure reducing valves depends on their parameters and characteristics. To select the optimal parameters of pressure reducing valves, various methods are used based on the search for the minimum of the target (target or criteria) function.The object of study is a three-line direct-acting pressure reducing valve, which ensures the determination of its optimal parameters. To calculate the optimal parameters of the pressure reducing valve, the method of orthogonal experimental design was applied. The main advantage of this method is that in this case all variables are varied simultaneously.The article presents the design features of a three-line direct-acting pressure reducing valve.The developed mathematical model of a pressure reducing valve is presented, which is a system of equations for a three-line direct-acting pressure reducing valve, which should be used to select the optimal parameters of the pressure reducing valve.To calculate the optimal parameters of the pressure reducing valve, the method of orthogonal experimental design was used. As an optimality criterion, the integral criterion of the squared error of the transient process, the change in the pressure level in the outlet line of the valve, was chosen.The optimal parameters of the pressure reducing valve are found, and transient processes of pressure change in the outlet line of the pressure reducing valve are calculated. The main requirements for optimization and selection of the optimal parameters of pressure reducing valves are formulated. A comparison of the transient processes of the outlet pressure before and after optimization is given.Based on the results of the work, the following conclusions were drawn:From the obtained comparative results of the transient processes of the level of outlet pressure in the outlet of the pressure reducing valve before and after optimization, it was found that after optimization the pressure reducing valve has a faster response.The speed has been increased from 0.35 s to 0.27 s, that is, the speed has increased by 1.30 times.The transient overshoot is less than 5%, and the static error is reduced by 1.9% and is completely eliminated.

System analysis of Pick and Place Control in Education

Pneumatic and electro-pneumatic mechanisms are a necessary component in the operation of production machinery and equipment. Their great development and wide application, especially in the last few years, have contributed to their advantageous characteristics, but also to their affordability. Reliability, safety at work, but also speed of operation together with control issues are such facts which are important to fully respect nowadays when designing assembly. With the progressive development of new processes, more sophisticated automation elements and, last but not least, management and control systems are associated. When designing a pick and place application, it is necessary to analyse the possibility and availability of using collaborative robots. This paper discusses the preliminary stages of the process of optimizing work movements and defines the "pick and place" of collaborative robots with the design of pneumatic and electro-pneumatic control.

Research of control method for pneumatic control of pneumatic microchips.

A novel composite control method for actuated chamber air pressure of pneumatic microfluidic chip via a three-way electromagnetic microvalve is presented in this paper. The purpose of the control methods is to improve air pressure controlling precision for pneumatic control. By using the Bang-Bang (on-off) controller for pneumatic control, the step-response time, air pressure steady-state accuracy, and air pressure fluctuations are performed with different maximum thresholds and minimum thresholds. Moreover, by using the k (proportional) plus PWM (Pulse-Width Modulation) control method for pneumatic control, the step-response time, air pressure steady-state accuracy, and air pressure fluctuations are performed with different carrier frequencies and carrier amplitudes. Both advantages and disadvantages of the two control methods are compared and analyzed based on the experimental data. According to the variable volume of the actuated chamber and the response characteristics of the three-way electromagnetic microvalve, the composite control method of the Bang-Bang plus k plus PWM is developed to control the actuated chamber air pressure. The experimental results show that when the absolute air pressure of the actuated chamber is set to 150kPa, the rising time is 69.3ms, which is about 8.0ms shorter than that of the k+PWM control method alone. The steady-state error is reduced from 0.90kPa to 0.65kPa, and the air pressure steady-state fluctuation is reduced from 1.60kPa to 0.90kPa, compared with the Bang-Bang control method alone.

A New Positioning Strategy Based on Parameter Tuning and Optimal Control Technique for Pneumatic Control Valve

To improve the accuracy, rapidity, and versatility of pneumatic control valves, mechanism modeling, and optimization analysis on pneumatic actuators were carried out, and then a new positioning strategy based on parameter tuning and optimal control technique was proposed consequently. Firstly, a dynamic model of valve position based on optimal control under constraint conditions was established, and the characteristic parameters of valve position motion were determined. Then, the adaptive processing of switching points was introduced into the optimal control strategy to improve the versatility of the control. Finally, according to different control strategy partitions, the interactive control of the piezoelectric air switch by fully open control and PWM improves the control accuracy of the algorithm. The experimental analysis of the control effect with other brand positioners shows that the proposed control strategy shortens the system adjustment time, improves the accuracy of valve position, and avoids the overshoot.

Constant Force Control of Centrifugal Pump Housing Robot Grinding Based on Pneumatic Servo System

In order to solve the problem of constant force control in the robot grinding process of a centrifugal pump housing a circular inner surface, this study used the force–position hybrid control mode based on a pneumatic servo system to realize the constant control of grinding force. In this process, the manipulator realizes the position and pose control of the end grinding device, and the end grinding device realizes the constant force control in the grinding process. The mathematical model of the pneumatic system is established and linearized by using the gas balance state equation, the adiabatic equation of the isentropic process, and the Sanville flow equation. The balance equation of the cylinder piston was established by using Newton’s second law, the transfer function of the contact force between the grinding device and workpiece was obtained, and the stability of the pneumatic control system was determined by the Hurwitz criterion. The PID algorithm was used to improve the displacement response speed of the system and eliminate the impact and oscillation in the force response. The feasibility, stability, and robustness of the system were verified by simulation experiments. This method has the advantages of simple control, a small amount of calculation, and a fast response, as well as providing a feasible scheme for the popularization and application of robot grinding technology.

An improved rational Bezier model for pneumatic constant force control device of robotic polishing with hysteretic nonlinearity

The pneumatic constant force control device has been widely used in robot deburring, sanding, polishing, and other fields due to its good flexibility, simple control, and low cost. The force control accuracy of the pneumatic constant force system could be greatly affected by its nonlinear hysteresis characteristics in the process from the cylinder input to the force output at the end of the device. A rational Bezier-based state fitting method (BSFM) has been presented for calibrating the inherent nonlinearity of the low-cost pneumatic constant force system. Compared with the most widely used PSFM, which is a polynomial-based state fitting method, the BSFM could calibrate the strong inherent nonlinearity of the system more smoothly with the lower ordered model and in a continuous form rather than the piecewise form of the PSFM. The BSFM could maintain a balance between simplicity and precision. Through a series of comparative experiments with different contact forces and feed rates, the proposed method has smaller force overshoot and when active force control is turned on, the force variation is greatly reduced to less than 2 N. The average roughness of the workpiece reached 0.4 µm after polishing.

Programmable soft valves for digital and analog control

In soft devices, complex actuation sequences and precise force control typically require hard electronic valves and microcontrollers. Existing designs for entirely soft pneumatic control systems are capable of either digital or analog operation, but not both, and are limited by speed of actuation, range of pressure, time required for fabrication, or loss of power through pull-down resistors. Using the nonlinear mechanics intrinsic to structures composed of soft materials-in this case, by leveraging membrane inversion and tube kinking-two modular soft components are developed: a piston actuator and a bistable pneumatic switch. These two components combine to create valves capable of analog pressure regulation, simplified digital logic, controlled oscillation, nonvolatile memory storage, linear actuation, and interfacing with human users in both digital and analog formats. Three demonstrations showcase the capabilities of systems constructed from these valves: 1) a wearable glove capable of analog control of a soft artificial robotic hand based on input from a human user's fingers, 2) a human-controlled cushion matrix designed for use in medical care, and 3) an untethered robot which travels a distance dynamically programmed at the time of operation to retrieve an object. This work illustrates pathways for complementary digital and analog control of soft robots using a unified valve design.

Design of FOPID Controller for Pneumatic Control Valve Based on Improved BBO Algorithm.

Aiming at the problems of nonlinearity and inaccuracy in the model of the pneumatic control valve position in the industrial control process, a valve position control method based on a fractional-order PID controller is proposed. The working principle of the pneumatic control valve is analyzed, and its mathematical model is established. In order to improve the accuracy of the model, an improved biogeography-based optimization algorithm is proposed to tune the parameters of the fractional-order PID controller in view of the wide range and high complexity of the fractional-order PID controller. The initialization of the chaotic graph, the adjustment of the migration model, and the improvement of the migration operator and the mutation operator are introduced to improve the algorithm optimization ability, which is used for the model identification of the control valve control system. The simulation and experimental results clearly show that, compared with the integer-order PID controller, the designed fractional-order PID controller has faster response speed and control accuracy, which can better meet the requirements of pneumatic control valve position control.

Redundant Robot with Pneumatic Artificial Muscles for Rehabilitation Works Using Iterative Learning Control

This study aims to develop a multi-functional robotic arm with a multi-degree of freedom using a pneumatic artificial muscle cylinder as the main actuator, with a wearable function. While wearing the robotic arm, it has four degrees of freedom and can be used as an upper limb rehabilitation aid to perform rehabilitation exercise tasks. The rotating axes are driven by pneumatic artificial muscle cylinders to ensure the safety and flexibility of the robot interaction. By integrating multiple pneumatic control valves and sensors with embedded interface cards, the control of pneumatic artificial muscle cylinders is performed, and the rehabilitation trajectory commands are planned through the kinematics of the robotic arm, and a closed-loop control system is established to enable the robotic arm to achieve the task of rehabilitation trajectory tracking. In the single-axis robotic arm controller experiment, it was found that the LMS-PID is superior to the conventional PID control method. In the control experiment of the robotic arm under the multi-axis recovery trajectory, the result showed that the training of drawing a circle on the wall could be successfully planned. In the multi-axis robotic tracking experiment under the rehabilitation trajectory, the result showed that the RMSE of the tracking trajectory decreased to 0.2444 and 0.2853. In the robotic arm joining/loading experiment, it was shown that the method of this study can withstand some loading effects. Moreover, this study introduces iterative learning control to improve the non-linear compensation and phase lag problems of the PID controller so that the robot arm can have a certain tracking accuracy under the round-trip robust trajectory.

Research on the roll control of the flapless aircraft with circulation control

The purpose of this paper is to study the roll control of the flapless aircraft under low-speed and high-speed flight states and investigate the equivalent control effect (ECE) and the power consumption of the pneumatic control. First, the roll moment coefficient of the aircraft with different aileron deflection angles is calculated. Then the intensity of the jet is adjusted to match the roll moment coefficient, so that the deflection angle of the ailerons and the intensity of the jet corresponding to the same rolling moment are found. Based on the realization of the roll control, the aerodynamic efficiency of the flapless aircraft is evaluated by using the equivalent lift-to-drag ratio ( Ecc) considering power consumption. The ECE curves of the pneumatic roll control under low-speed and high-speed flight states are obtained. Under low-speed flight state, the increment of aerodynamic efficiency brought by the jet cannot make up for its power consumption. Under high-speed flight state, the aerodynamic efficiency increment brought by the pneumatic control can compensate its power consumption before Cl = 0.061.

A More Precise Modeling Method for Pneumatic Cabin Pressure Control System considering the Ambient Environmental Impacts

Pneumatic cabin pressure control system (PCPCS), with its exceptional electromagnetic compatibility, is expected to become the major equipment on a high-performance airplane again in the future. Although the PCPCS has been mature for a long time, the broad popularization of the digital cabin pressure control system (DCPCS) has left the PCPCS in the cold for decades. This makes the PCPCS unable to meet the severe cabin pressure regulation requirements of high-speed aircraft today. For this purpose, a more precise PCPCS modeling method is proposed. Through this method, the relation between different parts in the PCPCS can be accurately characterized. Moreover, the impact of the ambient environment on the PCPCS is taken into consideration. This method can be used to accurately analyze the PCPCS under maneuvering flight. And it also assists in the verification of the system improvements of dynamic performance in the future. Simulation results show that the aircraft acceleration disturbs the PCPCS slightly, and the cabin air inflow fluctuation has a significant impact on the cabin air pressure.

Pneumatic cylinder speed and force control using controlled pulsating flow

An application for accurate and low-cost force and velocity control of a pneumatic actuator, which can be used in any pneumatic circuit, is described in this paper. Control of a pneumatic cylinder is proposed via a pulsating flow technique. The technique uses on/off solenoid coils in the direction control valves in lieu of expensive servo controllers, such as proportional directional control valves. Pulsating air frequencies of 1.5, 3, and 4.5 Hz are applied by the designed circuit to investigate inlet constant pressures ranging from 1.72 to 5.17 × 105 Pa. The speed and force of a pneumatic cylinder rod are controlled using the generated pulsating flow and the results show success of idea of ​​controlling the speed and force of the pneumatic cylinder rod using the pulse flow technique. Empirical correlations suitable for later use in automatic control circuits are derived and are shown to exhibit an accuracy of up to ∼ 90–95.5% in predicting output force and velocity. It is also used to select the required frequency to obtain the speed and force required for the cylinder. To validate the pneumatic cylinder speed and force control using pulse flow technique, simulations are carried out using the Automation Studio program. The results show an improvement in control of the pneumatic cylinder mechanical performance and demonstrate that improvements are a function of the frequency of compressed air source pulses and pressure. An empirical correlation is also derived for predicting the cylinder rod speed and force at any source pressure and pulse frequency.

Evaluation of Pneumatic Insertion Stability of Utah Slanted Electrode Arrays in Rat Sciatic Nerve.

The Utah Electrode Array (UEA) and its variants (e.g., the Utah Slanted Electrode Array, or USEA) have been prominent contributors to advances in the field of neural engineering over the past decade. The most common means of inserting UEA and USEA devices into neural tissue is pneumatic insertion performed by an insertion wand and a pneumatic controller. As design changes from the well-established standards occur to better suit specialized surgical applications, it becomes essential to verify that the alterations do not compromise the structural integrity of the device during insertion. This paper characterizes and demonstrates the reliability of specialized USEAs and insertion wands designed for auditory nerve implants following pneumatic insertion into a rat sciatic nerve. The results show that proposed changes in the USEA form factor and pneumatic insertion ergonomics do not compromise implant stability and device structural viability.

A MIG Welding Clamping Scheme for Power Battery Enclosure’s Deformation Restrain

Aiming at the inward shrinkage between the frame and the bottom plate of the power battery enclosure after MIG (melt inert-gas) welding, a welding clamping scheme with hook-pull devices was designed. By adjusting the clamping force of the hook-pull device, the MIG welding deformation force was counteracted, so the inward shrinkage deformation of the frame after welding was restrained. To obtain the deformation force during the MIG welding, the welding simulation model of power battery enclosure was established. Gaussian heat source model was selected as temperature load. Through the numerical simulation and experimental analysis of the temperature field, the numerical simulation results are in good agreement with the measured thermal cycle curve in terms of temperature value and change trend. The error between numerical simulation result curve and measured thermal cycle curve at the measurement point is no more than 10%, which can meet the simulation requirements. Based on the simulation model and the load of the temperature field, deformation force curves were obtained by simulating the welding process. To counteract the MIG welding deformation force, a pneumatic servo control system of the welding clamp was designed, which can generate equal and reversed welding deformation force. The experiments show that the actual output force of the system has a tiny time delay and fluctuates with the varies of the pneumatic servo control system. The maximum fluctuation error is 6.96 N, which is within the permitted error range. The welding experiments were carried out to verify effectiveness of the control system and the welding clamp. The field results have shown that the maximum inward shrinkage deformation after welding is 0.6 mm, which is less than 1.2 mm required by the MIG welding process.

Metaheuristics Based Modeling and Simulation Analysis of New Integrated Mechanized Operation Solution and Position Servo System

Inadequate environmental protection is a problem, and to address it, the efficiency and quality grade of mechanical operations should be improved. A new comprehensive mechanized operation solution is proposed. The position control of a servo motor utilizing a PID (proportional, integral, derivative) controller and soft computing optimization approaches is explored in this paper. The essential technological realization techniques are reviewed and assessed, which serves as a reference for comprehensive mechanization solutions. The simulation model may be used to examine system features and explore control strategy by reflecting the characteristics of the actual system. A PID controller is designed by establishing a mathematical model based on the position servo system. It is verified that the PID control link is added to the pneumatic position servo control system. Through the comparison of the PID control experiment and PID control simulation data, the system can achieve high-precision position control, and the error is less than ±20 mm, meeting the requirements of rust removal and spraying design, and showing that the control system works stably and reliably to achieve high-precision simulation of the pneumatic position servo system.

Comparison of Proportional and PWM Pneumatic Control in Terms of Positioning and Compressed Air Consumption

In this paper is shown a comparison of proportional pneumatic control and Pulse Width Modulation (PWM) pneumatic control in terms of positioning and compressed air consumption. All experimental tests were performed on a device for lifting and holding of the workpieces, which consists of one vertically mounted rodless cylinder with integrated vacuum gripper. In the case of the proportional pneumatic control, cylinder piston is always positioning in the correct position, but position losses are recurring during the time (in majority of cases, the position loss is 4 mm). As the control system constantly returns the cylinder piston to the desired position, that increases the compressed air consumption. In the case of the PWM pneumatic control, the position error is occurring (in majority of cases, the absolute value of the relative position error is less than 2%), but there is no position loss during the period of workpiece holding, i.e. there is no additional compressed air consumption. The compressed air consumption differential is approximately 18.6%. In addition, in case of Meter-out control in combination with previously defined types of control, the positioning is more accurate but the compressed air consumption slightly increases with decreasing the opening level of the one-way flow control valve.

Teaching Research of “Pneumatic Control System Installation and Commissioning” Course Based on Job Competence Requirements

Most of the professional courses of engineering technology will follow the requirements of post ability, which is 
 helpful to improve the personal professional ability of vocational students and quickly adapt to the job requirements. In order to 
 achieve this goal, teaching methods should be reformed and post ability requirements should be integrated into the whole teaching 
 process. Thus, the students’ learning objectives are integrated with the teaching objectives, enhancing their interest in learning and 
 improving the learning effect.

Technical note: Low-cost MR-compatible pneumatic respiratory organ motion simulator for the development of MR-guided thermal therapy.

In magnetic resonance (MR)-guided thermal therapy, respiratory motion can cause a significant temperature error in MR thermometry and reduce the efficiency of the treatment. A respiratory motion simulator is necessary for the development of new MR imaging (MRI) and motion compensation techniques. The purpose of this study is to develop a low-cost and simple MR-compatible respiratory motion simulator to support proof-of-concept studies of MR monitoring approaches with respiratory-induced abdominal organ motion. The phantom motion system integrates pneumatic control via an actuator subsystem located outside the MRI and coupled via plastic tubing to a compressible bag for distention and retraction within the MRI safe motion subsystem and phantom positioned within the MRI scanner. Performance of the respiratory motion simulator was evaluated with a real-time gradient echo MRI pulse sequence. The motion simulator can produce respiratory rates in the range of 8-16 breaths/min. Our experiments showed the consistent periodic motion of the phantom during MRI acquisition in the range of 3.7-9mm with 16 breaths/min. The operation of the simulator did not cause interference with MRI acquisition. In this study, we have demonstrated the ability of the motion simulator to generate controlled respiratory motion of a phantom. The low-cost MR-compatible respiratory motion simulator can be easily constructed from off-the-shelf and 3D-printed parts based on open-source 3D models and instructions. This could lower the barriers to the development of new MRI techniques with motion compensation.

Design and Simulation Experiment of Rigid-Flexible Soft Humanoid Finger

This paper is based on the “Fast Pneumatic Mesh Driver” (FPN) used to couple a silicone rubber soft body with a rigid skeleton. A rigid-flexible coupling soft-body human-like finger design scheme is proposed to solve the problem of low load on the soft-body gripping hand. The second-order Yeoh model is used to establish the statics model of the soft humanoid finger, and the ABAQUS simulation analysis software is used for correction and comparison to verify the feasibility of the soft humanoid finger bending. The thickness of the driver cavity and the confining strain layer were determined by finite element simulation. The mold casting process is used to complete the preparation of human-like fingers and design a pneumatic control system for experiments combined with 3D printing technology. The experimental results show that the proposed rigid-flexible coupling soft body imitating the human finger structure can realize the corresponding actions, such as the multi-joint bending and side swinging, of human fingers. Compared with the traditional pure soft-body finger, the fingertip output force is significantly improved. The optimal design and simulation analysis of the human gripper and the feasibility of the application have practical guiding significance.