Proportional control technology is a control technology developed in the late 1960s that is reliable, inexpensive, and has control accuracy and response characteristics that can meet the actual needs of industrial control systems. Electro-pneumatic proportional control technology is a control method between the on-off control technology of ordinary pneumatic valves and electro-pneumatic proportional control technology. It can continuously and proportionally follow the control signal to change the air pressure. Therefore, the control performance of the electro-pneumatic proportional control technology is better than the on-off control of ordinary pneumatic valves. Comparing with the servo valve, due to the proportional valve has a dead zone in neutral position, there is still a slight gap in the control accuracy and response speed. However, its obvious advantage is that it has strong anti-pollution ability, which greatly reduces the working failure of pneumatic system caused by contaminant. On the other hand, the cost of proportional valve is lower than servo valve, and the structure is also simple, which has been widely used in many occasions.
After decades of continuous development, proportional control technology has reached a relatively complete level. It is mainly manifested in three aspects. First, feedback and electrical correction methods such as pressure, flow rate, displacement and dynamic pressure are adopted, which improves the steady-state accuracy and dynamic response quality of the valve. It indicates that the design principle of proportional control has been perfected. Second, Proportional technology and cartridge valve have been combined to give birth to proportional cartridge technology. Last, the birth of proportional volume components represented by proportional control pumps further expands the application of proportional control technology.

1. Types of Electro-Pneumatic Proportional Valves and how they work
There are many structural forms of electro-pneumatic proportional valve, similar to electro-pneumatic pressure regulator, usually composed of electro-mechanical converter, pneumatic amplifier (pilot valve and power main valve) and detection feedback mechanism. If it is a single valve, there is no pilot valve or it is a multi valve.
Oransal solenoid valfler, kuvvet motorları veya tork motorları gibi elektromekanik konvertörler, pilot valfi hareket ettiren bir yer değiştirme veya dönme açısı oluşturmak için giriş elektrik sinyallerini oransal amplifikatörler aracılığıyla kuvvetlere veya torklara dönüştürmek için kullanılır. Pilot valf ayrıca ön kademe (sürgülü valf, kaldırma valfi, nozul bölme valfi veya kartuş valfi olabilir) olarak da adlandırılır ve mekanik miktarı dönüştürmek için düşük güçlü elektromekanik dönüştürücülerden yer değiştirme veya köşe sinyali girişini almak için kullanılır. Ana valf (sürgülü valf, kaldırma valfi veya kartuş valfi) pilot kademe valfinin pnömatik basıncını akış veya basınç çıkışına dönüştürür ve algılama geri besleme mekanizması (hidrolik, mekanik, elektriksel geri besleme vb. Olabilir) giriş ve çıkış dengesini sağlamak için ana valf kontrol portunun basınç, akış veya sürgülü valf yer değiştirmesini pilot valf girişine veya oransal amplifikatör girişine geri besler.
Oransal kontrolün çekirdeği oransal valftir. Oransal valfin giriş ünitesi, giriş sinyalini mekanik bir miktara dönüştüren elektromekanik bir dönüştürücüdür. Dönüştürücüler arasında servo motorlar ve step motorlar, kuvvet motorları ve tork motorları ve oransal solenoid valfler bulunur. Bununla birlikte, en yaygın oransal valfler oransal solenoid valfler kullanır. Oransal solenoid valf, mekanik miktarların (kuvvet veya tork ve yer değiştirme) bir giriş elektrik sinyali (akım) üretmesine neden olan ve daha sonra pnömatik sistemin basıncını, yönünü ve akışını sürekli olarak kontrol eden solenoid valf prensibine göre tasarlanmıştır. Oransal solenoid valfın yapısı Şekil 2'de gösterilmektedir. Bobinler, armatürler, atıcılar vb. Bir sinyal giriş bobini olduğunda, bobindeki manyetik alan armatür üzerinde bir kuvvet oluşturur ve armatür, sinyal akımının büyüklüğüne ve yönüne göre manyetik alanda bulunur. Sürekli olarak orantılı olarak hareket eder ve daha sonra sürgülü valfin hareketini kontrol etmek için itme çubuğunu sabit bir pimden hareket ettirir. En yaygın kullanılan oransal solenoid valf, yüksek voltajlı DC oransal solenoid valftir.

The types of proportional electromagnetic valves are mainly divided into the following categories according to their working principles:
(1) Force control type
The stroke of this type of electromagnetic valve is short, only 1.5mm, and the output force is proportional to the input current. It is often used in the pilot control stage of the proportional valve.
(2) Stroke control type
It is composed of a force control type plus a load spring. The force output by the electromagnetic valve is converted into an output displacement through the spring. The output displacement is proportional to the input current. The working stroke reaches 3mm and has good linearity. It can be used in direct Controlled proportional valve.
(3) Position adjustment type
After the position of the armature is detected by the sensor in the valve, an in-valve feedback signal is sent out, and the position of the armature is re-adjusted after the comparison in the valve, forming a closed-loop control in the valve, with high precision. Regardless of the force, it can almost be compared with the servo valve in terms of accuracy. The proportional valve produced by many famous companies in the world adopts this structure.
Proportional valves are classified into four categories according to their main functions: proportional pressure regulators, flow control valves, directional control valves, and proportional compound control valves:
(1) Electro-Pneumatic Pressure Regulator
There are relief valve, pressure reducing valve, sequence valve, which can continuously adjust the system pressure.
(2) Proportional directional valve
The polarity of the input current determines the flow direction of the air flow, the stroke of the valve core is proportional to the size of the input current, and the directional valve is divided into two categories: with position sensor and without position sensor.
(3) Proportional flow control valve
There are proportional speed regulating valve and proportional overflow flow control valve, which can continuously adjust the system flow or speed.
(4) Proportional composite control valve
Generally, it is composed of two kinds of valves with different functions, suitable for use in open-loop control systems. Each type can be divided into two structural forms: direct control and pilot control. Direct control is used in low-flow and low-power systems, and pilot control is used in large-flow and high-power systems to form electro-pneumatic proportional valves.

2. Selection of proportional valve
(1) Select the type of proportional valve according to the purpose and the controlled object.
(2) Understand the dynamic and static indicators of proportional valve correctly, mainly including rated output, initial current, hysteresis, repeatability, rated pressure loss, temperature drift, response characteristics, frequency characteristics, etc.
(3) Select the accuracy of proportional valve according to the working accuracy requirements of actuator, and the valve with feedback closed loop has good steady-state and dynamic quality. If the inherent characteristics of proportional valve, such as hysteresis, nonlinearity, etc., cannot make the controlled system achieve the desired effect, software programs can be used to improve the performance ofsystem.
(4) If you choose a proportional valve with a pilot valve, notice the requirements of pilot valve on oil pollution degree. Generally, it should meet the ISO18/15 standard, and install a 10 oil inlet oil filter on the oil road.
(5) The orifice of proportional valve should be the flow of actuator at the maximum speed. If the orifice is too large, the resolution of system will be reduced. The proportional valve must use the matching amplifier. The distance between the valve and the amplifier should be as short as possible. The amplifier adopts current negative feedback, and sets the ramp signal generator to control the boosting, decreasing time or motion acceleration and deceleration. When power is off, the spool can be placed in a safe position.

3. Proportional control system
The proportional control system has direct proportional control and electro-pneumatic proportional control, which is similar to the servo system control in essence, and can be analyzed with reference to the servo system. According to whether there is feedback, it is divided into open-loop control and closed-loop control. The proportional valve-controlled hydraulic cylinder or motor system can control parameters such as speed, displacement, rotational speed and torque.

4. Comparison of Electro-hydraulic Servo System and Proportional Servo System

Elektrik-pnömatik oransal basınç regülatörleri hakkında daha fazla bilgi için lütfen
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