From the traditional point of view, cylinders and electric actuators have always been considered as automation products belonging to two completely different fields, but in recent years, with the continuous improvement of the degree of electrification, electric actuators are slowly immersed in the field of pneumatics. Applications are both competitive and complementary. In this column, we will compare the advantages of cylinders and electric actuators in terms of technical performance, purchase and application costs, energy efficiency, applications and market conditions.
Technical performance
As we all know, compared to electric actuators, cylinders can work reliably in harsh conditions, are simple to operate, and are basically maintenance-free. The cylinder is good at reciprocating linear motion, especially suitable for the most conveying requirements in industrial automation - linear handling of workpieces. Moreover, stable speed control can be easily achieved simply by adjusting the one-way throttle valves installed on both sides of the cylinder, which has become the biggest feature and advantage of the cylinder drive system. Therefore, for users who do not have multi-point positioning requirements, most of them prefer to use cylinders from the perspective of ease of use. At present, most of the applications of electric actuators used in industrial fields require high-precision multi-point positioning. This is because it is difficult to achieve with air cylinders, and the result is the second best.
The electric actuator is mainly used for rotating and swinging conditions. Its advantages are fast response time and precise control of speed, position and torque through a feedback system. However, when the linear motion needs to be completed, it needs to be converted through mechanical devices such as toothed belts or screw rods. Therefore, the structure is relatively complex, and the professional knowledge of the working environment and operation and maintenance personnel is relatively high.
Advantage
(1) The requirements for users are low. The principle and structure of the cylinder are simple, easy to install and maintain, and the requirements for users are not high. The electric cylinder is different, engineers must have certain electrical knowledge, otherwise it is very likely to be damaged due to misoperation.
(2) The output force is large. The output force of the cylinder is proportional to the square of the cylinder diameter; while the output force of the electric cylinder is related to three factors, the cylinder diameter, the power of the motor and the pitch of the lead screw. The larger the cylinder diameter and power, and the smaller the pitch, the greater the output force. A cylinder with a cylinder diameter of 50mm can theoretically output a force of up to 2000N. For electric cylinders with the same cylinder diameter, although the products of different companies are different, they basically do not exceed 1000N. Obviously, the cylinder has more advantages in terms of output force.
(3) Strong adaptability. The cylinder can work normally in high temperature and low temperature environment and has the ability of dustproof and waterproof, and can adapt to various harsh environments. The electric cylinder has high requirements on the environment and poor adaptability due to the large number of electrical components.
The advantages of the electric cylinder are mainly reflected in the following three aspects:
(1) The system composition is very simple. Since the motor is usually integrated with the cylinder block, plus the controller and cables, the entire system of the electric cylinder is composed of these three parts, which is simple and compact.
(2) The number of stopping positions is large and the control accuracy is high. Generally, electric cylinders are divided into low-end and high-end. The stop positions of low-end products are 3, 5, 16, 64, etc., which vary according to different companies; high-end products can reach hundreds or even thousands of positions. . In terms of accuracy, the electric cylinder also has absolute advantages, and the positioning accuracy can reach ¡ 0.05mm, so it is often used in precision industries such as electronics and semiconductors.
(3) Strong flexibility. There is no doubt that the flexibility of the electric cylinder is far stronger than that of the cylinder. Since the controller can be directly connected with the PLC, it can precisely control the rotation speed, positioning and forward and reverse rotation of the motor. To a certain extent, the electric cylinder can move at will according to the needs; due to the compressibility of the gas and the Inertia, even if the coordination between the reversing valve and the magnetic switch is good, the accurate positioning of the cylinder cannot be achieved, and the flexibility is out of the question.
In terms of technical performance, I believe that electric and pneumatic have their own advantages. First of all, the advantages of electric actuators mainly include:
(1) Compact structure and small size. Compared with pneumatic actuators, electric actuators are relatively simple in structure. A basic electronic system includes actuators, three-position DPDT switches, fuses and some wires, which are easy to assemble.
(2) The drive source of the electric actuator is very flexible. Generally, the on-board power supply can meet the needs, while the pneumatic actuator needs an air source and a compression drive device.
(3) Electric actuators have no danger of "air leakage" and are highly reliable, while the compressibility of air makes pneumatic actuators slightly less stable.
(4) There is no need to install and maintain various pneumatic pipelines.
(5) The load can be maintained without power, while the pneumatic actuator requires a continuous pressure supply.
(6) The electric actuator is quieter because no additional pressure device is required. Usually, if the pneumatic actuator is under heavy load, a silencer should be installed.
(7) Electric actuators are superior in control accuracy.
(8) In pneumatic devices, it is usually necessary to convert electrical signals into gas signals, and then into electrical signals. The transmission speed is slow, and it is not suitable for complex circuits with too many components.
The advantages of the cylinder lie in the following four aspects:
(1) The load is large and can be adapted to the application of high torque output (however, the current electric actuator has gradually reached the current pneumatic load level).
(2) Quick action and quick response.
(3) Good adaptability to working environment, especially in harsh working environments such as flammable, explosive, dusty, strong magnetism, radiation and vibration, it is superior to hydraulic, electronic and electrical control.
(4) The motor is easily damaged when the stroke is blocked or the valve stem is tied.
Buy and apply cost comparison
Generally speaking, electric servo drives are more expensive than pneumatic servo drives, but they also depend on specific requirements and occasions. Some low-power DC motors make up an electric slide (electric servo system) that is actually cheaper than a pneumatic servo system.
For example: when the load is 1.5kg, the working stroke is 80mm, the speed is between 2170mm/s, and the accuracy is ¡ 0.1mm, acceleration 2.5m/s2 and other working conditions, FESTO company adopts electric servo system composed of small electric sliding table, controller, motor cable, control cable, programming cable and power cable, etc., its price is higher than pneumatic servo system. 25 percent cheaper. The same is true for electric cylinders with piston rod. It should be noted that if an AC motor is used, the price of the formed electric servo system is about 40 percent higher than that of the pneumatic servo system.
From the perspective of purchase and application costs, the current cylinder still has obvious advantages. For the pneumatic system, the control system and the actuator are very simple. Each cylinder only needs to be equipped with a solenoid valve to complete the switching of the gas circuit and perform motion control. The probability of cylinder failure is relatively small, maintenance is simple and convenient, and the cost also low.
For electric actuators, although the acquisition of electric energy is relatively simple and the energy cost is low, the purchase and application costs are relatively high. At the same time, the use of electric actuators requires a lot of protection measures. Wrong circuit connections, voltage fluctuations and overloading of the load will cause damage to the electric drive. Therefore, it is necessary to install a protection system on the circuit and machinery, which increases a lot of extra expenses. In addition, because the electric actuator drive unit has many parameterized settings and high integration, once it fails, the entire component needs to be replaced. And when the driving force required by the system increases, a complete set of replacement components can also be achieved. Therefore, it can be seen from a comprehensive comparison that the cylinder has a greater advantage in terms of purchase and maintenance costs.
Energy Efficiency Comparison
The results of our study show that in the horizontal reciprocating motion with a short reciprocating period (less than 1 min), the operating energy consumption of the electric actuator is usually lower than that of the cylinder, that is, it is more energy efficient. When the reciprocating period is longer (greater than 1min), the cylinder becomes more energy-efficient. This is first because the controller of the electric actuator usually consumes about 10W of electricity when the terminal stops, while the cylinder only consumes electricity from the solenoid valve and gas leakage, which is generally lower than 1W, that is, the longer the terminal stops, the better it is for the cylinder; Secondly, the rated efficiency of the motor under the condition of continuous rotation can reach more than 90 percent , but the average efficiency under the condition of table-shaped acceleration and deceleration in the linear reciprocating motion (screw conversion) is less than 50 percent . During vertical reciprocating motion, the holding action of clamping the workpiece requires continuous supply of current to the electric actuator to overcome gravity, and the cylinder only needs to close the solenoid valve, which consumes less electrode. Therefore, the energy consumption advantage of the electric actuator compared with the cylinder is not very large during the vertical reciprocating motion.
It can be seen from the above that the efficiency of the motor itself is very high, but considering its efficiency drop and the power consumption of the controller in the reciprocating linear motion, the electric actuator may not necessarily be more energy-efficient than the cylinder, and the specific comparison depends on the actual working conditions, that is, the installation direction, reciprocating Movement cycle and load rate, etc.
Application comparison
Pneumatic and electric systems are not mutually exclusive. Rather, it's just a matter of asking for something different. The advantages of pneumatic drives are obvious. When faced with harsh environmental conditions such as dust, grease, water or cleaning agents, pneumatic drives are more suitable for harsh environments and are very durable. Pneumatic drives are easy to install, provide typical gripping functions, are inexpensive and easy to operate.
Electric drives with servo motors offer advantages in situations where forces are rapidly increasing and precise positioning is required. Electric drives are the best choice for applications that require precise, synchronous operation, adjustable and specified positioning programming. Electric drive systems consisting of servo or stepper motors with closed-loop positioning controllers can complement the deficiencies of pneumatic systems. place.
From the perspective of technology and use cost, the cylinder has obvious advantages, but which technology should be used for drive control in actual use should be comprehensively considered from multiple factors. Various systems in modern control are becoming more and more complex and sophisticated, and it is not just a certain drive control technology that can satisfy the various control functions of the system. The cylinder can simply realize fast linear circulatory movement, simple structure, convenient maintenance, and can be used in various harsh working environments, such as explosion-proof requirements, dusty or humid working conditions.
Electric actuators are mainly used in applications that require precise control. Now the flexibility requirements in automation equipment are constantly improving. The same equipment is often required to meet the processing needs of workpieces of different sizes. The actuator needs to perform multi-point positioning control, and the actuator needs to be controlled. The running speed and torque can be precisely controlled or synchronously tracked, which cannot be achieved by traditional pneumatic control, and electric actuators can easily achieve such control. It can be seen that the cylinder is more suitable for simple motion control, while the electric actuator is mostly used for precise motion control.
market situation comparison
Cylinder-driven systems have rapidly gained popularity in industrial automation since the 1970s. Today, the cylinder has become the mainstream actuator for PTP (PointToPoint) handling in the field of industrial production at home and abroad, and the market size of pneumatic components centered on the cylinder drive system has reached a scale of 11 billion US dollars.
Since the 1990s, the rapid development of motors and their microelectronic control technology has made the application of electric actuators in industrial automation possible. Moreover, the rise of the semiconductor industry has directly promoted the expansion of the application of electric actuators that can realize high-precision multi-point positioning in the industrial field.
In the late 1990s, Japan and other major industrialized countries even once appeared that electric actuators were about to replace air cylinders and that air cylinders would withdraw from the stage of history. Because it is generally believed that the energy conversion efficiency of the motor in the electric actuator is high, and the energy conversion efficiency of the cylinder is low, the inefficient products will be eliminated. However, ten years later, electric actuators have not been popularized in industrial sites, and their market size is still far behind that of pneumatics. Moreover, both in industrially developed countries and in newly industrialized countries such as China, the sales of cylinders have not only not decreased, but have also been growing steadily. In China, the annual growth rate of cylinder sales has been maintained at more than 20 percent in recent years.
If it is necessary to scientifically and objectively evaluate the two, the LifeCycleAssessment method must be adopted, and the comprehensive indicators of the three stages of manufacturing, use and disposal must be compared. Specific indicators include cost, energy consumption, and burden on the environment (mainly emissions, etc.). For example, cost, electric actuators have advantages in operating energy consumption (use phase) cost, but maintenance cost (use phase) and acquisition cost (manufacturing phase) are much higher than cylinders, the comparison on this index should be based on the sum of all costs.
In terms of total cost, our findings show that air cylinders have certain advantages in most industrial applications.
Based on the above analysis, we should see that the cylinder and the electric actuator have their own characteristics, and their advantages and disadvantages cannot be evaluated simply by the level of efficiency. With the development of electrical technology, the cost of electric actuators will be further reduced, and its application fields are expected to be further expanded, but it is unrealistic to completely replace the cylinders with self-priming and non-clogging sewage pumps.
From the perspective of the market form, it has been mentioned earlier that if the electric cylinder is produced with reference to the shape and installation connection dimensions of the cylinder from the beginning, it is a good start. For rodless cylinders and pneumatic slides that do not have ISO standards at present, the corresponding shapes and installation connection dimensions are also adopted. This convenient measure can eliminate unnecessary competition between pneumatic drives and electric drives in terms of installation, addition or replacement. . FESTO's electric drive products include more than 300 freely combinable handling modules and multi-axis systems. At Festo, electric drives are not a competitor to pneumatic drives, but a perfect complement to the performance of pneumatic drives. Electric drives are characterized by precision and flexibility. Electric drives are the ideal solution for non-clogging self-priming sewage pumps in applications where forces are rapidly dissipated and precise positioning is required.
Therefore, the development of cylinders and electric actuators should be in a very benign state and complementary in the future, and they will certainly develop in accordance with the natural laws of scientific development of these two technologies.
