Views: 294 Author: Leapion Publish Time: 08-02-2022 Origin: https://www.leapion.com
The linear motor was invented by the British in 1845, but the air gap of the linear motor at that time was too large and the efficiency was very low, so it could not be applied. After the 1970s, Kollmorgen was also launched, but its development was limited due to high cost and low efficiency. It was not until the 1970s that linear motors were gradually developed and applied in some special fields. In the 1990s, linear motors began to be used in the machinery manufacturing industry. Now some technologically advanced machining center manufacturers in the world have begun to apply them to their high-speed machine tools. For example, well-known companies are launching high-speed and high-precision machining centers using linear motors. Leapion also uses a linear motor in LF-6060Mi high-precision fiber cutting machine launched.
The following mainly refers to the comparison of several main characteristics of the high-speed silent lead screw and linear motor, as a reference for the relevant industry.
Linear guides have considerable advantages in speed
Linear Motor
Speed: 300 m/min
Acceleration: 10g
Ball screw: 120 m/min
Acceleration: 1.5g
Compared with the speed and acceleration, the linear guide has a considerable advantage, and the speed of the linear motor will be further improved after the heating problem is successfully solved, while the speed of the "rotary servo motor + ball screw" is limited and it is difficult to renew Improve more.
In dynamic response, linear motors also have absolute advantages due to the problems of motion inertia, clearance, and mechanism complexity.
In speed control, due to its fast response and wider speed regulation range, the linear motor can achieve the highest speed at the moment of the startup, and can quickly stop when running at high speed. The speed regulation range can reach 1:10000.
linear motor
In energy consumption, the linear motor is roughly twice that of the "rotary servo motor + ball screw" when providing the same torque. The "rotary servo motor + ball screw" is an energy-saving and force-increasing transmission component, and the reliability of the linear motor is controlled. The stability of the system has a great impact on the surrounding area. Effective magnetic isolation and protection measures must be taken to block the impact of strong magnetic fields on the rolling guide and the adsorption of iron filings and magnetic dust.
Through the following example, will be easy to understand some features of linear motors and "rotary servo motors + ball screws":
A Japanese company's ultra-high-speed gantry machining center. The X and Y axes are driven by linear motors with V=120m/min. Why didn't the company apply the "rotary servo motor + ball screw (HIWIN SUPER S series)" although the DN value of SUPER S has experienced a speed-up process from 70,000 to 150,000 to 220,000 for traditional screws, due to the existence of pure The soft underbelly of mechanical transmission, its linear speed, acceleration, and the increase of stroke range are always limited. If the product of Φ40×20mm is selected, then Vmax=110m/min, due to the high speed of Nmax=5500 rpm, the stroke range is limited by critical Obviously, the restriction of rotational speed Nc cannot be too long. If a product with a large lead of Φ40×40mm is used, Vmax=220m/min, which obviously cannot meet the occasion of high positioning accuracy. It can reach a DN value of 220,000, which reflects HIWIN from one side. If we choose Φ40×20 (double head) mm product and use it under the condition of n≈4000～5000 rpm and V=80～100m/min, its safety, reliability, and working life are all good. It can be higher than the expected value. In fact, so far, in high-speed and high-precision CNC metal cutting machine tools (except CNC forming machine tools), the speed V ≥ 120m/min still uses SUPER S series drives. The best application of "servo motor + ball screw" is mid-range high-speed CNC equipment and some high-end CNC equipment that require V=40~100m/min, acceleration 0.8~1.5(2.0)g, and accuracy P3 or higher.
ball screw + servo motor
In accuracy, the linear motor reduces the problem of interpolation lag due to the simple transmission mechanism. The positioning accuracy, reproduction accuracy, absolute accuracy, and feedback control through position detection will be higher than that of "rotary servo motor + ball screw", and it is easy to achieve.
Linear motor positioning accuracy can reach 0.1µm.
"Rotary servo motor + ball screw" positioning accuracy up to 2-5µm, requires CNC, servo motor, backlash-free coupling, thrust bearing, cooling system, high-precision rolling guide, nut seat, table closed loop The transmission part of the entire system must be Lightweight and high grating accuracy.
If want to achieve high stability "rotary servo motor + ball screw", you need to adopt a dual-axis drive. The linear motor is a high-heating component, and it is necessary to take strong cooling measures. To achieve the same purpose, a linear motor has to pay a higher price.
Although the two driving methods of linear motor and "rotary servo motor + ball screw" have their advantages, they also have their weaknesses. Both have their optimal scope of application on CNC machine tools.
The linear motor drive has unique advantages in the following CNC equipment fields: high-speed, ultra-high-speed, high acceleration, and large production batches, many movements requiring positioning, and frequent changes in speed and direction. For example, the production line of the automobile industry and the IT industry, the manufacture of precise and complex molds.
Large-scale, ultra-long stroke high-speed machining center, "hollow-out" processing of light alloy, thin-walled, and high metal removal rate integral components in aerospace manufacturing. For example, the "Hyper Mach" machining center (46m) of CINCI ATI Company in the United States; the "HYPERSONIC 1400L ultra-high-speed machining center" of Japan MAZAK Company. In terms of price, the price of linear motors is much higher, which is also the reason for limiting the wider application of linear motors.
The fact that the two driving methods are used simultaneously in Germany's DMG also shows that they have their advantages. There is more room for improvement of linear motors. In the future, the technology of linear motors will become more mature, the output will increase, the cost will decrease, and the application will be more extensive. However, from the perspective of energy saving and consumption reduction, green manufacturing, and the characteristics of the two structures themselves "Rotary servo motor + ball screw" drive still has its broad market space. While the linear motor will become the mainstream driving method in high-speed (ultra-high-speed) and high-end CNC equipment, "rotary servo motor + ball screw" will continue to maintain its mainstream position in mid-range high-speed CNC equipment.
