Ball screw and linear motor performance comparison

April 01, 2022

With the development of direct drive technology, the comparison between the linear motor and the traditional “rotary servo motor + ball screw” drive method has attracted the attention of the industry.

In 1845, the British had invented the linear motor, but the linear air gap of the linear motor at that time was too low to be applied. In the 1870s, Kollmorgen was also introduced, but its low cost and high efficiency limited its development. Until the 1970s, 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 of the world's most advanced processing center manufacturers have begun to use them on their high-speed machine tools. Well-known companies such as DMG, Ex-cell-O, Ingersoll, CINCI ATI, GROB, MATEC, MAZAK, FANUC, SODICK have all introduced high-speed, high-precision machining centers using linear motors.

As a world leader in linear products, ALM has successfully developed and produced linear motors in recent years after successful ball screw and linear slides, and achieved good results in high-speed and high-precision fields.

The following main reference ALM's advanced high-speed silent screw SUPER S series (DN value of up to 220,000) and ALM linear motor to do some comparison on several major features, for the relevant industry to provide a reference.

Speed comparison:

Speed linear motors have considerable advantages. The linear motor speed reaches 300m/min and the acceleration reaches 10g. The ball screw speed is 120m/min and the acceleration is 1.5g. From the standpoint of speed and acceleration, the linear motor has considerable advantages, and the speed of the linear motor will further increase after successfully solving the heat problem. However, the "rotary servo motor + ball screw" is limited in speed. Increase more.

From the dynamic response, linear motors also have an absolute advantage because of problems such as the inertia of motion and clearance and the complexity of the mechanism.

Speed control on the linear motor because of its fast response, wider speed range, can achieve the maximum speed at the start of instant, high-speed operation and can quickly stop. The speed range can reach 1:10000.

Accuracy comparison:

In terms of accuracy, the linear motor can reduce the interpolation lag due to the transmission mechanism. The positioning accuracy, reproduction accuracy, and absolute accuracy are all higher than those of the “rotary servo motor + ball screw” through the position detection feedback control, and are easy to implement.

Linear motor positioning accuracy up to 0.1μm. "Rotary Servo Motor + Ball Screw" up to 2~5μm, and requires CNC-Servomotor - No-gap coupling - Thrust bearing - Cooling system - High-precision rolling guide - Nut seat - Worktable closed loop Drive of the entire system Some should be lightweight and the grating accuracy should be high.

If you want to achieve higher stability, "rotary servo motor + ball screw" to take two-axis drive, linear motor is a high heat component, need to take strong cold measures, to achieve the same purpose, linear motor will have to pay a higher price .

Price comparison:

The price of linear motors is much higher in terms of price, which is also the reason for limiting the wider use of linear motors.

Energy consumption comparison:

The energy consumption of the linear motor when providing the same torque is more than double the "rotary servo motor + ball screw". The "rotary servo motor + ball screw" belongs to the energy-saving and force-increasing type of transmission components. The reliability of the linear motor is controlled by the control system. The impact of stability, the impact on the surrounding must be effective to take magnetic and protective measures to cut off the impact of a strong magnetic field on the rolling guide and adsorption of iron dust magnetic dust.

The following example will make it easier to understand some of the features of linear motors and "rotary servo motors + ball screws":

A Japanese company ultra-high speed gantry machining center. The X and Y axes are driven by a linear motor V=120m/min. Why doesn't the company apply the "rotary servo motor + ball screw (ALM SUPER S series)"? Because SUPER S has undergone a speeding up process from 70,000 to 150,000 to 220,000, the increase in line speed, acceleration, and stroke range is always limited due to the weakness of purely mechanical transmission. If Φ40×20mm product is selected, then vmax=110m/min, because nmax=5500r/min, the rotational speed is very high, and the travel range is obviously not too long due to the limit rotational speed Nc. If a large lead Φ40×40mm product is used, then Vmax=220m/min, which obviously cannot meet the requirements of high positioning accuracy. The ability to achieve a DN value of 220,000 reflects ALM's design and manufacturing standards from one side. If we choose Φ40×20(double-head)mm product, it can be used in the state of n≈4000~5000r/min, V=80~100m/min. Its safety, reliability and working life can all be higher than expected. In fact, so far, successful examples of the SUPER S series drive at speeds V ≥ 120 m/min in high-speed, high-precision CNC cutting machines (except for CNC forming machines) have not been seen. In fact, the best application of "rotary servo motor + ball screw" is: the requirements of V = 40 ~ 100m/min, acceleration 0.8 ~ 1.5 (2.0) g, precision P3 above the level of high-speed CNC equipment and some high-end numerical control equipment .

Application comparison:

In fact, both the linear motor and the "rotary servo motor + ball screw" drive method have their own weaknesses despite their advantages. Both have their own best range of application on CNC machine tools.

Linear motor drives have unique advantages in the following numerical control equipment: high-speed, ultra-high speed, high acceleration and large production volume, requiring more movement for positioning, frequent changes in speed and direction. For example, production lines for the automotive industry and IT industry, and the manufacture of sophisticated and complex molds.

Large-scale, ultra-long-stroke high-speed machining center, "hollowing out" processing of light alloy, thin-walled, metal-removing integral components in the aerospace manufacturing industry. For example, "Hyper Mach" processing center (46m) of CINCI ATI, USA; "HYPERSONIC 1400L ultra-high speed machining center of MAZAK of Japan.

High dynamic characteristics, follow-up at low speeds and high speeds, and highly sensitive dynamic precision positioning are required. For example, a new generation of high-performance CNC electric machining machines represented by Sodick, CNC ultra-precision machine tools, a new generation of CPC crankshaft grinding machines, cam grinders, CNC non-circular lathes.

Light load, fast special CNC equipment. For example, Germany DMG's "DML80 Fine Cutting" laser engraving and drilling machine, Belgium's LVD's "AXEL3015S" laser cutting machine, MAZAK's "Hyper Cear510" high-speed laser processing machine.

German DMG company is famous for producing all kinds of high-performance numerical control equipments in batches. It adopts linear motor earlier in its servo feed system, and its adoption rate is also very high (after the machine model number is marked with “Linear”), the company has two There are three types of drive configuration:

All axes are equipped with linear motor-driven "fast" CNC equipment. For example: DMC85V Linear, DMC75V Linear, DMC105V Linear, DMC60H Linear, DMC80H Linear and DML80-Fine Cutting laser processing machine.

Hybrid drive type. For example: DMF500 Linear Column type large vertical machining center with linear motor on the X axis (stroke 5m), V=100m/min; on the Y and Z axes it uses “rotary servomotor + ball screw”, V= 60m/min.

The "power type" machining center of "rotary servo motor + ball screw" is all arranged on each coordinate axis. For example: DMC63H high-speed horizontal machining center, V = 80m/min, acceleration 1g, positioning accuracy of 0.008mm. There are also DMC80H and DMC100H, DMC125H (duoBLOCK) and DMC60T.

The simultaneous use of the two driving methods at the German DMG company also shows that they have their own advantages. The linear motor has a lot of room for improvement. In the future, the technology of the linear motor will become more mature, the output will increase, the cost will decrease, and the application will become more extensive. However, considering the energy conservation and consumption reduction, green manufacturing, and the characteristics of the two structures themselves The "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 (high-speed) and high-end numerical control equipment, the "rotary servo motor + ball screw" will continue to maintain its mainstream position in mid-range high-speed CNC equipment.

お問い合わせ

Author:

Ms. Kathy

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sales@alm-linearmotor.com

Phone/WhatsApp:

+8615862406535

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