Comparison between linear motor and ordinary rotary motor + ball screw
Principle：
The linear motor is similar to the ordinary motor in principle. It is only the unfolding of the cylindrical surface of the motor. This type is same as traditional motor. Such as DC linear motor,AC permanent magnet synchronous linear motor, AC induction asynchronoous linear motor, step linear motor. Like a brushless rotating motor, there is no mechanical connection between the mover and stator. Linear motors use the same control and programmable configuration as rotary motors. The shape of the linear motor can be flat and U-shape, And the most suitable configuration, it depends on the specifications and working environment of the actual application.
Advantage:
1. Dynamic performance
Linear motion applications have a wide range of dynamic performance requirements. Depending on the specifics of a system’s duty cycle, the peak force and maximum speed will drive the selection of a motor:
An application with a light payload that requires very high speed and acceleration will typically utilize an ironless linear motor (that has a very light moving part containing no iron). As they have no attraction force, ironless motors are preferred with air bearings, when the speed stability has to be below 0.1%.
2. Wide force-speed range
Direct drive linear motion deliver high force over a wide range of speeds, from a stalled or low speed condition to high velocities. Linear motion can achieve very high velocities (up to 15 m/s) with a trade off in force for ironcore motors, as technology becomes limited by eddy current losses.
Linear motors achieve very smooth velocity regulation, with low ripple. The performance of a linear motor over its velocity range can be seen in the force-speed curve present in the correponding data sheet.
3. Easy integration
Magnet linear motion are available in a wide range of sizes and can be easily adapted to most applications.
4. Reduced cost of ownership
Direct coupling of the payload to the motor’s moving part eliminates the need for mechanical transmission elements such as leadscrews, timing belts, rack and pinion, and worm gear drives. Unlike brushed motors, there is no contact between the moving parts in a direct drive system. Therefore there is no mechanical wear resulting in excellent reliability and long lifetime. Fewer mechanical parts minimize maintenance and reduce the system cost.
Disadvantage:
There is an inevitable "Edge Effect", that is, the distortion of the end magnetic field of the linear motor affects the integrity of the traveling wave magnetic field, so that the loss of the motor increases, the thrust decreases, and there is a large thrust fluctuation.
Comparison between linear motor and ordinary rotary motor + ball screw
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Index
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Rotary motor+ball screw
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Linear motor
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Precision (µm/300mm)
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10
|
0.5
|
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Repeat precision (µm)
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5
|
0.1
|
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Maximum speed (m/min)
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20~30
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60~200
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|
Maximum acceleration (g)
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0.1~0.3
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2~10
|
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Static stiffness (N/µm)
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90~180
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70~270
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Dynamic stiffness (N/µm)
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90~180
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160~210
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|
Stationarity (% speed)
|
10
|
1
|
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Adjustment time (m/s)
|
100
|
10~20
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Lifetime (h)
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6,000~10,000
|
50,000
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