Linear motion made easy

Linear motion is needed in many applications. In optics, for stable zoom and focus operation, or in lab analysis machines, to handle the sampling probes in fast and reliably way, or in pick-and-place heads where fast and silent movement is required.

Pneumatic solutions for small movements require a lot of space: a bulky and noisy compressor, plastic tubes hanging around, electro-valves and pressure sensors for the actuation control are a typical setup, and the available space is never enough for a compact design.

A classic approach for linear movements is the combination of a rotary motor (DC, brushless or stepper technologies) combined with a lead screw with a pitch P (the linear movement corresponding to one screw revolution) and efficiency η. The advantage of using motors instead of pneumatics is that the actuator's force can be easily controlled by means of the motor torque, proportional to the motor current: with a good motion controller this can be also done via communication interface.

Let's consider a force F to move the load connected to the nut at linear speed v: the motor torque M and speed n can be calculated with the simple formulae on this picture. With F = 100N, v = 50mm/s, a screw with η = 60% and P = 1mm the motor torque and speed are M = 19.9mNm and n = 3000minˉ1

Based on the above data it's not complicated to find a suitable motor and encoder combination. The FAULHABER Drive Selection Tool can be used for the drive system selection: just select the lead screw on the load transmission drop-down menu, enter the required data and find the ideal solution: the results can also be downloaded as PDF file.

During the nut movement there are axial forces acting on the front motor bearing: if this exceed the maximum motor axial force recommended in the data-sheet then the bearing (and thus the motor) lifetime will be reduced. For this reason it's necessary a special motor design with reinforced bearing configuration, for combination of motors and screws.

Direct drive operation is ideal for linear movements with relative small load, because the limit is given by the motor torque. This solution is very compact and it's typically used in motorized zoom and focus operation in optics, with micro-camera sensors. A good example is the combination of leadscrew and stepper motors for direct drive operation.

In many application the torque required is higher, so a drive system with motor, encoder, gearhead and screw must be used. The coupling between screw and gearhead may be source of headaches: for this reason FAULHABER made the L series, a complete series of geared lead screws and ball screws, with 22 and 32 mm diameter.

This is the combination of a powerful GPT gearhead and screw: lead screw with metric thread (MT) for high force generation during linear movement, or ball screws for high efficiency, linear movements with 24 μm accuracy (SB) or high-precision with 13μm accuracy (PB).

A second solution for linear movements can be used to replace small pneumatic systems, for high-accuracy controlled linear movements together with a small motion controller. This solution is the QuickShaft linear DC servomotor series.

Basically it's like a brushless motor with linear movement: the magnets are inside the moving rod and the coil is inside the stator, of course made of non-magnetic metal. Three analog Hall sensors are placed in the PCB, measuring the rod's magnetic field and providing three sinusoidal signals used by the motion controller to easily control the motor position. The system is plug-and-play: just connect the motor wires to the motion controller, match motor and controller characteristics using the software Motion Manager, and operate the motor with RS232, CANopen or EtherCAT, depending on the motion controller type. The lifetime is limited by the sleeve bearing, made of special auto-lubricant polymer, ensuring up to 100 times the lifetime of a ball screw. If you use a linear guided system, you will be surprised to replace the guide before the motor during the operating lifetime.

FAULHABER sales engineers are available for any technical request, just contact us with your requirements in case of applications with linear movement.

Just in case you need more information on the FAULHABER LM motor series:

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