Linear motors were invented more than 150 years ago, but until recently they found use only in high-tech areas like semiconductor production or machine tool engineering. But the new generation of industrial linear motors is now being adopted in general mechanical engineering.
The history of linear motors
The idea of generating linear motions directly instead of deriving them from a rotary motion by means of mechanical elements is by no means new.
Industrial linear motors
Industrial linear motors are targeted not on extreme high-end applications but rather on the needs of mechanical engineering generally:
- Suitability for general industrial environments (dirt, maintenance)
- Simple attendance and commissioning (plug and play)
- Long life
- Industrial prices
These requirements show that what is really needed is a linear moving element that is rugged, long-lived and easy to handle. Under no circumstances does the user want to be bothered with sensing or fitting stators and sliders. Bearings, position sensing and sensor amplifier are accommodated in a strong stator housing, safeguarding them against dirt and shocks. As far as the user is concerned the entire motor consists of only two parts: stator and slider. To put the motor into operation only the cable connecting the associated electronics has to be plugged in.
Criteria for employing industrial linear motors
Owing to physical laws, electromagnetic linear motors do not attain the same forces as pneumatic or hydraulic cylinders of comparable size. Thus for example, the peak force from a motor of 37 mm (1.5 in) diameter is about 200 N (45 lbs). Otherwise industrial linear motors are versatile and have the following properties in particular:
- Freely controllable and regulable linear motion (incl. profile curves)
- Usable from low to high dynamics (e.g. reversing motion with 10 Hz)
- Compact, simple design (two parts only: stator and slider)
- Completely integrable in modern drive and control concepts.
Modern design principles favour smaller moving masses, while at the same time there is a need for ever faster machines with high flexibility (quick resetting), consequently the possible applications for linear motors are growing all the time.
A decision to employ a linear motor is reached after comparing it with other moving elements and the capabilities and costs of these. The framework conditions in particular play a decisive part. If, for example, compressed air would have to be supplied to a machine for a single pneumatic cylinder, the use of a linear motor should be examined even if there are no special demands otherwise in the way of free positionability, dynamics, position feedback or service life. Many engineers are still not aware of the additional capabilities of an industrial linear motor, going far beyond just moving into any position:
Application: movement profiles
Pick-and-place applications or the fitting of a part can be performed quicker and better if the drive follows a predetermined curve profile. The movements can then be matched optimally to the process and the cycle times shortened, leading directly to higher productivity.
Application: rotary and linear motion
In addition to its linear motion the continuous slider can transmit a rotary movement from a rotary motor as well. Classical uses for this are screwing lids onto bottles or tubes. Further interesting possibilities are to be found in handling, as for raising parts for assembly and then turning them about an axis.
Application: sensing and testing
Linear motors may be employed directly for sensing and measuring (with limited accuracy). For this the maximum force of the motor is restricted to a low level and a slow movement is performed till the slider stops upon reaching the measuring position. With subsequent readout of the actual position it is possible for example to check whether an assembly part has been fitted properly or is stuck canted.
Application: fitting and inspecting
If the maximum force of an industrial linear motor is set to a desired value and an assembly part is then pressed into another part, the exact position in which the motor is arrested, while pressing-in can be utilised as a quality and checking signal.
The advantages of the LinMot industrial linear motors are felt where linear motions have to be performed simply and with little development outlay and/or dynamically and freely programmable. Further capabilities like force adjustment and position measuring offer the designer numerous possibilities for innovative solutions. Industrial linear motors provide the foundation for a quantum leap in areas like packaging, textile machinery engineering, robotics, handling or special mechanical engineering.
Industrial linear Motors are available from Birrer Industries .