Linear Motors Expand their venue
A linear motor has dual forcers that can move in either direction without input from optical encoders
Bologna slicers and church organs might not have much in common, but both are employing a novel linear motor that provides quiet operation and extremely precise repeatability.
The ServoTube from Copley Controls Corp. puts Hall Effect sensors inside the forcer with the motor's drive coils. The Hall Effect sensors develop precise sine and cosine output, providing resolution and repeatability of 12 microns, 10 times the precision of competitors, says Copley Vice President George Procter.
Removing the encoder also eliminates the need for a bearing system, which is replaced with a large air gap. Dropping the encoder also cuts cost by as much as half, he adds.
Unlike conventional linear motors, multiple forcers can be put on the thrust tube that houses permanent magnets. Two or three forcers on a long rod can increase drive force, or forcers can move in opposite directions, giving design engineers versatility without requiring much space. The motor's straight line configuration means the forcer is surrounded on all sides by air, giving it better cooling characteristics than conventional U-shaped linear motors, Copley says.
All these factors make linear motors suitable in applications that previously used techniques such as rotary motors and ball screws. In church organs, the motor moves louvers that control what's called expression, basically the volume of a pipe organ.
Organ designers at Goulding and Wood say that other benefits of fully digital electronic controls are more precise control and the ability to put the pipes farther from the organ. Quiet operation is also a major factor for organs, as well as for commercial equipment such as meat slicers and tortilla stackers.
CONTACT:George Procter, Copley Controls Corp. e-mail: firstname.lastname@example.org://rbi.ims/ca/4388-503
Look Ma—No hands!
Bernoulli Effect lifts objects without contact
In the spirit of "if it ain't broke don't fix it," a replacement for the venerable vacuum pick-and-place system may seem inappropriate. However, there are many situations where vacuum systems do not work well, or do not work at all. For example, a vacuum system has problems when a rough or porous surface prevents the seal from forming and just draws air and does not lift the object. This can cause filter clogging if the environment or object has loose particles or debris that are drawn into the system.
The answer to these types of problems is eliminating the seal in a non-contact system designed by Bosch Rexroth that relies on pressure instead of vacuum. The Non Contact Transfer (NCT) system operates using the Bernoulli principle. Similar to an airplane wing where airflow over the curved surface creates a lower pressure zone and lift force on the wing, the NCT design is an upside down version that creates lift by the lower pressure on the curved underside drawing objects to it.
The lifting capability is quite linear with N=(4P-1)/3, where N, the lifting in Newtons, is within about 5 percent over working pressures from 1 to 7 bar (15 - 105 psi) with the input pressure provided by readily available, non-lubricated compressed shop air.
Whenever the air is applied, the object rises towards the NCT, but the air gap caused by the airflow prevents the object from touching the NCT. Unfortunately, the air barrier does not allow sideways movement of an object. Adding a silicone rubber pad at a key touch point creates sufficient friction to move the object horizontally in those applications that require sideways movement. The touch point provides far less contact and stress than a vacuum system. If horizontal movement is required without touching the surface, an edge contact or finger pushes the product in the required direction. For example, this technique can move semiconductor wafers to avoid touching sensitive circuitry on the surface. Other applications include handling electronic circuit boards and other objects with perforations, or soft objects such as paper and plastic bags.
The pressure system eliminates a vacuum pump, vacuum ejector, and filtering requirements and does not change or increase the filtering for the shop air supply. The NCT series is available in four sizes and a variety of designs providing lift capacities up to 0.9 kg (approximately 2 lbs.).
Bernoulli's Effect Provides Lift:
Airflow enters the NCT (noncontact transfer system) at A and the reduced
cross section causes a higher velocity air stream with reduced pressure at
the outlet, B, applying a lifting force, C, for up to two pound objects
(D). This is similar to the way the camber of an airplane's wing causes an
increase in the velocity of the air passing over the top resulting in a
decrease in the pressure in the air creating
CONTACT:Al Turney, Bosch Rexroth Corp. Tel: : 859-254-8031; e-mail: Al.Turney@BoschRexroth-US.comhttp://rbi.ims/ca/4388-504