Floating Magnets vs Sliding Captive Magnets on Transducers

Magnetostrictive linear transducers are feedback sensors that give an analog or digital signal relative to the position of a magnet along the waveguide.  One of the common questions we are asked is should I use a captive or floating magnet?  The answer depends on the application and the environment. 

Floating Magnets

Floating magnets are attached to the moving part with the transducer mounted parallel.  The magnet is not directly coupled to the transducer and thus an air gap exists between the transducer and the magnet.

• Floating magnets overcome the typical issue of debris and sticky fluid buildup overtime on the transducer track or rod. This is the main cause of mechanical failure on a sliding track magnet. 
• They can be mounted directly on the moving part, so machine wear is compensated, giving you a more realistic position over time. It allows you to monitor machine part wear. 
• They are easier to mount to the moving part versus a rod and possibly 2 ball or eye swivels- where you have 1 on the magnet and one on moving part.
• Magnetostrictive technology has advanced to allow a greater gap between the sensor inside the track and the magnet itself.  Distance is dependent on transducer and magnet type. 
• The technology advances have also allowed slightly more variance in magnet to transducer distance (X) over the length of the device within reason. Also, non- parallel movement (Y) is now more forgiving. Still should not allow both!  The transducer should be mounted parallel to the moving part. 
• There are many options available for floating magnet types.
• One issue is they cannot be mounted directly to steel or iron. Insulated mounting blocks are available with the magnets, or you can make your own non-ferrous mount. 
• EMF or high inductive local interference will also affect floating magnets.  In these environments do not use a floating magnet. 

Captive Magnets

Captive magnets ride in a track on the transducer and are linked with a mechanical linkage to the moving part.

• Captive magnets are used in relatively clean environments.
• They are used where you cannot put the transducer body close to the moving part.  
• A common perception is that the bearing surfaces and swivel eyes will wear with time. This is true only where direction change is sudden and at high speeds. Also -dirt/oil. Usually not an issue.
• As position repeatability is the most typical and desired function of any transducer even if play develops it may not be an issue if measurement is only in one direction. 
• 3 more parts to break. 
• The main reason for captive magnet use? X/Y variance of magnet distance to the transducer will never vary and a floating magnet will not work in the application.

Have questions on transducers?  Contact us and we will be glad to assist with your application.

Application Spotlight - Ultrasonic Sensors

Ultrasonic Sensors - Sound solutions for object detection and measurement

Whether your application is position detection, distance measurement, or the detection of solid, powder, or liquid media: BUS ultrasonic sensors are precise all-around performers. They remain high-performance independent of color, transparency, and surface properties. Even poor lighting conditions and dark, transparent, or highly reflective objects pose no problem.

Ultrasonic sensors show their true strength when long operating ranges with high accuracy are needed. In dusty, humid, and hazy environments, they are sometimes the only alternative. Even in the case of heavy debris, BUS sensors have proven themselves.

Ultrasonic sensors can be used in many application areas

Foil tear monitoring Ultrasonic sensors
with switching output can be used for foil tear
monitoring. If large waves are formed in the foil,
the sensor should be operated as a diffuse
reflective sensor. This operating mode functions
reliably even if the sound is reflected by waves in
the foil.

Height and width measurement
Through the use of multiple BUS M30 or
BUS 18M ultrasonic sensors, three-dimensional
measurements can be made for everything from
small boxes to large cartons.

Presence verification BUS detect filled or
empty pallets and measure the content of
transport containers. If a box or a container is to
be inspected with multiple sensors, they can be
synchronized with each other.

Robot positioning Due to their small dimensions, BUS are
ideally suited for exactly positioning robot arms:
BUS 18M ultrasonic sensors in threaded
sleeve and BUS R06K in block-style housing.

Control foil sag and monitor roll diameter Using an ultrasonic sensor with analog output, the material on a roll or a coil is detected and the roll drive or a brake readjusted. Another sensor with analog output readjusts the material infeed at the dancer roller as a function of the cable loop.








Scott Equipment offers a complete line of ultrasonic sensors from Balluff.  For additional information on Balluff ultrasonic sensors contact us or visit the Balluff Website.




Application spotlight provided by Balluff: 
Balluff, Inc.
8125 Holton Drive
Florence, KY 41042
www.balluff.us

Analog feedback for Grippers

Many applications have a need for precise jaw position feedback on pneumatic grippers.  Precise jaw position feedback may be needed for higher process speeds or improved quality control.  A few of ideas for use of the analog feedback on pneumatic grippers are to:

• Differentiate objects by physical size based on jaw position.
• Feedback to an analog pressure control circuit to control grip pressure based on position to prevent object deformation while ensuring a secure grip on the object.
• Part present in gripper detection.

Balluff offers a number of sensors and technologies ideal for analog feedback relative to jaw position on pneumatic grippers:

Measurement with analog magneto-inductive linear sensors (BIL or Micro BIL)
An analog sensor that uses magneto-inductive linear technology is attached to the gripper in a position where it will sense the grippers internal magnet mounted on the piston.  The Micro BIL unit (pictured below) can slide into the t-slot of many modern grippers, taking the place of existing hall-effect or reed-switches and providing analog feedback.

Measurement with analog inductive sensor
To use this method you utilize an analog proximity sensor.  The analog proximity sensor measures position based on the amount of the sensor face  covered by a moving target on the gripper.  The image below shows an example of how this could be mounted and used.

Analog prox sensor detects jaw position.

Direct measurement of a inclined target

Better suited for large grippers with longer strokes a inclined target, like shown below, moves with the gripper jaw.  An analog inductive sensor detects the inclined target and feeds back jaw position.

For more information contact Scott Equipment.  We will be glad to assist you in specifying a Balluff analog sensor for your application.