3-D hall sensor algorithm developed in Maple produces a more efficient washing machine design.

Dr. Frank Allmendinger leads a research and development project team at Marquardt GmbH, a German company that develops and manufactures switches and switching systems.

Over the last three years, his team designed an innovative three-dimensional load and imbalance sensor, which is used in a new washing machine model from a well-known company in the "white goods" sector.

In the industry, the trend for washing machines is to move from a drum capacity for 5 kg of laundry to larger ones with a capacity of 7 or 8 kg. However, these large drums are still being placed in the standard washing machine housing with a width of 60 cm leaving a smaller space between the drum and the housing and making collisions more probable.

Therefore, it is necessary to measure the position of the drum relative to the housing to identify impacts of the drum against the housing in advance to react accordingly.

Marquardt’s sensor was developed to detect the relative position in the three dimensions of the washing machine drum to the housing.

The ability to measure the drum position gives several advantages: 

• It senses imbalances and detects resonant frequencies of the mechanical system
• Reduces  imbalances by slowing the rotation speed and distributing the weight more evenly.
• It measures a load of clothing as it is placed into the machine and gives a recommendation of how much detergent to use.

The Marquardt team and the Fraunhofer Institute for Integrated Circuits developed a new 3-D Hall sensor application specific integrated circuit (ASIC) that measures the three vector components of a dipole magnetic field.

The complete measurement system consists of a magnet affixed to the drum in the washing machine and the 3-D Hall sensor ASIC attached to the unit housing. The Hall sensor measures both the direction and strength of the magnetic field, determining the relative movement of the magnet simultaneously in all three dimensions. This information is communicated to the onboard microcontroller, which uses a proprietary algorithm to determine how to control the movement of the drum.

The Marquardt group used Maple to develop the algorithm. Dr. Allmendinger was able to work on complex problems such as modeling the magnetic fields, estimating the allowed tolerances for the magnet and determining whether the tilt of the 3-D-Hall-Sensor module was within a very small tolerance of approximately two degrees. The resulting algorithm was translated to C code to run on the controller.

Dr. Allmendinger was impressed by Maple’s ability to work with symbolic mathematics, its powerful graphing tools, its technical document interface and its export capabilities to other languages (such as C, MATLAB, and Java).

“It was very simple to work in Maple, even with the complex mathematics involved. We found it quite easy to enter and modify equations, determine whether they had a solution, then go back and make necessary changes,” Dr. Allmendinger says.

“I found Maple’s user interface very easy and smooth to work with; especially the export capabilities and interoperability with other technical programs have become much better, and it is now invaluable in rapid solution development.”

The new 3-D positioning algorithm in the Hall sensor has several advantages: 

• Assembly is simple because there is no mechanical connection between the magnet and the sensor.
• The sensor system offers the option of calculating speed so the three magnetic field components  can be measured simultaneously.  
• The design enables natural resources to be handled more responsibly.
• The use of mathematic field modeling makes it possible to discard traditional 3-D mapping techniques and use a smaller, more cost-effective microcontroller.
• Fewer resources are used by creating the considerably smaller magnet.

Marquardt is currently discussing further applications of its 3-D sensor with other well-known customers. These applications include general position sensing in regular production and automation technology and multimedia interfaces in the automotive industry, such as the I-Drive system in a BMW vehicle.

The company is also considering further development of this sensor concept, extending its capabilities to determine not only the 3-D distance of a Hall sensor from a magnet but also the 3-D solid angle.

For more information visit www.maple-systems.com