Load detection in washing machines

Load measurement in washing machines is required to lower operating costs and environmental damage. The load must be measured before the washing starts to determine the appropriate dosage of detergent required to wash a certain amount of clothes. A cost-effective and efficient way to do this is by using magneto-inductive displacement sensors. These sensors are directly integrated into the damper.

The sensors are capable of detecting the position of the piston in the damper continuously and with high dynamics. The sensor has a highly compact structure and a measuring range of 40mm and above. On loading the washing machine, the suds container sinks, thereby generating a change of displacement on the damper. The relationship between the displacement and loading leads to optimizing the operation and washing results.

During the washing and spinning process, the sensor dynamically controls the imbalance of the drum and detects the rotational speed. It doesn’t depend on any additional hardware to perform that operation. This configuration enables an improvement in the device operation and spinning, which ultimately improves the service life of the machine. The magneto-inductive displacement sensors are designed for large volume applications and are easily integrated into restricted spaces. The measured values are output using a rectangular signal evaluated via digital inputs from micro-controllers.

The displacement sensor ILU (Integrated Load and Unbalance Sensor) measures the depression of the suds container when the washing machine is loaded and its deviation during the spinning stage. Due to the inductive measurement principle, the sensor provides an absolute position acquisition for static and dynamic processes. The patented VIP sensor principle enables the integration of the sensor into a compact frictional damper. This gives the following additional advantages:

– The sensor is protected against ambient effects in the washing machine.
– The sensor is mounted in the washing machine with the frictional damper as an integrated constituent part in one working step.
– Simple fitting of the sensor system through the implementation of application-specific interfaces.

The operation and washing results are optimized through the load measurement. The displacement sensor supplies an output signal proportional to the weight of the washing. The sensor signal is converted by the electronics into a visible bar display for the user. The momentary loading status is continuously displayed visually, enabling the washing drum to be optimally and fully loaded. In parallel to this, the amount of washing agent is calculated depending on the load and displayed. The operating costs are reduced and the environment is also preserved. The sensing of unbalance enables the speed to be adapted during the spin-dry stage. The running of the appliance and the spin-drying performance are improved and the service life increased.

Application

The sensor forms a component with distributed electromagnetic parameters (R, L, C). It consists of a measuring coil with two connections, an intermediate layer and an electrode. The target (measuring ring) surrounds the measuring coil and can be moved along the measuring coil without making physical contact with it. The measuring signal is tapped off from the electrode and evaluated with the aid of an operational amplifier, whereby the output signal UOUT is proportional to the position X of the target. Consequently, an optimized ratio of sensor length to measuring range is achieved and the sensor can be integrated into the spring/frictional damper system.

Technical details
– Measuring range: 50 mm
– Reslution: 11 BIT

Sensor model
– I LU-50-O-10-SR

Reasons for the sensor selection
– Statically and dynamically effective sensor principle.
– Economical vip electronics.
– Sensor can be integrated into the frictional damper due to the short installed length.