Robust draw-wire sensors for series integration and OEMs

K and MK draw-wire sensors from Micro-Epsilon are specially designed for OEM and series applications. They stand out due to their excellent price-performance ratio combined with compact dimensions and robust design. This enables flexible design conditions and significant cost optimisation. The sensors are primarily used in mobile machinery, medical equipment and industrial applications, says Glenn Wedgbrow, Business Development Manager at Micro-Epsilon UK.

Draw-wire displacement sensors measure linear movements using a highly flexible steel wire. The wire drum is connected to a sensor element, which produces a proportional output signal. Measurements are performed to a high accuracy and dynamics. Due to their high quality components, the sensors benefit from a long service life and high operational reliability.

The K and MK draw-wire sensors from Micro-Epsilon are specially designed for series production and OEM applications. They measure distances from 50 mm to 8 m and can be used at temperatures from -40°C to +85°C, depending on the model. Applications include medical technology, mobile machinery such as telescopic handlers and cranes, as well as various industrial applications. Due to their excellent price-performance ratio, the sensors are particularly suitable for cost-sensitive applications. Due to their compact dimensions, the sensors are also ideal for applications with limited installation space.

The wireSENSOR WPS-K100 draw-wire sensors are characterised by their extremely robust design. The glass fibre-reinforced plastic housing offers a high degree of protection up to class IP67 or IP69K. In addition, the separate drum and spring chamber optimally protects the spring from environmental influences, making the K100 series ideal for outdoor applications. Measuring ranges up to 8 m are possible with the compact sensor housing. Signals are output via CANopen (digital) or via potentiometer, current or voltage (analogue).

The draw-wire sensors can be customised for special OEM requirements that are not covered by standard models. Cost effective implementation can be achieved even for medium quantities, depending on the type and number of modifications.

Telescopic supports and booms

Elevating work platforms and mobile cranes are used for numerous tasks. The available load torque of any lifting application plays a major role, as this determines which loads can be raised over which (lateral) range. Exceeding the permissible load torque may lead to serious accidents caused by the crane or platform tipping over. Therefore, load torque limiters monitor the maximum permitted load that can be moved. In the limit area, the load torque limiter must automatically recognise whether the crane must be shut down.

One important factor for the maximum permissible lifting capacity is the support arm displacement and the extension range of the boom. In many cases cranes and elevating work platforms are used in confined spaces where the support arms cannot be fully extended. In these situations only a reduced load torque is permitted. Fully variable support now makes it possible to determine and approve the maximum load torque for any support displacement considering the current extension range. The position of the support displacement and the booms is automatically measured using draw-wire sensors with typical measuring ranges of 1,500mm to 4,000mm, with booms ranging between 5,000mm and 15,000mm.

Connection of the sensors to the vehicle’s electronics can be either analogue or digital via fieldbuses. In particular, the telescopic capability and simplified mounting (retrofits are also possible) make draw-wire sensors the ideal choice for these applications.

Safety in cranes

Fig 1 - Risk profile

In addition to the functional and technical characteristics of the crane and the sensor technology, ‘functional safety’ is also a critical factor. Many national and international standards and regulations must be adhered to. The primary goal is to avoid personal injury. This is achieved by determining the default probability of each component and taking the latter into account when evaluating the whole system. Ultimately, the default probability of the crane must correspond to a certain performance level or SIL class. However, this is not compulsory for the individual components.

Intelligent evaluation and plausibility checks of (redundant) sensor signals provide maximum safety without having to execute costly qualifications and certifications at component level. Micro-Epsilon also provides key figures such as B10 or MTBF for evaluating the respective application.

Draw-wire sensors in outdoor applications

Shocks, vibrations, heat, water, ice, dirt and stone chippings – outdoor applications are subject to harsh conditions that may impair the use of draw-wire sensors. Although the list of influencing factors is long, corrective measures can be taken. In order to optimise reliability, close collaboration between the sensor provider and crane manufacturer is required, particularly during the concept design and qualification phase. The fewer environmental factors that affect the sensor, the more reliable the measurements during operation will be. Experience shows that the best solution is to install the sensor in the support or in the boom, where it is protected. If the sensor is installed in such a protected environment, customers can profit from low cost sensor designs.

If the sensor is installed outside (e.g. with retrofitting) additional sensor features (e.g. pulley wheel wire guides, integrated heating, higher spring forces, etc.) can increase reliability (see Fig 1).

Customer-specific designs

More than 120 draw-wire sensors with different designs, measuring ranges and output signal types cover a wide range of applications. For special requirements that are not met by standard models, the draw-wire sensors can be suitably modified. A commercial implementation can already be achieved with medium-sized quantities.

For more information on the K and MK series draw-wire sensors, please visit Draw-wire sensors for serial integration & OEM | Micro-Epsilon or call the Micro-Epsilon sales department on +44 (0)151 355 6070 or email info@~@micro-epsilon.co.uk