Precision mechanical components and instruments || Huygens Engineers

Micrometric precision and high-precision physical measurements

When micrometric precision or high-precision physical measurements are a determining factor, the design process must consider the effects of various types of spread (thermal effects, tolerances, load, control) in the implementation. Our simulation and calculation methods play an important part in this.

Temperature-compensated cutting machine

For a manufacturer of modular conveyor belts, Huygens Engineers designed a machine that cuts plastic modules of various sizes at high speed and with an accuracy of 0.1 mm. Upon small fluctuations in the ambient temperature, the modules can expand or shrink up to 1.0 mm in length due to the high thermal expansion of the plastic. The machine is made to recalibrate automatically. It detects the length of the module and determines where it should cut.

Various sensors were implemented to achieve this. For example, the actuators that clamp the modules also measure their length. An algorithm keeps track of the statistics of the length of modules, in order for the system to only recalibrate when necessary. This keeps the production speed high. Just before cutting, the system can determine whether the module is still within tolerance and reposition the module. This is achieved using a database of tolerances depending on the length, position and type of the module. The cutting blades are very thin, which results in lower distortion in the products to be cut. The blades are clamped with a precision down to 0.02 mm and heavily prestressed to en-sure they cut as evenly as possible.

Calibration machine for weight transponder

To accurately measure the weight of products moving on a conveyor belt, a client of Huygens Engineers uses a belt with sensors: small measuring cells with double membranes, whose degree of deflection is related to the weight placed on them. We developed a machine that determines the deflection of the membranes for a baseline series and simultaneously carries out fatigue tests. With this machine, the client can determine when the sensors require recalibration and easily perform this calibration. To develop this machine, we simulated the deformation of the membrane for a large number of cases of dimensional deviations and loads and compared this with actual measurements. By using these simulations to construct an FEM model, we were able to determine the behaviour of the membranes. This ensures that the calibration machine accurately measures the sensors and can ac-curately validate the durability.

Magnetic brake

A tension amplifier uses an electric motor that acts as a brake to ensure stability in a system that could find itself in a situation without tension. However, in this much used principle, the braking force depends on the speed of rotation. To solve this issue, Huygens Engineers designed a different system in which a tension amplifier can rotate at any speed without changing the rolling friction. The starting point is a magnetic brake (eddy current brake), consisting of rotating magnets in a stationary, conductive drum. This generates eddy currents, which in turn generate contactless magnetic forces.

And this latter aspect means there is no wear. Using the finite element method, we investigated the influence of all parameters of the setup on the torque, including the strength of the magnets, geometric variations, rotational speed and temperature. The design was tested in practice for its sensitivity to each parameter. The distribution curves from the tests allowed us to find at an accurate yet simple design. This eventually led to a stable system that works at constant speeds at 2000 and 5000 rpm, with deviations of only ±5%.

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