Cedrat Technologies, innovation in mechatronics

In many cases piezoelectric actuators reach limitations in terms of maximum displacement and cycling frequency. Most amplified actuator technologies struggle to go over the millimeter of stroke. Furthermore certain closed-loop applications demand stroke measurement integrated into the actuator. While few amplifiers on the market can offer 20Amps current over a few 100ms, development of high power supply units runs parallel with actuator improvements. However with the introduction of high power supplies comes the problem of self-heating of the piezo ceramic. Finally extreme environmental conditions in terms of harsh conditions and high temperatures need to be addressed in order to open these markets for piezo actuators. Cedrat Technologies has been heavily investigating in solutions to overcome all of these drawbacks and these solutions are presented here.

Constant expansion of new materials requires fretting or fatigue machines in order to test their failure. In many cases tests must be performed in severe conditions and at high frequency. These requirements come from the use of the materials in highly demanding applications. At the same time it is expected to reduce the time required to characterise such materials. Piezoelectric actuators are more and more common in testing machines, but they still reach limitations in terms of maximum displacement, cycling frequency or power. In order to cope with these issues, Cedrat Technologies has been investigating solutions. In this paper long stroke and high frequency actuators, coupled with powerful driving control are introduced. These actuators are based on piezoelectric materials and can be easily integrated into the fatigue machines. In order to improve precision of these tests, two of the most common displacement sensors used in smart actuators are also presented in this paper.

Ultrasonic-based SHM (Structural Health Monitoring) applications usually rely on the use of piezo-electric patches to emit and receive ultrasonic surface acoustic waves. The principle is to study the propagation of the waves through a structure to assess its health. Because of the elevated number of echoes and possible modes of propagation of the acoustic waves within the structure, those applications suffer from a burden of signal processing. This paper presents a composite piezo-electric patch and its electronics that were designed and successfully tested for reducing the complexity of the SHM detection schemes.

Miniature Brushless DC motors (less than 5gr) offer some challenges both in the design and the manufacturing. They are used in several mass volume applications, such as hard disk drive, gyroscopes, and more recently in some unnamed aircraft vehicles (UAVs), where Cedrat is involved. For this last application, the efficiency is of upmost importance. Cedrat has used its Flux software solution to optimize the Brushless motor design: Some materials and dimensions have been changed in the motor to improve its efficiency.

Magnetorheological fluids (MRF) are magnetically controlled fluids and they find more and more industrial applications in actuation functions. These include shock absorbers, semi-active dampers, clutches, brakes, haptic actuators & devices. Several of these applications have been studied by Cedrat Technologies for its industrial customers, and a device-oriented test bench has been developed in order to characterise the magneto-mechanical properties of MRF such as the magnetisation curve, the yield stress ….

Thanks to the help of intensive modelling, the two first prototypes realised in the framework of the M2 EMS project are functional. It consists of prototypes of single-phase stepper motor whose structure has been transformed from the Lavet motor so as to take into account collective production of the magnet film layers, which are developed in the M2 EMS project.

Sandia National Laboratories has previously tested a capability to impose a 7.5 g-rms (30 g peak) radial vibration load up to 2 kHz on a 25 lb object with superimposed 50 g acceleration at its centrifuge facility. This was accomplished by attaching a 3,000 lb Unholtz-Dickie mechanical shaker at the end of the centrifuge arm to create a “Vibrafuge”. However, the combination of non-radial vibration directions, and linear accelerations higher than 50g’s are currently not possible because of the load capabilities of the shaker and the stresses on the internal shaker components due to the combined centrifuge acceleration.