Optimal construction of the thermo-elastic actuator

Electro-mechanical actuators seem to be one of devices which produce mechanical forces as a result of eddy-currents influence. The most optimal of them are electromagnetic actuators constructed as ferromagnetic devices and thermo-elastic actuators constructed as bimetallic or mono-metallic are shown in Fig. 1.

Fig. 1.

Arrangement of the thermo-elastic actuator and distribution of electromagnetic field: 1- dilatation element, 2 - field coil, 3 - sleeve, 4 - ring, 5 - frame, 6 - body

The ferromagnetic cylinder 1,that plays the role of dilatation element, is clamped to non-ferromagnetic ring 4. The ring is pressed in a sleeve 3, which is fixed to frame 5 of the tool machine. A cylindrical coil 2 is replaced between the ring 4 and dilatation element 1. The coil supplied with harmonic current of effective value

I

ext

and frequency

f

, generates time variable electromagnetic field. Due to consequent induction heating the temperature of dilatation element 1 rapidly rises. As a result of temperature rise element 1 is pushed to the body 6 with a contact force

F

C

. This kind of the actuator is characterized by a relatively big dispersion of magnetic field. The paper deals with analysis of possibilities of construction optimization of the device in order to minimize losses of electromagnetic energy and consequently to increase total efficiency and to match electromagnetic compatibility requirements. The aim is to find the construction of the actuator making possible to use practically all the electromagnetic energy for induction heating of the dilatation element. The task formulated as a weakly- coupled electromagnetic — temperature - heat stress problem is solved by means of FEMbased numerical method. The results for illustrative example are presented and discussed.