Thermal-bimorph (bimaterial) actuators are basic elements of MEMS ciliary arrays used for moving and positioning of small objects [
]. The arrayed actuators are deformable microstructures that may curl into and out of the substrate plane. Objects placed on the array are moving on the tips of actuators cyclically going down and up. Motion of the ciliary actuators is due to different thermal expansion of two polyimide layers with an integrated heater resistor between them. When an electric current is passed through the heater resistor, the temperature of the actuator increases and the structure, initially deflected out-of-plane, deflects downward. The above process requires of the actuators to generate not only large deflections but also a considerable force. The triangle-shaped actuator proposed in the paper [
] is such a structure. Two perpendicular bars rigidly connected at the moving tip and firmly fixed to the substrate plane at the unconnected ends are a stiffened frame structure with additional kinematical constrains. These constrains generate interaction forces between the connected beams during the forming process. In turn, the interaction forces have influence on the internal forces generated during the loading process. In the presented article, the triangle-shape actuator is considered as initially flat, layered frame structure, which becomes the curved 3-D stiffened structure during the cooling process. The cooling down beams are bent in two orthogonal planes not only due to change of the temperature, but also due to additional kinematical constrains. Relations between bending moments, curvature variations and temperature changes enable to find the residual internal forces on the purely analytical way.