An adaptive precision ball screw drive concept is presented in which a self-sufficient actuator is able to adjust the axial preload during the operation. The adjustment is effected by thermal shape memory alloy pucks, which either expand or contract according to the surrounding temperature field of the process. For this purpose, no external energy is needed and so the system is self-supported (energy harvesting). In this case, the extrinsic two-way shape memory effect occurs and the reversible full cycle of shape change is accomplished by a bias force of a flexure. Basing on temperature and force measurements on a double nut ball screw, a thermo-mechanical model is developed. Using the investigated principles adaptive mechanisms, a shape memory-based actuator is designed. Initial tests reveal an unwanted reduction of the preload of up to 800 N with rising temperature. Due to the shape memory actuation device, experiments results show an increase in axial load in approximated 70 % of the reduction.
Shape memory alloys (SMA) like Nickel-Titanium possess a very high mechanical energy density in relation to
conventional drives. Fiber reinforced plastics (FRP) will be increasingly applied to create lightweight structures.
Combining both innovative materials will evolve synergy effects. Due to functional integration of SMA sheets into a
base of FRP it is possible to realize adaptive composites for resource-efficient constructions as for instance flaps or
spoilers on cars. For this purpose the interaction between SMA as an actuator and FRP as a return spring need to be
designed in a suitable way. The computation of such structures is complex because of its non-linear (SMA) and
anisotropic (FRP) mechanical behavior. Therefore, a structural simulation model based on the finite element method was
developed by means of the software ANSYS. Based on that simulation model it is possible to determine proper
geometrical parameters for a composite made of SMA and FRP to perform a certain mechanism. The material properties
of SMA or FRP could also be varied to investigate their influence. For exemplary components it could be shown that the
stress-strain behavior is computable.
In machine tools several time and position varying heat sources causes complex temperature distributions. The resulting
problems are varying thermal deformations which cause a loss of accuracy as well as non optimal drive conditions. An
option to deal with that issue is to use structure integrated SM-actuators which use the thermal energy accumulated by
machining processes to yield an actuator displacement. That creates a structure inherent control loop. There the shape-memory-
elements work as sensing element as well as actuation element. The plant is defined by the thermal and
mechanical behaviour of the surrounding structure. Because of the closed loop operation mode, the mechanical design
has to deal with questions of stability and parameter adjustment in a control sense. In contrast to common control
arrangements this issues can only be influenced by designing the actuator and the structure.
To investigate this approach a test bench has been designed. The heat is yielded by a clutch and directed through the
structure to the shape memory element. The force and displacement of the actuator are therefore driven directly by
process heat. This paper presents a broad mechanical design approach of the test bench as well as the design of the SM-actuator.
To investigate the thermo-mechanical behaviour of the structure-integrated actuator, a model of the test bench
has been developed. The model covers the thermal behaviour of the test bench as well as the thermo-mechanical
couplings of the shape memory actuator. The model has been validated by comprehensive measurements.
Machine tools for small work pieces are characterized by an extensive disproportion between workspace and cross
section. This is mainly caused by limitations in the miniaturization of drives and guidance elements. Due to their high
specific workloads and relatively small spatial requirements, Shape-Memory-Alloys (SMA) possess an outstanding
potential to serve as miniaturized positioning devices in small machines. However, a disadvantage of known actuator
configurations, such as SMA wire working against a mechanical spring, is that energy is steadily consumed to hold
defined positions. In this paper we present a novel SMA actuator design, which, due to an antagonistic arrangement of
two SMA elements does only require a minimum amount of energy whilst holding position. The SMA actuators were
designed regarding material, geometrical parameters, applied load, and control aspects. Furthermore, closed loop control
concepts for positioning applications are implemented. These not only cover approaches using sensors, but also sensorless
concepts which utilize the distinctive length - resistance - correlation of SMAs for position controlling. Furthermore,
an actuator demonstrator has been used to demonstrate the designs capabilities to serve as miniaturized positioning
device in small machines. In addition the novel design concept of the SMA actuator will be compared with commonly
Problems in using shape memory alloys (SMA) in industrial applications are often caused by the fragmentary knowledge
of the complex activation behavior. To solve this problem, Fraunhofer IWU developed a Matlab®-based simulation tool
to emulate the properties of a SMA wire based on the energy balance. The contained terms result of the characteristic
material behavior combined with thermal, electrical, and mechanical conditions. Model validation is performed by
laboratory tests. It is shown that there is almost no difference between the measured and the simulated actuator
movement. Due to the good quality of the model it is possible to use it in a control loop. Knowing current and voltage
enables the computation of the electrical resistance of the actuator and can therefore be used for feedback control.
Implementation of the results into industrial applications is exemplified by integration of an actuator in a flap as used in
air condition systems of cars. Furthermore, the SMA-based drive will be compared to an electromechanical drive.
The paper reports the holistic development of an active piezo-based component concerning the mechanical design and
the control. The active component is used for the reduction of torsional vibrations in a strut of a tripod parallel kinematic
machine. By means of this new component the main drawback of the x, y, z-tripod structure can be eliminated. A
calculation shows the compliance of the connection between actuators and the adjacent mechanical parts as the most
sensitive point of the design. The characteristic values of the piezo actuator were transformed into the active component
with the help of design factors. For reducing the structural vibrations a control laws is presented that changes the
properties of the electro-mechanical structure, like damping or stiffness. This is possible by a feedback of motion signals,
e.g. velocity. The described electro-mechanical model was used for the control design. Experiment results, which are
finally presented, show a reduction of structural vibrations.