Mechatronics is nowadays a dominating concept in design of various kinds of systems and technical devices. High speeds of data processing by control units of mechatronic systems, as well as high dynamics of their actuators allow the systems to be applied in wider fields. This refers to the medicine as well, especially while making attempts to replace lost human motor abilities by means of robots aiding the man. These devices can be divided into three groups: exoskeletons designed to strengthen the natural force of human muscles, orthotic robots that restore lost or weakened functions of human limbs, and prosthetic robots replacing an amputated limb. The first and the third group are known quite well, whereas the orthotic robots are at an initial phase of their development. The authors have worked on a device for aiding the motion of disabled people suffering from paresis of the lower limbs. The paper presents a concept and a structure of the system that has been created, comparing it with similar devices that have already existed. There are indicated some connections and areas where the subunits merge, as well as the rules of their working with the user.

Effects of a fully natural aging of MEMS accelerometers are evaluated with regard to changes in their performance. Two models of commercial dual-axis accelerometers (two pieces of ADXL 202E and 203 by Analog Devices Inc.) with analog outputs were tested over a period of about 10 and 4 years, respectively. A custom computer controlled test rig was used for performing relevant experimental studies, employing the gravitational acceleration as the reference source. A methodology of determining the proposed indicators of aging phenomena is presented and discussed. Changes of the offset voltage and the scale factor were observed and a way of evaluating the overall error due to combined influence of these two parameters is proposed. It was found out that the changes of the output voltage generated by the tested accelerometers were considerable, resulting in respective maximal errors of about 52 mg (2.6%) (ADXL 202E) or 20 mg (1%) (ADXL 203). Simple ways of reducing the effects of aging are proposed.

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