Stepping motor driven constant-shear-rate rotating viscometer

Despite the frequent use of stepping motors in robotics, automation and in a variety of precision instruments, they can hardly be found in rotational viscometers. This paper proposes the use of a stepping motor to drive a conventional constant-shear-rate laboratory rotational viscometer, in order to avoid the use of a velocity sensor and gearbox and, thus, simplify the instrument design. To investigate this driving technique, a commercial rotating viscometer has been adapted to be driven by a stepping motor, which is controlled via a PC. Special circuitry has been added in order to microstep the stepping motor at a selectable step size, and to condition the torque signal. Tests have been carried out using the prototype to produce three flow curves for a standard Newtonian fluid (920 mPa.s at 25°C) but employing a different microstep size for each of them, within the shear rule range from 50 s^-1 to 500 s^-1. The results indicate the feasibility of the proposed driving technique.