Traditionally, haptic interfaces use active actuators such as electric motors to generate force feedback. It is well-known that these interfaces can suffer from instability
issues depending on the simulated environment. In several applications, instability is a particular concern as it represents a true danger to the user.
Passive actuators such as brakes and dampers are intrinsically stable and safe. We demonstrated that small-scale magnetorheological (MR) fluid brakes
combined with small DC motors can increase the performance and safety of force-feedback devices. The picture on the left shows the hybrid actuator we developed comprising two unidirectional MR brakes and a DC motor.
The complete system can produce 7.9 times more torque than a volume-equivalent DC motor with lower inertial and frictional torques.
The device has been patented and transferred to one of our industry partners in Europe.
Read the news story published on eeNews Europe: here.
One out of eight Canadian men will be diagnosed with prostate cancer during their lifetime. In Canada, prostate cancer accounts for roughly one-quarter of all cancer
cases in men, making it the leading cause of cancer deaths with 24,000 diagnoses and 4,100 deaths every year. Brachytherapy is a popular treatment for men with early prostate
cancer due to its high success rate, minimal side effects, and patient convenience. It involves the insertion of needles loaded with tiny radioactive seeds into the prostate.
Once the needles are fully inserted, they are pulled back to permanently leave the seeds in locations inside the prostate, where the radiation released
from them treats the cancer cells. The radioactive seeds must be implanted in target locations with great accuracy.
However, current techniques only enable surgeons to place seeds to within 5 mm of an intended target.
The figure on the felt shows the hand-held instrument we developed that helps surgeons place seeds with an accuracy of 0.33 mm. It steers the needle automatically by rotating its base as the surgeon inserts it. Delivering radiation with pinpoint accuracy will lead to better prostate cancer control and fewer side effects for patients. It can also allow treating prostate cancer situations that are not possible with the current imprecise technique. One example is treating only a part of the prostate for early prostate cancers.
Magnetorheological (MR) fluids have emerged as a promising technology for new actuator design. An MR fluid is an active material
composed of a suspension of soft ferromagnetic micron-sized particles (typically 1 to 10 microns) dispersed in a carrying liquid
(mineral oils, synthetic oils or water). Under the action of an external magnetic field, these particles form
chain-like structures or aggregates aligned roughly parallel to the magnetic field, changing the apparent
viscosity of the fluid (see the animation on the left).
Classical approaches for designing MR brakes have not accounted for fluid nonlinearity and magnetic saturation while addressing tradeoffs in terms of repose time, off-state torque, power supply, desired torque and volume. We showed that performance is strongly dependent on electromechanical design and introduced a new model for optimal actuator design. This resulted in an actuator with 23% more torque in a volume 76% smaller than a commercially available MR brake (second figure).
Spastic movement disorders are prominent features of
impaired function of the motor system and are frequently associated
to stroke, multiple sclerosis, spinal cord injury, and cerebral
palsy. They are best characterised by changes in reflex
excitability, muscle tone, and restricted range of motion, all
leading to difficulties in performing voluntary movements.
Recent development in robotics has opened new avenues for patients affected by such severe movement disorders. It allows patients living with impairments of limb movements to accomplish activities of daily living, such as feeding, and leisure, that would otherwise be difficult or impossible to perform. The teleoperation system on the left uses a nonlinear mapping between the identified patient’s range of motion and that of the object that is being manipulated. It refines the patient’s motion and reduces the effects of tremor and spasms. It can also be used to upscale the range of motion allowing the patient to accomplish tasks in a workspace that he would otherwise not be able to reach. The second figure shows an 8-DOF kinematic model through which the patients tolerable range of motion can be evaluated.