Q2. What are the drawbacks of a pneumatic joint?
The drawbacks of a joint actuated by two pneumatic muscles are the nonlinear characteristic, the slow dynamics (especially depressurizing the muscle is slow), the presence of hysteresis, and the need for pressurized air.
Q3. What is the simplest way to alter the cross section of a spring?
One technique to alter the cross section is to use a beam with non-unity aspect ratio where stiffness can be changed by rotating the beam through 90° since the moment of inertia in the Bernoulli-Bar equation is the analogy to the cross section area.
Q4. What is the advantage of using a third compliant element to tune the motors to nominal?
Cross-coupling allows setting of preload forces to tune it to nominal working conditions, using (a fraction of) each motor’s torque in both directions.
Q5. What is the effect of the introduction of two conjugate poles on the stability of the joint?
The introduction of two complex conjugate poles also creates a sharp increase in phase lag, decreasing the stability margin when controlling the joint for link quantities and making the control difficult on the motor side due to the introduction of an anti-resonance at the same frequency.
Q6. What is the disadvantage of using antagonistic motors?
The main disadvantage of using antagonistic motors is that both motors need to work synchronously to either change the equilibrium position or the stiffness.
Q7. What is the definition of a velocity based controller?
The velocity based controller generates velocity commands that are a function of the desired virtual stiffness using the spring deflection state.
Q8. What is the advantage of a two dof degree-of-freedom finger?
De and Tasch designed a two dof degree-of-freedom finger, which again uses leaf springs, but can also control the coupling stiffness [75].
Q9. What is the maximum joint torque of the uni-directional case?
When tension-only tendons are considered for the uni-directional case [29], the maximum joint torque can not be more than that of each single motor, and no net torque is available when stiffness is at maximum.
Q10. What is the way to adjust the stiffness of a joint?
Note that holding the sheets together is very difficult because the shear forces are very high, but this system does benefit from simple construction and a wide stiffness range, although friction makes precise control of the stiffness difficult.
Q11. What is the main drawback of the antagonistic springs?
This subclass uses nonlinear springs, which is often a drawback, but the antagonistic springs also reduce energy efficiency and energy storage capacity.
Q12. What is the behavior of a MR and ER fluid?
The behavior of ER and MR fluids is given using Bingham viscoplastic models: Fd = −sign(q̇r)(g(µ, |q̇r|) + Cu) , (3) where g(µ, |q̇r|) represents the viscous component of the damping force, µ the viscosity of the fluid, u the electric field or the current for ER and MR respectively and C denotes a coefficient that depends on the physical properties of the fluid and on the geometry of the damper.
Q13. What is the advantage of the coupler?
Another advantage is that the coupler of each four-bar linkage is easily equipped with two pairs of strain gauges for joint torque measurements.
Q14. What is the difference between the two antagonistic springs?
This design (with two identical antagonistic springs) results in a constant joint stiffness characteristic, independent of the joint angle deflection.
Q15. What is the difference between the no load and the spring preload categories?
Compared to the no load category, the spring force is parallel to the spring displacement, hence to change the stiffness, energy has to be stored in the springs and may not be retrievable.