04 - Technical Prerequisites

Question 1

Sensor, transducer def

Answer 1

• sensor = e/ of a mechatronic or msrmt syst that produces msrbl chg in response to a physical cdt°
• transducer = active e/ of a sensor that transforms a signal from a physical domain to another

Question 2

Sensor classification

Answer 2

• by modality

- by attachment

Question 3

Physiological data recording

Answer 3

• EMG = summation of action potentials from the muscle fibers under the electrodes placed on the skin
• EEG = msrmt of electrical activity in the brain produced by large neuron pop° (spectral content 0-50 Hz)
• ECG = msrmt of the electrical impulses generated during the heart cycle (10 µV - 5 mV, 0.5 - 100 Hz)
  P = atrial depol°, QRS = ventricular depol°, T = ventricular repol°
• metabolic fct
• respiration
• …

Question 4

Position and motion recording

Answer 4

• types of sensors
• – resistive (potentiometers, ∆R)
• – capacitive (∆C)
• – inductive (∆inductance or ∆V)
• – optical methods
• – ultrasound methods
• goniometers
• inertial sensors = gyroscope, accelerometer, IMU (inertial msrmt units = gyroscope + accelerometer + …)
• motion tracking
• – optical: spatial accuracy, but challenging tracking
• – acoustic: cheap, but sound reflexion
• – magnetic: no obstacle occlusion, but field deformation
• hand/eye tracking

Question 5

Force and moment recording

Answer 5

• resistive methods (strain gauge)
• piezoelectrical methods
• optical syst
• capacitive methods
• ground-mounted / body-mounted

Question 6

Actuator and actuation principle

Answer 6

• def: mechcl device which converts energy into some kind of force and/or motion (or other modalities)
• electromagnc actuators: F = I x B
• fluidic actuators
• – pneumatic = soft and compliant
• – hydraulic = stiff and higher inertia
• thermomechcl actuators (∆T° => state chg)
• electroactive polymers = EAPs (∆i or ∆V => chg size/shape)
• actuator system
• – torque T = F.L_lever
• – motor torque T_m = F_tensile.r_shaft
• – power P = T.w

Question 7

Kinematic structures

Answer 7

• parallel kinematics
• – hexapod
• – delta systems
• – tripod
• – pantographs
• serial
• – linear
• – rotary
• – combination
• structure location
• – end-effector based: easy to adjust but no fully determined, inj risk
• – exoskeleton: fully determined but robotic and anatomical axes alignment challenging

Question 8

Setup for actuators

Answer 8

• ctl
• – position-based
• – force controllers: impedance/admittance ctl
• safety features: mechcl, elcl, software methods