Lecture 7: Human haptics

Transcription

1 ME 327: Design and Control of Haptic Systems Winter 2018 Lecture 7: Human haptics Allison M. Okamura Stanford University

2 types of haptic sensing kinesthesia/ proprioception/ force cutaneous/ tactile Related to the skin. A sense mediated by end organs located in muscles, tendons, and joints. Stimulated by bodily movements. Johansson and Westling

3 types of haptic sensing tactile spatial form (SA I) stereognosis (SA I, Proprioceptors) texture (SA I, PC) movement (RA) pain flutter vibration (RA) (PC) pricking pain (A δ) burning pain (C fiber) muscle force (Golgi tendon organs) temperature cold (A δ) warm (C fiber) body position/movement (SA II, joint afferents, muscle spindles)

4 sensory homunculus mapping the human somatosensory cortex (Kandel, Schwartz and Jessel)

5 active vs. passive touch Active touch Focus on the object Passive touch Focus on the sensation experienced Try it Is active touch better? Purposiveness vs. movement over skin In 3D, yes How is this important to haptic device design?

6 mechanoreception

7 mechanoreceptive afferents classified by depth: rapidly adapting (RA) 1: closer to skin surface II: deeper beneath surface response classified by rate stimulus of adaptation: rapidly adapting = phasic slowly adapting (SA) slowly adapting = tonic classified by sending modality: e.g., receptor structure response stimulus

8 cross section of glabrous skin

9 Merkel (SA 1) form and texture perception low-frequency vibrations Shape: disk Location: near border between epidermis & dermis Type: SA I Best Frequencies: Hz Stimulus: pressure

10 Ruffini (SA 1I) static and dynamic skin deformation skin stretch Shape: many-branched fibers inside a roughly cylindrical capsule Location: dermis Type: SA II Best Frequencies: Hz Stimulus: stretching of skin or movement of joints

11 Meissner (RA I) motion, slip/grip dynamic skin deformation Shape: stack of flattened cells, with a nerve fiber winding its way through Location: in dermis just below epidermis Type: RA I Best Frequencies: 3-40 Hz Stimulus: taps on skin

12 Pacinian Corpuscle (PC / RA II) high frequency vibration gross pressure changes Shape: layered capsule surrounding nerve fiber Location: deep in skin Type: PC Best Frequencies: 10 to >500 Hz Stimulus: rapid vibration

13 cutaneous mechanoreceptors Receptor Diam. Density (Fibers/cm 2 ) Response Percep. Function SA I RA SA II PC Merkel 2mm 100 curvature form & texture Meissner 5 mm 150 motion motion & grip control Ruffini 8mm 20 stretch hand shape, lateral force Pacinian Hand 20 vibration tools & probes

14 kinesthesia

15 kinesthetic sensing perception of limb movement & position, force muscle receptors (muscle spindles and Golgi tendon organs) joint receptors (in capsules and ligaments of joints) skin receptors (slowly adapting cutaneous mechanoreceptors that measure skin stretch): Ruffini endings, Merkel Cells in hairy skin

16 force sensing Resolution 0.06 N Grasping force: 400 N! Which of the following objects weighs about one Newton? automobile, Isaac Newton, bowling ball, baseball, a dime baseball ~145g 1.421N = lb (1 N = lb, 1 lb = N)

17 proprioception derived from Latin, proprius, meaning belonging to one's own self in general, it provides a sense of static position and movement of the limbs and body in relation to one other and the world in much of the literature, proprioception is defined as the perception of positions and movements of the body segments in relation to each other (without aid of vision, touch, or the organs of equilibrium). This is in contrast to exteroception.

18 Just Noticeable Differences at Joints Proximal-InterPhalangeal (PIP) Joint MetaCarpalPhalangeal (MCP) Joint ~2.5 /*6.8 ~2.5 /*4.4 Wrist 2.0 Elbow 2.0 H. Z. Tan, M. A. Srinivasan, B. Eberman, and B. Cheng, "Human factors for the design of forcereflecting haptic interfaces." In Proc. of 3rd Int. Symp. Haptic Interfaces for Virtual Environment and Teleoperator Systems, ASME Dynamic Systems and Control Division, 55(1): , L. A. Jones, Kinesthetic Sensing, unpublished, Shoulder (front) 0.8 Shoulder (side) 0.8

19 movement and position threshold can depend on velocity and whether muscle is contracted Movement detection threshold (deg) elbow relaxed index finger elbow contracting Angular velocity (deg/sec) Jones, 2000

20 Reading discussion

21 discussion points MacLean: 1. are there new trends since this was written in 2008? 2. what gives rise to the bottleneck in haptic systems? 3. what are haptic icons? 4. what is affect? Hannaford & Okamura: 5. What is the commercial market for haptic devices like? 6. What factors affect the stability of haptic devices? and what are the implications for haptic interaction design? Weir & Colgate, Gillespie & Cutkosky: 8. What relationships exist between the human user and these control-theoretic works?

22 activity Two-point discrimination experiment