20-Bio-B7 Ergonomics · May 2016
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
National Exams May 2016 — 04-Bio-B7, 3 hours, closed book (one aid sheet allowed, written on both sides; approved Casio/Sharp calculator only). Six questions are printed; the first five as they appear in the answer book constitute a complete exam paper (all six are answered here as a complete study resource). Each question is of equal value; some require an essay-format answer.
Reference texts: M. P. Groover, R. Weiss, R. N. Nagel & N. G. Odrey, Industrial Robotics: Technology, Programming, and Applications (2nd ed. — robot configurations, end-effectors/grippers, machine vision, sensors and transducers); M. P. Groover, Automation, Production Systems, and Computer-Integrated Manufacturing (5th ed. — Geneva mechanisms/dial indexing, PLC ladder logic, production-rate and line-efficiency analysis).
Question text not reproduced: the examination questions are © Engineers and Geoscientists BC. Open the official past paper (linked at the top of this page) to read the question, then follow the worked solution below.
The five classical arm/body configurations, distinguished by their sequence of joint types and the shape of the reachable workspace they generate, are shown below (R = revolute, P = prismatic/linear):
1. Cartesian (rectangular/gantry). (a) Joints: three prismatic joints (P, P, P) along mutually perpendicular linear axes. (b) DOF: 3 translational (x, y, z). (c) Sketch: see column 1 of Fig. 3 — three right-angle sliders, each marked with a square (P) joint symbol. Simple, decoupled kinematics give excellent positioning accuracy and rigidity, but a large physical footprint and limited reach; used for pick-and-place and gantry-mounted tooling over a fixed work envelope.
2. Cylindrical. (a) Joints: one revolute base joint (θ) plus two prismatic joints, a vertical lift (z) and a radial extension (r). (b) DOF: 3. (c) Sketch: see column 2 of Fig. 3 — a circle (R) at the base, two squares (P) for the vertical and radial slides. The workspace is a section of a cylindrical envelope; compact and fast for vertical reach, common for machine loading/unloading.
3. Polar (spherical). (a) Joints: two revolute joints — base rotation (θ) and shoulder elevation (β) — plus one prismatic (telescoping) reach joint (r). (b) DOF: 3. (c) Sketch: see column 3 of Fig. 3 — two circles (R) in series feeding a squared (P) telescoping link. The workspace approximates a sphere-shaped envelope; this was the configuration of the early Unimate arms, giving a large reach for a modest base footprint.
4. SCARA (Selective Compliance Assembly Robot Arm). (a) Joints: two revolute joints whose axes are both vertical and parallel (θ1, θ2, both rotating in a horizontal plane) plus one prismatic vertical stroke (z) at the wrist. (b) DOF: 3. (c) Sketch: see column 4 of Fig. 3 — two stacked circles (R) on a vertical column, then a square (P) for the vertical wrist stroke. The arm is compliant (flexible) horizontally but rigid vertically, ideal for fast vertical-insertion assembly tasks (e.g. inserting components onto a PCB).
5. Articulated (jointed-arm/anthropomorphic). (a) Joints: three revolute joints — waist, shoulder, and elbow — mimicking a human arm. (b) DOF: 3 (plus wrist joints for full 6-DOF orientation control). (c) Sketch: see column 5 of Fig. 3 — three circles (R) in series along the waist/shoulder/elbow chain. This gives the largest workspace-to-footprint ratio and the most flexible reach/orientation of any configuration, at the cost of the most complex (non-linear) inverse-kinematics computation; it is the most common general-purpose industrial-robot type.
