Industrial Robot Components

Industrial Robot Components

1. Controller

   • initially mini computer
   • now multi purpose processor system

2. Arm

   • Degree of Freedom
     • number of independent position variables that would have to specified in order to locate all parts of the mechanism
     • number of single axis rotational joints in the arm
     • higher number increased flexibility
     • standard 6 D.O.F
       • 3 joints controlling position of end effector
       • 3 joints controlling orientation of end effector
   • joints
     • sliding/prismatic (P)
     • rotating/revolute (R)
     • Wrist
       • SCARA
         • limited to vertical and horizontal movement
         • 1wrist joint for roll
         • pitch and yaw result in tilting of part when encounters contact force
       • revolute
       • 2 joints sufficient (pitch and roll)
       • pitch
       • roll
       • yaw
   • Configurations(from base)
     • PPP
     • RPP
     • RRP
     • RRR
   • Base
     • Pedestal
     • Gantry
       • large workspaces
   • Types
     • Articulated
       • dominent type
       • Parallel
         • 3 joints operate in parallel
         • high contact forces
         • high speed
         • high stiffness
         • high accuracy
         • limited workspace
       • Series
         • high flexibility
         • low accuracy
         • low stiffness
         • large workspace
     • Polar
       • perpendicular axis (RRP)
       • not common
     • SCARA
       • RRP
       • Parallel Axis
       • 2nd most popular
       • assembly applications

3. Driver

   • each individual joint must be driven independently
   • Pneumatic
     • drive manipulators or pick and place because suitable for mechanical stops and clamping
     • low cost
     • reliable
     • poor positioning
     • inability to stop quickly
     • overshoots because air is highly compressible
     • NOT viable choice for joints of arm
   • Hydraulic
     • oil highly incompressible
     • no overshoot problem
     • higher power to weight ratio than electric motors
     • high cost
     • high pressure oil system required
     • precision engineered servo valve required
     • now virtually non existent
     • initially used for paint spraying b/c flammable fumes dangerous from electric spark
     • before advances in electric used in all larger machines e.g. spot welding
     • cost does not decrease with size
     • heavy motors reduce lifting capacity and increase inertia
   • Electric
     • initially small robot application
     • power to weight ratio not important for small robot
     • cost less than equivalent hydraulic
     • no need for oil supply or servo values
     • cost of actuators decreased with lifting capacity
     • technical advances produce reduction in size and weight
     • power depends on current
       • current limited by heat
         • brushless motors / oil cooling systems allow higher currents
         • brushes a main source of heat
     • drive majority of joints near 100%
   • Drive Transmission Systems
     • Direct Drive
       • gearing causes mechanical problems limiting spend and accuracy
       • motor at each joint directly drives joint
         • but motors have to run below optimum
           • larger motors larger toque but increases inertia and so decreased lifting capacity
       • SCARA AdeptOne
         • 2 joints driven directly
         • 2 joints driven remotely
         • belt drive instead of gearing
         • expensive
     • to reduce inertia actuators are located as close to the base as possible
       • so some joints must be driven remotely
         • transmission system between motor and joint

4. End Effector

   • Grippers
     • Mechanical
       • 2 fingers that move parallel to each other
     • Vacuum
       • one or more suction cups connected to vacuum pump or air ejector
       • handling light weight components on smooth surfaces
     • Magnetic
       • electro magnets
       • ferrous components
       • picked up/released by switching on/off current
   • Manufacturing Implements and Tools
     • all end effectors that are not grippers
       • spray guns
       • welding torches
       • drills
       • grinders
       • ladles
   • increasingly fitted with sensors
     • opticile lenses
     • tactile pads
   • Automatic tool changer can be used to change the end effector