Roadmap

1
Roadmap

• Boards Buses
• Communications
• Sensing
• Software
• Goals

2
Electronics Overview
3
Advanced Digital Logics MSM-P5S
Processor Intel Pentium 166MHz Ports 2(4)
Serial, 1 Parallel Memory 32 MB Storage
E-IDE HD Floppy Power _at_5V lt 8W Features
Ethernet Video-In Size 101.6 x 91.4 x
50.8 mm Weight 0.17kg Cost 1307
4
Operating System

• Red Hat Linux 5.2
• Expected control rate of ?100Hz
• Large development support base
• Familiarity
• Inexpensive

5
Offboard Communication
6
Onboard Communications Bus

• RS-485
• Increased Noise Immunity
• Balanced signals
• Multiple transmitters/receivers on a single chain
• Processor uses standard serial ports (RS-232)
• Converter translates RS-232 to RS-485 signals,
  allowing multiple motor controllers to talk to
  the same serial port
• RS-485 bus has 4 branches
• 3 Joints (1,2,3) Gripper A
• 4 Joints (4,5,6,7) Gripper B
• 4 Joints (8,9,10,11) Gripper C
• 3 A/Ds for the 6 IR sensors and F/T sensors

7
Motor Control

• Distributed
• 14 JR Kerr PicServos
• Independently and group addressable
• High Speed
• Coordinated control rate of 100Hz
• PID servoing loop runs at 20kHz
• Easy to interface
• Direct interface with 3 channel encoders
• Plugs into standard serial port through converter

8
Control Layers
9
Sensing

• Skyworker
• Forces
• Joint Angles
• Gripper Sensing
• Future Enhancements
• Position/Localization Sensing
• Compensate for dead reckoning errors during large
  traverses
• Expensive and unnecessary for prototype
  operations
• Improved Gripper Sensing
• Allow for larger errors in world model

10
Force Torque Sensor Placement
11
Force Sensing

• Record forces exerted by Skyworker
• Capable of measuring large torques and small
  forces
• Three JR3 6-DOF force-torque sensors
• 67 mm diameter x 25 mm thick
• 200N sensor (actual performance is a function of
  the forces applied along each axis)
• Approximately 170g

12
Joint Sensing

• Sense properties of joints to support multiple
  tasks
• Walking gripping insertion etc
• Detect and report joint angles
• Joint angular resolution of 2633 ticks/degree
• Gripper angular resolution of 1077 ticks/degree
• Gearing Errors
• Planetary Drive 1.3 degree positioning error
  (0.78 arc min after 1001 harmonic)
• Harmonic Drive Repeatability 1.4 arc seconds,
  Hysteresis 1 arc min
• 1.55mm of error due to backlash

13
Gripper Sensing

• Utilize two IR range sensors to determine the
  orientation and location of the target
• Precision of 0.7 (0.9 mm) at 13cm
• Sampling rate of 100Hz

14
Gripper Sensing

• Detect presence of objects
• Detect approach errors/ world model errors
• Utilize the Sharp GP2D12 as a LADAR
  representative sensor
• Sensing range 10-80cm
• Non-linear analog output (higher resolution at
  shorter ranges)

15
Communications Model

• Publish/Subscribe paradigm
• Allows for extensibility
• Information sharing
• Control transfer
• Tasks to be performed are published
• Robot is specified in the message
• Task completion and robot telemetry published
• Allows for visualization and is potentially
  useful in cooperative behavior

16
Inter Process Communication

• Anonymous Publish/Subscribe model
• Robust operation
• Safe to stop start Producers/Consumers
• Client crash wont take down network
• Simple interface
• Local expertise
• Developed at CMU by Reid Simmons

17
Communication Layers
18
Software Design

• Control partitioning and scalability concerns
• Modularity
• Easy interchange and upgrade of component
  elements
• Decoupled components allow melding of simulation
  and real world
• Provide a common interface to both simulation and
  operation

19
Software Blueprint
20
Viz

• Allows programmer to create and manipulate
  complex three dimensional scenes
• Imports VRML and OpenInventor (ProE exports both
  of these types)
• C and Python programming language interfaces
  through XDR
• Maintained by NASA Ames

21
Robot Configurator

• Provides a technique for visualization of the
  joint configurations using Viz.
• Allows the user to specify joint angles for all
  11 DOF and select between anchor grippers.

22
Sky Script

• Tool for developing high-level scripts to
  coordinate various Skyworker actions

23
Sky Coordinator

• Receives plan messages from user interface
• Parses scripts and queues actions in the
  coordinator robot models
• Broadcasts high level actions to robots
• Waits for acknowledgment of completion before
  sending further commands

24
Sky Robot

• Breaks high level actions into smaller components
  and passes them to Sky Onboard
• Keeps track of robots world position and
  internal state
• Transforms requested end effector positions into
  internal joint angles
• Queues actions if they are received before they
  cant be immediately processed
• Generates telemetry packets for visualization

25
Kinematics

• Use D-H joint labeling
• Inverse Kinematics performed through inverting
  the Jacobian utilizing a singularity robust
  inverse (SRI)
• Idea
• Take small straight line steps through world
  space to desired position
• Iterative algorithm
• Limit step size so as to chose the joint
  configuration nearest to current posture
• SRI idea
• Check to see if the Jacobian is becoming
  singular, if it is, nudge the desired position
  so as to avoid the singularity

26
D-H Model
Gripper A holding structure
27
D-H Model
Gripper B holding structure
28
Onboard Controller

• Provides interface between hardware and software
• Specifies joint angles and velocities to the
  motor controller
• Interprets and reacts to sensor inputs
• Utilizes a library of predefined joint
  trajectories
• Generates low level telemetry packets 10-30 times
  a second

29
Initialization

• Script is parsed by Sky Coordinator
• Robots and their Onboard counterparts are
  spawned on machines identified in the script
• All Sky Robot processes are homogenous
• Sky Onboard is instantiated with either a
  simulated or actual motor controller
• Sky Onboard performs axis homing and other
  initialization before reporting that it is
  available
• Sky Coordinator waits until the Sky Robot and Sky
  Onboard are reported as operational before
  issuing any commands

30
Software Progress
31
Skyworker Organizational Chart
32
Budget
33
Outcomes of Skyworker Phase I

• robots performing representative SSP assembly,
  inspection and maintenance tasks
• physical demonstrations
• a few fundamental scripted operations at
  laboratory scale
• first evaluations of force, energy and control
  considerations
• simulations
• large scale / long duration operations
• multiple robots working in coordination

34
Outcomes of Skyworker Phase I

• new approach to space robot worksystems
• walking manipulator
• motion by successive attachment to structure
• constant velocity motion of payloads (walking
  under the payload)
• limbs function as legs or arms
• proprioceptive
• self-contained

35
Outcomes of Skyworker Phase I

• opportunity to investigate important issues
• static/dynamic interactions of robot and facility
  structure
• energy consumption
• control strategies
• infrastructure requirements imposed on the SSP
  facility by robots
• robot coordination and task planning
• robot workforce productivity

36
Skyworker Phase II - Robot

• Push the performance envelope
• better adaptation to structures
• lighter walking
• alternative grippers
• ambitious maneuvers and tasks
• Increase our understanding of the important
  issues
• verify analyses of Skyworker performance through
  physical experiments
• explore motivations (and solutions if needed) for
• global position estimation
• unit robot autonomy

37
Skyworker Phase II - Simulator

• Push the performance envelope
• task decomposition and scheduling
• robot cooperation
• Increase our understanding of the important
  issues
• control bandwidth
• study task duration vs. robot specifications
• investigate robot workforce requirements
• explore alternative robot/facility scale ratios