Introduction to the Personal Assistant  tm
The Personal Assistant is a culmination of engineering design and development over the past twelve years.  Conceived in 1993, this design was a departure from previous mechanical Hands concieved and built by myself as early as 1985.  This machine included not only anatomically similar mechanical Hands, but Arms as well, packaged into a supporting chassis.  The effort began with a complete redesign of previous mechanical Hands, having fewer parts and better actuators.  Compact packaging of finger- joint actuators allowed for anatomically proportioned lower and upper arm sections; proportion defined as link lengths, not currently diameters.  Design and packaging for a three-axis shoulder onto the arm was next, followed by integration of the arm assembly into a support chassis measuring only 9 inches in diameter by 19 inches long.  The working load for each hand is 10 lbs, using a design factor of safety of three.  No-load joint speeds were designed for 90 degrees /sec.  All fabrication drawings (over 100) were completed using AutoCad by December, 1997.

Recent Advancements in Development of the Personal Assistant 1999
The design phase and final fabrication drawings using AutoCad were completed in December, 1997.  Pre-prototype development began by verifying all drawings for dimensional accuracy during the last quarter of 1999.  The design tool chosen for this was Pro Engineer.  A truely powerful software package, Pro /Engineer advanced this development effort through the creation of a 3 dimensional part from each drawing, thereby proving out form, fit and function of all parts and sub-assemblies.  Several dimensional inaccuracies were caught and corrected.  Also, certian designs were modified and improved.  Mass properties were obtained such as weight and center of gravity of each part and sub-assembly.  Pictures of the Personal Assistant may be viewed below:
 

Picture 1           Picture 5               Picture 9

Picture 2           Picture 6               Picture 10

Picture 3            Picture 7                Picture 11

Picture 4           Picture 8               Picture 12

A specifications list on the personal assistant may be viewed in thefigure #2.

 

Fundamental Design Assumptions

• Selection of body, arm, hand and head dimensions to closely match the 50th percentile, Male Military recruit would result in the closest match of link lengths to the general population of  potential teleoperators.
• Typical range of motion for human joints measure up to 90 degrees.  Human hand to eye coordination response is approximately 3/4 second.  Therefore, robot joint speed (no load) was chosen to be 90 degrees per second.
• Robot manipulation includes derivatives of power and precision grasping.  Power grasping requirements were derived from an automotive industry study concluding that most objects manipulated by a person during daily activity weigh under 4 lbs.  Load capacities of each hand were increased to 10 lbs. to accommodate testing with heavier objects.
• Precision grasp requirements are derived from angular joint resolution.  Angular resolution at a given robot joint was determined to be +/- 2 degrees.
• Unlike industrial robot design requirements, a high degree of accuracy (position of the robot arm in space to a programmed point) and repeatability (return of robot arm to a point as a function of linkage tolerances) are not tightly required in this design, since these attributes are not emphasized in performing object manipulation by humans.
• Design to incorporate ease of manufacturability, ease of assembly and ease of repair.
• Design considerations to include manufacturing from plastic wherever possible.