Prefect's Pages.. Engineering .. Robotic Arm (Phase II)

Engineering Projects: Robotic Arm (Phase II)

Photograph of the Phase II arm removed from table. It became very apparent after the completion of Phase I that I was in it for the long haul. Everything from the Phase I arm system was dismantled and some useful components such as motors were salvaged and recycled for Phase II. After extensive brainstorming and designing, an entirely new arm, table, control system and electronics were created. The arm would eventually serve as the basis for Phases IIIa and IIIb, and the table with linear track served as platform for the arm system through the final phase of the project.

Vital Statistics

Years	Summer 1990 - Spring 1991
Construction Materials	Wood, steel, carpenter's glue, sheetrock screws, nylon mason's line, threaded rod, bearings, surplus satellite dish rotator motors, misc. surplus motors, misc. plumbing parts
Degrees of Freedom	Three plus grip (linear base, shoulder, elbow). Cartesian (box) work envelope.
Drive Techniques	Winching nylon line around a pulley on DC motors to raise joints. Gravity needed to lower joints. Base used a feed-through style winch with tensioning turnbuckle.
Feedback	Two potentiometers (shoulder, elbow). Optical interrupter sensor for linear encoder (base). Limit switches on base, gripper. Magnetic sensors on gripper to differentiate grasped objects (some had embedded magnets).
Control Computer	12MHz 286 PC with a CGA monitor and 40 megabyte hard disk
Interface	ISA card with two 8255 peripheral I/O chips for 48 lines of digital I/O. The card was constructed on a Jameco ISA prototyping card. The digital I/O lines connected to a series of external rack-like boxes which contained the power supply, motor control, etc. Unsophisticated relay motor control was again used. Analog inputs were originally to be connected with an external ADC, but problems with that solution lead to the use of a PC game port.
Software	Largely written in QuickBasic 4.5. Experimental transition to Turbo Pascal 6.0 made during latter part of this phase, but core code remained in QB.
Capabilities	Automated pick-and-place operations using custom language (ATL). Manual control via modified Nintendo Advantage joystick with rudimentary training capabilities (e.g. position arm, record position of sensors, repeat). Accuracy and repeatability improved greatly over first phase implementation.

Additional Photos


Phase II arm, control computer and table at the first science fair of Phase II in February 1991. Clearly visible are the NES Advantage joystick used for manual mode, the external LED box which provided visual indication of operating status, and the unfinished table which would form the foundation for phases II through IV. A bit harder to see is that the gripper in this shot retains the same motor from Phase I (one working one was built out of two damaged ones). In the gripper photo below, which was taken after Phase IIc was complete, notice that the gripper motor had been changed.	Phase II arm, angled view. Note feedback potentiometers on shoulder and elbow and mechanical limit switch on base (red button).	Phase II arm, rear view. The shoulder and elbow winching mechanisms are plainly visibly in this photo.

Phase II gripper. Primitive implementation derived from the Phase I design. Note magnetic sensor (gray plastic bar on right) and limit switch. The magnetic sensor was used in some demonstrations to distinguish objects on the table. The motor had been changed after problems arose with the motor carried over from Phase I.

Software Screenshots


Digital Multimeter Simulator to show ADC values, voltages, percentage of potentiometer rotation, angle, etc.

Simulated oscilloscope software for demonstration and diagnostics of digital and analog input signals.

Prototype image scanner display software. The scanner was not implemented until Phase III of the project. Note at this time that a 3D image scanner was planned, but complications led to the development of two generations of 2D scanners in later phases.

Arm Task Language (ATL)

ATL Task File V2.2
This is a DEMO showing joints
19:52:57
03-14-1991

; ATL: Arm Task Language file - Compiled with BUILDATL V1.0


; This is an example of a COMMENT in ATL

; The arm is now returning to the "home" position where all tasks begin
; from.
HOME
; This is an example of LINEAR motion (called the TRACK).
MOVE TRACK TO 25
; This is an example of a ROTATIONAL movement (the SHOULDER).
MOVE SHLDR TO 90
; This is another ROTATIONAL movement (the ELBOW).
MOVE ELBOW TO 75
; This is an example of GRIPPER use, it will OPEN now.
OPEN GRIPPER
; Elbow again...
MOVE ELBOW TO 80
; And Shoulder again...
MOVE SHLDR TO 80
; And finally, closing the gripper.
CLOSE GRIPPER
; Now to just HOME the arm after the task is complete.
HOME
END

END

Table of Contents

Robotics Home

Phase I 1989-1990

Phase II 1990-1991

Phase IIIa 1991-1992

Phase IIIc 1992

Phase IV 1992-1993

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