13-12-2012, 04:14 PM
ROBOT ARM WITH CONTROLLER
ROBOT ARM WITH CONTROLLER.pdf (Size: 506.22 KB / Downloads: 49)
DESCRIPTION
One use for the CONTROLLER is to enable
the five motors in the ROBOT ARM to be
controlled using position feedback. This
document details the use of the
CONTROLLER with the ROBOT ARM.
The central control element for the
CONTROLLER is a Picaxe-40X
microcontroller. The CONTROLLER may
be incorporated into initial design of the
ROBOT ARM or may be used to convert
the ROBOT ARM at a later date.
The CONTROLLER may also be used for
mechanisms that require up to six axes of
motor control with position feedback. Other
devices may also be connected to the
unused inputs and outputs.
THE PROJECT
To carry out the project, the student must:
• Design and build the ROBOT ARM
incorporating changes required for the
CONTROLLER. Alternatively, a
completed ROBOT ARM may be
modified to use the CONTROLLER for
the next stage of development and
testing.
• Assemble the printed circuit board,
connect the wiring, motors and position
feedback potentiometers.
• Program the Picaxe microcontroller and
adjust the program parameters.
Figure 1 Robot Arm Controller
PCB Assembly
Figure 2 Robot Arm with Controller
IMPORTANT: This unit must be used together with the ROBOT ARM unit and component kit – it
does not replace it.
COMPUTER REQUIREMENTS
• To install the PICAXE programming editor software requires a PC running Windows 95 or later
with approximately 20MB free space. Any PC that runs the Windows operating system will
work in textual 'BASIC' mode, however a Pentium 4 processor or later is recommended for
graphical flowcharting. (We have also used an iMac running OSX and Windows XP.)
• A PC with 9-pin serial (RS-232) interface. (The PC may require an USB to RS-232 adapter.)
• The PICAXE editor can be downloaded from www.rev-ed.co.uk or from www.picaxe.co.uk.
• A PICAXE serial interface cable. This can be purchased from a number of suppliers or may be
constructed as per the instructions in this document.
MOTOR OUTPUTS
• All of the motor outputs are digital (0V or +V).
• Two output legs on the Picaxe are required to drive one motor.
• Each of the motor outputs is directly connected to an input on an L293D motor driver IC. A
total of six motors can be driven from the circuit without modification.
• To incorporate a seventh motor, use Analogue 7 (Leg 10) and two other outputs (Leg 15 to Leg
18). An additional L293D (or another H-bridge circuit) will be needed.
• A red/green pair of LEDs and resistor (optional) may be connected to each motor's terminals
used to indicate which direction a motor is currently being driven. These LEDs may be useful
during faultfinding.
POTENTIOMETER INPUTS
• All of the potentiometer inputs are analogue. Because the outer arms of each potentiometer are
connected to 0V and +V, the voltage that appears on the wiper arm (driven by the motors), is
between 0V and +V.
• Each of the potentiometers is associated with an analogue-to-digital converter. In the Picaxe, an
analogue-to-digital converter translates an analogue voltage to a numerical value that can be
used by the program.
OTHER INPUTS
To obtain information from the outside world, switches and sensors can be added to unused input
pins on the Picaxe. You should add these devices only after the basic design has been built and
tested because you will need to modify the program. Some ideas for inputs include:
• A push-button switch (normally open) may be connected to the reset input. When the reset
switch is pressed, the program starts from the beginning.
• A toggle switch for the program to select between two programmed sequences.
• Emergency stop switch to halt the ROBOT ARM when the button is pressed. Another switch
could be used to detect if a "guard" or "fence" is opened. A separate button should be used to
restart the ROBOT ARM.
• Gripper switch to indicate that an object is between the jaws.
• Keypad (4x4 matrix or 4x5 matrix, as per telephone/calculator keypad) to provide direct control
of motors. The concept could be extended as a "teaching" pendant.