Robotic Lab Practical file M.tech EST

1. EXPERIMENT NO. 5
AIM:
To study and design the implementation of Brushless DC Motor Six Step Control.
Apparatus Used:
Microsoft Windows XP, Professional Version 2002, Intel® Pentium® Dual CPU. E2180 @2.00
GHz, 2.00 GHz, 199 GB of RAM, Lab VIEW Robotics 2011 SP1
Theory:
LabVIEW (short for The Laboratory Virtual Instrumentation Engineering Workbench) is a
platform and development environment for a visual programming language from National
Instruments in which you create programs using a graphical natation (connecting functional
nodes via wires through which data flows), in this regard, it differs from traditional programming
languages like C, C++, or Java in which you program with text. However LabVIEW is much
more than a programming language. It is an interactive program development and execution
system designed for people, like scientists and engineers, who need to program as part of their
jobs. The LabVIEW development environment works on computers running Windows, Mac OS
X, or Linux. LabVIEW can create programs that run on those platforms, as well as Microsoft
Pocket PC Microsoft windows CE, Palm OS, and a variety of embedded platforms, including
Field Programmable Gate Arrays (FPGAs), Digital Signal Processors (DSP), and
Microprocessors.
Procedure:
Execution is determined by the structure of a graphical block diagram on which the programmer
connects different function nodes by drawing wires. These wires propagate variables and any
node can execute as soon as all its input data become available. LabVIEW ties the creation of
user interface (front panels) into the development cycle. LabVIEW programs/subroutines are
called virtual instruments (VIs). Each VI has three components; a block diagram, a front panel,
and a connector panel. The last is used to represent the VI in the block diagram of other, calling
VI. Controls and indicators on the front panel allow an operator to input data into or extract data
from a running virtual instrument. However, the front panel can also serve as a programmatic
interface. Thus a VI can either be run as a program, with the front panel serving as a user
interface, or when dropped as a node onto the block diagram, the font panel defines the inputs
and outputs for the given node through the connector pane. This implies each VI can be easily
tested before being embedded as a subroutine into a larger program. The graphical approach also
allows non-programmers to build programs simply by dragging and dropping virtual
representation of lab equipment with which they are already familiar.

2. Execution of VI’s and Sub –VI’s:
Main VI:
Block Diagram:
Sub VI:
BLCD Six Step Controller:

3. Triangle wave:
Hall Sensor:

4. Result:
This “Single Control Loop” example is useful for robots that do relatively simple repetitive
algorithms. This design uses simulated LIDAR data with the Vector Field Histogram obstacle
avoidance algorithm and steering API. Insert code for acquiring and processing sensor data and
controlling the robot inside the Timed Loop controls timing and is configured to run at 10 Hz.
However, all processing must execute fast enough to keep up with this loop rate.
Timed Loop:
Execute one or more sub diagram, or frames, sequentially each iteration of the loop at the period
we specify. Use the Timed loop when we want to develop the VIs with rate timing capabilities,
precise timing, feedback on loop execution, timing characteristics that change dynamically, or
several levels of execution priority.
Steering Frame:
To create the steering frame of robot there are steering VIs under Robotics VIs in which
“Ackermann steering VI” is used in this design. The center of the steering is at the midpoint of
the wheel separation width between the rare wheels. Figure 2 shows the VI of Ackermann
Steering Frame. In this figure1 and 1.5 in Ackermann VIis wheel separation width and length
respectively. In this VI there are two steering front wheel and two fixed rear wheel is used. To
create them we use separate VIs for “Create Steering Wheel.vi” and “Create Fixed Wheel.VI”. In
both VIs wheel parameters and steering parameters is set according to our design and movement
of frame. Wheel object is created using controls which are in pink boxes.
Using Read Saved LIDAR data VI:

5. This VI reads the saved data extracting from LIDAR sensor attached to robot. LIDAR Sensor
sensors scan a sector of angle and return the distances to nearest object in every direction. Thus
this VI gives two output data magnitude in mm and direction of that length.
Simple Vector Field Histogram VI:
Output from LIDAR sensor VI is input of this VI. Identifies obstacles and gaps or open areas, in
the robot environment, which we can use to implement reactionary motion in a robot vehicle.
Panic range defines the range at which this VI identifies an obstacle as an area of the
environment to avoid. A distance specifies the distances between the robot sensor and objects in
the robot environment. A direction angle specifies the angles at which objects are located with
respect to the center of the sensor. Positive values represent locations to the right of the center of
the sensor, and negative values represent positions to the left of the center of the sensor.
Elements in direction angles correspond to elements in distances. Distance threshold specifies
the distance at which this VI does not consider objects to be obstacles. This VI ignores any
objects at distances greater than distance threshold. Largest gap describes the largest open area in
the robot environment. Histogram returns the histogram data that represents the distances to
objects in range of the sensor, arranged by angle and direction. Now output from VFH is angle to
gap which decide that how much robot rotate it’s steering to get the right direction for forward
movement.
Apply Velocity to wheels VI:
Now according to angle to gap this VI apply the right velocity to move the robot in maximum
gap path. Steering frame in is a reference to the steering frame on which to operate. Steering
frame velocity specifies the velocity of the steering frame, error in describes error conditions that
occur before this node runs.
Precautions:
 To avoid hanging the user interface with front panel locking, configure all events you
want a VI to handle in a single Event structure or always make sure there is only one
Event structure in a loop.
 Additionally, make sure there is always an Event structure available to handle events as
they occur.