Description
1. For assembly of electronic components on a printed circuit board (’PCB’ shown in Fig. 1A), an [8]
automated machine (a ’Robot’) is used. The robot has an arm to pick and insert the electronic components (such as chips, transistors, resistors, capacitors, etc.) on the PCB.
The PCB is mounted
on a positioning table which moves it in X and Y direction such that the component is inserted at
the desired location on the board. Design a stepper motor-driven leadscrew actuator for each axis
(X and Y) of the positioning table.
The design parameters include the range of travel in mm, the
minimum number of step angles for the motor, and the minimum number of bits for the control
memory for each axis.
Assume pitch of the leadscrew to be 2 mm. Inherent mechanical errors in
the table positioning can be characterized by a normal distribution with a standard deviation of 5
microns. Dimensions of the PCB are shown in Fig. 1A. Example component is shown in Fig. 1B.
All the components have identical lead diameters of 0.5 mm.
Note: Clearly state all your assumptions in your answer.
2. Design a robot for the assembly of electronic components on a printed circuit board (PCB) (’PCB’ [15]
shown in Fig. 1A). Once a PCB is placed at a fixed position in the robot workspace, the robot
should be able to pick up the electronic components (such as chips, transistors, resistors, capacitors, etc.) from a convenient location in its workspace, move them to the desired hole location,
and insert them vertically in the PCB.
The robot should be cylindrical with TLL (Twist, Linear,
Linear) joint configuration. Also, the configuration of the last link and end effector must be such
that the robot does not collide with previously inserted components.
Figure 1: (A) Blank PCB, and (B) Assembled PCB with a typical electronic component
Please provide a sketch, schematic or a 3D model of the robot to describe your design along with
the design parameters. The design parameters for the robot must include the joint parameters
(ai
, αi
, di
, θi) (provide a value for a fixed parameter and a range for a variable parameter) as
well as some of the other important geometrical information such as the dimensions of the base
link, coordinates of the base with respect to the global reference frame attached to the center of
the PCB (assume the PCB has zero thickness).
Find the transformation matrix that connects the base reference frame on your robot to the endeffector reference frame (Neglect wrist/gripper to simplify the problem).
To make your robot reach the center of the hole at the lower left corner of the PCB in Fig. 1A),
what should be the specific values of the joint parameters (ai
, αi
, di
, θi)?
Note: clearly state your assumptions, if you need to make any.
3. Propose a process plan to manufacture the robot designed by your team in Question 1. The process [5]
plan should be represented as a part-machine incidence matrix.
The parts that need to be fabricated are the parts that constitute the links and joints for your
robot (fasteners are bought ready-made). All the surfaces that have relative motion between them
are required to have a smooth surface (Ra < 20 nm). Rest of the external surfaces will be
spray-painted to prevent corrosion.
Assume all the parts will require some drilling operation to
accommodate actuators, electronic components etc. You have following machines in your shop
(i) Saw, (ii) 3-axis CNC vertical milling machine, (iii) Drill, (iv) Lathe, (v) Polishing wheel, and
(vi) Spray-painting equipment. The raw material is available in the form of sheets, rectangular
blocks or cylindrical rods of stainless steel.
4. Once you have a process plan as a part-machine incidence matrix, write a function in MATLAB [22]
or Python to generate possible cell designs based on the Single Linkage Cluster Analysis (SLCA)
algorithm. Include the code in your report. Make sure your code is generic enough to accept ANY
size part-machine matrix.
5. Seeing how you can successfully build a functional prototype of the robot, you team would now [15]
like to start manufacturing these robots on a commercial scale. As a first step, you would like to
redesign the base with your company’s name (a brand name) on it.
Design a new base for the robot with following considerations,
• Your base design conforms to the dimensions provided in Fig. 3
• Curve C can be any curve except a straight line.
• Your brand name is milled on any of the flat surfaces on the base part. The brand name
of your team should be formed by the initials of one of the members (the ’CEO’) and last
digit of his/her IIT Bombay ID (E.g. Soham Mujumdar with ID XXXXXXX1 has the brand
name ’SM1’). The depth of the letters should be at least 2.5 mm and width should be at least
5 mm.
Figure 2: CAD of the robot base
Use CAM function in PTC Creo Parametric to generate NC program and tool path for your base
part. Note: Creo parametric has a free student license. Step-by-step instructions for an example
part are uploaded for your reference. Alternatively, you may use any other CAM software that
you can access.
• Use a workpiece block with the dimensions (L x W x H) 300 mm x 200 mm x 30 mm
• Create the reference at the lower left corner of the top surface of the block
• Create a mill window that is slightly larger than the block
• The milling operations consist of two sub-operations: roughing with Tool 1, and finishing
with Tool 2 (see tooling parameters below).
• Use drilling to drill the holes using Tool 3.
• Provide two screenshots of tool paths generated by the software. One for roughing, one for
drilling.
• Provide the complete G-code generated by the software.
Figure 3: Tools and machining parameters