- Microcontrollers/Electronics
Identifying an Embedded Controller
You have been tasked with sourcing the hardware for a robotic arm pictured below. You have the physical arm components, but need to source the motors, speed controllers, embedded controller, and any other hardware components necessary (you don’t need to account for items such as bolts/screws). For simplicity, assume the two arm segments are 0.5m long and have a mass of 500g each. The arm should capable of carrying a payload of 1kg at the end of the arm. You do not need to include any end effectors or motors (at the end of the arm).
You don’t need to have calculations for all possible geometries/angles, but you make reasonable assumptions and make sure to mention those assumptions.
(a)
Identify motors/gearbox/etc. that meet the given specifications. Provide any calcu- 6%
lations you used to come to your selection. Make sure to provide enough information to verify the equipment does indeed meet your requirements.
In selecting the motors, torque requirements will be the guiding factor and this is determined as follows:
Toque per arm:
1st Joint
T1= F1xL1
F1= (M1+M3)x g= (0.5+1)x9.81= 14.715N
T1= 14.715x 0.5= 7.3575N-m
For 2nd Joint:
T2= F2(L1+L2)
F2= (M1+M2+M3) x9.81= (0.5×2+1)x9.81= 19.62N
T2= 19.62 x1.0= 19.62N-m
The total toque T= T1+T2= 19.62+14.715= 34.335N-m
Assuming a speed of 76 rpm and an overall efficiency of 87%, the motor rating can be calculated:
Power= T. w= T.2πN/60= 34.335 x 2π x76/60= 0.273kW
Power input requirements= 0.273/0.87= 0.314 fix at 0.35kW (this is the rating of the motor such that a commercially available can be selected, preferably a stepper motor since it is suitable for this operation)
The gear box selected with will have an output speed of 76/10.1=7.6rpm. also the gearbox selected must be able to effectively regulate torque and speed given the dynamic nature of the robot in question especially in rapid movements from hole to hole and settling after drilling.
(b)
Identify motor controllers/speed controllers that meet the given specifications. Pro- 6%
vide any calculations you used to come to your selection. Make sure to provide enough information to verify the equipment does indeed meet your requirements.
-Variable speed drive which self regulates the system speed given the nature of operation to be executed. It will provide effective motor speed control and save the available power from motor. In the process, the performance of robot is boosted. Hence it is possible to obtain precision in both location and movements.
-PID microcontroller: It will provide real time processing and manipulation of digital data for high resolution and control. This will be the brain of the robot in which perceived signals such as turning are processed in a closed loop fashion. Error (the difference between the referenced variable and the actual variable) is to be maintained at minimum. The system loop is such that it self-regulates the control of the arm. Suppose when locating the drilling point, it misses by a fraction of millimeter, this will be encoded and signal perceived for real-time correction. It must operate within the specified accuracy.
(c)
Identify an embedded controller to operate the arm. Make sure to provide enough 6%
information to verify the equipment does indeed meet your requirements.
The wireless master slave can come in handy as it provides continuous operating mechanism where the anthropomorphic of the arm is considered. The force sensors are signaled to operate in sync with the embedded controller such that there is no mismatch in commands. The device is composed of potentiometers that handle both linear and rotary maneuvers of the arm. In other words, it integrates some level of functional flexibilities at the end effectors where both drilling and handling of light weight material can be done interchangeably hence economizing manufacturing of special purpose robots.
(d)
Identify any additional electromechanical components necessary to create a usable 5% robotic arm. Provide any calculations you used to come to your selection. Make sure to provide enough information to verify the equipment does indeed meet your requirements.
Integrate the following:
-Encoder to provide precise positioning and regulation of the velocity during movement and settling
-Servo-drive motors can replace the conventional dc/ac motors. It provides auto controlled actuation eliminating the need for gearbox. Hence it provides precise location for the drilling action by directing the end effectors to almost the exact location and ensures a follow through of the planned profile is executed more accurately. Although the algorithm is often complex and may require a higher level of machine language
Accelerometer and digital read out with LED display, the latter displays output such as force and object proximity
(e)
If you have a sensor (i.e. rotary encoder) that outputs a voltage between 0 − 5V , 4%
but your microcontroller can only tolerate 0 − 3.3V , what could you do? Think back to circuits (you will need to draw a simple circuit diagram here).
A voltage boost converter can be used by integrating as shown in the simple circuit below:
Normally it eliminates the use of transformer and boots input voltage accordingly
- Filtering
You are attempting to measure the oscillatory motion of a squirrel scratching it’s ear with a leg-mounted accelerometer. In order to estimate the current angle of the leg you will have to integrate twice. To help overcome the issues created when integrating you decide to implement a digital filter before integrating (filtering the acceleration data).
You may want to watch videos on Youtube to get a reasonable frequency range of the squirrel itching motion. Knowing the accelerometer will have quite a bit of noise, you decide to sample at 200 Hz
(a)
Identify an appropriate digital filter type (low pass, band pass, etc.). Explain why 5%
(b)
Identify an appropriate digital filter name (elliptic, Butterworth, moving average, 5% etc.). Explain why you selected this choice.
(c)
Identify an appropriate cutoff frequency or frequencies. Explain why you se- 5% lected this choice.
(d)
Identify an appropriate filter order. Explain why you selected this choice. 5%
(e)
How might you evaluate and modify your values (i.e. if you have the raw data how 5% can you tell if you have the right parameters)?
- StateEstimation
Download the Exam1 Data.csv file from BlackBoard to complete this problem. The data was collected from an open-loop high excitation quadcopter test (constrained to move in only the roll axis)
(a) (b)
Calculate a low-pass filtered roll angle estimate with the provided accelerometer 7%
data. The low-pass filter cutoff frequency should be selected to be appropriate for a complementary filter. Show a labeled plot of the angle vs. time.
Describe/discuss your angle estimate. 3
Calculate a high-pass filtered roll angle estimate with the provided gyroscope data. 7% The high-pass filter cutoff frequency should be selected to be appropriate for a complementary filter. Show a labeled plot of the angle vs. time.
Describe/discuss your angle estimate. 3
Calculate the roll angle using a complementary filter. Show a labeled plot of the 7%
angle vs. time.
Describe/discuss your angle estimate. 3%
- Control
Explain the difference between a proportional controller and a bang-bang (ON- 3% OFF) controller.
(b)
Explain how you would tune a PID controller used to control the oil flow rate in an oil refinery. (Hint: It does not matter much what the system is, the conceptual tuning process is the same/similar.)
You implemented a PID controller for a Lasik eye surgery laser beam system. The 5%
laser responds well, with minimal oscillations; however, it burns the cheek rather than fixes the eye. What gain(s) should be adjusted in the PID controller? Should the gain(s) be increased or decreased? Explain your reasoning.
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100 |
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