The Deutsches Museum is one of the largest museums I’ve been to. There were so many topics on technology that the museum had. They had the usual topics on flight, ship building, engines, etc., but they had even more exhibits on classical mechanics, electromagnetism, chemistry, nuclear physics, mining, semiconductors, computers, cartography, microsystems, space exploration, printing, etc.

There was even a cool demonstration of arc lightning.

The section of space exploration was quite interesting too, but it wasn’t as big as the exhibit at the Smithsonian Museum of Flight.

The clean room exhibit reminded me a little bit of the type of work I did during my internship at Bosch.

Of course in any exhibit on computers, there has to be a computer from Remington Rand.

Here is the experimental apparatus that was used to discover nuclear fission.

The stuff I looked at was only scratching the surface of the museum. I pretty much skipped entire sections like time keeping, wind turbines, bridge building, among other things. I was there for four hours too and I didn’t even look at any one section in a lot of detail. To see everything, one would have to spend days here.

Link to photo album here

1.0 Motors

The chosen motors are:

• Finger grasping – Cytron IG32E-264K at a cost of USD $57.03 from RobotShop
• Finger sliding – Cytron MO-SPG-30E-20K at a cost of USD $22.58 from RobotShop

Both motors meet the torque speed requirements for this project.

1.1 Finger Grasping Actuation

From the initial budget, the budget set for actuators was set at $325.  The torque requirement needed for gripping was also calculated and each finger would require 4 Nm at its output to lift a 4 kg object using only the fingertips.  The evaluation criteria states that the device grasp as fast as possible and that the client would have the highest satisfaction if the device cost was less than $700.

Looking on several websites that sold motors, the following DC motor was chosen: Cytron IG32E-264K at a cost of USD $57.03 from RobotShop.  The specifications are as follows:

At 12 V with gearing included, the stall torque would be 20.7 Nm (without consideration of mechanical efficiency).  A motor with a high stall torque is also beneficial because it lowers the gear ratio required, which leads to the use of less space for gearing.  The motor also comes with its gearing, which contributes to its high torque.  Given the high stall torque of this motor addition gear reduction is not required.  During grasping, the motor will be exerting high torque at low speeds and therefore, the motor will be operating near the stall torque.  The torque here is more than sufficient even with mechanical efficiency losses accounted for.

For finger actuation before grasping occurs, there is a low load and therefore the motor will be operating closer to the no load speed.  The no load speed with gear reduction is 27.7 rpm (without consideration of mechanical efficiency).  Split among three output shafts, the speed would be 9.21 rpm.  Even with the load of the fingers accounted for, this is still acceptable. based on requirements and evaluation criteria.

While the torque is a lot higher than required, this motor was only more expensive than a motor of one size smaller by less than three dollars.  The electrical characteristics were also identical.  With a higher motor torque, the grasper would be comfortable in lifting objects even heavier than 4 kg, which is another benefit based on the evaluation criteria.

1.2 Finger Sliding Actuation

The motor required here does not require a large torque since motion in this degree of freedom is not expected to handle heavy loads.  This motor only requires enough torque to overcome the friction of the finger on the power screw that it is mounted on.  Therefore, a low-cost motor (relative to the grasping motor) will suffice.  The DC motor of choice is the Cytron MO-SPG-30E-20K at a cost of USD $22.58 from RobotShop.

The specifications are as follows:

The consistency of the stated specifications do not match the previous motor because the information that was provided by the manufacturer was not consistent.

An initial estimate of two 200 g fingers sliding on a 1/2” diameter power screw with a steel-steel sliding interface (friction coefficient of 0.8) shows that only 20 mNm of torque is required.  Therefore, this motor meets the requirement.  The power screw also has 13 threads per inch, and at the rated 185 rpm, the power screw would slide linearly at 6 mm/s.

1.3 Motor Type

DC and servo motors are motors that are suitable for the project.  An investigation between DC and servo motors showed that many manufacturers of motors did not provide the necessary specifications for choosing a servo motor in terms of the values of the no load, stall torque, and stall current.  While servos generate a lot of torque relative to their size when compared to DC motors, it is not feasible to use a servo motor because of the unknowns in the specifications.  It is possible to buy several servos and test them, but this is costly and time consuming.  At this stage in the project, the team is not able to commit the time to investigate further.

Comparison of the cost of the grasping motor relative to motors from Maxon Motor, a supplier of motors for UBC Thunderbots, shows that the price of a motor of the same power output costs approximately the same amount.  However, a fundamental difference is that the motor from Maxon does not include a gearbox, while the chosen motor for this project does.

2.0 Microcontroller

The microcontroller of choice is the Arduino Diecimila.  The primary motivator for using this board is because the UBC Thunderbots team already has this board and is currently unused.  The Thunderbots team has generously provided the board for use on this project.

The MCU will allow the turning the motors on and off, changing motor direction, changing motor speed, and reading encoder feedback.

3.0 Voltage Regulation for Encoders

Since the power supply is likely going to be run at 12 V, the encoders will require voltage regulation down to 5 V (the operating voltage of the encoder for the motors).  The chosen voltage regulator is the MC78L05A at a cost of USD from Digikey.  According to the typical application diagram of the datasheet, two capacitors will also be required (0.33 μF and 0.1 μF).  The cost of these are less than $1.

The voltage regulator will be wired up in this way as the datasheet shows:

The input will be from the 12 V source, and the output will be to the encoders.

4.0 Motor Driver

To control the motors, an H-Bridge is to be used.  However, due to the different current flows for each motor, one motor driver will require a high current capacity while the other one will not.  The high current capacity motor driver consists of a driving circuit using two half-bridges.  The low current capacity motor driver is made up of 1 IC.

4.1 Finger Grasping Motor Driver

To design the H-Bridge for controlling the motor, an L6205 motor driver will be used.  Each of them costs USD $11.36 from Digikey and can withstand a continuous current of 2.8 A and a peak current of 5.8 A and can be interfaced with the microcontroller with PWM inputs.  The driver can also be run in a parallel mode to double the current ratings by using both of its full bridges together.  The datasheet provides an application circuit as follows:

Output pins from the Arduino can turn the motor on and off through the enable pins.  Direction is controlled by adjusting the voltage polarity between IN1 and IN2.

There are also two output pins for current sensing.  By using it to measure the current draw, the microcontroller program can determine what the torque is through the use of the motor curves provided in the motor specifications.

4.2 Finger Sliding Motor Driver

The motor driver of choice is the L293D and each one costs $2.50 from Digikey.  Bidirectional control of a DC motor can be achieved by adapting the application circuit from the datasheet:

The 1A and 2A pins determine the direction of the motor or the motor deceleration.  A truth table is provided in the datasheet.

5.0 Power Supply

To power the grasper, a power supply plugged into the wall will be used.  It is expected that the future robot will have a power source of its own which will power the hand as well.  Therefore, for the purposes of testing the grasper for this project only a wall power supply will be required.

Looking at the maximum electrical power consumption of the two motors, the total comes to ~65 W (12 V * 5 A + 12 V * 0.41 A).  The other components also consume power and so the final power consumption will be higher.  To compensate, a 12 V power supply with a maximum wattage and current of 84 W and 7 A was selected.  The part number is CENB1090 and each costs USD $70.48 from Digikey.

6.0 Power Supply Connector

The power supply chosen has one port that uses a Molex Mini-Fit Jr. Receptacle.  Therefore, a proper receptacle must be used so that proper wire routing can power all the circuitry.  This also means that the future robot will also require a matching plug for this receptacle.

7.0 Fuses

Fuses will also be used as a redundant mechanism to stop the motor in case the current draw is too high.  The primary method of stopping the motor is through the current sense pins on the motor driver.

After about three years or more of laptop use, one of the components that is likely to break is something in the LCD assembly.  The LCD assembly is a collection of components that allows the laptop to display things on the screen.  The following is a list of the primary components and their purpose:

• LCD Panel – the part of the assembly that displays the images and is what people are looking at when using the laptop
• CCFL Tube/Lamp – provides the light on the display.  The LCD panel provides the image, and the lamp provides the light required to see the image.
• LCD Inverter – transfers power to the CCFL lamp

The following instructions are general and do not pertain to one specific model of laptops.  The theory still applies however.

Problem Symptoms

In problems regarding a laptop display, these are the common problems among others that are quite prevalent among laptop users.

• Black corner – on one corner of the screen, a black triangle can be seen. The mouse can be moved under it, which shows that the LCD is just not displaying that part of the screen. The black corner is also hot to the touch. In some cases, the black triangle can change size over time (on the order of a few minutes or hours).

• Dim screen – the LCD is still displaying a picture, but it cannot be seen because there is no backlight.  Shining a bright light (such as a desk lamp) illuminates the screen slightly, but not to the brightness that the screen was at before.

The first problem tends to lead to the second one.  The CCFL tube burns out and leaves a dim display.

Determining the Cause

In general, if one experiences at least one of the problems above, there is a clear hardware issue.  Some exceptions are when one has turned the brightness all the way down, but this usually isn’t the case for people.

If one simply sees a dim display, it is due to either the CCFL tube or the Inverter.  It is not possible to to determine which part is the culprit without opening up the laptop.  Refer to instructions specific to the laptop in question to open up the screen assembly.  During disassembly, take note of what screws go where.  Different sized screws get used for different places and it is very easy to forget which ones go where.

The first image shows the laptop with the cover taken off.  The second image shows the disassembled LCD assembly with the CCFL tube lying on top.

CCFL Tube

Finding the CCFL Tube on the laptop is a lot more involved than finding the Inverter.  It involves opening the LCD panel (see this website for instructions for a Dell Inspiron 1520).  Visual inspection of this part can sometimes show clear signs of damage.  Burn marks should be apparent.

If burn marks are not apparent, then the cause is likely due to the Inverter.  One can also test the CCFL Tube, by turning on the computer with everything still plugged in (but disassembled).  If the CCFL Tube lights up, then there is nothing wrong with the CCFL Tube.

LCD Inverter

It isn’t possible to test this part directly without the proper tools.  However, if one has a dim display but has checked whether the CCFL works, one can be more certain that the Inverter is the culprit by process of elimination.

The Inverter is the part in orange in the top photo.  The bottom picture shows the Inverter by itself.

Solution

Once the cause has been determined, the next step is to replace the part.  However, one has a choice:

• Replace the entire LCD assembly – costs more (~$100), but the labour is easier
• Replace the problematic parts individually – costs less (~$5 – $20), but more difficult labour

One source for parts is Ebay, but it might take around three weeks for the part to arrive.  This is cheaper than the $300 that Dell charges for shipping the laptop, buying the components and the labour.  Replacing these parts is an involved process will take at least one hour.

Here are some things to watch out for when replacing the CCFL Tube:

• It is difficult to take the part out of the LCD panel
• Watch out for dust that could get in between the layers in the LCD (will show up as black specs under the screen
• It is hard to lay out the layers flat again when the CCFL Tube is replaced so there might be some uneven lighting after the CCFL Tube is replaced

After replacing the parts, turn on the computer again and the screen should be bright again.

Link: http://en.wikibooks.org/wiki/Serial_Programming/Serial_Java

Link: http://java.sun.com/developer/Books/javaprogramming/cookbook/11.pdf

According to the writer of the guide, undervolting simply reduces the voltage applied to the processor.  Since all processors have a different voltage requirement, they all use one standardized value which is most likely higher than the amount that the processor itself requires.  By reducing this excess voltage, the power dissipated by the processor will decrease, and thus reduce heat and increase battery life.  It should also be noted that this process will not impact performance since the performance of a processor is governed by its clock speed.

By doing this, I’ve reduced the temperature of my laptop by about 12-15 degrees Celcius.  The laptop’s keyboard and touchpad are no longer warm to the touch and the side heat vent no longer feels like burning.  Definitely a major improvement!

Link: http://forum.notebookreview.com/hardware-components-aftermarket-upgrades/235824-undervolting-guide.html

http://www.ladyada.net/learn/arduino/

Concept

I was given the circuit shown below (from Microelectronic Circuits 6th Edition by Sedra and Smith):

I was asked for the voltage of the output terminal and the current flowing through the diode.  Finding the current was easy, but I didn’t quite get the voltage.  I thought to myself, “from what two points do I measure the potential difference?”, because after all, voltage measurements are always taken relative to two points.  It took me the longest time before I could just use ANY two points and the measure the voltage.

What I figured is that, for part a, since the diode is in forward bias, the diode will act as a short circuit.  I then can say that V – (-5) = 0, since the voltage difference along a short is 0.  From there, I can easily determine that V = -5.  I can apply that same logic to the other three.

Nodal Analysis

I was given the circuit shown below (from Microelectronic Circuits 6th Edition by Sedra and Smith):

From class, I remember the professor saying that since we cannot tell right away which diodes are on and off, we can only make an assumption about the states of the diodes and then apply the usual analytical techniques.  In the event that the result is unreasonable, we know that our assumption wrong.  I made my assumptions, but afterward, I didn’t know where to go next.  I had forgotten how to analyze these circuits.

Later, I realized that I could use nodal analysis.  Since I assumed the two diodes in part a were both on, I replaced them with short circuits.  I used the intersection right before the current splits as my node.  For part a, the current into the node was 3 V/5 kΩ = 0.6 mA.  The current leaving was some unknown current for diode 1, and a current for diode 2.  I could determine the current of diode 2 by taking the potential difference between the node and the -3 V output and dividing that by the resistance in the path.  The result was (0 – (-3))/ 10 kΩ = 0.3 mA.  From the nodal analysis equation 0.6 mA = current from diode 1 + 0.3 mA, the current from diode 1 is 0.3 mA.  And as for the voltage V, the potential difference between V and the -3 V output is equal to the voltage across the resistor, (0.3 mA)(10 kΩ) = V – (-3).  Therefore, V = 0.  Alternatively, I can use the potential difference between the node and the output, which equals zero, thus yielding the same result.

Boolean Logic

The next issue I had was determining the Boolean outputs of a diode logic circuit.  Again, the picture below is from Electronic Circuits 6th Edition by Sedra and Smith.

The issue I had here is that I did not know current sources have no voltage if there is no current running through them.  Looking back that sounded pretty intuitive.  Finding all possible combinations of inputs A and B for this logic circuit, we get the truth table below:

A B X Y
0 0 0 0
1 0 0 1
0 1 0 1
1 1 1 1

The outputs of X reveal an AND gate.  Setting A or B to a logic 0 in (a) will cause current to flow through that path.  The potential difference X – A or X – B (depending which one was set to 0), will yield 0, thus the output X will be zero as well.  When A and B are both set to logic 1, it causes the diodes to go into reverse bias, and node X will be powered by the current source.

The outputs of Y reveal an OR gate.  Setting A or B in (b) to have different inputs, either 1,0 or 0,1, will cause the diode to be in forward bias for the input that has the logic 1.  For the input with logic 0, the diode will in reverse bias.  Since one of the diodes is on, current will flow and output Y will yield a logic 1.  In the case of both diodes being off, no current will flow, thus causing output Y to yield logic 0.

Other Notes

In the case of multiple parallel diodes in the same direction, if one of them is on, chances are they are all on (provided that the voltage across them is positive).  However, there may be a case where one parallel diode will want to flow into the other because of a greater voltage difference.  For example, if there were two parallel diodes, one with a 3V input and the other with a 2 V input both going to the same node, current from the 3 V input will want to flow into the diode connected to the 2 V input.  This will cause a reverse bias in the diode connected to the 2 V input, thus turning it off.

There is also another case where there are parallel diodes with different output voltages.  If current is flowing toward it, they will all be on, so they will all be a short circuit.  Which path will the current go to?  The path with the larger current.