H-Bridge for Robots with High Current DC Motors

DC Motors which need high current and high voltage usually give high velocity and high torque. For small robots like line follower robot or fire fighting robot, I think IC motor driver L298 (up to 2A total current) is better choice. While for large and heavy robot, you need high current DC motors also H-Bridge suit to your DC motor.

This article sould be useful for you to build high current H-Bridge. H-Bridge schematics provided…

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The H-Bridge is the link between digital circuitry and mechanical action. The computer sends out binary commands, and high powered actuators do stuff. Most often H-bridges are used to control rotational direction of DC motors. And unless you buy a potentially expensive motor-driver, you need an H-bridge to control any robot with a motor.

This is a quickly sketched H-Bridge circuit with supporting circuitry.
H-Bridge

First lets talk about what a transistor is. These nifty chips revolutionized the electronics industry and you would be hardpressed to find something electronic that does not have at least a few thousand of these in them. So what do they do? They can control a flow of electrons by applying a voltage to them. The plumbing equivalent would be a water valve. By rotating the valve, a very large flow of water can easily be controlled.

MOSFET, Transistor
There are several types of transistors, such as the PNP and NPN, but for sake of making your life easy I will only talk about a MOSFET (Metal-Oxide Semiconductor Field Effect Transistor). These neat things have only been around for a decade or two, but are way better than the more traditional transistor. First they are more efficient. They are easier to calculate mathwise. Plus they usually have built in protection diodes so you don’t need to add them in later. They even have PWM (explained later) optimized MOSFET’s.

So to operate a MOSFET, you apply a voltage to the gate (from your microcontroller), and suddenly a current of electrons passes through the other two pins. Connect a motor (M) in line with one of the pins and your robot is set to go. In the above schematic you will notice the letters A and B. These are your two control lines which you apply this logic voltage to. Since you have two pins, and only a binary control, there are four possible things that can happen.

A=0 B=0 : Nothing happens, the motor is turned off
A=1 B=0 : Motor rotates clockwise
A=0 B=1 : Motor rotates counterclockwise
A=1 B=1 : Your circuit explodes into pretty sparks

Here is a ghetto visual graphic of the H-bridge logic chart:
H-Bridge A

H-Bridge B

So now lets talk about how to operate the MOSFET’s. Basically all you need to do is attach the gate to your digital output of your controller. When the digital output is turned on, 5V will be applied to the gate, turning the MOSFET on. However it is better to amplify that 5V to a value higher and I will explain why. The gate voltage controls the MOSFET internal resistance. Zero voltage makes the resistance too high for it to work. A very high voltage has a very low resistance. Resistance leads to loss of energy thermally. This means your MOSFET will heat up and possibly burn out. Take a look at the MOSFET picture above and you will notice my finger print in it. That is what happens when you touch a hot MOSFET - pain! So although you do not need to amplify the gate voltage, it is best to do so. You should also put a heat sink on it.

Square Wave for Pulse Width Modulation PWM
Ok so what if you want speed control, and not just an on/off switch? PWM! Pulse width modulation. PWM is when you send a square wave at a certain frequency to control the MOSFET as shown above. Basically you are telling your controller to turn on and off the motor at very high rates. So through inductance the motor is neither fully on or fully off, but somewhere in between. Such as at a slower speed. Also a note that motor torque, under PWM, remains the same whether fully on or only a percentage on. However, varying voltage for speed control reduces torque. So with PWM you have maximum torque yet slower speeds! You will have to experiment with wave length for both on and off periods, as well as frequency, to optimize your speed control. But a guess usually works.

Make sure the MOSFET you have has built in protection diodes. If not, install them on your circuit as shown. This is to prevent back currents from your DC motor. Also do not forget to put a small capacitor across the leads on your motor to reduce electronic noise and increase motor life. You might also want to refer to the tutorial on robot power regulation to help you design a better power source for your H-bridge.

It is also recommended to put a slow blow fuse after the power supply, resistors of a few 100 ohms on the gate logic, and the additional capacitors on your circuit as shown. This will prevent melting, large voltage surges, and high frequency emission.

Robots In CIS Applications

Robots have started receiving greater attention in medical/surgical applications. Tasks beyond human manipulation/precision capabilities are being trusted to assitant systems that only perform that small portion of the procedure, under human supervision. Despite intial skeptical response due to safety, and cost concerns the role of robots in surgery is likely to grow.

Surgical robots present an environment unlike most other applications where robots are applied. e.g. industrial plants. Mechanical components of surgical robots tend to be simpler, slower than their industrial counterparts, but the electronics, safety, and guidance systems are usually far more complex. A set of complex planning, guidance, and safety systems (often redundant) are involved in operating a surgical robot.

A team designing a surgical robot is faced with several difficulties. A complex system takes several years to develop, and development is often sequencial. E.g. The guidance system can not be tested until the hardware is available, and software developing and testing is highly dependent on availability of functioning hardware. Surgical robots are developed to deal with specific surgical procedures, and so each application results in the repetition of the design cycle.

A modular system allows software development to be independent of hardware design. It also allows existing modules to be used for new applications. It improves design clarity and testing and finally develops interfaces making interoperability between different systems easier.

There are several ways to develop modular/flexible software to control a robot: use/develop a programming language with all the facilities of object oriented design. But this would create yet another language, with a learning curve and user acceptance issues. An alternative approach is to develop interfaces, and implementations of the same in an acceptable programming language. This provides libraries that can be shared, swapped, and developed independently of each other. Furthermore, it allows the programming language to be changed, while preserving the interfaces (most programming languages provide ways of calling other language libraries, if need be).

The modular robot control(MRC) library is one such library. While the set of robots under consideration is mostly serial manipulators, the interface design can be easily extended to parallel architectures. The interface design is independent of the programming language, and the first implementation uses C++ classes. The library classes have a layered structure, each new Layer inheriting significant functionality from its parents.

This documentation is for the MRC library version 1.1 The class most commonly used by an application as an instantiable robot is the mrcRobot class and this should also be the base for all derived robot classes. Detailed implementation documentation exists separately.
s.

plasma arc

Some of the well-known global firms
are Westinghouse Plasma Corporation
(WPC), Integrated Environmental
Technologies (IET), The Solena Group
and Startech. Their proprietary plasma
gasification systems are described
below.
Westinghouse Plasma Corporation
(WPC). WPC’s proprietary
plasma gasification vitrification reactor
design (Fig. 5) combines a movingbed
gasifier with its industrial plasma
torch technology. WPC, in conjunction
with Alter Nrg (an engineering firm),
is able to provide full gasification
equipment, complete with feed handling,
slag removal and gas cooling
systems, for various applications. The
system engineering drawing is shown
in Fig. 6.
WPC has commercially operating/
under-installation facilities in Japan,
USA and India.
Japan. Hitachi Metals’s waste-toenergy
facility, located in Utashinai,
Japan, was constructed in 2002 and
has been operational since 2003. The
facility processes 200-280 tonnes/day
of a mixture of auto shredder residue
and municipal solid waste to produce
electricity.
A second facility, built near the
neighbouring cities of Mihama and Mikata,
Japan, was commissioned in 2002
to treat 20 tonnes per day of municipal
solid waste and four tonnes per day of
sewage sludge for production of heat
utilised in a municipal waste-water
treatment plant.
India. Two hazardous
waste disposal plants with
a capacity of 72 tonnes/
day and using WPC gasification
technology and
plasma torches to produce
electricity are under
construction in Pune and
Nagpur, by SMS Infrastructures,
India. When
operational, these are expected
to produce 5 megawatts
of electricity.
USA. One WTE facility
is at approval stage in
the US. When completed,
Geoplasma’s WTE plant in
Florida will be the largest
plasma gasification facility
in the world processing
up to 3000 tonnes per day
of municipal solid waste
and producing 120 MW of
electricity. The first phase will process
1500 tonnes per day and produce
60 MW of electricity, which is enough
to power 60,000 homes. The facility
is expected to become operational by
mid-2010.
Integrated Environmental Technologies
(IET). It uses a plasmaenhanced
melter (PEM) to transform
waste into highly stable glass-like
residues, recoverable metals and
hydrogen-enriched gas (Fig. 7). The
technology is unique in that it combines
three processes: plasma arc

using multiple graphite electrodes,
joule (resistance) heating using glass
melter technology and superheated
steam. This combination results in a
stable and highly controllable treatment
system.
The plasma operates at temperatures
from 3000°C to 10,000°C in an
oxygen-free environment with the
presence of superheated steam ensuring
that pyrolysis and steam reforming
reactions dominate. A high-efficiency
scrubber is used to remove volatile
metals and other pollutants from
the hydrogen-rich product gas (100
BTU/scf or more), a portion of which
may be recycled to provide power
to the PEM and
the other portion
used to generate
electricity.
Metals in the
waste are recovered.
The glassy
aggregate is also
recovered and
may be recycled
as road building,
blasting grit
or construction
material. Volume
reductions are up
to 98 per cent depending
on how
the process is run
and the composition of the waste.
IET is more interested in treating
radioactive, hazardous, industrial, municipal,
tire, incinerator ash and medical
waste streams. It has sold several
commercial PEM units throughout the
world to process a wide range of waste
materials. For details, visit ‘www.inentec.
com/commercial.html.’
The Solena Group. The Solena
Group, a strategic partner of Westinghouse,
uses the integrated plasma
gasification combined cycle (IPGCC).
It is a unique process that uses a
patented plasma gasification vitrification
(PGV) technology for conversion
of low-value fuels/feed stocks
(such as coal waste, petroleum coke,
bio-mass and different waste forms
including municipal solid waste)
into a low-heating-value synthesis or
syngas containing carbon monoxide
and hydrogen gases. This gas is then
employed as a primary fuel for a gas
turbine.
The IPGCC can also be viewed as
a two-stage processor of an opportunity
feedstock. The feedstock is first
gasified (partially oxidised) in a gasifier
using high-temperature plasma
heating systems at atmospheric
pressure. The gas is then cleaned and
combusted (completely oxidised) in
the gas turbine to produce electricity.
The PGV reactor, in essence, cleans
the solid/liquid and/or dirty fuels/
feed stocks by converting them into a
valuable byproduct fuel gas or syngas
to power a gas turbine.
The IPGCC system generally
consists of four separate processes:
feedstock handling, plasma gasification
and vitrification, gas cooling and
clean-up, and gas turbine combined
cycle.
The IPGCC system offers significant
advantages over standard IGCC.
By applying the PGV technology for
gasifying the feedstock, the plasma
heating system provides an independent
and extremely powerful heating
by the plasmagenerated
heat
and undergoes
partial oxidation
to be released as a
mixture of H2 and
CO. The syngas
has a heating value
of about onethird
to one-sixth
of natural gas. All
inorganic or nonh
y d r o c a r b o n -
based materials in
the feedstock are
simultaneously
vitrified into an
inert glassy slag,
suitable for use as
construction materials
including
aggregates, tiles
or bricks.

Live 3D Breadboard

Using the Live 3D Breadboard tool in TINA, you can automatically build a life-like 3D picture of a solderless breadboard (sometimes called a “whiteboard”). When you run TINA in interactive mode, components like switches, LEDs, instruments, etc. become “live” and will work on the virtual breadboard just as in reality. You can use this capability of TINA to prepare and document lab experiments.

You can either assemble the circuit step-by-step or by generating the whole circuit on the breadboard. Pick up and move parts on the breadboard using the mouse, and TINA will automatically rearrange the wiring while retaining connectivity. In the same fashion, you can select and move wires for clearer appearance. Note that you cannot change the endpoints of a wire this way–wiring integrity is preserved.

The breadboard tool is mostly intended for educational purposes to prepare laboratory experiments in a safe 3D environment. You can also use this breadboard to guide you in actually wiring a physical breadboard for lab verification.

Microsystems for Medical Technology

Social demand is the driving force for new developments in miniaturised medical technology. Well-informed patients have high requirements in terms of improving the quality and safety of their lives. That can be achieved by a marked miniaturisation of medical devices, instruments and sensors that ensure that patients have less traumatic operations or can benefit from mobile monitoring systems. Microsystem technology provides potentials that meet those new social and medical requirements to the point. Major applications of microsystems are, for example, intelligent implants, patient monitoring and minimally invasive technologIntelligent Implants

A very important field in medicine is the development of intelligent implants based on microsystems technology. The pacemaker is a wellknown example. The new generation of devices do no longer stimulate the heart by inflexible, constant impulses only, but collect data like heart rhythm and react self-sufficiently with variable adjustments. In this way, this therapy is becoming more flexible and physiological. Meanwhile these systems can absolutely hold their own on the market. Implanted defibrillators that stimulate the heart directly in case of cardiac arrest have also been developed. A strong electric impulse restores the heart function. These devices are also successfully being introduced into the market. The leading German supplier in that field is the company Biotronik GmbH & Co.

Patient monitoring

A second very interesting application for microsystems is the continuous monitoring of physiological patient data. Therefore sensor systems inside or outside the body are needed. Up to now only stand-alone solutions are available, that means data remain stored in the device. Examples for ambulant devices with limited storing potential are 24-hour-bloodpressure measurement or 72-hoursblood sugar measurement. Using miniaturised sensors future systems in domestic surroundings should measure continuously and precisely blood pressure, intraocular pressure, electrocardiogram (ECG), level of blood sugar or respiratory sounds. The collected data will be wireless transmitted to the physicians. In this application field German companies like Siemens AG Medical Solutions, Dräger Medizintechnik GmbH, Philips Medical Systems, Weinmann GmbH, Fresenius Medical Care AG und B. Braun Melsungen AG play an important role.

Minimally Invasive Technology

Minimal invasive operation techniques would be unthinkable without microsystems technology. In this field microsystems in terms of miniaturised mechanical and optical systems were introduced to the operating rooms already 15 years ago. German companies like KARL STORZ GmbH & Co. KG, AESCULAP AG & Co. KG und Richard Wolf GmbH are international leading players in this market with endoscopes and intelligent instruments. In future miniaturised instrument systems will be improved by sensors generating tactile feedback to the operating surgeon. Based on this tactile feedback, navigation systems can support the surgeon in planning and operating.

German medical technology is in a good position internationally

Internationally, German companies rank among the leading suppliers of microsystems in medical technology. They play an important part in the worldwide turnover in this market segment ( 12 billion in 2002) [1]. Microsystem technology is a key technology for the development of innovative medical products. Its great importance helps to strengthen the medical technology industry in Germany. In 2004 the total turnover of this industry sector was 18 billion Euros, employing 100,000 people in 1,200 companies [2]. Because of highly increasing exports, a turnover of 25 billion Euros is expected in 2010 [3]. "Made in Germany" is still a good reputation for medical products. The share of the turnover in foreign countries is almost 55% and it is expected to rise steadily until 2010 [4]. This underlines the international competitiveness of the German medical technology industry. With 38% of all exports, the EU states are the main customers of medical technology from Germany, followed by the US with 20% [4]. Two German companies belong to the worldwide top ten: Siemens Medical Systems ranks fifth and Fresenius Medical Care AG seventh [4].

Beside industry, national research institutes are a guarantee for success. More and more of them are combining R&D in microsystem technology with biomedical engineering. Wellknown representatives are IMTEK, Prof. Stieglitz, University of Freiburg, ITIV, Dr. Stork, University of Karlsruhe, IWE, Prof. Mokwa, RWTH of Aachen, and Fraunhofer IBMT, Prof. Fuhr, St. Ingbert. University hospitals like the Charité in Berlin, Erlangen- Nürnberg and others apply biomicrotechnologies for innovative solutions in diagnostics and therapy.

Future developments will imply new challenges The main challenge to be coped with in the field of microsystem technology is the connection of technological components with the biological surroundings. In future, top innovations can be achieved in the following applications:

* Enhancement of active implants by biocompatible coating
* Intelligent drug targeting according to data determined by microsystems
* Linking of data for complex diagnostics in an environment close to the patient without necessarily consulting a physician or going to hospital
* More complex and individual analysis of biological, chemical, pharmacological, toxicological and medical data .. Continuous advancement of imaging systems for instrument navigation and better acquisition of parameters relevant to therapy

Fingerprinting

What is a fingerprint?

Fingerprints are an early example of biometrics, the science of identifying individuals by their physical characteristics. There is no clear date at which fingerprinting was first used, some examples being from prehistory. However, some significant modern dates are as follows.

* 1880 - Dr Henry Faulds published his first paper on the subject in the scientific journal Nature in 1880. Returning to Britain in 1886, he offered the concept to the Metropolitan Police in London but was dismissed.
* 1901 - Sir Edward Richard Henry devised the Henry Classification System used in England and Wales.
* 1902 - Dr. Henry P. DeForrest used fingerprinting in the New York Civil Service.n

There is some controversy over the uniqueness of fingerprints. Even those who accept their uniqueness sometimes argue that the techniques used to compare fingerprints are fallible.

Fingerprint analysis (or Dactylography, a term mainly used in the US) is the science of using fingerprints to uniquely identify someone. Humans leave behind prints of the ridges of the skin on their fingertips when handling certain materials. The pattern of ridges is thought to be unique for each person and in practice has proved unique enough to identify the person who left the fingerprint.

Fingerprint analysis emerged in the early 20th century, when it was the first method in forensic science for unique identification. As a result of its early success, it acquired a mystique of infallibility. It has only recently been subjected to systematic analysis by investigators from outside the field.

Fingerprint examiners have certainly disagreed with one another: the case of Shirley McKie was a notable case involving fingerprints.

What is the technology involved?

Sometimes the prints are invisible, in which case they are called latent fingerprints, but there are chemical techniques such as cyanoacrylate fuming and ninhydrin spray that can make them visible.

Recently the American Federal Bureau of Investigation adopted a wavelet-based system for efficient storage of fingerprint data, developed by Ingrid Daubechies.

What does the future hold for fingerprinting technology?

In the 2000s, electronic fingerprint readers have been introduced for security applications such as identification of computer users (log-in authentication). However, early devices have been discovered to be vulnerable to quite simple methods of deception, such as fake fingerprints cast in gels.

Future application of this technology range from computer access to office and home security to automobile locks. Example of personal fingerprint scanner:

Much of this article is from Wikipedia. All text is available under the terms of the GNU Free Documentation License

MEMRISTOR

Researchers at HP Labs have solved a decades-old mystery by proving the existence of a fourth basic element in integrated circuits that could make it possible to develop computers that turn on and off like an electric light.

The memristor — short for memory resistor - could make it possible to develop far more energy-efficient computing systems with memories that retain information even after the power is off, so there's no wait for the system to boot up after turning the computer on. It may even be possible to create systems with some of the pattern-matching abilities of the human brain.

A mathematical model and a physical example that prove the memristor's existence appear in a paper published in the April 30 issue of the journal Nature.

illiams and co-authors Dmitri B. Strukov, Gregory S. Snider and Duncan R. Stewart were able to formulate a physics-based model of a memristor and build nanoscale devices in their lab that demonstrate all of the necessary operating characteristics to prove that the memristor was real. "This is an amazing development," Chua says. "It took someone like Stan Williams with a multi-disciplinary background and deep insights to conceive of such a tiny memristor only a few atoms in thickness." Williams has a background in physical chemistry. Strukov is a theoretical physicist, Snider is a computer architect and Stewart is an experimental physicist.

Possible replacement for D-RAM

By providing a mathematical model for the physics of a memristor, the team makes possible for engineers to develop integrated circuit designs that take advantage of its ability to retain information. "This opens up a whole new door in thinking about how chips could be designed and operated," Williams says. Engineers could, for example, develop a new kind of computer memory that would supplement and eventually replace today's commonly used dynamic random access memory (D-RAM). Computers using conventional D-RAM lack the ability to retain information once they are turned off. When power is restored to a D-RAM-based computer, a slow, energy-consuming "boot-up" process is necessary to retrieve data stored on a magnetic disk required to run the system. Memristor-based computers wouldn't require that process, using less power and possibly increasing system resiliency and reliability. Chua believes the memristor could have applications for computing, cell phones, video games - anything that requires a lot of memory without a lot of battery-power drain.

Brain-like systems?

As for the human brain-like characteristics, memristor technology could one day lead to computer systems that can remember and associate patterns in a way similar to how people do. This could be used to substantially improve facial recognition technology or to provide more complex biometric recognition systems that could more effectively restrict access to personal information. These same pattern-matching capabilities could enable appliances that learn from experience and computers that can make decisions.

Nanoscale electronics experience

In the memristor work, the researchers built on their extensive experience - Williams founded the precursor lab to IQSL in 1995 - in building and studying nanoscale electronics and architectures. One goal of this work has been to move computing beyond the physical and fiscal limits of conventional silicon chips. For decades, increases in chip performance have come about largely by putting more and more transistors on a circuit. Higher densities, however, increase the problems of heat generation and defects and affect the basic physics of the devices. "Instead of increasing the number of transistors on a circuit, we could create a hybrid circuit with fewer transistors but the addition of memristors - and more functionality," Williams says. Alternately, memristor technologies could enable more energy-efficient high-density circuits. In 2007, the team developed an architecture for such a hybrid chip using conventional CMOS technology and nanoscale switching devices. "What we now know," Williams says, "is that these switches have a name - memristor.

he memristor first appeared in a 1971 paper published by Professor Leon Chua, a distinguished faculty member in the Electrical Engineering and Computer Sciences Department of the University of California Berkeley.

Chua described and named the memristor, arguing that it should be included along with the resistor, capacitor and inductor as the fourth fundamental circuit element. The memristor has properties that cannot be duplicated by any combination of the other three elements.

Although researchers had observed instances of memristance for more than 50 years, the proof of its existence remained elusive - in part because memristance is much more noticeable in nanoscale devices. The crucial issue for memristance is that the device' atoms need to change location when voltage is applied, and that happens much more easily at the nanoscale