Monthly Archives: January 2014

What is a brushless DC motor?

Most electrical appliances have an electric motor that rotates to displace an object from its initial position. Various motors are available in the market such as servomotors, induction motors, stepper motors, DC motors (both brushless and brushed), etc. The choice of a motor depends on the requirements of an application. Most new designs favor brushless DC motors, also referred to as BLDC motors.

The working principle of brushless DC motors is similar to that of brushed DC motors, but their construction is very close to that of AC motors. Like all motors, a brushless DC motor too has a stator and a rotor as its major parts.

The stator of a brushless DC motor, similar to the stator of an induction AC motor, is made up of laminated CRGO steel sheets stacked up to carry the windings. The stator windings follow one of two patterns, star and delta. Motors with stators wound in star pattern produce high torque at low RPM compared to motors whose stators are wound in a delta pattern. For motors required to run at very high speeds, the stator core has no slots, as this lowers the winding inductance.

Lack of slots in the lamination stack means the stator has no teeth, which reduces the cogging torque. Teeth in the stator align with the permanent magnets in the rotor, holding the rotor in a stationary position. When starting to move, additional torque, known as the cogging torque is required to make the rotor break free. However, slotless cores are more expensive as a larger air gap is necessary and that means more winding to compensate.

A typical brushless DC motor has its rotor made out of permanent magnets. The number of poles in the rotor depends on the requirements of the application, as more number of poles gives better torque. However, this reduces the maximum possible speed. Torque produced in a brushless DC motor also depends on the flux density of the material of the permanent magnet; higher flux density material produces higher torque.

Brushless DC motors are popular due to several advantages they offer over other types of motors. Compared to brushed type of motors, a BLDC motor produces higher torque because it has no brushes where power may be lost. Lack of brushes also means higher operating life and lower maintenance. Compared to AC motors, the rotor construction is simpler as it has no windings.

The cost to performance ratio of brushless DC motors is the lowest among all the types of motors available. One reason for this is the stator of a BLDC motor is on its outer periphery, which makes it dissipate a larger amount of heat. Additionally, commutation of brushless DC motors is simpler through electronic switches. That makes it easier to control the speed of BLDC motors.

Whether you are looking at single-speed, adjustable speed, position control or low-noise applications, brushless DC motors are the clear winners over all other types. As they are easier to control, maintaining speed of brushless DC motors is simpler with variations in load. A brushless DC motor generates very low amounts of EMI and audible noise.

How noise affects touch screens

Although not understood explicitly, touch-screens in devices are susceptible to noise. The offending noise sources may be both internal as well as external. Most common sources of noise affecting touch-screens are display and charger noise. Cheap chargers entering the market are inherently noisy, and this affects the functioning of touch-screens. In addition, as devices get thinner, display noise increases.

In addition, many other items of everyday use generate noise that may cause interference. This includes the AC mains, radio signals and the ballasts used for fluorescent lights. When noise is present, low-performance capacitive touch systems may distort the position reported and this may impact the overall system reliability and accuracy.

Injected noise causes large amounts of jitter (highly variable touch coordinates reported for a stationary finger), false touches reported even for no touch on the screen, non-recognition of a finger actually touching the screen and sometimes a complete lock up of the device. For example, noise may prevent you from being able to unlock your phone, since your finger touch is no longer reported or you dial wrong numbers because of jitter and false-touch reporting.

A user experience of touch interface quality is directly dependent on how well a touch-screen controller combats interference from noise. Poor touch performance when noise is present can make customers unhappy, resulting in an increase in returns. However, since noise may be of different types, touch-screen controllers must be able to detect, differentiate and combat noise, especially the two sources most problematic to users – chargers and displays.

The proliferation of Switch Mode Power Supply or SMPS type chargers has reduced the size, weight and cost of mobile chargers. However, this has also led to the market being flooded with chargers that prioritize cost over performance, using lower grade components and not using certain components that would assist in reducing common-mode noise.

High amplitude, high frequency, common-mode noise emanating from chargers is a major problem resulting in degradation of touch performance of capacitive touch-screen devices. Some manufacturers have addressed this problem of noisy chargers by providing limited functionality when a device is plugged into such a charger. Others may show a message on the screen that the charger is not supported when it is not the approved charger for the device. Online forums reveal customer dissatisfaction of touchscreen performance due to noisy chargers is quite prevalent.

Common-mode noise causes fluctuations of both, the power and ground supplies of the charger voltage, relative to earth ground, but keeping the same voltage differential between them. Such fluctuations affect the performance of the touchscreen only when the finger of the user touches the screen. Since the potential of a finger of the user is roughly the same as that of earth ground, and the charger’s ground and power lines are fluctuating relative to it, the resulting noise enters the touchscreen through the finger.

Manufacturers aggressively pursuing thinner form factors for touch-screen devices has led to displays coupling more noise into the touch-sensors because of their proximity. Earlier, touch-screens had an air-gap or a shield layer for protection. With devices getting thinner, such shields and air-gaps have disappeared and the touch sensor is now laminated directly atop the display.
This increases the capacitance, while the sensor electrodes are closer to the noise producing VCOM layer of the display, increasing the coupling.

Get ready to talk to your gadgets

Google has many things always in the development stages so that they will remain at the forefront of action for internet users and smart phone users. Expectations are high that gadgets in the future will have voice-interface so that users can command different devices verbally. Talking to gadgets will be possible and Google is making sure that it is a part of such breathtaking developments. Smartphones will be the mode for talking to these gadgets and Google is gearing up to provide the necessary tools for the user for home activity from any location. The recent takeover of Nest Labs, which makes smoke detectors and thermostat controllers, by Google at an estimated deal of $3.2 billion, is thought to be precisely for that purpose.

Speaking to kitchen gadgets is likely to become a reality in the near future. The process is known as the “Internet of Things” and is likely to be in the thick of daily routine activities. When launched, it will totally change the nature of human activity at home and will enhance the popularity of the smartphone. According to the research company Gartner, Inc., the Internet is likely to be linked to more than 26 million objects suitable for verbal command and interface. Additionally, connectivity to PC, smartphones and tablets will substantially add to this figure. Tony Fadell is the founder of Nest Labs, and he is an Apple veteran who assisted in designing the iPhone and the iPod.

According to Forrester Research analyst, Frank Gillett, the reason Google bought Nest is “to learn about this world where even more information is going to be accessible by computers.” Nest has already been successful in offering thermostats to users for controlling the cooling and heating of devices at home. Nest, in the last few years, sold their products in the USA, Canada and the UK; it has been well received.

Google has not made any disclosures about the type of activity lined up for Nest for the immediate future. Angela McIntyre, the Gartner analyst, believes that, “They need to gather as much information as they can to understand the context in how we live our lives”, in order to take over all the activities which are routine and have no need for physical presence at home to perform it. It is likely that the mapping software from Google could be utilized to map out the home layout. This will be essential for delegating tasks to a robot if employed at home. It could also lead to navigation of the entire home from a remote place by a smartphone.

Although, at present, it is known that Google’s main source of revenue is from advertising and search requests, there is no doubt that the acquisition of Nest Labs is in the direction of involving with people’s personal activities in a more significant manner without in any way sacrificing their privacy. On the whole, Google could be of assistance with these new tools for people not at home to perform activities through the internet and smart phones even from remote places.

FishPi: How Raspberry Pi controls an autonomous ocean explorer

FishPi is a project for developing the prototype of a sun-powered autonomous ocean-going surface transport controlled by a Raspberry Pi (RBPi). The project is working on a small boat, to be propelled by solar energy to traverse the Atlantic Ocean and during its journey, the boat will be taking pictures and gathering data.

The goal of the FishPi project is simple. They intend to develop FishPis ranging from vessels running on batteries for a few hours to solar powered vessels full of features and capable of sustaining months at sea. The vessels will be MUSV or Marine Unmanned Surface Vessels, which will be capable of crossing the Atlantic ultimately and unaided.

An RBPi unit will provide all the command and control features of the FishPi vessels. The vessel will have an onboard solar panel, and the RBPi will control the data logging, navigation, power management and control of other devices on-board. The solar panel will charge a Lithium-ion battery pack, which will be driving a ducted propeller system. The Amateur Radio Satellite Network will be used to transmit images from the FishPi to the shore, by using satellites to integrate the ship-to-shore communication system.

During its journey, FishPi will use its environmental monitoring and data-gathering capabilities to measure the temperature of the air and sea, salinity and pH, barometric pressure, light levels and more. It will transmit some of the data along with images relayed in real-time.

For this, the RBPi is attached to a 16-channel PWM, a temperature sensor, a compass, a GPS, a USB webcam, a USB Wi-Fi dongle and a RockBLOCK satellite communicator. All these, except the compass and the webcam, are within a box on the FishPi Proof-of-Concept Vehicle or POCV now.

Initially, the base-station was planned to be connected to the POCV with a 32-core cable. However, this became too complicated and caused a lot of interference, so it had to be abandoned. Presently, the base-station contains another RBPi, connected to a USB hub and a 4-port Wi-Fi Router. The Wi-Fi link allows real-time remote control possibilities with the use of xrdp and the FreeRDP client. Additionally, this allows live video streaming to the world over the internet.

The electronic speed controller, the webcam, rudder, temperature sensor, the GPS and the compass are integrated with the C&CS or Command & Control System of the POCV. Currently, the coding is for manual control only, and the POCV can move forward, backward, to the left and to the right. With the webcam as a visual guide, the POCV can be driven remotely, but so far, this has been tested only indoors.

In the future, this control will be automated to the extent of giving the POCV the command and leaving it to navigate itself. For tracking, routing and waypoints, GPX files are being used while GeoTiff file formats are being used for the maps. Telemetry is an important function for any ocean-going vehicle. The POCV will be communicating both ways via the RockBLOCK Satellite Communication link.

There is always a chance that the vehicle can capsize in rough seas, and therefore, next in line is a self-righting mechanism.

Magneto resistive random access technology (MRAM) for better memory storage

Technologists researching at the laboratories of the National University of Singapore in the department of Electrical and Computer Engineering have developed a new technology that will help in enhancing storing information in electronic systems in a better and more durable manner. Called Magneto Resistive Random Access Technology, this innovative method increases the storage space considerably and ensures that all fresh data will remain intact, even when there is a power failure. The team of researchers, led by Dr. Yang Hyunsoo, has filed for a provisional patent in the USA. They claim that the development will bring about a structure that will be of use to MRAM chips of the next generation.

This innovative method of storing information has a very wide field of application. All devices in the field of electronics such as Personal computers, laptops, mobile phones and all mobile devices will benefit from this unique technology. Data storage is required in various fields of activity such as in transportation, avionics, military, robotics, industrial motor controls, management of energy and power. Another major user is electronic equipment for health care.

According to Dr. Yang, the new technology will increase storage space, and enhance the memory. According to him, computers, laptops, etc., do not need booting up and there is no necessity for using the “Save” key regularly. Fresh data is not deleted even when there is a stoppage of power, unlike the current DRAMs in use. What is of greater significance is the memory will last for a minimum of 20 years and maybe for an even longer period. Compare this to the present method of storing information, which gives the user only about a year of stored data. One of the best uses is in the case of mobile phones. According to Dr. Yang, “we usually need to charge them daily. Using our new technology we may need to charge them on a weekly basis.” This will be a substantial cost-saver.

MRAM, the new technology, enables data to be retrieved even if the equipment concerned is not powered up. Additionally, MRAM consumes low power and has high bit density. The new technology is expected to bring about a sea of changes in computer architecture. Manufacturers will find it easier to use MRAM as flash memory can be dispensed with. That will also help in bringing down the cost substantially. The success of MRAM has induced major semiconductor manufacturers like Intel, IBM, Samsung and Toshiba to conduct further research.

Currently, MRAM uses technology based on current induced magnetization in a horizontal plane. It requires ultra-thin ferromagnetic structures, less than 1 nanometer, which are difficult to manufacture, has low reliability and the retention period is less than a year. The NUS team collaborating with Saudi Arabia’s King Abdullah University of Science and Technology has developed a multi-layer magnetic structure of 20-nanometer thickness. It effectively provides a film structure that helps in the storage of information and data for at least 20 years. The team is looking for collaboration with the industry.

Difference between SCARA, Six-Axis and Cartesian Robots

Both high-volume manufacturing lines and small-scale operations use robots to automate their activities. What type of robots to use and when depends on many factors. Because of several benefits that robots offer, their use is increasing not only on manufacturing lines with high volumes, but for executing tasks in many smaller-scale tasks as well.

Implementing robots is becoming simpler. Use of all types of robots is on the rise, including SCARA or Selective-Compliance-Articulated Robot Arms, six-axis and Cartesian types. Robots automate several tasks by accelerating cycle times and increase throughput by eliminating bottlenecks. Not only this, advanced controls are making robots more user-friendly and their backend programming requirements are declining. In several cases, online tools let OEMs and end users select and configure robot features quickly.

For example, packaging of products requires a robot that can pick boxes off a high-speed conveyor and place them on a pallet. This requires a cantilever action as the picker has to extend a full meter for grabbing the boxes and moving them down to the floor and on to a pallet. This application is best suited to a Cartesian robot, and it is also the most cost-effective.

Many creative and new applications are increasingly using robots of all types. However, use of Cartesian robots is specifically proliferating because of standardized components such as modules and linear servomotors along with operator-friendly controls that lower their costs and boost their performance. Cartesian robots are also called gantry robots. These are mechatronic devices using motors and linear actuators for positioning a tool. Their movement is linear in the three axes, X, Y and Z.

In contrast to the Cartesian robots, six-axis and SCARA robots are typically mounted on a pedestal. Similar to the Cartesians, SCARAs also move in the X, Y, and Z-axes and planes, but they have a theta-axis at the end of the Z-plane for rotating the end-of-arm tooling. Vertical assembly operations usually benefit from such SCARA robots, for example, when inserting pins into holes, as the SCARA robots can do this without binding. However, the reach of a SCARA robot is limited, since the joints are load points and need robust bearings with high-torque motors for handling loads when the arm extends.

One can think of six-axis robots as Cartesian robots consisting of a basic system building block but customized for specific activities. For example, pick and place activities become simpler because six-axis robots can move up and down, forward and back, and can yaw, pitch and roll for offering more directional control as compared to SCARAs.

SCARA robots are better suitable for jobs that require precision. They have predefined ratings of accuracy that makes it easy to define their repeatability of movement. However, that also means these robots lock their owners into one level of accuracy at the time of purchase, which makes SCARA and similar six-axis robots rather expensive.

SCARA and similar six-axis robots may also come equipped with defined motion and speed specifications that allow them to deliver better performance right out of the box. However, they may cost more since they usually have proprietary controllers for executing complicated tasks and require more programming for making complex movements