Monthly Archives: September 2018

How Efficient are Light Emitting Diodes – LEDS?

Almost all commercial and residential establishments are moving over to light emitting diode (LED) illumination, as they are guaranteed to be more efficient compared to other forms of lighting such as incandescent and fluorescent. Unless designed with care, LEDs can suffer from premature failure due to thermal issues. Under thermal stress, LEDs can permanently lose their brightness, while degrading much quicker than the manufacturer intended. That means designers and engineers need to balance the additional cost of emitters with the thermal design for providing not only an elegant design solution, but also the long life that solid state lighting promises.

With roughly 50% of the electrical energy produced worldwide being used for lighting, and the world population growing, the only two alternatives to meet the growing needs of energy are to either generate more or to make more efficient use of what we already have. Generating more energy can take several years to plan and install power plants, but improving the efficiency of lighting can effectively mitigate the rising trend of power consumption.

Providing over 100 lumens per watt, LEDs are being increasingly used for a large selection of general applications. When converting fixture designs for incandescent bulbs to those for LEDs, engineers faced issues because of the difference of their thermal characteristics. For instance, manufacturers publish the life curves for LEDs as a function of temperature, while fixture designers do not know how to handle the information.

Incandescent bulbs were actually heaters that emitted some visible light. Nearly 90% of the light emitted by incandescent bulbs fell into the region beyond 700 nanometers—the infrared region—invisible to the human eye, but perceptible as heat. This would often cause problems in the kitchen, with waste IR light promoting premature spoilage in food illuminated by incandescent bulbs.

LEDs produce light via a different mechanism. When electrons in the LED junction cross over a forbidden energy zone called band-gap and combine with holes, they produce light because the electrons lose energy. Physicists tailor the energy by adjusting the width of the band-gap, thereby producing various frequencies of light. For instance, a white LED actually generates intense blue or Ultra Violet light, which then excites a phosphor placed in its optical path, thereby turning it into white light.

However, the process of converting electrons to light photons within the junction of the LED is not a perfect one. A vast majority of the photons created within the junction is never emitted and ultimately recombine to produce waste heat. Additionally, Stokes Shift, the phenomenon that shifts the frequency of the LED emission in the phosphor to produce white light, also generates waste heat. Waste heat from both of these mechanisms must be removed from the LED junction to prevent severe damage.

Unlike their incandescent predecessors, LEDs rarely fail catastrophically. Their slow degradation affects the photon emission mechanism, resulting in a dimming effect. Engineers use two industry end-of-life metrics for measuring the life of LEDs. One is the L70 or time taken to reach 70% of original emission, and the other is L50 or time taken to reach 50% of the original emission. The industry uses the L70 point as the useful life of an LED fixture or bulb.

What is Cabinet-Free Motion Control?

Controllers, drivers, and servomotors usually control automated platforms and machines in the automated production industry. With the evolvement of technology for machine motion, control and driving of individual machine axes is being increasingly taken over by highly intelligent electronics. Therefore, the control cabinet is assuming the central role with the rest of the system being designed around it.

With the rest of the machinery developing much more slowly, the faster evolving complex automation design and development becomes a cost-constraint for the OEM, system designers, and end users. Control cabinets need redesigning, especially with the increasing numbers of servo-driven axes. Typically, the location of the control cabinet is relatively fixed on the machine, which limits the manufacturers’ ability to modify and update the footprint of their machines.

As a solution to the above constraints, system designers are moving towards a new concept where the motion control and servo-drive mechanism is distributed rather than bound within a physical cabinet. By locating the controllers, servo drives, and power supplies nearer to the motors and axes they control, OEMs and system designers overcome several challenges arising from installation, cabling, and multiple engineering.

Initially, system designers had reoriented their designs in attempting to drive multiple machine components with a single servo motor. Although this approach had the benefit of reducing the physical number of servo motor and drives, it required a larger motor with higher power to handle the load, and several additional mechanical components for delivering the centralized power. A Cartesian motion system with a single motor for a palletizing application is an example of such a centralized approach.

By separating the servo motors on each axis, mounting them on the independent frames, and driving them separately, system engineers were able to use smaller motors, thereby reducing the overall power requirement, and developing a solution with higher efficiency.

One of the barriers to cabinet-free motion control architecture comes from PLC limitations. By limiting the axis count supported by their PLCs to 16 or 32 axes, some manufacturers force users to purchase a second PLC, which means addition of a more expensive control box with higher capacity.

For some time now, OEMs have been following a common practice of moving power supplies, servo drives, and related devices out of the control cabinet and placing them closer to each motor and its drive axis. This trend began with several leading suppliers introducing electric motors with their drives integrated into the motors’ housings. This required control electronics to be shock and vibration resistant as well as capable of withstanding the higher temperatures usually associated with environment outside the control cabinet.

Recent advances of cabinet-free components include separate ac-to-dc power supplies, independent drive units capable of mounting close to the servomotor on the machine, and power cables integrating communication capable of daisy-chaining several drive-integrated servomotors into a single circuit.

A further introduction of newer motion controllers or PLCs is helping the cabinet-free technology portfolio. These integrate the controller hardware into modules capable of mounting on the machine along with the necessary power supplies and drives. This eliminates the requirement of a control cabinet entirely.

BrailleBox with the Raspberry Pi

Reading, whether online or from the page of a book is a simple affair for those endowed with the power of sight. However, for those who are sightless, or have lost their eyesight, totally or partially, reading can be cumbersome, if not impossible. The Braille system, by allowing a changeover to the sense of touch, helps sight-impaired people to read.

Braille uses a system of raised dots that blind or those with low vision can follow with their fingertips. It is not a separate language, but rather a code for representing individual alphabets of a language. So far, the Braille system covers several languages, including Chinese, Arabic, Spanish, English, and dozens of others. Thousands of people all over the world use the Braille system of dots in their native language, providing a means of literacy for all.

The main code for reading materials in the US is the Unified English Braille, and seven other English-speaking countries use this code.

As such, Braille is useful when the material is in printed form. However, the challenge lies in reading online material. Although text-to-speech software packages are available, they are expensive and not very useful when the reader, say, wants to move back and forth while reading.

As a solution to the above problem, Joe Birch has built BrailleBox, a simple device to convert online news stories to Braille. His BrailleBox works with Android Things, News API, and the popular single board computer, the Raspberry Pi 3 or RBPi3.

Being a symbol system for people with visual impairment, the Braille system consists of letters and numbers as raised points in an array. Commercial systems are available and they produce Braille dynamically, but they are very expensive and out of reach of most people. Therefore, Joe built a low-cost alternative, the BrailleBox, which is simple to create.

Joe uses the News API as a tool that fetches jSON metadata from more than 70 news sources online. The API can integrate articles or headlines into text-based applications and websites.

The Braille system uses an array of six dots arranged in an array of three rows and two columns. Apart from representing the alphabets and numbers with various combinations of the six dots, they also represent whole words, sometimes in contraction. For instance, contracted braille includes 75 short form words and 180 different letter contractions. These help to reduce the volume of paper necessary for reproducing books in Braille.

To make the six dots for forming the Braille symbols, Joe attached wooden balls atop solenoids. He arranged the solenoids in an array of 2×3, and wired them individually to GPIO pins of an RBPi3.

Being an Android engineer, Joe controls the solenoids through Android Things, running on the RBPi3 as self-booting BrailleBox software. The reader has to push a button, which makes the program fetch a news story using the News API. As the RBPi3 deciphers the alphabets, it operates the solenoids, moving the dots.

Joe’s project is still in prototype stage, and he is yet to move all hardware inside a proper box. He also wants to add a potentiometer, preferably foot operated, so the readers can set their own reading speed.

Industrial Motors for Machine Automation

Industrial engineers use different types of motion control devices for improving the production rates and efficiencies on the floor of automated factories. Three major types of motion control devices are in demand for machine automation—stepper motors, servomotors and variable frequency drives (VFDs).

In general, stepper motors along with their drives, and controllers are widely used as they offer simple implementation, beneficial price/performance ratios, and high torque at low speeds. This motor is essentially a brushless DC version, moving in equal fixed steps during rotation, and only a single step at a time. Not requiring tuning or adjustments, stepper motors provide very high torque at speeds below 1000 RPM. They are cost-effective, as their prices are substantially lower than the cost of comparable servo systems. Since the torque they produce decreases as they speed up, it makes their operation difficult. Therefore, the work done by stepper motors becomes impractical at speeds in excess of 1000-1500 RPM.

Servomotors come with a motor, drive, a controller, and a device for positional feedback. For variable load applications, engineers prefer them to stepper motors, as they deliver high torque when rotating at speeds above 2000 RPM. Servos require adjustments and tuning, making them more complex to control compared to stepper motors. Including maintenance costs, their positional feedback arrangement can push their prices well beyond those of stepper motors.

Costing less than stepper motors or servomotors, VFD systems include an AC motor and a drive, but are unable to provide positioning. However, they can be good for applications requiring speed control on variable loads. For applications where the motor need not run continuously at full load, a VFD system can save considerable amount of energy. Another feature of VFDs is their soft-start capability, allowing a limit to high inrush currents.

In a stepper motor system, the controller regulates the position of the step, the torque generated by the motor, and the speed of the motor as it moves from one step to another. The driver operates on the control signals the controller generates by modifying and amplifying these signals to regulate the direction and magnitude of the current flowing into the motor’s windings. This way, it drive rotates the shaft of the motor to its desired position, and holds it in position with the required torque for the required time.

Controllers for stepper motors can be either open or closed loop types. Open-loop controllers are simpler, not requiring any feedback from the motor, but are less efficient. Open-loop controllers operate on the assumption the motor is always at the programmed step position and is producing the desired torque.

On the other hand, closed-loop controllers always operate with feedback based on the effective load on the motor. Therefore, the performance of the closed-loop stepper motor controller is similar that of a servo motor, and makes the operation more efficient.

Making a stepper motor rotate through each of its steps requires energizing the several windings within the motor in a specific sequence. Typically, stepper motors rotate 1.8 degrees per step, necessitating 200 steps to make a complete revolution.