标签: motor

Robotics is hot these days, and it's certainly deserved. Today's robotic arms and systems are faster, cheaper, more precise, and lighter by large factors compared to those of even just a decade ago. The result is the deployment of these units in stationary and mobile applications that were impractical but are now very feasible. If you think this is just the usual post- CES type of public-relations hype, think again. Check out this article in a recent issue of Design News, "Mechatronics Solution Is Adept Enough to Produce a Bow-Tying Robot," which details a robotic system which ties decorative ribbon bows on boxes of chocolate. (The YouTube video here is both mesmerizing and hypnotizing, IMO.) The article is more than a puff piece on how smart the design team was; it explains some of the problems they encountered, the constraints they faced, the tradeoffs they juggled, how they used simulation tools to test out ideas in advance, and more. Also note that this is not a "science project" robot demonstration–though there is nothing wrong with that–this one is in daily commercial use on a production line.   This robotic arm and feed is able to consistently tie bows around boxes using loose, flexible ribbon, but be warned, the related video is hypnotizing in a strange, unintended way.   If you have ever worked with earlier robotic arms powered by hydraulics, you know how powerful and terrifying they can be, and at the same time, they can deliver lots of torque and power (different but closely related quantities). But they are nasty, with pumps, values, seals, leakage, and more. When things went bad, the result was often both a mess and dangerous, such as hydraulic fluid leaking, or worse, spraying out. Some fluid-powered systems eliminate the hazards of hydraulic fluid by using compressed air (pneumatics) in its place, but the air pressure has to be fairly high to get useful power, and high-pressure systems bring their own risks. Still, it's a very good alternative for low-load situations, such as the bow-tying one. Many of today's robotic systems have gone all-electronic, with fast, low-mass, precisely-controlled motors (BLDC or stepper). Even if hydraulics did not have the fluid pressure and leakage issues, they still have a major drawback compared to an electric-motor system: due to the inherent mass and compressibility of the fluid, there is an unavoidable time lag between changes directed to the servovalves and the end-effecters. These lags complicate the closed-loop control algorithms when you need fast, precise operation. While it is possible to add various compensation factors to the control algorithms to take this mass-based reality into account, this adds complexity and risk to the software along with additional errors. In contrast, with electric motors there is only a negligible lag of electronic switches and current flow that occurs between directing power to the motor and having it initiate motor action. This means the algorithms are dealing with a much crisper system, in control terms. Further, the lighter weight of the today's motors with their powerful magnetics compares favorably to hydraulic actuators, and this high power/weight ratio simplifies the remainder of the control design. By combining the best features of electric drives and pneumatic ones, a good system engineer can develop a system which meets previously unattainable objectives. Think about that fast-food production line; that's a likely application area. Coupled with improved algorithms for both sensored and sensorless control (such as vector field control, also called field-oriented control or FOC), the electric motor has become a powerful element – literally and figuratively – in the advances of high performance, easy to use, reliable robotics. Hydraulics still has many places where it is the best choice in terms of massive power delivery, torque, non-sparking, or other factors, of course. If you doubt that watch this 50-minute documentary " Sunken Ship Rescue " on the righting and salvage efforts of the cruise liner Costa Concordia . Still, for many small-to-moderate applications, electric is the way to go. What has been your experience with electric, pneumatic, and/or hydraulic robotic drives?

We are all aware of the conventional wisdom and generally understood guidelines associated with circuit design, but a good engineer knows to re-check these carefully. They may be obsolete due to technical change and developments, or simply may not apply in the specific circumstances of the project. For power supply ICs and power supplies, three often-repeated "truisms" come to mind: Conventional wisdom No. 1: Switching regulators are more efficient than LDOs (low-dropout regulators). Generally true, yes. Yet, each year, hundreds of millions of LDOs are sold, and many new ones are introduced, so they still do have a vital role. These LDOs are not used just for those situations where the design team is stuck and says, "What the heck, we'll just stick an LDO in there and move on past that power-rail problem." In fact, in some cases, those LDOs can actually have equal or roughly comparable efficiency to a switcher. A recent blog/application note, " Multi-string LED lighting systems and the top four linear regulator questions " from Texas Instruments, shows where LDOs can be just as efficient as the switcher in some circumstances, and at lower cost. Conventional wisdom No. 2: Switchers are inherently noisy, so if noise is a concern, use an LDO. Again, generally true. However, some of the newest switcher ICs are extremely quiet, so don't rule them out too quickly for many supposedly "low-noise" design situations. The real questions are: How low a noise level do you need, and is there a switcher whose noise is low enough and that also has the other specifications and pricing that you need? Look for example, at the LT8614 42V/4A regulator from Linear Technology, which has radiated noise between 15 and 20 dBµV/m from 30 to 300MHz, which is below the CISPR25 Class 5 radiated-noise requirement. (As a comparison, its LT3065 45V/500mA LDO offers 25µV RMS noise from 10Hz to 100kHz). The switcher vs. LDO decision obviously depends on how much noise you can accept, and where it is in the spectrum. Conventional wisdom No. 3: If you need increased efficiency, get a better power supply. Whether it is done to increase run time from the battery, decrease system thermal load and dissipation needs, or save on operating costs, a more efficient power supply seems like the smart first thing to do. But is it really? Look at it this way: Most supplies now operate in the 70% to 90% efficiency range when properly sized to their load. That means that about two-thirds or more of the power dissipation is at the supply's load, not the supply itself. Therefore, while using a more efficient supply will certainly save power, reality is that the load is where the real loss is. Instead of looking at the supply, look at making the load—your circuit—more efficient; you could save a lot more power, and probably do so more easily than trying to squeeze another percentage or two from the supply. Of course, when the load is a motor or similar mechanical device, it's often hard to boost load efficiency, as the motor has to do real work in the physics sense and therefore must receive a certain amount of power to operate. But if the load is mostly electronics, using lower-power components may allow you to cut the circuit dissipation by 10 or 20 points—a far greater power saving than you can get from a more efficient supply. Are there other supply-related truisms you hear or assume? Are they really true in all or most cases? Have you ever stepped back to examine them, and were surprised by the results?  

You may already know the Hammond B-3 organ—it was a fixture in rock bands in the 1960s and 1970s. You may not be as familiar with the Hammond A-100 , which is a console version of this classic organ . My mom has an early 1960s manufactured Hammond A-100 that was not working. She moved into a smaller house with no room for this spinet style organ, so we loaded it into the back of a truck (it's heavy!) and took it to our house. It sat untouched for almost three years, until I had a large chunk of time to take a look inside and diagnose the problem. This chunk of time came along in summer of 2004—the organ was about 40 years old at the time. We also had an old Wurlitzer organ I had repaired previously, and it was full of vacuum tubes, maybe 35 or 40, many for oscillators. When I opened the Hammond I was surprised to find only about a dozen tubes in an internal power amp and a big, long, heavy box suspended inside the organ enclosure. Simply as a matter of principle, I first replaced all the tubes in the amplifier and in the preamp of the built-in mechanical reverb. Afterward, the organ did in fact make tones, only not when the vibrato function was enabled. Before we get too deep into this story, some background on the Hammond "tone wheel" organs is needed. I've seen these organs described as "over-engineered," but my own description is "masterpiece." This machine is one of the most amazing electromechanical consumer products I've ever seen. The basic tones are generated by what's known as a tonewheel that starts with a synchronous electric motor whose rotational speed is set by the frequency of its AC power source, in this case, 60Hz. A shaft extends from the motor on one side, all the way across the width of the organ's internal cavity. A set of tone wheels are mounted on this shaft, which are not fully round, but instead, toothed wheels. As the shaft rotates, the teeth extend to almost touch a magnetic bar placed at the edge of the wheel. This whole motor and shaft assembly is mounted in that big, long, heavy, spring suspension shock isolated metal box. The magnets have a coil around their ends, and as a wheel's teeth pass by a magnet, they modulate the magnetic field, which in turn generates a current in the coil. The frequency of the AC current is set by the rotational speed of the wheel and the number of teeth on it. As an analogy, consider it as a guitar pickup that, instead of a vibrating steel string nearby, you have a rotating toothed wheel. The AC current of one or more of the 48 tone wheels is summed into an amplifier to make the organ sound, depending on which keys are pressed. Each key has a fundamental and eight harmonics. The standard signal path was working, it was the vibrato that was broken. I bought a copy of the service manual from Manual Manor and studied the schematic. There is also a service manual web page that discusses the operation of the vibrato. It describes a series of delays, via a cascade of low pass filters, that feeds into a rotating capacitive pickup. There is a cylindrical chamber driven from the same synchronous motor that drives the tone wheels, only on the other side of the shaft coupler. It connects taps from the delay line, in forward and reverse, to the amplifier's summing point by coupling them through a commutator inside the chamber via rotating air gap capacitors created by meshing parallel plates on a rotor with fixed plates in the chamber. After locating the signal path in and out of the assembly, an oscilloscope showed the signal out was shunted to ground when the vibrato was engaged. In other words, there are a set of static parallel plates through which a set of moving plates pass. The phase delayed signals are coupled into one of several sets of plates that create capacitors. The phase delayed signals are summed back into the primary tone to create a true frequency modulated vibrato (vs. tremolo which is amplitude modulation).   The chamber (upper left), the parallel plates, (lower left except two commutator plates centre right) and the phase delayed signal connectors (lower right). Also you can see the synchronous motor at centre left, which incidentally has a separate starter motor because the synchronous motor doesn't have enough torque to self-start. After a thorough examination of the disassembled contraption and more measurements, I figured out that 40 years of wicked (both wik-ed and wikd) oil had crystallized into a low impedance carbon coating inside the rotation chamber. Out it the garage, a long session with a spray can of Gumout and some rags eliminated the short circuit. Another four or five hours of careful reassembly, including re-stringing cotton thread through some tiny crevices, and IT'S ALIIIIIVVVVVE!! Brian Lowe submitted this article as part of Frankenstein's Fix, a design contest hosted by EE Times (US).  

In the early half of the 1970s I purchased (second hand, of course...) a monster cassette tape deck. Monster for many reasons—I'll just name a few. While back then the energy to engage and disengage the tape heads and mechanisms usually came from the user's finger, that deck employs (big) solenoids and a control logic made of relays and SCR. This permits functions like auto repeat and (wired) remote control. Pure science-fiction at the time. It also featured a Dolby-B that could be calibrated, all made by discreet components. No ICs! No LEDs! It only had micro-miniature lamps, of course. The capstan was directly the axle of a brushless motor (direct drive!) working also as a flywheel. After years of faithful operation I started hearing some flutter, then suddenly the motor stopped. I dismantled the deck to investigate. The brushless motor control part was all analogue with germanium power transistors. I made some static measurements and checked some wires and soldering: Nothing was wrong. I turned the deck on and the motor ran. How could I fix something that was working? After a week or so the motor stopped again. Dismount again and repeat the checks—nothing. I turned the deck on and the motor runs. Things repeated like that, with up-time intervals randomly going from a day or less to a couple of months. Then one day my hand slipped, and I made a short on the motor connector while the circuit was energized. I saw a spark. Okay, I knew it, now either the motor or the controller was gone—R.I.P. Wrong: the motor was running beautifully and kept working for a year and half! Then it stopped again. I repeated the checks and the situation was a replica of the pre-short era. My patience reached the limit and I bundled the deck off to an authorised repair shop. It took more than six months and a lot of money to get it back. The motor worked barely a week. Replacing the motor and controller was impossible, as it was too difficult to find a replacement and too costly. Time to buy a new deck! Years later I tried once again to investigate: After measuring the continuity of the rotor-position-sensing coils of the motor with an ohmeter, I discovered that the motor worked for a while. Got it! Here is what I diagnosed: The position sensing coil's permanent magnets slowly lost their magnetism. The controller had an insufficient, weak position feedback and was missing synchronisation—therefore the motor couldn't run. The DC current of the ohmmeter (mind the polarity!) restores a bit of magnetism and the motor runs for some days. Obviously, when I made the short, the current was more intense and the magnetisation lasted much longer. The fix was then a no-brainer. That deck is still operating in my backup Hi-Fi stack. Spagni Maurizio has been an electronics enthusiast for a long time, He transformed his hobby into his job. He's an electronics designer but often does some repairing for himself and his friends for every kind of electronic device. He submitted this article as part of Frankenstein's Fix, a design contest hosted by EE Times (US).  

Energy efficiency is a significant design consideration these days, and why not? Using less is a good idea, all other things being equal. But all other things are often not equal. In the past few years, we've replaced a dishwasher and washing machine, and are now looking for a refrigerator, after their predecessors served long and well. All the replacements are far more efficient (electricity and water) than the existing units, which should be good. But this also has its downsides. The dishwasher, for example, takes at least 70 minutes for a regular load, while the unit it replaced needed only 35 minutes; the front-loading washing machine also has a much-longer cycle time than the top-loader it replaced. At first, I thought the dishwasher cycle time was unique to our model, but I did some research and it turns out that nearly all dishwashers now are this way: they have traded cycle time for efficiency. I also found out that the new refrigerators save energy both by using a more-efficient motor/compressor, of course, but also apparently by using thicker walls, which then reduces their internal volume significantly (their external sizes are often constrained by the need to fit into existing kitchen cabinet cut-outs, in replacement situations). So there's the dilemma when an overriding design goal—whether set by regulations, standards, new rules, or trends—has consequences or downsides that are ignored or glossed over. I understand that there are some extreme-design situations where there is no choice, and one design imperative truly carries more importance than others. For example, for an ultra-low-power, remote-monitoring datalogger which must run for years on a single battery or merely harvested energy, dissipation is far, far more important than size. But in appliances, it would be nice to have a choice, where I might choose a little less efficiency in exchange for shorter run times. After all, real design is about making tradeoffs and managing the weightings among various conflicting priorities; the same guideline applies to purchasing decisions. As the saying goes, "there is no such thing as a free lunch." Unfortunately, the laudable goal of energy efficiency seems to be given priority status that other objectives don't merit. As engineers know, the law of unintended consequences often follows close behind, such as more materials needed (those refrigerator walls) or lighter, more fragile structures employed (an automobile chassis). Have you had design situations where a single goal—besides low cost—strongly dominated your project? Or where the downside of this was either ignored, or not realized until much later?