As near as I can recall, the pivotal change toward cordless tools came around 1985, when the Makita 6012DWK cordless drill came out. This drill fundamentally changed the way contractors do things and allowed electricians to keep their extension cords on the truck for most work. It had a five-position clutch, triple reduction gearing, dual speed select, and a “beefy,” removable 9.6-V battery pack with nickel-cadmium (NiCd) cells arranged in tandem four-cell towers. In my opinion, it is the foundation for all modern cordless tools.
In 1990 when the rock band Van Halen recorded and played the song “Poundcake,” Eddie Van Halen placed the Makita 6012 (with added EVH styling) across the bridge of his guitar and pressed the single-speed trigger repeatedly during the song’s guitar intro. The drill was that popular. It was rugged, drop-tested, and versatile, and it had GREAT tonality with a Stratocaster! This is where the cordless tool revolution started.
Since 1985, there have been some major advances. The industry transitioned (thankfully) from memory-prone NiCd cells to nickel-metal-hydride (NiMH) cells, and then in the past few years to lithium-ion (Li-ion) cells. The gear stacks that reduce the motor speed and gain up the torque were made planetary. The clutch springs, plates, and detents were integrated into the planetary gear stack. Variable-speed chopper-based trigger assemblies were added.
Also, radical advances in magnets have produced materials like 1.6T neodymium iron boron that produce much more flux in the gap of the motor compared with other magnets. Brushes have advanced to allow more current into the motor and lower resistances, and the impedance of the batteries has dropped significantly, allowing the batteries to deliver that much more current.
Today’s drill is a workhorse. The old 6012DWK could drive perhaps 50 large deck screws before needing a new battery pack or a charge. Today’s drill can drive larger screws at faster rates for half a day before needing a fresh battery pack. Further, impact drivers are now designed to drive high-torque screws without the continuous stress and near-stall currents required from a conventional high-torque, low-speed drive system.
There are reciprocating saws, angle drills, grinders, and a plethora of other wonderful cordless tools available today. This is great stuff. As a heavy user of these tools, I thank the innovators for moving this far forward from the old 6012DWK.
It’s going to get even better. In my opinion, there will be widespread adoption of permanent-magnet brushless direct-current (BLDC) machines in cordless tools in 2011. This will bring better control and higher power-to-weight ratio. These tools also will be more efficient and more reliable (with no more brushes to change).
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Motion control will mean more than a chopper in the trigger module. I expect constant torque features, constant speed features, and perhaps more advanced algorithms. The battery packs will continue to get better as Li-ion technology progresses along the upward slope of its lifecycle curve. And, advances in magnetic materials will be adopted into the rotors of the new BLDC machines. The culmination of all of these advances will offer tools that are absolutely incredible.
What then does this mean for the electronics industry? These tools will require high-torque, high-efficiency BLDC motors. The motors will require motion control and inverters to process the power to the motor. IR DirectFets are a great candidate for the inverters due to their small size and lowest possible on resistance per unit area of footprint. IR also makes HVICs to drive the MOSFETs in the inverter.
Next, battery packs will require enhanced protection due to their increasingly higher voltages and lower output impedance. Several MOSFETs from IR can work in these overcharge/overdischarge applications. The battery packs will require intelligence to report status and other attributes. The chargers that charge these batteries will continue to use larger and larger offline switch-mode power supplies. The IRS2795 family of LLC half-bridge controllers is a good choice for higher-power chargers.
Since Eddie Van Halen touched that drill to his guitar, the cordless tool industry has seen phenomenal growth. If we couple that growth with all of the technological advances that are being made in battery capacity and cell impedance, magnets, motion control, and power electronics, the cordless tool is the perfect vehicle to deliver all of these technologies to the hands of the consumers.
There has been some adoption of various technologies by various tool manufacturers, but I think we will see more of a system-level adoption in 2011 offering the best of everything. The electronics industry can assist these innovations and lead in some cases with innovative circuits, controls, and power semiconductors.