How a cordless and cordless screwdriver works

Many perceive the screwdriver as a small cordless drill. But when performing a number of tasks it is more convenient to work with a screwdriver. It starts smoothly and instantly stops rotation, the range of possible rotation speeds is lower than that of the drill. Most models are really rechargeable, but this is not a key feature. Any screwdriver has a mechanism that limits torque. Due to what a screwdriver works like this, it can be understood from its design features.

The choice of screwdriver

Screwdrivers are rechargeable and network, low or high power, equipped with additional features or without them.

Electrical part

Electronic and mechanical filling is enclosed in the body of the pistol type. The drive of the working body through the mechanism of limiting torque and gearbox is carried out from the DC motor. Such an engine has a permanent magnet stator and a rotor with copper windings. Power to the windings is supplied through the collector node. The rotor rotates freely in the bearings.

Cordless screwdriver

A cordless screwdriver is convenient to use when working in hard-to-reach places, since with it you can approach the object from any direction.

The engine is powered from several battery cells combined in one case. Depending on the required torque, issued by a screwdriver, the output voltage of the battery pack for different models varies in the range of 9-18 V.

The speed of rotation of the rotor of the electric motor depends on the voltage coming to the brushes collector node. A pulse width modulator is responsible for the stepless variation of the supplied voltage.

The principle of its operation is based on the fact that a constant voltage, which is provided by a battery, is converted into a system of high-frequency pulses with some short period. During the period, the input voltage is passed through the modulator only a fraction of the time, and then until the end of the period it is blocked. The ratio of the time of the presence of voltage at the output of the electronic component and the time of its absence forms some average value. That is, when the input voltage is 12 V and the ratio of the pulse period to its duration is 2, the output voltage for the motor will be 6 V. Due to the high frequency of the pulses, the voltage jumps are imperceptible.

Screwdriver adjustments

Many screwdrivers regulate the speed, reverse, switch drill and drill.

The formation of the ratio occurs depending on the position of the trigger tool. The harder you push it, the longer the impulse. The average voltage on the rotor windings rises accordingly. Torque increases, and with it the speed of rotation. The reverse is realized by simply changing the polarity on the collector brushes. To do this, each screwdriver has a separate switch.

Smooth start of the engine is realized with the help of an additional block of transistors. Even if you press the trigger sharply, the screwdriver without a jerk is gradually gaining momentum. An instantaneous stopping is performed by closing the rotor windings short-circuited or low resistance. Both functions allow better control of the instrument.

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Mechanical part

Small low-powered screwdriver

A small, lightweight screwdriver is convenient because the hand does not get tired to hold it.

The rotation from the motor to the clutch torque limit is transmitted through the planetary gearbox. In such a gearbox, a high gear ratio is combined with compactness and the absence of radial loads on the input and output shaft.

A central sun gear is mounted on the input shaft from the electric motor. The outer ring gear with internal teeth is rigidly fixed on the gearbox housing. The satellite gears rotate between the sun gear and the ring gear. Satellites impaled on the shafts of the carrier. The central shaft of the carrier is the output shaft of the gearbox.

To tighten the hardware with a screwdriver, very little turns are needed, so they are completed with two- and three-stage gearboxes. A sun gear of the 2nd stage is mounted on the output shaft of the 1st stage carrier and so on. A versatile tool that can be used not only for twisting and unscrewing operations, but also for drilling holes of small diameter, often has the ability to block 1 stage to extend the range of revolutions.

Screwdriver can not be called such without a mechanism for limiting torque.

It is also called a rattle. The performance of such a node from different manufacturers may differ, but the general principle is always the same. Torque is transmitted through 2 disks. On the end surface of the drive disc there are jagged radial projections or grooves. On the slave there are spring-loaded fingers with spherical ends or balls. The contact surfaces are polished and hardened.

Net screwdriver

Network screwdriver allows you to not depend on the battery charge, but not convenient when used in hard to reach places.

The degree of tightening the spring adjusts the maximum torque transmitted by the node. When it is exceeded, the spring is compressed, and the balls or fingers slip relative to the projections or grooves, the cartridge stops. To visualize the adjustment process on the ratchet body there is a scale. The number of possible positions for different models and manufacturers varies from 6 to 24. Figures do not mean any specific torque, the scale is conditional.

The holder of the nozzle for screwing can be 1 of 2 versions. For a highly specialized tool, a magnetized hexagonal socket is used, which makes changing curly bits very convenient.

In universal models that can perform the function of drilling, as well as for a drill, the keyless chuck is used. It can hold both the bit and the drill of small diameter.

The motor and other components of the device heat up during operation. To cool them, an impeller is mounted on the motor shaft. When the shaft rotates, the impeller pumps air through the holes in the housing.

To reduce fatigue when working with a screwdriver, designers seek to distribute its mass on the body so that the center of mass falls in the palm area. That is why heavy batteries are always placed in the end of the handle.

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Exceptions and Features


Often two batteries are included in the screwdriver kit, while one is in operation, the second is on charging.

When works are performed in the immediate vicinity of the power source and are not associated with the need to penetrate hard-to-reach places, it is more convenient to use network screwdrivers. They allow you to not depend on battery charging. Such models are particularly suitable for the home master when the tool is used sporadically.

In network screwdrivers, powerful AC motors are used, and instead of a pulse-width regulator, a triac is used. In a triac, a portion of the sine wave is cut off, and the average voltage value decreases.

Power supplies for cordless screwdrivers, which are installed in place of the battery, are on sale. To increase mobility, some models are equipped with 2 batteries. While 1 is in operation, the 2nd is charging.

Occasionally there are models where instead of a planetary gearbox, the classic one with spaced shafts is used. This is typical for universal models, more suitable for drilling. For a screwdriver with a bit holder, the use of the keyless chuck is also realistic. To do this, use cartridges with a shank, like a bit. In addition, there are nozzles that change the angle of twist or offset the axis of rotation.

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