An actuator in a hard drive is a component that moves the read/write head assembly across the platters to access data. It enables the precise positioning of the heads over the desired track on the disk platter to read or write data. The actuator arm hosts the read/write head at its end and connects to a pivoting mechanism typically consisting of a voice coil and magnet assembly. Together, these components work to swing the arm and position the head accurately. Hard disk actuators play a crucial role in allowing rapid access to data locations dispersed across the platters. Their speed and precision determine the drive’s performance. This ability to quickly move and settle the head over the desired track enables fast data transfers.
Components
The main components of a hard drive actuator include the voice coil, arm, suspension, and magnets.
The voice coil is a coil of wire attached to the end of the actuator arm that moves the arm and read/write heads across the platters. It works similarly to a speaker, with electric current flowing through the coil in the presence of a magnetic field to create motion 1.
The actuator arm is made of precision aluminum or magnesium alloy and pivots to move the read/write heads over the platters. The arm attaches to the voice coil on one end and the suspension on the other end 2.
The suspension is a thin metal sheet holding the read/write heads that allows them to fly over the platter surfaces. It is designed to keep the heads at an extremely small distance from the platters for accurate reading and writing 3.
Permanent magnets provide the magnetic field that interacts with the voice coil to create the pivoting motion. They are precisely positioned on both sides of the voice coil 1.
Function
The primary function of the hard drive actuator is to move the read/write heads so they can access data on the spinning platters inside the hard drive. The actuator arm has read/write heads mounted on the end that are positioned nanometers above the disk surfaces. When the control circuitry receives a request to read or write data, it will move the actuator arm and position the heads above the correct track on the platter where the data is located. This allows the heads to either read data from the platter or write data onto the platter surface. Without the actuator, the heads would be unable to move and access data stored across the platters. So in essence, the hard drive actuator provides the mechanical work and precision needed to access data stored anywhere on the disk by rapidly moving the heads to the proper track location.
According to https://mobilseries.com/how-to-run-hard-disk-motor/, hard drives generally need power to run the actuator arm, and the actuator relies on power delivered through the hard drive’s power cable.
Types
There are several types of actuators used in hard drives:
Rotary Actuator: This is the most common type and uses an electromagnetic motor to pivot the actuator arm across the disk platters. The rotary motion allows the heads to move quickly to locations across the multiple platters.1
Linear Actuator: Instead of pivoting, the actuator arm moves back and forth in a straight line. Linear actuators are less common but allow for more precise head positioning.2
Dual Actuator: Some drives use two independent actuators to allow simultaneous access to multiple platters. This improves performance but increases cost and complexity.2
Microactuators: Small actuators attached to the slider that provide fine positioning of the head, enhancing the precision of the primary actuator.1
Materials
Actuators in hard drives utilize various advanced materials in their construction to maximize performance. Here are some of the key materials used:
Metals: Aluminum, stainless steel and copper alloys are commonly used to fabricate the structural components like voice coil, arm and base plate. These provide high strength to weight ratios.
Magnets: Rare earth magnets made from neodymium or samarium-cobalt are used to create strong magnetic fields for actuation. Their high coercivity allows miniaturization.
Composites: Engineering plastics and carbon fiber reinforced polymers help reduce weight and damping. PZT ceramics are used in piezoelectric actuators.
The choice of advanced materials enables the high precision and speed needed from actuators used in modern hard drives.
Manufacturing
Actuators are manufactured using precision machining and assembly processes. The base and arm are typically machined from aluminum alloys for stiffness and light weight. The heads are fabricated through thin film processes and attached to suspensions via micro-welding or adhesive bonding.
The components are assembled in a clean room environment to prevent contamination. The heads are attached to the suspensions, which are mounted to the actuator arm. The arm is connected to the pivot bearing in the base. Powerful rare earth magnets are integrated to supply the magnetic force.
Each completed assembly undergoes rigorous functional testing. Key parameters like track following, seek times, and data throughput are verified. Shock and vibration testing ensures reliability under real-world conditions. Any units not meeting specifications are rejected before final quality assurance approval.
Specifications
The actuator arm in a hard drive needs to move quickly and precisely to position the read/write heads over the desired track on the disk platters. Some key specifications for hard drive actuators include:
Speed – The actuator arm needs to be able to move fast enough to reach any track on the disk within a few milliseconds. High performance drives aim for average seek times under 10 ms (HDD Surgery).
Precision – Positioning precision is critical to make sure the heads are centered over the target track. Track widths today are extremely narrow, down to just a few tens of nanometers, so sub-micron precision is required (Ratliff).
Power – The actuator arm needs to accelerate quickly but smoothly to minimize vibrations and settle precisely over the destination track. Voice coil actuators are designed for optimal power usage to meet these needs (Seagate).
Evolution
Hard drive actuators have evolved significantly over the decades to enable increases in capacity and performance. In 1956, IBM released the first commercial hard drive, the 350 RAMAC, which contained 50 24-inch platters and had an actuator that moved on a track to access data [1]. Early hard drives in the 1960s and 1970s continued using linear actuators to move read/write heads in straight lines across disks.
Through the 1980s and 1990s, actuators evolved to pivot and rotate rather than move linearly, enabling access to multiple platters and tracks. The IBM 3380 drive in 1980 was the first to use a rotary actuator, which became the standard [2]. Read/write heads became smaller, allowing higher track densities. Voice coil actuators were introduced, using electric currents to finely position heads.
In modern drives, actuators have become extremely precise, using triple stage actuators and microactuators to position read/write heads within nanometers. Speeds have increased substantially – modern drives have average seek times under 10 ms, compared to times of 50-100 ms in early drives. Smaller, faster, and more accurate actuators continue to enable hard drive evolution.
Failure modes
There are several main failure modes that can occur in hard disk drive actuators:
Contamination
Dust, smoke particles and other contaminants can enter the hard drive housing and interfere with the motion of the actuator arm. This can cause the arm to stick or lose precision over time (Hard disk drive failure). Hard drives for servers or other high-reliability applications often include air filters to prevent contamination.
Wear
The repeated motion of the actuator arm can cause wear on the pivot bearings over time. This results in progressively more play and imprecision in arm movement, eventually leading to read/write errors (Mechanical Failure of Hard Drives). High performance drives need more durable components to withstand heavier workloads.
Current spikes
Sudden power loss or electrical spikes can cause the actuator arm to be stuck in between tracks. The heads may crash into the platters when power is restored. Circuitry protection and emergency retract mechanisms help avoid these failures.
Future outlook
The future of hard drive technology looks promising with new innovations on the horizon. However, there are also challenges as demand for higher capacities and faster access times continues to grow.
One emerging technology is the use of dual actuators, which allows the read/write head to move independently and access data faster. Companies like Seagate and Western Digital are developing hard drives with dual actuator technology to enable higher performance and capacity. However, technical challenges remain in areas like power consumption, mechanical design, and firmware.
Other innovations in hard drive technology include triple-stage actuators for more precise head positioning, and the use of technologies like heat-assisted magnetic recording (HAMR) and microwave-assisted magnetic recording (MAMR) to increase data density. The introduction of sealed helium-filled drives has also enabled higher capacities.
Challenges for future hard drives include further pushing the limits of areal density, reducing the size and weight of components, improving reliability, and managing power consumption. As solid state drives become more prevalent, hard drives will also need to continue improving cost-per-gigabyte to stay competitive in the storage market.
