Seiko Spring Drive SMK005J

During the Basel-world exhibition in 2002, Seiko unveiled the Spring Drive SMK005J watch in a luxurious design featuring an 18-carat white gold case and genuine crocodile leather strap.

Seiko Spring Drive is a state-of-the-art watch movement that merges traditional horology and electronic watchmaking. At first glance, it looks like a hand-wound watch mechanism. But in fact it is an amazing example of Seiko’s unique micro-mechatronic prowess, because only Seiko Spring Drive offers quartz accuracy.

Seiko Spring Drive SMK005J
Seiko Spring Drive SMK005J, Image Credit: SEIKO

The unwinding mainspring not only drives the smooth sweep movement of the large hands, it also powers a rotor whose tiny electrical output induces a quartz crystal to emit a reference signal. An integrated circuit measures any divergence between this signal and the rate at which the spring is unwinding and adjusts the unwind rate as necessary.

These refinements ensure the watch is accurate to ±15 seconds per month. The IC runs on only 25 nanowatts, half the power used by a conventional chip. This remarkable ultra low-power, low-voltage IC is one of the unique technologies that have made Seiko Spring Drive possible.

Spring Drive in detail

Spring Drive is based on the foundation of all mechanical watch technology, a mainspring, but uses an entirely new system for time regulation that delivers the equivalent to 1 second per day accuracy, and, uniquely, glide-motion hands that represent the continuous, even motion of time.

The idea of Spring Drive was conceived in 1977 by an engineer at SEIKO EPSON’s Suwa plant in Japan. It took more than two decades to realize the first Spring Drive timepiece which incorporates innovative technologies as follows:

1. The Spron 510 Mainspring: While SEIKO has made its own mainsprings in-house since 1959, none of the existing springs were considered strong enough to deliver the industry-leading performance dreamed of by the engineering team. An entirely new spring was created using a new high-elasticity material called Spron 510 to create more power. The result is a mainspring that delivers more power, more smoothly and for longer.

2. The ‘Magic Lever’: The new ‘Magic Lever’ system allows for more efficient transmission of the rotor’s power to the mainspring. It is fitted directly to the shaft of the rotor and thus creates more efficient winding of the spring. This new system is 30% more efficient than traditional winding systems.

3. Tri-synchro regulator: This new device replaces the escapement and thus eliminates the weakest and most vulnerable part of the traditional watch mechanism. It regulates the three kinds of energy used in the Spring Drive mechanism, the mechanical power of the mainspring, the electrical energy, created from this mechanical power which activates a crystal oscillator, and the electro-magnetic energy that turns the glide wheel precisely 8 times per second.

Spring Drive has nearly all the characteristics of a classical mechanical watch, however it does not require an escapement. The escapement uses the back and forth motion of a balance wheel to regulate the speed at which the spring drives the hands and it is this high-friction motion that makes the traditional mechanical watch vulnerable to inaccuracy and damage.

The genius of Spring Drive is that all the motion in the movement is in one direction, so that the friction is all but eliminated. It is also this one-way motion that allows the hands to move with the unique glide-motion that reflects the real nature of time. Spring Drive is a natural revolution in timekeeping.

The Spring Drive technology utilizes both the traditional and electronic technologies. The mainspring power supply, the gear train, the power reserve system and the Magic Lever are classical, mechanical watch components. 80% components are those incorporated in mechanical watches. Like the highest grade mechanical watches, Spring Drive has 30 jewels to ensure low friction and high accuracy, and each watch is assembled by hand by SEIKO’s most skilled craftsmen and women.

The electronic components of Spring Drive are state-of-the-art. While other companies have attempted to develop a mechanical watch with an electronic time regulation system, only SEIKO has succeeded in realizing this dream.

It required new advances in electro-magnetics to develop the braking system within the regulator and new advances in power generation and IC to convert part of the mainspring’s mechanical power to an electrical signal; just 25 nanowatts are all that is required to power the circuit and the crystal oscillator. This is 50% of the power needed in any conventional watch circuit.

In 1999, Seiko launched three limited edition Seiko Spring Drive watches for the Japanese market. The references are as follows:

(1) Seiko Spring Drive SMK001J (also known as SBWA001): This hand-wound spring drive watch features stainless steel case and bracelet. It has a black dial with rectangular hour-marker indices, sword-shaped hour and minute hands and a long central second hand. Equipped with the manual-winding spring drive calibre 7R68, this rough and sport timepiece displays a date at 3 o’ clock and a power reserve indicator. It is fitted with a curved sapphire crystal glass. Its hour and minute hands as well as dotted hour-markers are embedded with Lumbrite technology. This model was limited to 500 pieces. Its stainless steel bracelet is fitted with a deployant clasp with push-button release.

(2) Seiko Spring Drive SMK003J: This reference has all the features of the above reference, but fitted with a crocodile leather strap instead of stainless steel bracelet.

(3) Seiko Spring Drive SMK004J (also known as SBWA002): This elegant model features an 18K yellow gold case, silver dial and calibre 7R68. Its rectangular indices, dauphine hour and minute hands as well as the central seconds hand are finished in gold.

In 2002, the Seiko Spring Drive watch was released in an 18K white gold case. The Seiko Spring Drive SMK005J is a serene and classic elegant wristwatch, with a stepped silver dial balancing the beauty of the mechanism when viewed through the skeleton caseback.

The Seiko Calibre 7R68 is a hand-wound Spring Drive movement, which offers one second per day accuracy, 10 times better than the chronometer mechanical standards such as COSC. The Cal. 7R68 is made of 276 components (280 in the small second hand version). It is also equipped with 30 jewels (32 in the small second hand version). The movement provides 72 hours of power reserve.

Technical details

Model: Seiko Spring Drive SMK005J

Seiko Spring Drive Calibre 7R68
Hand-wound spring-driven mechanism
No battery
Accuracy of ±15 seconds per month
Operates for up to 48 hours when fully wound
Power reserve indicator

18K white gold
Glass: Dual curve sapphire crystal
Water-resistant: 30m water-resistant
Transparent caseback

Silver dial with dauphine hands for hour and minutes
Central seconds hand
Date at 3 o’ clock
Power reserve indicator

Black crocodile leather strap