The SEMPRE watchwinder is the first and only watchwinding device that will keep virtually any hand-wound mechanical watch with an accessible crown fully wound when unworn.
This patented design is truly unique in that it replicates the human action of fingers winding a watch by rotating the winding crown similarly in a clockwise direction.
The SEMPRE design substitutes a mechanical finger arrangement, called a "collet", which grasps the watch's crown securely and rotates it. Several different size collets are provided to fit any watch crown diameter from 3 to 9 millimeters. These collects are custom made of acetal plastic to prevent scratching or marring of polished watchcase surfaces. The collet is mounted in a rotating tubular drive shaft, supported by low-torque precision ball bearings. It is powered by a miniature servomotor coupled to a techno-polymer drive gear system fitted with a safety slip clutch. The collet is opened by pushing a spring-loaded plunger at the opposite end of the drive shaft. Releasing the plunger closes the collet, clamping it on the watch crown.
Just as an individual winding his or her watch senses the increasing turning resistance of the crown as the watch is being wound, the microprocessor "brain" of the SEMPRE winder monitors the electrical current drawn by the gear motor as it rotates. The amount of force required to wind the mainspring of a mechanical watch, known as the winding torque, increases as the watch is being wound. As the torque increases, the drive motor draws more current. The control circuit is user-adjustable to shutdown the system when it senses that the current has reached a pre-set limit, one which is well below the maximum torque that the watch mainspring can handle. To prevent "overbanking", the drive reverses the crown momentarily after shutdown. For safety purposes, the drive system is fitted with a mechanical slip0-clutch which has been factory set to slip at a safe torque in the event of a microprocessor failure. This redundancy eliminates any possibility of stressing or breaking the mainspring of an expensive, and perhaps delicate, mechanical watch.
In operation, the winder automatically turns on every twenty-four hours. Upon actuation, the drive motor begins rotating the collet for 8 minutes. With the collet rotating at approximately 6 rpm, this provides a maximum of 48 crown rotations per day. However, in practice, the actual number of rotations is controlled by the current feedback circuit whose priority is to shown down the motor based on torque, rather than by time.
Interestingly, the SEMPRE winder will also wind "self-winding" automatic watches. The winding action of an automatic watch differs from a hand-wound mechanical watch in that there is a built-in slip-clutch in the mainspring mechanism watch to prevent overwinding rather than a finite stop as in a hand wound. In this case, the timing circuit of the SEMPRE comes into play as there may not be enough current draw increase to signal the system to shut down automatically. Either way, this hybrid control circuit provides redundant safety for winding any type of mechanical watch; hand wound or automatic.
In use, after the proper collet has been selected, the watch is placed in position on a mounting "shuttle" which supports the watch both horizontally and vertically. All contact points are non-metallic, protecting the finely finished watch surfaces from scratching or abrasion. Using a provided "spacer" even allows watches with screw-down crowns to be wound safely and conveniently. Many hand wound pocket watches can be accommodated with this system by using the supplied extender kit.
Owners of fine hand wound or automatic mechanical watches with numerous complications will find the SEMPRE watchwinder ideal for keeping their watches continuously wound and "exercised." Operating by battery, the winder ca be stored in a safe for 10 to 12 months without attention. Alternately, the winder may be powered with the high quality "switcher" type AC/DC converter supplied with each unit, which operates at any voltage from 90 to 240 VAC, 50 or 60 Hz and provides perfect 6 VDC.
The winder is housed in an elegant maple burl veneer case with a plate glass viewing panel. The case is provided with a solid brass, gold-plated lock whose fold-up latch also serves as a lifting handle. All hardware is also solid brass, with all exposed parts gold-plated and lacquered for durability. An extension kit is also supplied for use with pocket watches up to 60mm diameter.