What is the escapement in a watch?
A control system is needed to ensure that watches keep a steady rate. This regulates the energy of the gear train generated by winding the spring and transmits it evenly. This function is performed by the escapement of the watch, which periodically brings the gear train to a stop and releases it again. Whether you are an experienced watch enthusiast or an interested newcomer to the world of watches – most people have probably never seen an escapement. However, the hypnotic sound of a perfectly functioning movement provided by the escapement is familiar to most people. This is created by the interaction of the escapement wheel and a part of the escapement with the balance.
The 7 phases of the escapement mechanism
The world's most well-known escapement is the Swiss lever escapement, also known as an inline lever escapement. Let us examine the general sequence of the escapement’s function step by step this type of escapement.
- Phase 1: The process begins when the impulse jewel of the roller meets the pallet fork.
- Phase 2: While the impulse jewel engages with the pallet fork, the lever’s arm is pulled back and lifted by a tooth on the escape wheel.
- Phase 3: The release stage ends when the tooth of the escapement wheel falls out of the lever's arm from the pallet jewel. This contact initiates the impulse phase.
- Phase 4: During the impulse stage, the tooth disengages from the pallet jewel of the lever and the escapement wheel rotates forward.
- Phase 5: While the tooth is released, the impulse jewel meets the end of the pallet fork again.
- Phase 6: This impact engages the opposite lever arm, which catches a tooth of the escapement wheel with the opposite pallet jewel and thus ends the impulse phase. At the same time, the pallet lever hits one of the banking pins.
- Phase 7: The impulse roller with the impulse jewel swings back and the movement starts again.
The different types of escapements in watches
This simple mechanism allows a great deal of freedom for further variations and innovations, which is why over 250 different types of escapements have been developed to date. For the sake of clarity, these can be divided into three subgroups: drawback, anchor and detached escapements.
Recoil escapements: The verge escapementThe first escapement systems in clocks were recoil escapements. In a recirculating escapement, the balance wheel is driven by an impulse and stopped in a first phase and in the second phase the direction of swing is reversed. So, the escapement wheel is always rotated a little in reverse.
The most common form of this escapement is the spindle escapement, also called verge escapement, which was the standard for mechanical watches from 1480 to 1720 and was even used for pocket watches until the 19th century. In the beginning, spindle escapements were still used with a verge rod, also known as a foliot, before switching to the pendulum as an oscillator. Later, the balance wheel with a mainspring prevailed, which made watches finally mobile and able to be worn on the arm – a decisive step in the history of the wristwatch.
The disadvantage of the recoil escapement is the limited range of the balance. The broader a balance can oscillate (preferably 220° and above), the more accurate it is able to work. With a spindle escapement, however, a maximum arc of 100° is possible, which led to limited precision in these timepieces. At the same time, pendulum clocks with less than 5° only need a very small oscillation range, which is why the wide swings of the spindle escapement led to high rate deviation.
Anchor escapements: Graham and cylinder escapementsUnlike the recoil escapement, the fixed escapement does not reverse the direction of the swing. Instead, the fixed escapement is periodically stopped by the rate regulator. The escapement wheel is thus almost constantly in contact with the oscillating system and is only released to continue turning. Experts refer to this escapement as a "resting disc" escapement. When the escapement wheel is at rest, the constant contact between the escapement wheel and the oscillating system generates a source of friction at the contact points.
The retroactive transfer of energy to the gear controller is realized through the so-called recoil when the escapement is at rest. After the contact between the pallet tooth and the resting surface, the tooth slides over the inclined surface of the pallet arm and lifts it up, thereby transmitting a forward impulse to the wheel.
The most well-known anchor escapement is the Graham escapement developed by George Graham. It is so influential that most pendulum clocks still apply the principles of Graham's work today. For portable watches with a balance wheel, Graham later improved the cylinder escapement invented by Thomas Tompion, which soon replaced the verge escapement.
Detached escapements: Glashütte and Swiss lever escapementsIn the case of detached escapements, an additional connector is located between the escapement wheel and mainspring. This piece is called the lever. In contrast to the anchor escapement, it is not in constant contact with the escapement wheel during the resting phase, and there is no friction at rest, so that the escapement wheel moves more freely.
The first detached escapement was the rack lever escapement developed by Thomas Mudge in 1757. The next stage involved the fine craft of German watchmaking: Adolf Lange developed the Glashütte lever escapement in Glashütte. These two escapements already had the same method of operation as the Swiss lever escapement, which evolved from and refined the Glashütte lever escapement at the beginning of the 20th century. As it became a characteristic element in Swiss watches, it became known as the Swiss lever escapement.
The innovations of Omega and Girard-Perregaux
The Swiss lever escapement is still the dominant and most commonly employed escapement. However, there have still been many attempts to develop even better types of escapements.
In 1970, George Daniels invented the co-axial escapement, which he patented in 1980. Since 1999, it has been used as the standard in all Omega watches, where it replaced the Swiss lever escapement. In contrast to the Swiss lever escapement, the co-axial escapement has no lifting phase, which has a significant effect on the accuracy of a watch. Over time, the friction between the tooth and the friction surface of the lever arm of the Swiss lever escapement changes, which can lead to discrepancies in the accuracy of the watch.
Girard-Perregaux also applied for a patent for a newly designed escapement. Developed by Nicolas Déhon, the constant escapement ensures that the impulses transmitted to the oscillation mechanism are uniform in size. This results in a consistent amplitude of the balance's oscillation and an extremely high degree of accuracy in a watch.