The prime mover is a mechanism for storing and transferring working energy. It can be divided into two types: heavy hammer prime mover and spring prime mover.
The power system of the heavy hammer uses the gravity of the heavy hammer as energy source. Mostly used for simple wall clocks (Figure 2) and floor pendulum clocks. The original drive system of the heavy hammer has a simple structure and stable torque, but when the heavy hammer rises, the drive system is disconnected from the original drive system and the clock mechanism stops working.
The spring power system uses the energy released by the spiral spring (spring) to recover its deformation as energy source. One end of the ribbon spring is connected with the shaft, and the other end is connected with the stationary part or the shell of the spring barrel. The spring prime mover system is used as the energy source of portable clocks and watches, and also as a pendulum clock. There are three types of spring prime movers: boxes with fixed rods, boxes without rods and boxes with movable rods.
The transmission system transfers the energy of the prime mover system to a set of transmission gears of the escapement speed regulation system. It usually consists of a series of wheels and toothed shafts (Figure 3). In the main drive, the wheel is the driving gear and the gear shaft is the driven gear. The transmission ratio is calculated according to the following formula:
i=Z 1/Z2
Where Z 1 is the number of teeth of the driving gear and Z2 is the number of teeth of the driven gear. For clocks with a second hand device, the transmission ratio from the blade of the central wheel to the toothed shaft of the second wheel must be equal to 60. The tooth profile of clock transmission system is mostly specially designed (see clock tooth profile).
The transmission system can be divided into two types according to the plane configuration of "two wheels" (hour wheel and minute wheel) in the watch movement: ① Two wheels in the center, and two wheels in the center of the watch movement. It also includes direct drive type, second spring type, short second hand type, no second hand type and double three-wheel type. ② Two wheels, and the two wheels are not in the center of the watch movement. It also includes head-wheel type, two-wheel type and three-wheel type.
Direct drive is one of the commonly used transmission systems (Figure 3). In this transmission mode, the upper part of the sub-wheel has a groove, and the sub-wheel cooperates with the central wheel tube through friction; The movement of the needle walking mechanism is driven by the central wheel.
The escapement speed regulation system consists of escapement mechanism and vibration system. According to the characteristics of vibration system, it can be divided into two categories: ① escapement speed regulation system with inherent vibration period. It has a vibration system, which can vibrate independently and has a stable period. The escapement speed regulation system of the travel time system in watches and alarm clocks belongs to this category. ② Escape speed regulation system without natural vibration period (Figure 4). It has no vibration system that can vibrate independently. The reciprocating vibration of the so-called vibration system in this speed regulation system depends entirely on the reciprocating motion of the escapement mechanism. The escapement speed regulation system of alarm system in mechanical alarm clock belongs to this category. This speed regulation system has the advantages of low precision, simple structure, reliable operation and strong anti-interference ability, and is widely used in mechanical timers and clock fuzes.
The escape mechanism is a mechanism that connects the transmission system and the vibration system. Its function is to transfer the energy of the power system to the vibration system to maintain the constant amplitude vibration of the vibration system; The vibration times of the vibration system are transmitted to the pointer mechanism to achieve the purpose of timing. There are many kinds of escapement mechanisms, which can be divided into two types according to their connection with vibration system. ① Non-free escape mechanism: the escape mechanism and vibration system always keep moving. It includes straight forward, backward and I-wheel escapement mechanisms. ② Free escape mechanism: only in the release and impact transmission stages, the escape mechanism keeps moving contact with the vibration system, and the vibration system is in free motion at other stages. It includes pin escapement, fork-shoe escapement and astronomical clock escapement.
① Telescopic escapement mechanism (Figure 5): widely used for low-precision pendulum clocks. The lock surface of the fork shoe and the punch surface are the same plane (working surface); The working surface of the tile is a cylindrical surface, and the center of its circle is not coincident with the rotation center of the escapement fork; The working surface of ceramic tile is flat. The fork shoe and the escapement fork are integrated. After the impact passes, the working face of the fork shoe will force the escape wheel to retreat at a certain angle.
② Fork-shoe escapement (Figure 6): One of the most widely used escapements. When working, the escape wheel gets energy from the transmission system, which is converted into impulse and transmitted to the escape fork through the action of the teeth of the escape wheel and the fork shoe (shoe in or shoe out); Impulse is transmitted to the vibration system through the interaction between the fork of the escape fork and the swing nail on the double-disc impact disc. The fork head nail, swing nail and bell mouth of double-disc safety disc and escapement fork are safety devices to ensure the normal operation of the mechanism.
(3) Pin escapement mechanism (Figure 7): The difference with fork shoe escapement mechanism is that two cylindrical pins are used to replace the fork shoes on the escapement fork, and the impulse is only transmitted along the tooth impact surface of the escapement wheel. This escapement mechanism is simple in structure, low in precision and convenient to manufacture. It is commonly used in alarm clocks and low-precision watches, commonly known as rough horse structure.
Vibration system as time reference mechanism. The vibration period of the vibration system multiplied by the vibration times of the measured process is the time that the process has experienced. The common vibration systems of mechanical clocks and watches include pendulum, torsion pendulum and hairspring vibration system.
① Pendulum: It consists of pendulum, pendulum rod, pendulum suspension device and period adjustment device. Used to fix the clock (Figure 2). When the pendulum deviates from the vertical line (equilibrium position) at any angle under the action of external force and is released, the pendulum will reciprocate around the fulcrum under the action of gravity. The vibration process is a process in which the kinetic energy and potential energy of a pendulum change alternately.
② Torsion pendulum: it is mainly composed of pendulum disc and messenger wire (Figure 8). The lower end of the suspension wire is fixed with a swinging disk, and the upper end is fixed on a fixed fulcrum. The cross section of the messenger wire can be rectangular or circular. Torsion pendulum often forms an escapement speed regulation system with backward escapement mechanism or fork-shoe escapement mechanism. Torsion pendulum has a long period of vibration (several seconds to tens of seconds), and is mostly used for fixed clocks with less energy and longer running time.
③ Vibration system of the balance balance hairspring (Figure 9): the inner and outer ends of the hairspring are fixed on the pendulum shaft and the pendulum splint respectively. When the balance wheel deviates from its equilibrium position and begins to swing under the action of external force, the hairspring is twisted to produce potential energy, which is usually called restoring torque. This moment causes the balance wheel to move to its equilibrium position.
The winding needle is a mechanical device used to tighten the spring in the prime mover and move the hour hand and minute hand to correct the time indicated by the clock (Figure 10). When winding, the vertical wheel and the clutch wheel are engaged. When the needle is placed, the clutch wheel and the vertical wheel are disengaged and engaged with the needle placement wheel.