What Is a Ratchet Gear?
Ratchet and pawl, a unidirectional intermittent motion mechanism composed of ratchet and pawl. The ratchet mechanism is commonly used in the intermittent feed or indexing of the rotary table in various machine tools and automatic machines, and it is also commonly used on the jack. The ratchet mechanism is used for unidirectional driving in bicycles, and ratchet mechanisms are often used to prevent reverse rotation in manual winches. The ratchet mechanism is often accompanied by noise and vibration, so its working frequency cannot be too high.
- The ratchet mechanism converts continuous rotation or reciprocating motion into a unidirectional step motion.
- The ratchet wheel teeth usually use one-way teeth. The pawl is hinged to the rocker. When the rocker swings counterclockwise, the driving pawl inserts the ratchet teeth to push the ratchet to rotate in the same direction. When the rocker swings clockwise, the ratchet The claws slide over the ratchet, and the ratchet stops rotating. To ensure that the ratchet does not reverse,
- The picture shows an external meshing ratchet mechanism commonly used in machinery. It consists of an active swing lever, pawl, ratchet, check pawl and
- There are several ways to classify the ratchet mechanism:
- The design of the ratchet mechanism should mainly consider: the choice of ratchet tooth shape, the determination of the modulus of the teeth, the determination of the inclination angle of the tooth surface, the adjustment method of the stroke and the dynamic stop ratio
- The toothed ratchet mechanism is taken as an example to illustrate the choice of tooth shape in its design method
- The picture shows the commonly used tooth profile. Asymmetric trapezoidal gears are used for applications with large loads. When the ratchet mechanism bears a small load, triangular or circular tooth shapes can be used. Rectangular and symmetrical trapezoidal gears are used for two-way ratchet mechanisms.
- Determination of modulus and teeth
- Similar to gears, the relevant dimensions of the ratchet gear also use the modulus m as the basic parameter for the calculation, but the standard modulus of the ratchet must be calculated according to the top circle diameter da of the ratchet.
- m = da / z
- The number of ratchet teeth z is generally selected by the use conditions and motion requirements of the ratchet mechanism. For the ratchet mechanism used for general feed and indexing, the number of teeth of the ratchet can be determined according to the required minimum angle of the ratchet (z 250, generally z = 8-30), and then the modulus is selected.
- The main uses of the ratchet mechanism are: intermittent feed, braking and overtaking. The following are application examples.
Ratchet mechanism intermittent feed
- The picture shows a bull's head planer. In order to cut the workpiece, the planer needs to perform continuous reciprocating linear motion and the table is intermittently moved. When the crank 1 rotates, the rocker 5 is driven to reciprocate by the connecting rod 2. The rocker 5 is equipped with a pawl 3 of a two-way ratchet mechanism, and the ratchet 4 is fixedly connected to the lead screw 6. Thereby, the nut (that is, the table) is intermittently fed. If the swing angle of the driving pawl is changed, the feed amount can be adjusted; changing the position of the driving pawl (fixed after rotating through 180 ° around its axis) can change the direction of the feed movement.
Ratchet mechanism brake
- The figure shows a lever-controlled belt brake. The brake wheel is fixed to the outer ratchet wheel 2. The pawl 3 is hinged to point A on the brake wheel 4. The brake wheel surrounds a steel belt 6 controlled by the lever 5. The brake wheel 4 rotates freely in the counterclockwise direction, and the pawl 3 slides on the back of the ratchet teeth. If the wheel rotates in the opposite direction, the four wheels are braked.
Ratchet mechanism beyond
- The illustrated ratchet mechanism can be used to achieve fast overtaking motion. The movement is transmitted from the worm to the worm wheel, which is driven by the pawl 3 mounted on the worm wheel
- Ratchet mechanism beyond