Ratchet mechanism drawing. Ratchet mechanism. Features of the work of bidirectional mechanisms

Consisting of a ratchet (gear) wheel with oblique teeth and a lever with an intermediate link (dog) fixed on it. The ratchet mechanism converts the reciprocating rotational movement of the lever into intermittent rotation of the ratchet wheel. During the rotational (working) movement of the lever, the pawl, under the action of the spring, with its free end rests against the tooth of the wheel and turns it at a certain angle. With the return (idle) stroke of the lever, the pawl slides freely along the oblique edges of the teeth until it stops. To prevent the lever from rotating in the opposite direction during idling, there is an additional locking pawl. During the next working movement of the lever, the pawl turns the wheel again. Thus, the rotational movements of the lever are converted into periodic rotation of the wheel in only one direction. To turn the wheel in the opposite direction, it is necessary to keep both pawls from contact with the teeth. The ratchet mechanism is used as a delay device - for example, in hoisting machines (the gear wheel is connected to the winch drum, and the pawl keeps the drum from spinning back under the weight of the load being lifted). The ratchet mechanism is used in spring-wound watches (when winding the watch, it prevents the mainspring from unwinding spontaneously).

1 - ratchet wheel; 2 - dog; 3 - lever; 4 - locking dog

Encyclopedia "Technology". - M.: Rosman. 2006 .

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The ratchet was first mentioned in ancient legends dating back to 400 BC, at the time of the war between Carthage and Syracuse. The legends speak of crossbows, the so-called gastrofetes, in which ratchet mechanisms were used. A groove ran along the gastrofet, in which a slider moved, designed to act on the arrow. On both sides of the groove, toothed racks were attached, on which the ratchets slid. These ratchets prevented the possibility of firing while the crossbow was being drawn.

In the 15th century, Leonardo da Vinci finalized and improved the ratchet mechanism. This made it possible to noticeably improve working conditions and increase the safety of workers who lifted and held heavy loads. That is why the ratchet is also called the seat belt of the 15th century.

1. Ratchet device.

or ratchet is a gear intermittent motion device, which is necessary to replace the reciprocating rotary motion with intermittent motion in only one direction. That is, the ratchet allows the axis to rotate in one direction and does not allow rotation in the opposite direction.

The shape of a ratchet is a gear wheel with asymmetrical teeth with an emphasis on one side (one side of the teeth is flat, and the other is undercut or sheer). The movement of the wheel in the opposite direction is limited by the pawl, pressed by the spring or its own weight. The device of the ratchet is simple.

Structurally, the ratchet mechanism consists of the following elements:

1. Ratchet wheel.

2. Shaft.

3. A pawl with an axle that must be attached to a fixed element.

4. Lever arm.

5. Sometimes, an additional locking dog is provided in the design.

The ratchet wheel is the main element of any ratchet mechanism. In appearance, this is an ordinary wheel in which teeth are provided. The ratchet wheel is made by forging or casting from different types of steel.

Ratchet mechanisms differ from each other in the number of teeth on the ratchet wheels. The number of teeth determines the proportion of the circle that the ratchet is supposed to turn. To provide a sixty degree turn, you will need six teeth (sixty degrees equals one sixth of a circle). To be able to rotate the mechanism by 30 degrees, you need a ratchet with 12 teeth (thirty degrees is equal to one twelfth of a circle). Etc. The minimum number of teeth for a ratchet is six. Ratchets with fewer teeth are usually not produced.

The ratchet wheel is mounted on a special shaft on which it can rotate freely. For maximum freedom of rotation, the space between the shaft and the wheel is lubricated with engine oil. The pawl is intended to limit the movement of the ratchet wheel. It engages with the ratchet and delays its movement in the direction of descent, but at the same time does not stop movement in the direction of ascent. In order for the ratchet to turn in the direction of the rise, the pawl must be disengaged from it. To do this, the dog must be unloaded using a special mechanism.

There are ratchet mechanisms that can provide rotation both to the right and to the left. In this case, the teeth of the ratchet wheel are made rectangular, and the pawl is reversible. If the dog is thrown from one side to the other, then the direction of rotation of the ratchet mechanism can be changed. In some variations of ratchets, an additional locking pawl is provided. It is needed to ensure higher reliability of the entire mechanism.

The dog is controlled using a lever that can both engage and disengage it. The larger the ratchet, the more leverage required. It is for this reason that ratchets are produced as small as possible (as far as possible). The height of one tooth is calculated as 0.3-0.4 of the pitch.

There are two types of ratchet mechanisms depending on the type of profiled surface:

1. Drums - the working profiled surface is a circle or its fragment.

2. Rack – the profiled surface of the mechanism is linear.

Depending on the profile of the ratchet wheel, the following types of ratchet mechanisms are distinguished:

1. Ratchet mechanisms with a rectangular profile.

2. Ratchet mechanisms with a flat profile.

3. Ratchet mechanism with radial profile.

Depending on the number of levers in the mechanism, there are ratchets of the following types:

1. Ratchets with one lever.

2. Ratchets with two levers.

Mechanisms with two levers provide greater stability and do not allow distortions during the operation of the mechanism.

According to the type of teeth, there are ratchets of the following types:

1. Ratchets with straight teeth.

2. Ratchets with beveled teeth.

In ratchets with beveled teeth, the stop for the pawl is more reliable, which ensures more reliable engagement of the component mechanisms.

2. The principle of operation of the ratchet.

Consider what is the principle of operation of the ratchet. The lever with the pawl near the ratchet is in free rotation. This dog with one end is on the ratchet, and the other is attached to the movable axial connection. When the ratchet mechanism is acted upon by thrust from another mechanism, the lever begins to swing in different directions. When the lever is deflected, the pawl simply slides along the flat side of the teeth without any effect on the rotation of the ratchet. If the action of the thrust stops, the pawl rests on the steep side of the tooth and prevents the reverse movement of the ratchet. That is, gradually swinging in one direction or the other, the lever with the pawl provides translational movements of the ratchet mechanism.

For example, consider the principle of operation of a ratchet in a lifting mechanism. Turning the handle, you can raise the load to a certain height. But if the handle is released, the load will not fall, but will be held in suspension due to the fact that the ratchet is engaged with the pawl. In order to be able to lower the load, you must first raise the pawl (hold the handle) and calmly lower the load at a slow pace by turning the lever.

3. Scope of ratchet mechanisms.

The use of ratchet mechanisms is very wide. They are used in many structures and devices, for example, in turnstiles, handcuff locks, wrenches, watch winders, screwdrivers, bicycle reverse gears, planers, overrunning clutches, encryption machines (for example, Enigma), power tool protection devices and in vehicles (in the crankshaft mechanism).

The ratchet mechanism is mainly used as a delay device. In hoists equipped with a winch, the ratchet gear is connected to the winch drum, and the pawl prevents the drum from spinning back under pressure from the load side. In spring-wound mechanical watches, the ratchet prevents the mainspring from unwinding on its own.

Ratchets are also used in vehicles. They are necessary to ensure an instant stop of the entire mechanism and prevent it from scrolling in the opposite direction. The ratchet mechanism in the crankshaft makes it possible to attach the starting handle. With the help of a ratchet mechanism, rotational movement is transmitted from the handle to the crankshaft, which ensures its start. In addition, the ratchet ensures that the crankshaft is disconnected from the handle in automatic mode after starting the engine in the shortest possible time.

The crankshaft ratchet is a well-known mechanism that is used not only in the automotive industry, but also in many industries. The first recorded historical mention of the ratchet mechanism refers to the wars of Ancient Greece. It was used in crossbow technology. When pulling the string, the ratchet prevented it from slipping in the opposite direction.

Today it acts as an integral element of various mechanisms and machines. The ratchet mechanism is widely used in the device of turnstiles, jacks, winches and many others. It also found application in crankshafts.

The ratchet is an intermittent movement mechanism that includes several components. Its main purpose is the ability to convert movements of a reciprocating rotational nature into intermittent rotation in one direction only. In other words, the ratchet prevents the rotation of the axis, which occurs against the given direction.

The mechanism of the ratchet device is represented by a gear wheel, the teeth of which are not symmetrical. They are equipped with an emphasis on one side. Reverse rotation is prevented by a pawl pressed against the gear wheel. The pawl can be pressed in two ways: most often, the pawl is pressed against the gear with a spring, a rubber ring, but there is another option - pressing through its own weight.

The pawl is connected to the yoke, which makes swinging movements near the center of the ratchet wheel, by a movable joint. It is necessary in order to capture the ratchet wheel, which grips the rocker when the lever is moved from side to side.

At the moment when the wheel moves in the opposite direction, the pawl easily jumps off a few teeth of the wheel. In the crankshaft, this simple but important mechanism acts as an instantaneous stop.

Another purpose of the mechanism is to prevent the shaft from turning. So the ratchet used in the design of the winch stops the reverse rotation of the drum when lifting the load.

If it is necessary to carry out alternate rotation of the shaft to the right and left, the teeth are made rectangular, and the pawl is cross over. Throwing the pawl allows you to change the direction of rotation of the ratchet.

The required rotation of the ratchet determines the number of teeth. What fraction of the circle is supposed to turn the ratchet, so many teeth are designed. A 60 degree turn will require 6 teeth (one sixth of a circle), a 30 degree turn will require 12 teeth (one twelfth of a full turn). The minimum number of teeth is 6.

When designing, such a feature is taken into account, the larger the ratchet, the larger the lever should be. Therefore, the ratchet is made as small as possible. The height of the tooth is calculated in 0.35-0.4 step sizes. The profile is traditionally rectangular, flat or radial. The design of the mechanism with two levers makes it more stable, preventing misalignment during operation. Beveling the end of the tooth makes the emphasis more reliable.

The crankshaft ratchet allows you to attach the starting handle. With its help, the rotational movement is transmitted, going in the direction from the handle to the crankshaft for starting. Also, the shaft is automatically disconnected from the handle as soon as possible after the start of the engine.

The ratchet is one of the oldest mechanical inventions of man. Its structural simplicity and functional efficiency have allowed it to remain relevant even in the digital age. Of course, target systems that use a ratchet mechanism can hardly be called technically highly developed, but this does not negate the operational advantages of their device.

Scope of application

Ratchets are also used for industrial units with components of engineering structures, and for the operation of small fittings for tools. This speaks to the versatility of the device and its flexibility in terms of technical integration. For example, the simplest ratchet for helmets allows you to adjust the head strap through a wheel that transmits movement to the locking system.

In tools, this device serves as a means of setting certain operating parameters. In the design of the secateurs, in particular, the ratchet allows you to clearly fix the cutting step within the specified range. If we talk about more responsible areas, then machine-tool production equipment will come to the fore. Cross planing units are equipped with external ratchet wheels that can withstand heavy physical loads. In cylindrical grinding machines, this device is used to ensure radial feeds - the installation is carried out in combination with piston drives. In addition, ratchets are used in winch systems, jacks, starter and clockwork mechanisms.

Structural version

The functional parts of the mechanism work to provide the intermittent motion required to move the gear in one direction. The latter is the most significant part of the system and is a metal disk with teeth. To ensure reliability, the wheel is initially made using forging technology or injection molding.

The number of teeth can be different - it depends on the working range of the target design. In typical models, the 30-degree rotation is provided by 12 teeth. The minimum number of transition slots reaches 6 - for example, this configuration is used in ratchet mechanisms for ratchet straps. In addition to the impeller, the design also includes a mounting "pawl", a locking mechanism, a shaft and a lever. The physical properties of the elements, the layout, the presence of individual functional components and dimensions may vary depending on the model and design features.

How does a ratchet mechanism work?

Each device has a kind of trigger element (lever, drive, hook) that sets the system in motion. Initially, the “pawl” is in contact with the wheel, but after the activation of the mechanism, axial rotation begins, which entails the displacement of the latch.

Thrust can be provided by different sources of thrust. In the same pruner, the start is facilitated by manual pressure, and in machines - by an electric motor. One way or another, during the movement of the wheel, the "dog" begins to slide and then move along the outer surfaces of the teeth. It is important to emphasize that at this point it has no effect on the wheel. But after the movement stops, the ratchet mechanism is locked by pressing the "dog" into one of the grooves. This cycle can be repeated until the desired result is obtained when adjusting, lifting or tuning according to certain parameters of the target system.

Varieties of the mechanism

There are many classifications that determine the diversity of ratchets. For example, a profiled surface can be rack or drum. The first option is used in special cases, since the linear placement of the teeth is less functional and ergonomic than the circumferential one. Drum systems are just devices with impellers. There is also a classification of the base profile on which the grooves are located. It can be rectangular, radial and gentle. Radial systems are more often used as the most convenient to use, reliable and compact. With a rectangular profile, a ratchet coupling mechanism is usually performed, since the small size of the regulating equipment in this case does not allow the use of teeth with pointed and inclined edges.

Features of the work of bidirectional mechanisms

One of the key features of the classic ratchet is that the wheel or rack rotates in only one direction. But there is also a separate class of mechanisms that retain the same operational effect, but act differently. Rotation in bidirectional systems is realized both to the left and to the right. Moreover, the teeth must necessarily be rectangular - only in this configuration can uniform displacement of the wheel be ensured. The main feature of the bidirectional type ratchet mechanism is the “dog” movement system. It does not move and does not slide along the surface of the wheel, but is thrown over. This expands the control of the system, but also complicates it, making it less reliable.

How to make a ratchet yourself?

The design technique will depend on the requirements of the system in which it will be used. As a basis, you can take a shaft in the form of a piece of metal pipe, a cutout from a steel sheet and a piece of profile that will play the role of a "dog". The main difficulty will be in adjusting the dimensions of these components, because only under the condition of optimal convergence can the ratchet mechanism be stable. You should also make a carrier base with your own hands - a metal frame assembled from the same steel sheets is used for it. By welding, a shaft is attached to it on both sides, on which a pre-machined disk with cut grooves sits. To install the "dog", a running clamp with a spring system should be provided. Installation is carried out by hardware or welding.

Finally

Ratchets have many advantages, but there are also weaknesses that must be considered when buying devices with such a mechanism. First of all, the system bears a high responsibility, which also leads to increased requirements for maintenance.

In the same machines and lifting units, a prerequisite is regular lubrication of the wheel and contact spots with the "dog". The use of a ratchet mechanism in small tools and accessories also has its drawbacks due to jamming of small parts. But in each case, the quality of the system will depend on the characteristics of the product. Large manufacturers use durable components with an optimal combination of performance properties in the construction of ratchets. Another thing is that the presence of such a mechanism can significantly increase the price tag of the device.

In various machines, for their normal functioning, not only continuous, but also intermittent rotational motion is used. In order to carry it out, specialized mechanisms, called ratchet.

In engineering ratchet mechanisms it is customary to call such kinematic devices that are used to convert a reciprocating rotational movement into an intermittent rotational movement having one direction. Distinctive feature ratchet mechanisms is that they allow you to change the magnitude of periodic movements of the working parts of machine tools and machines for various purposes, moreover, in a very wide range and quite finely.

Ratchet mechanism can be characterized as a device that periodically creates an obstacle to the action of force on the mechanism and again creates conditions for its movement. In addition, they are used to eliminate the possibility of moving any links of machines and mechanisms in one direction. One more purpose of ratchet mechanisms is to allow interconnected links to freely rotate in one direction. All ratchet mechanisms subdivided into gear and friction.

Main elements toothed ratchet mechanisms are gear rack or gear ratchet wheel and a slider or rocker, on which the so-called " dog". On the ratchet wheel can be located internal, external, as well as end ratchet teeth. Concerning " dogs”, then in most cases they are made rotary. They are pressed against the wheels either under the influence of their own weight, or under the action of special springs.

Often there are situations when it is necessary to provide rotation ratchet both in one direction and in the other. To ensure this functioning of the device, its pawl is made toggle, and the teeth are used in a rectangular configuration. To change the direction of rotation ratchet, you need to switch doggy from one position to another.

Friction ratchet mechanisms are widely used in modern technology. They are divided into shoe, cam and roller.

Often friction ratchet mechanisms are used when it is necessary to ensure reliable adhesion of various elements at significant speeds, and in any of their angular positions relative to each other. Movement in one specific direction in such mechanisms is carried out due to the fact that when the intermediate links of the friction clips are jammed, a large friction force arises.

Scope of application ratchet mechanisms different types and designs is very wide. Most often they are used in a wide variety of machine tools. For example, without ratchet mechanisms with outer ratchet wheel practically no modern cross-cutting machine is used. In planer equipment, commonly used mechanisms with end ratchet clutches. They are installed in feed drives. In the design of some cylindrical grinding machines, ratchet mechanisms with piston drives. They are mounted in radial feed systems.

Beyond the machine tool industry ratchet mechanisms are also used in instrument making, automotive industry, aircraft industry. They can often be found in various reading devices, winding mechanisms, starters, winches, jacks, etc.