Spatial lever mechanisms (1984)

Hands typing on a typewriter.

Mechanisms moving in three-dimensional space.

The trajectories of points on the links of these mechanisms describe complex spatial curves.

Spatial lever mechanisms consist of links and kinematic pairs.

The concept of a kinematic pair.

The elements of a kinematic pair are points, lines, and surfaces of contact between links.

A hemisphere standing with its rounded surface on a rectangle.

Pairs in which the contact of links occurs at points or along lines are called higher.

Contact of a cylinder and a prism.

Pairs where contact occurs along the surface are called lower.

An example of such contact.

Depending on the type of contacting surfaces in lower kinematic pairs, a distinction is made between a spherical kinematic pair (designation of such a pair in the kinematic diagram), a cylindrical kinematic pair (designation of such a pair in the kinematic diagram), a rotational kinematic pair (has two designations in the kinematic diagram), a translational kinematic pair, and a screw kinematic pair.

Screw, translational, and rotational kinematic pairs have one degree of freedom.

Any body freely moving in space has 6 degrees of freedom.

The connections between the links limit their relative motion.

The number of freedoms taken away determines the class of the kinematic pair.

Examples of determining the class of a kinematic pair.

A spherical pair with a pin belongs to the fourth class of pairs.

In practice, instead of a spherical pair with a pin, which is difficult to manufacture, a universal joint is usually used, which has an additional link - a crosspiece and two non-collinear kinematic pairs of the fifth class.

A cylindrical pair also belongs to the fourth class of pairs.

Alternation of pairs of the fifth class.

Spatial lever mechanisms use combinations of kinematic pairs of different classes.

Examples of lever mechanisms.

Technical problems solved by spatial lever mechanisms.

Spatial lever mechanisms with lower kinematic pairs are simple in design and reliable in operation.

Car steering.

The force applied to the steering wheel is transmitted to the running wheels using a lever, left longitudinal rod and trapezoid.

The type of mechanism is distinguished by the number of links.

The steering mechanism uses 8 links and the mechanism is called eight-link.

Mechanism diagram.

Spatial lever mechanisms are widely used in agricultural machinery.

Examples of use.

Mower.

Rotational movements of the engine shaft are converted into reciprocating motion of the knives by means of a bevel washer mechanism.

Image of the mechanism and its diagram.

A machine in light industry that overcasts the edge of fabric.

The lever mechanism used in this device.

This mechanism is two spatial four-link mechanisms, which are phase-shifted by an angle close to 180 degrees.

The rocker arm of the left four-link mechanism carries the needle.

The rocker arm of the right one is connected via an intermediate lever to an additional lever, which allows for the counter motion of the looper needles.

The looper is driven by a spatial crank-rocker mechanism.

The spatial four-link mechanism with a kinematic pair of the second class is used in the chain of the mechanism for transverse movement of the needle of the button sewing machine.

The oscillatory movements of the rocker arm are transmitted via a connecting rod to the Ralche rocker arm.

The needle bar performs reciprocating movements.

A four-link crank-rocker spatial mechanism is used in the lifting carriage mechanism of the weaving loom.

From the rocker arm, the movement is transmitted to the carriage by flat four-link rocker-slider mechanisms.

Spatial lever mechanisms with lower pairs are capable of receiving and transmitting significant forces with little wear.

Higher kinematic pairs.

Scheme of such a pair.

Hands press the keys of a typewriter.

In such machines, higher kinematic pairs of the fourth class are used, but in kinematic diagrams they are depicted as lower.

Spatial lever mechanisms with higher pairs are most widely used in instruments.

Cockpit.

Instrument panel in the cockpit.

The altimeter uses a two-stage mechanism of crossing levers.

The leading lever in this mechanism transmits the movement of the membrane box to the slave lever of the first stage and then to the leading lever of the second stage, the slave lever, the gear transmission and the pointer.

Kinematic diagram of the mechanism.

The deformation in the manometric box in the pressure gauge is converted into the movement of the pointer by two lever mechanisms.

In the first mechanism, the input link is the membrane, the output link is the rocker.

This is a flat crank-slider mechanism, its output link is simultaneously the crank of the spatial articulated four-link mechanism.

The rocker arm of the spatial mechanism is connected to the pointer of the device.

Alternation of frames with different spatial mechanisms.

Spatial hinged four-link mechanism.

The link relative to which the movements of other links are determined is called the frame or rack.

A fixed link is usually taken as a rack.

Position function.

This function shows the dependence of the output link position on the input link position.

The position function can be written in graphical form as a diagram or in analytical form as an equation.

Analysis of the position function equation.

The positions of other links are determined in a similar way.

The nature of the mechanism position function depends on the relative sizes of the mechanism links.

Depending on the relationship between the links and the mutual position of the kinematic pairs on the rack, different types of position functions can be obtained.

Thus, the position function can have an approximately horizontal section - a dwell.

In such a section, the output link has an approximate stop with continuous movement of the input link.

There can be two such sections.

A section in which the mechanism provides an approximately constant gear ratio.

In spatial mechanisms, the position function may have a bifurcation point.

The position function branches here and the link can move arbitrarily along one of the branches of the position function.

The human hand is a natural analogue of a complex spatial lever mechanism.

The fingers of the hand, which have many degrees of freedom, can perform complex spatial movements when obeying the brain's command.

The hand draws a spatial mechanism.

Manipulators are created in the image and likeness of the human hand.

The work of manipulators is demonstrated.

Automated production line.

Robotic systems.

The main part of such a system is spatial lever mechanisms.

Alternation of frames with the work of manipulators.

The manipulator screws in a light bulb.

Classic robots.

When creating artificial structures, a person uses analogues of the living world.

Questions for students based on the material of the film.