Structure of mechatronic module mechanisms

175
sical and mental labor rights. These devices include various components: 
mechanical, electrical, electronic and information. Mechanical components are 
mechanisms [8].
The mechanism is a system of mutually interconnected different types 
of connections of solids, realizing the motor function, i.e. which transforms 
the motion of one or several solids of the system into the required motions 
of others. Solid bodies that are part of the mechanism and are its functional 
elements are called links. The Link of Mechanism constructively may consist 
of several parts that do not have among themselves relative movement. The link 
taken as a fixed one is called the base (rack). The link, to which the movement 
is conveyed, transformed by mechanism into the required movements of other 
links, is called the input. The maximum number of input links is equal to the 
number of controllable generalized coordinates or to the number of degrees of 
mobility of the mechanism. The link making the movement for which is inten-
ded mechanism, called output. The links between the input and output links are 
called intermediate.
Kinematic pairs are understood as links. 
Kinematic pair (KP)
– connection 
of two adjoining links, allowing their relative movements. Each kinematic pair 
has certain mobility. Kinematic pairs can be conditionally divided into passive 
and active.
Kinematic pairs can be conditionally divided into passive and active. Passive 
kinematic pair (hereinafter kinematic pair) is connection of two links does not 
allow carrying out the specified controlled movement of one link of the pair 
relative to the other link.
Kinematic pairs are classified according to the number of constraints 
imposed on the relative motion of the links on the kinematic pairs of the fifth, 
fourth, third, 
second and first classes (Table 2.1) [8].
By the nature of the contact, they are divided into lower ones, if the elements 
of the links touch only on the surface, and the higher ones, if the elements of 
the links touch along the lines or at the points.
In this case, a linear or point contact is assumed to be initial when the links 
touch, without effort, and under load the links forming the higher pair will 
touch on some actual surface, called the contact spot.
The advantage of lower kinematic pairs in comparison with higher is the 
possibility of transferring large forces, because the contact surface of the 
contacting links of the lower pair can be very significant. The use of higher 
pairs allows reduce friction (for example, ball bearing) and get the right ones, 
the most varied laws of motion of the output link by giving a certain form to 
the links forming the higher pair.

176
 
 

Table 2.1 – Classification of kinematic pairs and degrees of mobility
The kinematic pairs largely determine the operability and reliability of the 
mechatronic module, since they transfer forces from one link to another, due 
to the relative motion, friction occurs, the elements of the pair are in a stressed 
state and in the process of wear.
Active kinematic pairs allow one of the links in the pair to be controlled by 
generalized coordinates. Such kinematic pairs are called degrees of mobility.
Degree of mobility (DM) is the connection of two links, which allows one 
of them to communicate a controlled generalized coordinate. The degree of 
mobility includes a drive that communicates motion to the link. If the degree 
of mobility does not affect the functional transformation of the mechanism, it 
is called excess.

177
An extra degree of mobility is a controllable generalized coordinate, inten-
ded for bringing into controllable movement of the link and not affecting the 
functional movements of the mechanism. If the degree of mobility causes 
additional functional transformations of the mechanism, then it is called an 
additional.
An additional degree of mobility is a controlled generalized coordinate, 
designed to give the mechanism additional functionality (motions). For example, 
the presence in the executive mechanism of the robot of additional degrees of 
mobility allows him to bypass obstacles, penetrate into narrow long spaces, etc.
It should be borne in mind that kinematic pairs and degrees of mobility have 
a different physical nature. Therefore, the degrees of mobility are graphically 
depicted differently than the kinematic pairs, but close to them conventional 
graphic images (Table 2.1) [8].
It should be noted that the concepts of «degree of mobility» and «degree 
of freedom» are often confused. The degree of mobility of the mechanism is 
a controlled generalized coordinate. The degree of freedom of the body is the 
independent possible movement of the body.
It should be noted that the concepts of «degree of mobility» and «degree 
of freedom» are often confused. The degree of mobility of the mechanism is 
a controlled generalized coordinate. The degree of freedom of the body is the 
independent possible movement of the body. A body in space can not have a 
number of degrees of freedom greater than six, while the number of degrees 
of mobility of the mechanism is unlimited. For example, a body fixed in the 
working body of a robot actuator moving in space can not have a number of 
degrees of freedom greater than six, while the actuator may have a number of 
degrees of mobility greater than six.
Thus, in order to realize the motion of solid body in a space with a given 
number of degrees of freedom, the number of degrees of mobility of the mecha-
nism must be equal to or greater than the number of degrees freedom of the 
body. If several links are connected to each other only by kinematic pairs, then 
we obtain a kinematic chain (KC). Such a kinematic chain with respect to one 
or more of its links will be fixed. To drive it, one or more kinematic pairs must 
be replaced by degrees of mobility and given them generalized coordinates-
independent controlled variables that determine the positions of all links of the 
mechanism relative to the post.
The kinematic chain consisting of the base (rack), moving links, degrees of 
mobility and kinematic pairs with indication of their type and mutual arran-
gement is a structural scheme of the mechanism. 
There are mechanisms that can consist only of a rack, moving links and 
degrees of mobility (for example, robot actuators). If the structural scheme 

178
 
 

shows the geometric parameters of the links (in most cases, length), then such a 
scheme, is called kinematic.
The structural scheme of the mechanism, containing the minimum number 
of moving links, kinematic pairs and degrees of mobility with indication of 
their type and relative location, necessary for realization of the required 
functional movement of the output link and having no excess contour links and 
excess mobilities are called the basic structural scheme.

жүктеу/скачать 11,25 Mb.

Достарыңызбен бөлісу: