Connect multiple basic mechanisms to realize complex laws of motion, motion trajectories, and non-detachable special motion mechanisms that are difficult to achieve with a single mechanism
The basic mechanism mainly includes link mechanism, gear mechanism and cam mechanism.
The combination mechanism is generally not a simple series connection of several basic mechanisms, but a more complex combination, which may be a gear link mechanism, a cam link mechanism, and a gear cam mechanism composed of different types of gears. basic mechanisms
can be a joint cam mechanism composed of the same type of basic mechanism
The combined mechanism movement is to obtain a new movement relation by analyzing the movement relation of each basic mechanism, and then linking it according to different combination ways
The gear link mechanism is made up of a crank rocker mechanism (see link mechanism drawing) and 3 gears (Figure 1)
Wheel I is attached to the crank and rotates at angular speed 1 at a constant speed
Drive wheel 5 is the output part
Its angular speed 5 changes with different positions of the mechanism, which is the angle of the crank
1 function
When the crank
AB rotates continuously at a constant speed, the driving wheel 5 can make a variety of regular rotating movements
Any given request
1 the corner 5 of the angular velocity of the wheel
[omega]
5 The method can be carried out in two steps: First, form a lever-jointed four-bar mechanism 1,2,4,6, the
[omega]
1 obtaining
omega
2 and
omega
4; then wheel 1, wheel 3, and rod 2 form one differential gear train, and wheel 3, wheel 5, and rod 4 form another differential gear train, to obtain
the relational expressions for
5 and
two ,
4
Since rod 1 and wheel 1 have the same speed, rod 2 and rod 4 are components in the wheel train and four-bar mechanism at the same time, and the
2 and
4 obtained in the four-bar mechanism The mechanism can be
substituted into the relational expression to obtain
5
In this way, omega
5 can be extracted
–
1 line in FIG
Curves 1, 2 and 3 are three different characteristics of reversal, instant stop and non-uniform rotation obtained by changing
l
1 /
r
1 or
l
6
Curve 1 corresponds to
the corner of the angle called inversion
Curve 2
= 0, theoretically it is an instant stop, but due to the influence of space on the moving torque and the elasticity of the member, in fact there is still a momentary stop time equivalent to the 45 ° rotation of the crank
When the reversal angle is small, the curve does not reflect the reversal movement, and in fact there is a longer dwell time.
The gear linkage mechanism can also achieve some complex motion paths
The articulation cam mechanism is composed of two fixed disc cams (Figure 2)
Two slide blocks are respectively added to the two driven parts, and the two slide blocks are connected by a hinge
The trajectory of the point M from the center of the hinge is mm
This combined mechanism can control the movement of the follower in the x and y directions through the coordinated cooperation of the two cams, so that it is necessary to realize the different motion tracks required.
Cam 1 and Follower 3 form one basic cam mechanism and Cam 2 and Follower 4 form another basic cam mechanism The displacement and rotation angle of the corresponding follower cam can be obtained through the two cams
The relationship between
x =
x (
) and
and =
and (
)
Since the two cam angles are
identical, eliminating the formula
trajectory relationship can be expressed
Y =
Y (
X )
Conversely, if the trajectory mm or the equation
y =
y (
x ) is extracted
, it can also be decomposed into two parts moving in the
x and y
directions, thus designing a contour of the cam
There are many types of combination mechanisms and their applications are becoming more extensive.
For the integration of combined institutions, most of them are still at the stage of specific analysis of specific institutions, and more studies are needed
