Swinging arm

Load-bearing swinging arm which causes an advance movement of a mobile device by means of its pivoting movement is pivotally connected to a supporting structure in a pivotal relationship thereto about an axis of rotation, and a pair of actuators for effecting the pivoting movement is provided between the swinging arm and the supporting structure. The points of action acting on the supporting structure by way of the actuators are provided on both sides of the axis of rotation. The points of action effect moment simultaneously about the axis of rotation, and they will also effect a force couple at least in some position, for example, in a position critical in view of the load, the forces acting through the points of action being parallel, of equal magnitude and having opposite senses in the force couple.

FIELD OF THE INVENTION 
The present invention relates to a load-bearing swinging arm which causes 
an advance movement of a mobile device by means of its pivoting movement 
and is pivotally connected to another construction in a pivotal 
relationship thereto about an axis of rotation, and where an actuator for 
effecting the pivoting movement is provided between the arm and the 
construction at the pivot. 
BACKGROUND OF THE INVENTION 
The swinging arm of the above type forms a leg or a part thereof in a 
machine that moves supported by arms. In these types of mobile devices, in 
which wheels are replaced with legs that are by turns lifted up and set 
against a support for advancement, the problem has been to control the 
very large force or moment present between the supporting structure and 
the arm in such a manner that the supporting structure will not be 
subjected to excess loads which are in the practice quite large and 
shorten the life of the bearings, keeping further in mind that the 
structure should not be too complicated. On the other hand there are 
situations where high speed and small force are needed. The present 
disposals of actuators can not satisfy these two opposite needs. 
SUMMARY OF THE INVENTION 
The present purpose of the invention is to overcome the above-mentioned 
drawbacks. For achieving this purpose the points of action acting on the 
construction through the actuator are provided on both sides of the axis 
of rotation. It is now possible to utilize the so-called force couple 
principle at the pivot. In the situations requiring large turning moment 
in the pivot both actuators are provided for effecting a moment in the 
same direction about the axis of rotation simultaneously. Because the 
actuators are situated on both sides of the axis of rotation, the senses 
of action of their forces are opposite, thus at least partly mutually 
compensating the effects of their forces. 
By taking into account the size of the actuators, the amount of supplied 
energy and the position of the points of action it is possible to 
accomplish a so-called ideal force couple. Consequently, only turning 
moment will be present in the pivot, and without the radial loads caused 
by the actuators. This has considerable importance as far as the moving 
sensitivity and service life of the pivot is concerned. 
The placing of the actuators in accordance with the invention makes the 
control possibilities of the arm more versatile. In a non-critical load 
situation it is possible to provide only one of the actuators with the 
supply of energy. It is thereby possible to reach a great speed of 
movement by means of a small energy supply. The actuators can thus serve 
as a sort of gearing. 
According to one advantageous embodiment the points of action are situated 
on the same line that intersects the axis of rotation. If the aim is an 
ideal force couple in several arm positions by means of a simple system, 
it can be .achieved by placing the points of action at equal distances 
from the axis of rotation and provide the actuators for causing equal 
forces at the points of action. 
According to one advantageous embodiment the swinging arm is also at its 
other end pivotally connected to another supporting structure in a pivotal 
relationship thereto about an axis of rotation. At this location all 
above-mentioned alternatives can be applied. Furthermore, the actuators 
acting on the supporting structure and on the other construction can be 
fixed on the same swinging arm, in which case the control of the whole leg 
will be facilitated because the actuators are in the same area. 
According to one advantageous embodiment the actuators are placed inside 
the swinging arm in a housing-like construction where they are well 
protected but perform an optimal function. The housing-like construction 
makes the arm lighter, and the arm will be at the same time strong. 
The present invention will be described in the following more closely by 
reference to the accompanying drawings, wherein

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
FIG. 1 shows a swinging arm 1 in accordance with the present invention as 
seen in its plane of pivoting, that is, in the direction of the axis of 
rotation A. A construction with respect to which the arm 1 is pivotal is 
denoted with reference numeral 2. At the pivot permitting the pivoting 
movement there is a pair of actuators designated as two actuators 3. One 
part of an actuator 3 is pivotally connected to the arm 1 so that it is 
relatively immobile with respect to the arm in the longitudinal direction 
of the actuator, and the other part that is movable with respect to the 
arm is attached to the construction 2. At this point is located the point 
of action of the actuator on the construction 2. The point mediates the 
turning of the arm 1 as the distance between the actuator part fixed on 
the arm and the point of action fixed on the construction changes due to 
the change of the length of the actuator. In accordance with the invention 
the points of action 3a and 3b are so placed that they are located on both 
sides of the axis of rotation A. In the practice this will have the effect 
that when the arm 1 is turned by means of the actuators 3, the distance of 
one of the points of action from the pivot point of the actuator on the 
arm will increase and that of the other will correspondingly decrease. 
FIG. 1 shows one of such extreme positions with uninterrupted lines and 
correspondingly the other of such extreme positions with broken lines. 
Dash-and-dot lines show the path of movement of the points of action 
between these extreme positions. 
As shown by FIG. 1, the points of action 3a and 3b are further located 
within the contours of the arm 1 when the arm is looked at in the 
direction of the axis of rotation A. Also the other parts of the actuator 
3, such as the actuator end pivotally connected to the arm 1, are also 
situated within the contours of the arm. The actuator 3 is pivotally fixed 
on the arm at point 3c using well-known solutions that make the path of 
movement of the points of action 3a and 3b possible. 
The actuators can be of any type capable of transmitting force for movement 
between the arm 1 and the construction 2 by influencing the points of 
action 3a and 3b by means of the actuator. Among the variable length 
actuators can be chosen devices operated by means of pressure medium, 
especially hydraulic cylinders. The body of the cylinder can be attached 
to the arm 1 and the end of the piston rod will form a point of action on 
the construction 2, the rod being mountable and secured at this point in a 
known manner that allow the piston rod and the construction to pivot with 
respect to each other. It is also possible to accomplish the mounting such 
that the cylinder body may be pivotally connected to the construction 2 
and the piston rod end correspondingly to the arm 1. 
An important advantage in the present invention is the fact that the 
pivotal movement can be accomplished by using only one of the actuators 3, 
because this will be in certain cases sufficient for effecting the pivotal 
movement around the axis A, for example when the arm 1 is swung in a 
position where it is not subjected to the load of the construction 
supported by the arm. In the case of a hydraulic cylinder the inlet line 
to the inactive actuator and the outlet line from the same can be coupled 
together to form a free circulation, or the actuators can also be 
connected in series in this situation. The volumetric flow supplied to the 
actuators can be minimized without any harmful effect on the speed of 
movement of the arm. It is, however, preferred that, when desired, the arm 
can be turned in such a fashion that the points of action 3a and 3b 
simultaneously effect a moment about the axis of rotation A. Further, it 
is preferable that each of the actuators 3 can be used for effecting a 
moment in either of the directions when desired. In the case of hydraulic 
cylinders they are consequently double-acting, that is, when the piston is 
acted upon it is possible to achieve either a pushing force or a pulling 
force. 
The points of action 3a and 3b can always be positioned and the actuators 
can be dimensioned in such a fashion that the points of action effect a 
force couple at least in one position, for example in a critical one in 
view of the load. At this particular phase of the swinging movement each 
of the points of action is so situated and the force exerted thereon is 
such that according to the laws of the mechanics the forces have opposite 
directions and are of equal magnitude. 
The function and control of the swinging arm 1 will be facilitated if the 
points of action 3a and 3b are situated on the same line that intersects 
the axis of rotation A. According to the laws of mechanics the actuators 3 
can be easily dimensioned with respect to each other in such a fashion 
that the optimal force couple effect will be present in points which are 
difficult in view of the load. FIG. 1 shows how the points of action are 
placed in this case at equal distances from the axis of rotation A. In an 
ideal case the actuators 3 are provided for effecting always equal forces 
at the points of action 3a and 3b. In the case of hydraulic cylinders this 
can be provided most practically by dimensioning the cylinders equal in 
size and making the work surface of the piston equal on both sides of the 
piston. In the practical solution embodying this idea the piston rod 
passes through the whole work space of the cylinder on both sides of the 
piston, which is schematically shown by broken lines in conjunction with 
the cylinders 3 of FIG. 1. In course of the swinging movement at whichever 
position into whichever direction at a predetermined work pressure 
prevailing in the cylinder at the given position independently of the 
direction of movement, the absolute value of the total moment is always 
equal at the given position. The individual moments influencing through 
the points 3a and 3b may slightly deviate from each other due to a 
slightly asymmetrical location of the force lines determined by the 
actuators 3, but for the purpose of the turning moment causing the 
movement of the arm this fact has little importance. 
FIG. 1 shows further the fact that when the points 3a and 3b are situated 
on the same line extending through the axis of rotation A, an ideal force 
couple can act through them at two separate positions, namely at the 
positions where the force lines are parallel and intersect the path of 
movement of the points having the form of a circle arc. 
When the points of action are situated on the same line that intersects the 
axis of rotation A, the forces of equal magnitude in the couple can be 
produced by means of hydraulic cylinders using the formula 
EQU p.sub.a .times.A.sub.a =p.sub.b .times.A.sub.b, 
wherein the left side is directly proportional to the force produced by one 
cylinder and the right side is in the same proportion directly 
proportional to the force produced by the other cylinder, whereby 
p.sub.a and p.sub.b are the work pressures prevailing in the cylinders, and 
A.sub.a and A.sub.b are the corresponding areas on which the aforementioned 
pressures are acting. 
In this way it is possible to always accomplish an ideal force couple at 
two points on the condition that the actuators are mounted at right points 
on the arm 1. 
It should further be noted that the formula illustrates the situation at a 
given time. The pressure is a factor that can be constantly varied and 
this possibility can be utilized during the movement. The pressures can 
also be variable independently of each other. 
The above-described dimensioning formula can be utilized in one direction 
of movement only, or in both directions of movement. In theory a force 
couple operative in whichever direction can be produced also by means of 
such cylinders where the work areas on the opposite sides of the piston 
are different, for example due to the fact that the piston rod is not 
passed through the cylinder within both work spaces. This provision 
requires different work pressures in the same cylinder, depending on the 
direction of movement. 
It is also possible to alter the force caused by the actuators during the 
movement, for example, in the case of hydraulic cylinders their work 
pressures can be altered. In this way a greater force can be applied at 
predetermined points within the range of movement. 
The above study with the formula applies in an analogical manner also to 
other actuators in addition to the hydraulic cylinders, factors A.sub.a 
and A.sub.b corresponding to the capacity of the actuator to produce a 
force in proportion to a force producing factor p.sub.a and p.sub.b 
supplied thereto. 
If the line between the points of action 3a and 3b does not intersect the 
axis A, an ideal force couple can be provided only at a predetermined 
position in case the actuators cause always the same constant force. Also 
this falls within the scope of the invention, even though in the case of 
FIG. 1, the dimensioning of the actuators and the positioning of the 
points of action is preferred in the sense that an ideal force couple will 
prevail at two critical positions regarding the load, either when the 
movement proceeds in one direction or when it proceeds in either 
direction. This kind of situation will be present for example when the arm 
1 supports the load in such a fashion that the arm forms an angle with the 
vertical plane. 
FIG. 1 shows further the corresponding arrangement at the opposite end of 
the arm for providing a relative movement between other construction 4, 
such as another swinging arm, and the arm 1. At this end there is a pair 
of actuators attached to the arm at points 5c, the pair comprising two 
actuators 5 and the corresponding points of action 5a and 5b acting on a 
construction, as well as an axis of rotation B situated between the points 
of action. The rotation of the arm 1 and the other construction 4 with 
respect to each other takes place around the axis of rotation. All 
alternatives mentioned in conjunction with the actuators 3 and the points 
of action 3a and 3b can be applied in an analogical manner to the 
actuators 5 and the points of action 5a and 5b. As illustrated by FIG. 1, 
both the actuators 5 and their points of action 5a and 5b lie also in this 
case within the contours of the arm as the arm is looked at in the 
direction of the axis of rotation B. Further, the Figure illustrates 
excellently how in this type of arm 1 incorporating the axes of rotation A 
and B at its both ends the actuators 3 and 5 causing the rotation can be 
provided in the same arm, that is, all actuators can be centralized in a 
single unit. 
In the following some practical solutions of the arm according to the 
present invention and other structures associated therewith are described 
in more detail. 
FIG. 2 shows a cross-section of the pivotal connection to the construction 
2 at the axis of rotation A. The arm 1 is made pivotal by fixing the ends 
of the actuators 3 on the construction 2 which in the Figure is formed of 
a part 2a surrounding the axis of rotation A and fixed on the body of the 
machine in a non-rotating relationship thereto. The part is equipped with 
bearings of circular shape in the plane perpendicular to the axis of 
rotation A (in the case of Figure slide bearings 6), inside which bearings 
part 2a is situated and on the outer circumference of which the arm 1 is 
mounted in pivotal relation thereto. The structure of the arm 1 will be 
described hereinafter more closely. As shown by FIG. 1, the bearings 6 are 
situated in the direction of the axis of rotation A on both sides of the 
points of action 3a and 3b, that is, on the opposite sides of the plane of 
the points of action 3a and 3b, whereby a symmetrical structure without 
any torsional forces can be provided. FIG. 2 illustrates further how the 
fixing points 3a and 3b of the actuators are located in the plane 
perpendicular to the axis A outside the bearing surfaces 6 in the brackets 
provided in the part 2a, and situated between the bearings 6 as seen in 
the direction of axis A. 
FIGS. 3 and 4 show another possible structure. Although it depicts the 
structure at one end of the arm 1 where the arm 4 pivotal with respect 
thereto is mounted, it can be also used at the location shown by FIG. 2. 
The parts of the arm 4 are here denoted with reference numeral 4b and the 
bearings are of the same principle as in FIG. 2. The Figure reveals also 
the housing-like structure of the arm 1, that is, all actuators 3 and 5 
and points of action 3a and 3b as well as 5a and 5b are situated well 
protected inside the housing-like arm, and thus they do not require much 
space. As in FIG. 2, also in this case the points of action, namely 5a and 
5b, are attached to a part 4b connected to the arm 4 in non-rotating 
relationship thereto and lying between the bearings 6. In the case of 
FIGS. 3 and 4 the part 4b is situated between the extension of the 
longitudinal side walls of the arm 4. Also the arm 4 can be of a 
housing-like structure, even if no actuators-were placed inside it. A 
light construction combined with strength will be the advantage in this 
case. 
FIGS. 5 and 6 show an advantageous way to fix a hydraulic cylinder serving 
as actuator on the arm and to provide the supply of pressure medium 
thereto. The cylinder is also in this case made pivotal at the pivot point 
3c inside the housing like structure. The pivotal connection is 
accomplished by a bearing piece 9 rigidly joined to the body of the 
cylinder, that is, to the part comprising the work chambers of the 
cylinder. The piece is at its both sides connected pivotally to the arm 1 
at the bearing points provided in the opposite side walls of the 
housing-like construction of the arm. Passages 10', 11' for pressure 
medium are provided in the bearing piece 9 in such a fashion that the 
passage 10' extending into one of the cylinder chambers opens on one side 
of the bearing piece and the passage 11' leading to the chamber on the 
opposite side of the piston opens on the side located on the opposite side 
of the pivoting plane of the piece. Because the bearing piece 9 and the 
body of the cylinder 3 are joined together to a substantially mutually 
immovable relationship, the construction formed by the piece 9 and the 
cylinder 3, that is, the construction situated inside the arm 1 does not 
require any flexible hoses for delivering pressure medium into the 
cylinder. One passage 10' for pressure medium is led along the bores made 
inside the bearing piece to a rigid pipe 10" remaining inside the arm and 
joined to the surface of the bearing piece. The passage continues along 
the pipe into a chamber at one end of the cylinder. The other passage 11' 
is led straight along a bore formed at the pivoting axis of the bearing 
piece into the other chamber, which is situated on the opposite side of 
the piston with respect to the chamber. The passages 10' and 11' open on 
the outer surface of the bearing piece on the opposite sides of the 
pivoting plane of the arm 1. These points are constituted of holes, which 
are concentric with respect to the pivoting axis C between the arm 1 and 
the bearing piece 9 and which are of such structure that the respective 
conduits 10 and 11 situated outside the arm and serving as inlet and 
outlet lines of the pressure medium (illustrated schematically by broken 
lines in FIG. 6) can be fixed thereon by using a rotating or flexible 
fitting. Due to the structure the fittings can be fixed outside the arm 1 
to the part 9 that is joined rigidly to the cylinder 3, and the flow of 
the pressure medium into and from the cylinder takes place inside the arm 
solely along the rigid and firm construction formed of the bearing piece 
9, cylinder 3 and pipe 10". No hoses and fittings which might cause some 
uncertainty factors in the operation of the device and make its 
maintenance difficult is thus needed inside the housing-like arm 1. 
FIG. 5 shows further the possibility that the pivoting point 3c for 
connecting the actuator 3 to the arm 1 need not necessarily be situated at 
the opposite end of the actuator in its longitudinal direction as seen 
from the connecting point between the construction 2 and actuator 3. 
According to FIG. 5 the pivoting point is situated in the cylinder 3 as to 
the construction 2 as possible, that is, in the part containing the work 
chambers of the cylinder at the point where the piston rod emerges from 
the cylinder. By this provision the strength and reliability of the 
construction can be increased, because forces tending to bend the cylinder 
due to a possible deformation of the arm 1 can be minimized in this way. 
Although reference is made above to the actuators between the construction 
2 and the arm 1, the same structure and fixing principles are applicable 
also to the actuators 5 between the arms 1 and 4. 
The actuators connected pivotally to both sides of the arm by the bearing 
pieces 9 in the fashion shown by FIGS. 5 and 6 are connected at their 
other ends preferably in the way shown by FIGS. 2 and 3, according to 
which the same arm is in a corresponding manner pivotally connected on 
both sides of the construction (2a and 4b) to which the actuators are 
pivotally connected. 
FIGS. 7 and 8 show a larger construction incorporating the above-described 
arm 1. The Figures show a leg of a machine travelling on a support for 
advancement. The advancement of the machine takes place through the 
movement of the leg. The construction 2 is in this case a construction 
through which the arm 1, which can be designated as thigh section, is 
mounted on the body of the machine. The construction 4 comprises another 
arm mounted at the opposite end of the arm 1, and it can be designated as 
shin section. The arms 1 and 4 form the leg which for its part supports 
the machine body, and this kind of apparatus comprises for example four, 
preferably six such legs symmetrically divided onto both sides of the 
longitudinal center line of the machine. A foot section 8 at the free end 
of the arm 4 serves as point of support against the support for 
advancement in this kind of leg. As is inferable from the Figures, the 
pivots at the axes of rotation A and B are subjected to quite large 
stresses when the leg is situated on the support for advancement, the fact 
which makes the present invention very applicable in this connection. It 
should be further noted that the paths of movement enabled by the pivots 
are quite extensive, which makes the possibility to provide the effect of 
the invention in all mutual positions of the arms and the machine body 2 
important. For example in case of FIG. 5 the turning of the arms 1 and 4 
can take place in such a way that the lines extending between the axes of 
rotation A and B and the foot section serving as the support point shift 
from one side of the vertical plane to the other side, in which event the 
provisions according to the invention are of particular importance. 
As the leg is free, that is, the support point is loose from the support of 
advancement, the pivotal movement about the axes A and B takes place only 
against the own weight of the arms 1 and 4. In this situation it is 
possible to use only one of the actuators 3 or 5 for accomplishing the 
corresponding movement, because the load is not great. In case of 
actuators operated by pressure media also smaller amount of flow of the 
working medium is sufficient, and for example if hydraulic cylinders are 
used, one of them can be switched to free circulation or the cylinders can 
be coupled also in series. 
FIGS. 7 and 8 show also some paths of movement of the arms 1 and 4, the 
respective extreme positions being denoted by dash-and-dot lines and by 
corresponding reference signs. In this connection it should also be noted 
that the arms 1 and 4 can be moved sideways within a certain angle on both 
sides of the vertical plane due to the fact that the arm 1 is attached to 
a part 2 which is pivotal with respect to the machine body, the pivoting 
movement taking place about a horizontal axis D perpendicular to the axes 
of rotation A and B. FIG. 8 shows further by broken lines an actuator 7 
that controls the pivoting movement, the actuator being in this case a 
hydraulic cylinder. The corresponding part of a slightly different 
structure is illustrated also in FIG. 2 by corresponding reference signs. 
The present invention is not restricted only to the embodiment disclosed in 
the Figures and description, but it can be modified within the scope of 
the invention. As mentioned above, both points of action do not 
necessarily take part in causing the turning moment at every instant, but 
it is important that this kind of possibility exists and that in critical 
load situations the force couple principle can be utilized for minimizing 
the loads on the bearings.