Fluid pressure actuator with anti-rotation slide attached to piston rod

The invention relates to a linear motor with a cylinder (5) containing a piston linked to a piston rod (8) projecting from either of the end faces of the cylinder (5). To secure the piston rod against torsion and rotation, a guide comprising at least two guide ribs (22, 22') arranged on the circumference of the cylinder (5) is provided, these ribs being arranged at a distance from each other and extending in the axial direction of the cylinder (5). A slide (19) seated on the outside of the cylinder (5) and guided on the guide ribs (22, 22') while at least partially encompassing them is fixed to the piston rod (8).

BACKGROUND OF THE INVENTION 
1. FIELD OF THE INVENTION 
The invention relates to a linear motor with a cylinder containing an 
axially movable piston to which a piston rod extending through at least 
one of the end faces of the cylinder is fitted, the section of the piston 
rod which is outside the cylinder being secured against torsion by being 
fixed to a co-moving torsion protection element movable in the axial 
direction of the cylinder in conjunction with a sliding guide fixed 
thereto. 
2. DESCRIPTION OF THE PRIOR ART 
Linear motors of this type are generally known, for instance from DE-GM No. 
85 05 017, and used for the linear displacement of a power take-off device 
linked to the piston rod outside the cylinder. The linear motor is 
actuated by suitable pressurisation, for instance by admitting air to the 
cylinder operating spaces separated by the piston. By securing the piston 
rod against torsion, i.e. rotation in relation to the cylinder, the power 
take-off device can be precisely positioned, which is vital in such fields 
as handling or robotics. Known linear motors are usually provided for this 
purpose with a rod extending parallel to the piston rod and connected 
thereto by means of a carrier, this rod being guided in a sliding guide in 
the shape of an eye provided on the cylinder. The axial dimension of the 
sliding guide is relatively short, leading to inadequate precision of the 
torsion protection element, especially in the extended position of the 
piston rod. This is particularly noticeable if the piston rod is subjected 
to torque by way of the power take-off device. This arrangement further 
requires expensive additional external measures to support the piston rod 
when displacing heavy weights, since known torsion protection devices are 
not suitable for supporting functions of this kind. The insufficient 
torsional rigidity of the known torsion protection device further makes 
the accurate positioning of the power take-off device virtually 
impossible. 
SUMMARY OF THE INVENTION 
It is an object of the invention to provide a linear motor of the type 
described above with a piston rod precisely secured against torsion and 
supported irrespective of the piston stroke and capable of precise 
positioning by simple means. 
This problem is solved by a design wherein the sliding guide comprises at 
least two guide ribs located on the circumference of the cylinder at a 
distance from each other and at least approximately extending along the 
entire length of the cylinder, and wherein the torsion protection element 
is a slide irremovably attached to the outside of the cylinder and guided 
flat along the guide ribs, said slide at least partially surrounding or 
encompassing the guide ribs. By guiding the torsion protection device 
independent of the piston stroke along a great axial distance on the guide 
ribs of the sliding guide, the piston rod is capable of absorbing high 
torques created by the power take-off device without even the slightest 
amount of twisting. Since the slide encompasses the guide ribs and is thus 
irremovably seated on the cylinder, an excellent support for the piston 
rod is provided, which is thus made capable of absorbing high transverse 
forces without the risk of bending. This construction provides a torsion 
protection element of virtually perfect torsional rigidity suitable for 
use in positioning and/or position sensing applications. In addition to 
all these advantages, the linear motor according to the invention is very 
compact in design and relatively simple and cost-effective to produce. 
Advantageous further developments of the invention are described in the 
sub-claims. 
According to one aspect of the invention, an accurate, tilt-free and 
low-wear guidance of the slide along two circular guides on the cylinder 
is provided. 
Additionally, the construction according to the invention provides a 
compact design. 
This construction also provides a linear motor which is simple to produce, 
involving in particular virtually no subsequent machining of the guide 
ribs. 
Further, additional components may be fitted to the outside of the 
cylinder, for example, a second slide to secure the piston rod against 
extreme loads. 
The linear motor construction according to the invention is particularly 
suitable for the precise positioning of the piston rod or for stroke 
measurement. Further switching functions may be actuated in dependence on 
the position of the piston rod, such as the reversal of piston rod 
movement or the initiation of separate machine components. 
The various features of novelty which characterize the invention are 
pointed out with particularity in the claims annexed to and forming a part 
of this disclosure. For a better understanding of the invention, its 
operating advantages and specific objects obtained by its uses, reference 
is made to the accompanying drawings and descriptive matter in which 
preferred embodiments of the invention are illustrated.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
The linear motor according to the invention has a cylinder 5 containing an 
axially movable piston 6 (see FIG. 3). End covers 7 are provided on both 
ends of the cylinder 5. The piston is provided with an axial piston rod 8 
extending coaxial with the cylinder bore 10 and through one of the 
cylinder end faces 9 or the associated end cover 7 respectively while 
forming a seal. 
There may, however, alternatively be a piston rod extending through both 
end faces of the cylinder. 
There is further provided a torsion preventing device 14 to secure the 
piston rod 8 against torsion relative to the cylinder 5. This device 
comprises a torsion protection element 18 in the form of a slide 19 guided 
in the axial direction of the cylinder along a sliding guide 17 fixed to 
the cylinder 5. The slide 19 is detachably and in particular irrotatably 
connected to a piston rod section 16 located outside the cylinder 5 by way 
of a carrier 15. 
The carrier 15 may be bracket-shaped and bolted to the slide 19 as 
illustrated in FIG. 1, or it may be integral with the slide 19. The 
bracket is suitably provided with a sleeve 20 for fitting and clamping to 
the piston rod 8, for instance by means of clamping screws 21. 
According to the invention, the sliding guide 17 has at least two guide 
ribs 22, 22' arranged on the circumference of the cylinder 5 at a distance 
from each other and extending at least approximately along the entire 
length of the cylinder 5. They are preferably designed formed integrally 
with the cylinder 5, as is the case with the embodiment having a profiled 
tube as a cylinder tube. 
The slide 19 is seated on the outside of the cylinder 5, at least partially 
surrounding or encompassing the two guide ribs 22, 22', thus being 
prevented from lifting off the cylinder 5 at a right angle to its axial 
dimension. During assembly, the slide is pushed on the ribs in a suitable 
manner. 
During operation of the linear motor, i.e. the stroke of the piston rod 8, 
the slide 19 is moved along, executing a traversing movement during which 
it slides flat along the guide ribs 22, 22'. Since the slide 19 partially 
encompasses the guide ribs 22, 22', there is the possibility of planar 
support against the cylinder 5, enabling it to absorb any transversal 
forces acting on the piston rod 8 and thus to protect the piston rod 8 and 
its seal in the area of the cylinder end face 9 against damage. The two 
guide ribs 22, 22' arranged at a distance from each other further provide, 
if viewed from the front as in FIG. 2, virtually for a two-point support 
of the slide 19, thereby enabling it to absorb high torques acting on the 
piston rod 8. 
In the embodiment in question, the cylinder tube 23 is, as has been 
mentioned above, a profiled tube with 4 ribs 24 spaced equally round its 
circumference and extending over the entire length of the cylinder 5; 
these four ribs are identical in their shapes. This means that each rib 24 
has another rib 24 diametrically opposed on the other side of the cylinder 
5, and viewed in cross-section as in FIG. 2, the four ribs are in the four 
corner areas of an imaginary square. In relation to the cylinder axis, the 
ribs project substantially radially from the surface of the cylinder 5, 
creating a gap or recess 30 between each pair of adjacent ribs. The four 
recesses produced in this manner are slightly concave towards the cylinder 
bore 10, there being a smooth transition between their sides 31 and the 
associated rib areas. 
Two of these ribs, which are adjacent to each other on the cylinder 
circumference, represent the guide ribs 22, 22' in the embodiment in 
question. The function of the remaining two ribs will be explained later. 
The slide guide face 32 of the guide ribs 22, 22', which acts in 
conjunction with the slide 19, is convex, having, if viewed in 
cross-section as in FIG. 2, an arcuate form. It can also be said to have 
the form of a section of a cylinder surface. The slide guide face as 
illustrated may suitably be represented by the entire surface of the guide 
ribs 22, 22', providing for a smooth transition into the concave recess 30 
at 31. 
The slide 19 is so seated on the cylinder 5 that it bridges the associated 
recess 30 with a base body 33 while encompassing the associated guide rib 
22 or 22' with claw-shaped guide extensions 34 integral with the base body 
33. The slide 19 has sliding faces 35 with a cross-section complementary 
to the slide guide faces 32 on which it slides with play; there are two 
concave sliding faces 35, which at the same time represent the areas of 
contact of the guide extensions 34 facing the cylinder. 
The base body 33 is preferably of a plate-shaped design, its length 
corresponding to the longitudinal dimension of the cylinder 5, resulting 
in an approximately C-shaped cross-section of the slide 19, the guide 
extensions 34 representing the two ends of the C. The possibility that the 
slide 19 might lift off the cylinder 5 is prevented by the fact that the 
two guide ribs 22, 22' are encompassed with regard to those parts of their 
circumferences which are opposite each other if viewed in the 
circumferential direction of the cylinder and that a section of each slide 
guide face points away from the slide 19 and towards the opposite side of 
the circumference of the cylinder 5. 
This being so, the slide 19 is guided on the cylinder 5 by the joint action 
of two sliding faces having curved shapes and extending in the direction 
of slide traverse, thereby ensuring a tilt-free traversing movement of the 
slide 19 while simultaneously centering it. 
The additional ribs 24 shown opposite the guide ribs in the embodiment of 
the invention may, if required, also be used as guide ribs or as guide 
rails for a further slide. This is to be recommended if the piston rod is 
subjected to extreme transversal forces or if the piston rod extends 
through both ends of the piston. In the latter case, one of the slides 
will be associated with the piston rod section projecting from one 
cylinder end face, while the other slide will be associated with the 
piston rod section projecting from the opposite cylinder end face. 
The precisely guided slide 19 offers the advantage of enabling the simple 
and accurate positioning of the piston rod or its power take-off device 
not illustrated here. For this purpose, at least one stop is provided in 
the traversing path of the slide 19, which will suitably be adjustable in 
the axial direction of the cylinder and lockable in any desired position. 
With reference to FIG. 1, a first stop 37 is shown in the cylinder face 
area 36 opposite the piston rod 8. This stop projects into the path of the 
slide 19 and is capable of acting in conjunction with the associated slide 
end 28 or a stop face provided thereon. In the embodiment according to 
FIG. 1, the stop 37 is bolted to the associated cylinder end face; it may, 
however, alternatively be adjustably fitted to a separate stop support 
(not illustrated). There is further the possibility of arranging the stop 
37, as shown in FIGS. 3 and 4, on the circumference of the cylinder 5, in 
particular in the area of the recess 30 between the guide ribs 22, 22'. In 
the latter case, a guide groove 44 is provided in the centre of the recess 
30, preferably extending along the entire length of the cylinder, in which 
guide groove the stop 37 is adjustable as indicated by the arrow 41. The 
first stop 37 determines the depth of piston rod retraction, its position 
of rest. 
Preferably a second stop 38 will be provided to limit the extension stroke 
of the piston rod 8. The second stop 38 is suitably associated with the 
cylinder face area 9 associated with the piston rod section 16 and is 
seated on the cylinder circumference between the guide ribs or rails 22, 
22'. It projects through a slot-shaped slide opening 39 extending in the 
axial direction of the cylinder. The length of the slide opening 
substantially corresponds to the maximum stroke of the cylinder. To limit 
its stroke, the end of the slide opening 39 forming a stop face 40 and 
adjacent to the first stop 37 is contacted by the second stop 38. 
The second stop 38, too, is suitably adjustable in the axial direction of 
the cylinder 5 in accordance with arrow 43. For this purpose, it is 
likewise supported in an axial groove which may suitably be identical with 
the guide groove 44 for the first stop 37 (see FIG. 4). 
An embodiment not illustrated here provides for the arrangement of both 
stops 37, 38 in the slide opening 39, each stop acting in conjunction with 
its adjacent slot end to limit the stroke of the piston rod. 
The linear motor according to the invention is further provided with 
proximity sensors 45, 46 emitting a signal, for instance for stroke 
reversal, on the approach or arrival of a slide face. For simplicity's 
sake, these proximity sensors 45, 46 are, in the embodiment shown, 
directly integrated into the stops 37, 38 and act in conjunction with the 
opposite stop faces 28, 40 of the slide 19. The proximity sensors are 
suitably designed as inductive proximity sensors or approach signal 
transmitters slightly sunk into the stops. 
The linear motor according to the invention is, in its embodiment according 
to FIGS. 3 and 4, further provided with means for positioning the piston 
rod 8. For this purpose, the slide 19 carries a co-moving sensor 47 in the 
area of one of the guide extensions 34, this sensor being suitably located 
at the slide end 28 and thus capable of sweeping along the entire length 
of the cylinder. This sensor 47 is capable of acting together with one or 
several pulse generators 48 arranged on the cylinder circumference near 
the guide extension 34 carrying the sensor 47. The sensor may, of course, 
alternatively be located on the cylinder, while the pulse generator/s 
would in this case be fitted to the slide. 
During the operation of the cylinder, the relative positions of sensor and 
pulse generator change, leading to their opposite placing in certain 
positions of the slide and the creation of a control signal in the sensor. 
This control signal may then be used, for instance for reversing the 
movement of the cylinder or to control external machines operating 
together with the linear motor. 
In the embodiment according to FIGS. 3 and 4, the sensor 47 is an inductive 
sensor emitting a magnetic field and transmitting a control signal when 
this field is changed, for instance by a piece of metal. A row of metal 
elements 49 is further arranged on the cylinder 5 in its axial direction, 
these elements serving as pulse generators. When the slide moves, the 
sensor 47 passes each of these metal elements in turn, each time 
transmitting its control signal. With the aid of these individual control 
signals, the travel of the piston can be measured. There is further the 
possibility of positioning the piston rod by interrupting the supply of 
pressure medium to the cylinder on reaching a certain number of control 
signals. 
The number of the pulse generators 48 can be chosen as required, being 
preferably limited to two to mark the stroke limits. 
In an embodiment not illustrated here, the sensor is designed as a reed 
contact, while the pulse generator/s is/are a magnetic component/magnetic 
components. 
The sensor and/or the pulse generator/s will preferably be adjustable and 
lockable in the axial direction of the cylinder. 
For a visual check of the momentary stroke position, the linear motor 
illustrated in FIG. 1 is provided with a scale 50 located on the slide 19 
and extending in the axial direction of the cylinder, this slide acting in 
conjunction with a pointer 51. The scale is arranged on the outer surface 
of either of the guide extensions 34, while the pointer 51 is arranged on 
the adjacent recess 30 next to the slide 19. In a fixed arrangement, the 
pointer 51 will suitably be in the area of the cylinder end face 9 
associated with the piston rod; in the embodiment in question, the pointer 
is movably located in a guide groove 52 extending in the axial direction 
of the cylinder for adaptation to varying stroke lengths. 
These stop and indicting systems can, of course, be fitted to the linear 
motor either individually or in any combination required. 
The length of the slide 19 is further, of course, so chosen that at least 
that slide end section which is opposite the carrier 15 is always in 
contact with the slide guide faces 32 of the guide ribs. There is no need 
for the sliding faces to extend over the entire length between the carrier 
and the slide end 28; this is, however, advisable because it simplifies 
the production of the slide.