Guide arrangement in a linear power unit

A guide arrangement in linear power units having a housing (1) and a slide (2) linearly movable relative to the housing, and is designed to relieve the slide of transverse forces, lateral forces etc., in order to reduce wear and eliminate jamming. According to the invention, this is achieved in that at least one guide rail (6) is arranged parallel to the direction of action of the linear power unit, that the housing (1) is fixedly connected to the guide rail (6), and that the slide (2) is hingedly connected in a manner to transmit push and pull forces only, to a guide device (7) guided on the guide rail (6).

The invention relates to a guide arrangement in a linear power unit. 
The term "linear power unit" as used herein relates to power units for 
producing linear movements, such as piston-rodless hydraulic, pneumatic or 
electrically powered cylinders, certain types of toothed belt drives, 
spindle assemblies, ball bearing screw assemblies etc. These linear power 
units typically have some type of a normally stationary housing or the 
like and some type of a normally movable runner or slide. Other movement 
patterns may also exist. 
One problem inherent in prior art linear power units results from the fact 
that the power-transmitting attachment of the slide is subjected not only 
to the forces of displacement of the power source but also to other 
forces, e.g. lateral forces and other moments of load. The slide and its 
attachment, as well as the means transmitting the linear propelling force, 
should thus be dimensioned for a strength sufficient not only for the 
intended push and pull forces, but also for said additional loads and 
stresses. This normally means an increased width and thickness of the 
material. 
However, in powered-cylinder type linear power units, for example, the 
housing cannot normally be completely closed but must have a slot of at 
least the above-mentioned increased width of the material and a length 
corresponding to the operating stroke length or exceeding it. Thus, an 
increase of the slot width means reduced rigidity of the housing. 
It is previously known, e.g. through the company Mortonair, to provide a 
linear power unit in the form of a piston-rodless pneumatic cylinder and 
to form the cylinder with external guide grooves on opposite sides thereof 
for guiding a guide which is mechanically and rigidly connected to the 
slide (FIG. 1). Since the cylinder has a longitudinal slot, i.e. a 
generally U-shaped cross-section, high pressures in the cylinder may urge 
the U-legs (sides) of the cylinder slightly apart, whereby the guide will 
jam. Such jamming most often results both in reduced mobility of the slide 
and in increased wear of the guide grooves, with a consequential increase 
in play and impaired accuracy. The risk of jamming and wear becomes still 
greater if lateral forces acting on the guide also occur. Moreover, 
restoring worn guide grooves involves high costs since the cylinder part 
must then normally be replaced in its entirety. A further drawback of such 
an arrangement is that the guide grooves are exposed to deposits of dust 
etc., which may also increase wear. Further, the guide can only be applied 
on the same side of the cylinder as the slot. 
One object of the present invention is to substantially reduce or eliminate 
the above-mentioned drawbacks. Another object is to relieve the slide of 
transverse and lateral forces and other moments of load. Also, the 
invention allows different mounting positions of the guide relative to the 
slide/power unit. 
According to the invention, these objects are achieved by a guide 
arrangement in which a guide rail is fixedly connected to the power unit 
housing, a guide device is mounted for linear movement on the guide rail 
in the direction of the push/pull forces, and the slide is coupled to the 
guide device by means transmitting only the push/pull forces between the 
slide and the guide device. Further developments and special, preferred 
embodiments are described hereinafter.

FIG. 1 shows a known linear power unit, having a piston-rodless 
pressure-medium cylinder 1 in which a piston (now shown) is linearly 
movable back and forth. Such linear piston-cylinder assemblies are 
available, e.g. under the trademarks Origa, Martonair and others. On its 
outside, the cylinder housing 1 has four grooves parallel to the 
longitudinal axis of the cylinder. The two upper grooves in FIG. 1 
cooperate, as shown, with a longitudinally displaceable guide device or 
slide 2 located above the cylinder. The slide 2 is rigidly connected to 
the piston in the cylinder by means of a piston attachment (not shown) 
extending through a longitudinal slot (seen between arrows P) in the top 
part of the cylinder wall 1. Arrangements of the type shown in FIG. 1 
suffer from the drawback that the "cylinder legs" resulting from the 
slitting of the cylinder in its longitudinal direction tend, at high 
pressures in the interior of the cylinder, to move apart in the direction 
of the arrows P, with the consequences discussed earlier. 
FIG. 2 shows an embodiment according to the invention. A pressure-medium 
cylinder 1 has an internal piston (not shown) connected to a piston 
attachment (slide) generally designated 2, which is movable along the 
cylinder. The cylinder housing, having a generally square cross-section 
and rounded corners, is provided on three of its four sides with 
respective pairs of longitudinal grooves 3a, 3b, 3c. The central planes 
(in the longitudinal direction of the cylinder) of the grooves are at 
angles to each other suitably ranging between 20.degree. and 160.degree.. 
Two strips 4, 4' each having a pair of profiled projections 5 are 
connected in a form-fitting and power-transmitting manner to the left-hand 
pair of grooves of the cylinder housing in FIG. 2, by insertion of the 
right-hand projections 5 of the strips 4, 4' in respective ones of the 
grooves 3a, whereupon screws may be passed through bores (not shown in 
FIG. 2) provided in one of the strips parallel to the plane of the 
drawing, screwed into respective threaded holes provided in the other 
strip 4 in alignment with said bore, and tightened. Since the cylinder, 
piston, slide, cylinder grooves, strips and profiled projections are prior 
art, these components will not be described in more detail here. 
However, before the above-mentioned tightening is effected, a guide rail 6, 
provided with a similar pair of grooves 3d as the cylinder housing 1, is 
fitted, in accordance with the inventive concept, to the left-hand 
projections 5 of the strips 4, 4'. The dimensions of the guide rail 6 can 
be selected with regard both to the expected loads and stresses exerted by 
the linear power unit 1,2 and to the loads to be displaced or 
supported/taken up by the linear power unit. 
The guide rail 6 cooperates with a guide device 7 which, by lower and upper 
guide members 8a and 8b, respectively, is displaceable on the guide rail. 
The lower guide member or members 8a in FIG. 2 are each suitably provided 
with a position-adjusting device 9, here a set screw 9, for adjusting the 
play/clearance between the guide rail 6 and the guide members 8a, 8b of 
the guide device 7. The guide members are suitably exchangeable so that 
they can be replaced at a low cost when worn. 
At its upper right-hand portion, the guide device 7 is connectedto the 
slide (piston attachment) 2 by means of a coupling 10. 
In accordance with the present invention, the coupling 10 should have the 
property of only transmitting push and pull forces between the piston 
attachment and the guide device, but not lateral forces, transverse 
forces, torque or other similar possibly deforming stresses. Suitable such 
couplings are known in various designs and, for the purposes of the 
present invention, may be selected through the exercise of routine skill 
in view of the above-mentioned and other desirable properties. By means of 
such a coupling, the cylinder will be relieved of a substantial part of 
the loads or stresses otherwise applied to it or, in other words, the 
cylinder 1 is stiffened by the guide rail 6 and the guide device 7 in such 
a manner that the stresses are instead taken up by the guide rail mounted 
together with the guide device (slide) on the cylinder housing. 
This means that it is now possible, thanks to the invention, to choose a 
power unit, i.e. in this case the cylinder 1, only on the basis of the 
required push and pull forces whilst, when earlier choosing the power 
unit, it was necessary to pay regard also to other stresses, which has 
always resulted in the use of cylinders of increased diameters and, thus, 
higher costs and also higher consumption of pressure medium. 
A smaller cylinder stabilized by means of a guide rail according to the 
invention will, however, almost always be less expensive than an equally 
stable, larger cylinder. 
As appears from FIG. 3, a cylinder according to FIG. 2 can also be provided 
with two guide rails 6, 6' or, in an analogous manner, though not shown in 
the drawing, even with three guide rails. The different guide rails may 
each have one guide device 7,7', as shown in FIG. 3, or all cooperate with 
a single guide device engaging one or more of the three guide rails. 
Further, the third guide rail may have no guide device and, for instance, 
then only serves as a rail for additionally stiffening the housing 1 of 
the power unit. 
Further, the guide device may in a known manner embrace one or more guide 
rails and, optionally together with bellows or the like, protect the slide 
surfaces from deposits, contaminants, such as dust, splashing etc., thus 
increasing the life of the slide surfaces. 
Of course, the guide rails 6 can also be connected to the cylinder housing 
1 other than by means of the above-mentioned strips 4, e.g. to the end 
walls of the cylinder. 
It is readily understood that the guide devices will not jam on the guide 
rails by the U-legs of the cylinders being slightly urged apart by the 
forces indicated by the arrows P in FIG. 1, since any such parting 
movement will be executed by both the guide rail and the guide device. 
As further appears from FIG. 2, the guide rail 6 may be provided with a 
pressure-medium channel 11. At one end, the channel 11 can be connected to 
one cylinder chamber located at said end, which means that the connection 
of both cylinder chambers to a pressure-medium source can be provided at 
one and the same cylinder end. 
Further, the guide rail 6 may be provided with additional channels 12, 12' 
for connecting e.g. hydraulic or pneumatic position-sensing devices for 
selected positions of displacement. Such a position-sensing device may 
consist e.g. of a valve and a cam provided in said selected position of 
displacement. In this case, the valve is fixed to the guide device 7. When 
the guide device with the valve passes the cam, the valve is opened or 
closed, whereby the supply or discharge of pressure medium can be opened 
or closed, respectively, for connection, via said channels 12, 12', to 
means operated by the position-sensing device. Of course, it is also 
possible in the channels 12, 12'to insert insulating conductors and 
connect them to corresponding electric sensing means. 
When using more than one guide rail 6, 6' (FIG. 3), only one guide rail 6 
may be provided with said channels 11, 12, 12'. Of course, it is also 
possible to use the alternative of arranging the pressure-medium channel 
11 in one guide rail 6 and the channels 12, 12' in the other guide rail 6' 
.