BACKGROUND OF THE INVENTION
[0001] The present invention relates to a spring lock device for high loads provided for
preventing axial and/or rotational motion of a rod or elongated member in respect
to a housing that surrounds and through which the same rod is axially sliding and/or
rotates; in particular, the invention is directed to a spring lock device for locking
a shaft or a rod of a machine, or of an actuator, for example a pneumatic cylinder
or for any other application in which it is required to allow or to lock a movement
of a member connected to or movably supported by a shaft or by the same rod.
[0002] The spring lock device according to the invention is particularly suitable for applications
in any field; however, only by way of illustration of the innovative features of the
invention, the spring lock device will be described hereinafter with reference to
locking of a linearly movable shaft or rod of a pneumatic cylinder, without this having
to be considered as limiting as regards other possible applications.
STATE OF THE ART
[0003] As is known, in pneumatic actuation systems usually available for moving mechanical
members it is often necessary to safety lock a load or a movable member, keeping it
in a predefined position and/or condition without the load or the mechanical member
being able to move and/or rotate under its own weight or as a result of the thrust
exerted by an actuator.
[0004] In this connection lock devices for shafts have been proposed comprising locking
jaws suitably hinged and provided with aligned holes for the shaft against which the
two jaws are resiliently biased and urged to prevent any movement. A pneumatically
actuated thrusting member acts on the free ends of the jaws against counteraction
springs to release the shaft, thus allowing again a linear movement. A locking device
of this kind is described for example in EP-A-0,824,994.
[0005] Although devices of this kind are able to achieve correct positioning of a shaft
or a load at the locked condition, in practice they provide relatively small locking
forces as a result of simple misalignment of the locking jaws. Moreover, since each
jaw is acting against the peripheral surface of the shaft with an edge of a side surface,
high locking forces could cause irreparable damage to of the shaft or the rod to be
locked; moreover the locking force of each jaw acts over a small arc of a circle,
exerting locally a high pressure force which tends to engrave or to cut into the surface
of the shaft.
[0006] Locking devices of this kind therefore require that the rod or the shaft to be made
of, or lined with a very hard material, by using special steel or by subjecting the
shaft to a rolling or surface hardening process. In all these cases, these lock devices
provide a clamping force which is equal to or slightly greater than the thrust exerted
by a so-called "equivalent cylinder", where "equivalent cylinder" is understood as
meaning the thrust, in kilogrammes, exerted by a pneumatic cylinder in accordance
with existing standards, having a diameter of the rod corresponding to the shaft to
be locked.
[0007] Purely by way of example, a shaft of 12 mm diameter, in accordance with the standards
referred to above, corresponds to a cylinder having a diameter of 32 mm, to develop
a thrust of about 48 kg with an air pressure of 6 atm, which must therefore be overcome
by the locking device.
[0008] Unless the lock device is made with larger dimensions, with the risk of damaging
the shaft or the rod against which the locking action is to be exerted, the currently
known locking devices are unable to provide particularly high locking forces or a
sufficiently high safety factor, for the reasons mentioned above.
[0009] Spring lock devices are also known, to prevent axial and/or rotational motion of
a rod with respect to a housing through which the rod is sliding or rotate; the device
comprises at last one coil spring encircling or fitted over the rod, in which the
coil spring has inside diameter slightly differing in respect to the peripheral diameter
of the rod, and in which control means are provided for causing the coil spring to
grip or disengage the rod, preventing or respectively allowing a relative movement
between the housing and the same rod.
[0010] Spring lock devices of the type referred to above are shown for example in US-A-4.201.096,
US-A-3.874.480 US-A-3.230.59 US-A-4.425.987; conversely, US-A-4.045.081 and EP-A-0
458 457 and the previously mentioned US-A-4.201.096 suggest the use of a pair of opposite
coiled springs fitted over a shaft to prevent movement by a frictional force.
[0011] Although the use of spring lock devices has been suggested by the above mentioned
documents, in which the locking forces are exerted by inside tensioning of a spring
having an inner diameter usually in close contact with the peripheral surface of the
rod, none of them describes or suggests the use of a spring lock device providing
a double gripping action, suitable for selectively generating high load locking forces
by a device of single and reliable design.
OBEJECT OF THE INVENTION
[0012] Therefore, the main object of the present invention is to provide a pneumatically
controlled spring lock device which does not use any locking jaw, and which at the
same time is able to provide the required high load locking force without damaging,
by using at least one or more coil springs suitably and simply fitted over a shaft
or a rod to be locked.
[0013] A further object of the present invention is to provide a spring lock device as referred
to above which is able to differently distribute the locking forces over a wide area
so as to significantly reduce the superficial stresses on the rod, ensuring at the
same time high clamping forces and a greater safety factor.
[0014] Yet another object of the present invention is to provide a spring lock device which
is constructionally simple, of low-cost and selectively actuable to control the locking
force.
BRIEF DESCRIPTION OF THE INVENTION
[0015] The above may be achieved by means of a spring lock device according to claim 1.
[0016] By using coil springs which are made with steel wire of a given diameter and also
by using coil springs with a sufficient number of coils or turns, it is possible to
exert locking forces which are able to oppose high thrusts, distributing at the same
time the stresses over a sufficiently wide area so as to reduce the specific pressures;
in this way the risk of damaging the surface of the shaft or rod is largely eliminated
or substantially reduced.
[0017] According to the invention, by loosely supporting the spring or leaving each coil
of the spring free to oscillate or slightly rotate around an axis orthogonal to the
longitudinal axis of the shaft or rod, owing to the misalignment of the coils of the
same spring, an increased locking force is obtained to more tightly gripping the rod
or the shaft.
[0018] From tests carried out on a 12 mm shaft, with an ISO cylinder of 32 mm supplied with
pressurized air at 6 bar (6 X 10
5 Pa), it has been possible to exert locking forces two or more times greater than
those which can be obtained with any known locking device, with a safety coefficient
of the order of 2.5 or higher, suitable for highly gripping or safe locking moving
parts on machines or mechanical devices.
[0019] The spring lock device according to the invention may be made in any desired shape
and size, with a normally open or disengaged spring, by envisaging a suitable form
or arrangement of the spring itself as well as the thrusting member and the respective
pressure actuated control device.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] These and further features of the spring lock device according to the invention,
as well as some preferred embodiments thereof, will be more clearly evident from the
description of some preferential embodiments and accompanying drawings, in which:
- Fig. 1 is cross-sectional view of a first embodiment of a spring lock device according
to the invention, in a normally disengaged condition;
- Fig. 2 is a cross-sectional view similar to that of Figure 1, with the spring lock
device in an engaged condition;
- Fig. 3 is a cross-sectional view along line 3-3 of Figure 1;
- Fig. 4 is a cross-sectional view, similar to that of Figure 1, for a second embodiment
of the spring lock device according to the invention, in a normally disengaged condition;
- Fig. 5 is a cross-sectional view of the spring lock device of Figure 4 in an engaged
condition;
- Fig. 6 is a cross-sectional view, similar to that of Figure 3, showing further features
of the spring lock device;
- Fig. 7 is a cross-sectional view, similar to that of Figure 6, showing another solution;
- Fig. 8 is again a cross-sectional view, similar to that of Figure 3, showing the use
of two locking springs.
DETAILED DESCRIPTION OF THE INVENTION
[0021] With reference to Figures 1 to 3 we shall describe a first preferential embodiment
of a spring lock device according to the invention.
[0022] As shown, the device comprises an external casing 10 defining a chamber 11 for housing
a spring locking member 16 which can be pneumatically actuated to prevent and allow
a sliding and/or rotational movement of a shaft or rod 12 through guide openings 13,
14 which are axially aligned at the two ends of the casing 10, as shown. Reference
15 in Fig. 1 denotes moreover a cover for the casing 10 comprising a pneumatic cylinder
or pneumatically actuated control means 17 for the spring lock device as explained
further below.
[0023] The innovative aspect of the lock device according to the invention resides in the
use of a locking member 16 provided by at lest one coil spring having a required number
of coils or turns, made from steel wire of suitable diameter, as schematically shown.
[0024] The coil spring 16 is encircling the rod 12 and is intended to clamp its coils against
the rod 12 so as to lock movement upon actuation. The coil spring 16 is therefore
of "normally open" type; for the purposes of the present invention, the expression
"normally open" is understood as meaning a coil spring loosely supported by the rod
12 which, in the unstressed condition, have an internal diameter of the coils slightly
larger, for example a few tenths of a millimeter greater than the peripheral diameter
of the rod 12 against which the said coil spring 12 locks as a result of the gripping
force caused by a twisting or coiling action of the control means 17 on the spring
itself.
[0025] In order to exert the necessary twisting action of the coil spring 16, the latter
terminates at each end with shaped arms 16A and 16B which are inwardly bent, the end
portion of each arm 16A, 16B being bent in a direction parallel to the longitudinal
axis of the coil spring 16.
[0026] As previously mentioned, the coil spring 16 is loosely fitted over the rod 12, inside
the chamber 11 of the casing 10 to allow each coil of the spring 16 to freely perform
a slight longitudinal and/or rotational movement in respect to the rod 12, about an
axis perpendicular to the same rod, so as to considerably increase the locking force,
as will be explained further on.
[0027] As already mentioned, the gripping action of the coil spring 16 against the rod 12
is performed by a thrust member 18 actuated by a pneumatic cylinder inside the cover
15 of the lock device.
[0028] As shown in the example of figures 1 and 2, the thrust member 18 is in the form of
a fork-shaped member downwardly pending from a piston 19 of a pneumatic cylinder.
The arms of the fork member 18 have facing sides 18' outwardly slanted or diverging
towards the coil spring 16 to engage the arms 16A and 16B of the same coil spring
16.
[0029] The piston member 19 of the pneumatic cylinder, is normally urged toward the lock
spring 16 by back springs 20 provided between the piston member 19 and the bottom
wall of the cover 15.
[0030] Pressurized air is fed into a side of the piston chamber 21 facing the casing 10,
by a feeding conduit 22, while the other side is vented to the atmosphere by a venting
hole 15A.
[0031] In the example according to Figure 1, the coil spring 16 is normally open that is
it does not grip the rod 12 when pressurized air is fed into the piston chamber 21;
therefore, in the absence of pressurized air the back spring 20 prevails to forward
the piston 19 and the thrust member 18 against the arms 16A, 16B to close the coils
of the lock spring 16 against the rod 12 gripping the same; therefore the spring lock
device of figure 1 may be referred to as a normally locked device. Obviously by reversing
the disposition of the back springs 20 and the air feeding, the spring lock device
will be in the form of a normally unlocked device.
[0032] As previously stated, the lock spring 16 is loosely supported by the rod 12 to allow
each coil to freely twist and/or rotate around an axis orthogonal to the longitudinal
axis of the rod 12, causing twisting of the coils merely by a pushing action on the
arms 16A and 16B of the same coil spring. Consequently the coils of the spring 16
will tend to adhere tightly against the peripheral surface of the rod 12, with an
increase of the gripping force.
[0033] This may be clearly understood with reference to figure 3 of the drawings; as shown
in figure 3 the end coils of the locking spring 16 from which the arms 16A and 16B
extend, are slightly contacting the end faces inside the chamber 11 of the casing
10, for example by a pivot point 23, avoiding any contact along a surface or a substantial
length of the end coil. Furthermore, the coils of the locking spring 16 may adhere
to each other or may be slightly spaced apart to aid twisting of each individual coil
of the same spring.
[0034] According to the solution of figures 1 and 2, in order to allow the sliding movement
of the rod 12, it will therefore be sufficient to supply pressurised air on the bottom
side of the piston 19 opposite to that of the wedge-shaped thrusting element 17. This
condition is shown in Figure 1 in which it can be seen that the two arms 16A and 16B
of the spring 16 are spaced apart contacting the forward ends of the thrust member
18, thus allowing releasing of the shaft 12; in this condition back springs 20 are
urged against the cover 15. Subsequent to the discharge of the air from the pneumatic
cylinder, the back springs 20 urge the piston 19 and the thrust member 18 forward,
turning the arms 16A, 16B of the locking spring 16 inside to grip rod 12 by twisting
the coils of locking spring 16 against the same rod, as shown in figure 2.
[0035] Figures 4 and 5 show a second solution similar to the solution of figures 1 and 2,
which makes use of a thrust member of different type; therefore in this case also,
the same reference numbers as in the preceding example have been used to indicate
similar or equivalent parts.
[0036] The solution of figures 4 and 5 uses a normally open locking spring 16 which is similar
to the locking spring 16 of figure 1, with the difference that the spring 16 in Figures
4 and 5 has intersecting arms 16A and 16B against which a disk-shaped thrust member
24 acts. The thrust member 24 is in turn connected to the piston 19 of the pneumatic
cylinder via a connecting pin 25 sliding through a guiding hole in partition wall
26 which closes the bottom side of the piston chamber 21 of the cylinder. Back springs
20 are again provided on the side of the piston member 19 which is opposite to the
side in which the air feeding conduit 22 opens.
[0037] In the examples described hitherto, the coil spring 16 comes directly into contact
with the rod 12 which, consequently, must be made of suitable material or treated
to have a harden surface.
[0038] In the case where it is required to use a shaft or a rod 12 made of shaft steel material,
it may be advisable to provide a protective annular member between the locking spring
16 and the rod 12 such as a bushing or an intermediate coil spring of material which
is softer than the steel material of the rod 12 so as to avoid scoring or damage to
the same rod.
[0039] This may be obtained by using a bushing 30 of soft material, for example plastic
material, or by arranging annular members of soft metallic material, for example brass
material, as schematically shown in Figure 6, or by using an intermediate coil spring
31 having coils arranged between the coils of the locking spring 16, and the rod 12
as schematically shown in Figure 7.
[0040] Figure 8 of the drawings shows a further embodiment which makes use of a pair of
locking springs 32, 33 which are co-axially arranged to the rod 12; each spring 32,
33 is provided with respective shaped arms 32A, 32B and 33A, 33B so as to be made
close and lock the rod 12 by using a single pressure actuator control device 17, in
the manner described above. The two locking springs 32 and 33 may be oppositely wound
as shown, or in the same direction. The use of two or more separate locking springs,
compared to a single spring of the preceding examples, in certain cases allows an
improvement in the locking conditions, also providing an anti-rotational action in
the opposite directions.
[0041] In order to verify the effectiveness of the spring lock device, tests were carried
out in order to lock a standard pneumatic cylinder having a chamber having 32 mm diameter,
and 12 mm rod. The cylinder was supplied initially with pressurized air at a pressure
of 5 atm (5 x 10
5 Pa which was then gradually increased to 17 atm (17 x 10
5 Pa), achieving locking forces higher than the axial thrust of the cylinder normally
ranging, at the test pressures, between 40 and 140 kg. Since the locking device are
usually actuated by cylinders supplied with air at 6 atm (6 x 10
5 Pa) , to which a thrust of 48 kg corresponds for the test cylinder, it is obvious
that with a locking device according to the present invention it is possible to obtain
locking forces of up to twice and several times greater than that which can be obtained
with a conventional locking device.
[0042] It is nevertheless understood that what has been stated and illustrated with reference
to the accompanying drawings has been provided purely by way of example of the general
principles of the invention and some preferential embodiments and that other modifications
or variations may be applied to the device or to part thereof, without departing from
the invention.
1. A locking device for preventing axial and/or rotational motion of a rod (12), comprising:
a casing (10) defining a chamber (11) having end faces, and axially aligned guide
opening (13, 14) in said end faces;
a rod (12) axially slidable through said guide openings (13, 14) of the casing (10)
at least one locking spring (16; 32, 33) in the casing (10), encircling the rod (12),
said coil spring (16; 32, 33) in the unstressed condition being loosely supported
and having an inside diameter slightly larger than the peripheral diameter of the
rod (12); and
control means (18, 19) for winding the coil spring (16) to grip against the peripheral
surface of the rod (12) characterised in that
pivot points (23) are provided for the end coils of the spring (16; 32, 33) at the
end faces of the chamber (11), said pivot points (23) being arranged to allow the
coils of the spring (16; 32, 33) to freely move and
rotate about an axis orthogonally arranged to the longitudinal axis of the rod.
2. Spring lock device according to Claim 1, characterized by comprising at least a first (32) and a second locking springs (33) coaxially arranged
with respect to the rod (12).
3. Spring lock device according to Claim 2, characterized in that the locking springs (32, 33) are provided with the same winding direction.
4. Spring lock device according to Claim 2, characterized in that the locking springs (32, 33) are provided with opposite winding directions.
5. Spring lock device according to Claim 1, characterized by comprising a protective bearing member (30, 31) of soften material, coaxially arranged
between the locking spring (16) and the rod (12).
6. Spring lock device according to Claim 5, characterized in that said bearing member comprises a plurality of elastically yielding annular elements
(30).
7. Spring lock device according to Claim 5, characterized in that said bearing member consists of at least one coil spring (31).
8. Spring lock device according to claim 1 characterized in that the control means (17) comprises a pneumatic cylinder.
9. Spring lock device according to Claim 1, characterized in that the locking spring (16) comprises parallely arranged arms (16A, 16B) longitudinally
extending to the rod (12) and in that a pneumatically actuated fork-shaped thrust member (18) having diverging facing surfaces
is provided to inwardly urge the end arms (16A, 16B) of the locking spring (16).
10. Spring lock device according to Claim 1, characterized in that the locking spring (16) comprises crossed arms (16A, 16B) longitudinally extending
to the rod (12) and in that a pneumatically actuated disk shaped thrust member (24) is provided to outwardly
urging the end arms (16A, 16B) of the locking spring (16).
1. Verriegelungsvorrichtung zum Verhindern von Axial- und/oder Drehbewegungen einer Stange
(12), mit
einem Gehäuse, das eine Kammer (11) mit Endflächen und axial ausgerichteten Führungsöffnungen
(13, 14) in den Endflächen aufnimmt;
einer Stange (12), die axial durch die Führungsöffnungen (13, 14) des Gehäuses (10)
gleitbar angeordnet ist;
zumindest einer Verriegelungsfeder (16; 32, 33) in dem Gehäuse (10), die die Stange
umschlingt, wobei diese Schraubenfeder (16; 32, 33) in entspanntem Zustand lose unterstützt
ist und einen Innendurchmesser geringfügig größer als der Umfangsdurchmesser der Stange
(12) hat; und
Steuereinrichtungen (18, 19) zum Aufwickeln der Schraubenfeder (16), sodass diese
gegen die Umfangsoberfläche der Stange (12) greift, dadurch gekennzeichnet, dass
Schwenkpunkte (23) für die Endwicklungen der Feder (16; 32, 33) an den Endflächen
der Kammer (11) vorgesehen sind, wobei diese Schwenkpunkte (23) so angeordnet sind,
dass die Wicklungen der Feder (16; 32, 33) sich frei bewegen und um eine Achse drehen
können, die orthogonal zu der Längsachse der Stange angeordnet ist.
2. Feder-Verriegelungsvorrichtung nach Anspruch 1, dadurch gekennzeichnet, dass sie zumindest eine erste (32) und eine zweite Verriegelungsfeder (33) aufweist, die
koaxial in Bezug zu der Stange (12) angeordnet sind.
3. Feder-Verriegelungsvorrichtung nach Anspruch 2, dadurch gekennzeichnet, dass die Verriegelungsfedern (32, 33) die gleiche Wicklungsrichtung aufweisen.
4. Feder-Verriegelungsvorrichtung nach Anspruch 2, dadurch gekennzeichnet, dass die Verriegelungsfedern (32, 33) entgegengesetzte Wicklungsrichtungen aufweisen.
5. Feder-Verriegelungsvorrichtung nach Anspruch 1, dadurch gekennzeichnet, dass ein schützendes Lagerelement (30, 31) aus weichem Material koaxial zwischen der Verriegelungsfeder
(16) und der Stange (12) angeordnet ist.
6. Feder-Verriegelungsvorrichtung nach Anspruch 5, dadurch gekennzeichnet, dass das Lagerelement mehrere elastisch nachgiebige Ringelemente (30) aufweist.
7. Feder-Verriegelungsvorrichtung nach Anspruch 5, dadurch gekennzeichnet, dass das Lagerelement aus zumindest einer Schraubenfeder (31) besteht.
8. Feder-Verriegelungsvorrichtung nach Anspruch 1, dadurch gekennzeichnet, dass die Steuereinrichtungen (17) einen pneumatischen Zylinder aufweisen.
9. Feder-Verriegelungsvorrichtung nach Anspruch 1, dadurch gekennzeichnet, dass die Verriegelungsfeder (60) mehrere parallel ausgerichtete Arme (16A, 16B) aufweist,
die sich in Längsrichtung der Stange (12) erstrecken, und dass ein pneumatisch betätigtes
gabelförmiges Druckelement (18) mit divergierenden gegenüberliegenden Oberflächen
vorgesehen ist, um die Endarme (16A, 16B) der Verriegelungsfeder (16) nach innen zu
drücken.
10. Feder-Verriegelungsvorrichtung nach Anspruch 1, dadurch gekennzeichnet, dass die Verriegelungsfeder (16) gekreuzte Arme (16A, 16B) aufweist, die sich längs der
Stange (12) erstrecken, und dass ein pneumatisch betätigtes scheibenförmiges Druckelement
(24) vorgesehen ist, um die Endarme (16A, 16B) der Verriegelungsvorrichtung (16) nach
außen zu drücken.
1. Dispositif destiné à empêcher le mouvement axial et/ou de rotation d'une tige (12)
comprenant :
un boîtier (10) définissant une chambre (11) ayant des faces d'extrémité, et une ouverture
de guidage alignée axialement (13, 14) dans lesdites faces d'extrémité ;
une tige (12) pouvant coulisser axialement dans lesdites ouvertures de guidage (13,
14) du boîtier (10) ;
au moins un ressort de verrouillage (16 ; 32, 33) dans le boîtier (10), encerclant
la tige (12), ledit ressort hélicoïdal (16 ; 32, 33), dans l'état non contraint, étant
supporté de manière lâche et ayant un diamètre intérieur légèrement plus grand que
le diamètre périphérique de la tige (12) ; et
un moyen de commande (18, 19) pour enrouler le ressort hélicoïdal (16) pour qu'il
adhère à la surface périphérique de la tige (12)
caractérisé en ce que des points de pivot (23) sont prévus pour les bobines d'extrémité du ressort (16
; 32, 33) dans les faces d'extrémité de la chambre (11), lesdits points de pivot (23)
étant agencés de façon à permettre aux bobines du ressort (16 ; 32, 33) de se mouvoir
et de tourner librement autour d'un axe orthogonal à l'axe longitudinal de la tige.
2. Dispositif de verrouillage à ressort selon la revendication 1, caractérisé en ce qu'il comprend au moins un premier (32) et un deuxième ressort de verrouillage (33) agencés
coaxialement par rapport à la tige (12).
3. Dispositif de verrouillage à ressort selon la revendication 2, caractérisé en ce que les ressorts de verrouillage (32, 33) présentent le même sens d'enroulement.
4. Dispositif de verrouillage à ressort selon la revendication 2, caractérisé en ce que les ressorts de verrouillage (32, 33) présentent des sens d'enroulement opposés.
5. Dispositif de verrouillage à ressort selon la revendication 1, caractérisé en ce qu'il comprend un élément de roulement protecteur (30, 31) en matériau mou, agencé coaxialement
entre le ressort de verrouillage (16) et la tige (12).
6. Dispositif de verrouillage à ressort selon la revendication 5, caractérisé en ce que ledit élément de roulement comprend une pluralité d'éléments annulaires déformables
élastiquement.
7. Dispositif de verrouillage à ressort selon la revendication 5, caractérisé en ce que ledit élément de roulement est constitué d'au moins un ressort hélicoïdal (31).
8. Dispositif de verrouillage à ressort selon la revendication 1, caractérisé en ce que le moyen de commande (17) comprend un vérin pneumatique.
9. Dispositif de verrouillage à ressort selon la revendication 1, caractérisé en ce que le ressort de verrouillage (16) comprend des bras parallèles (16A, 16B) qui s'étendent
longitudinalement jusqu'à la tige (12) et en ce qu'un élément de poussée fourchu (18) actionné pneumatiquement et ayant des surfaces
frontales divergentes est prévu pour pousser vers l'intérieur les bras d'extrémité
(16A, 16B) du ressort de verrouillage (16).
10. Dispositif de verrouillage à ressort selon la revendication 1, caractérisé en ce que le ressort de verrouillage (16) comprend des bras croisés (16A, 16B) qui s'étendent
longitudinalement jusqu'à la tige (12) et en ce qu'un élément de poussée en forme de disque (24) actionné pneumatiquement et ayant des
surfaces frontales divergentes est prévu pour pousser vers l'extérieur les bras d'extrémité
(16A, 16B) du ressort de verrouillage (16).