TECHNICAL FIELD OF THE INVENTION

The present invention relates to a steady rest according to the preamble of claim 1 for firmly supporting an elongated workpiece. The invention also relates to a machining tool comprising such a steady rest and use of such a steady rest for firmly supporting a workpiece.

When performing cutting machining, especially turning, of an elongated workpiece, cutting forces occur far from the positions where the workpiece is clamped to the chuck and support stud of the machining tool. These forces cause deflection of the workpiece, which in its turn leads to impaired precision in the machining. To counteract the deflection of the workpiece and increase the stability, a steady rest can be mounted to the machining tool frame and used to firmly support the workpiece during the machining operation.

The steady rest prevents radial movement of the workpiece by means of three support rollers. A lower support roller is rotatably mounted to a middle steady rest arm of the steady rest, wherein this middle steady rest arm is moveable in its axial direction by means of a hydraulic or pneumatic cylinder. The other two support rollers are rotatably mounted to a respective one of two outer steady rest arms, which are configured to be moved in conjunction with the middle steady rest arm in such a way that the centre of the workpiece can be held in a fixed position by the steady rest regardless of the diameter of the workpiece. This allows the steady rest to be mounted centered against a workpiece, wherein the workpiece can be replaced with workpieces of other diameters without the need to center the steady rest again. Cam arrangements are often used to synchronize the movements of the three steady rest arms and thereby the movements of the three support rollers towards the centre.

BACKGROUND ART A conventional steady rest is described in DE 3543806 A. One problem with steady rests of this type is that they have a limited grip area, which means that for instance a component manufacturer using lathes and other machining tools needs to have steady rests of many different sizes to be able to provide the machining tool with a steady rest suitable for the dimensions of the workpiece to be processed in each specific case. This implies large investments for the manufacturer and a significant set-up time between different cutting operations. Another previously known steady rest is shown in US 2016/0332271 A1. This steady rest provides a larger grip area as compared to the steady rest described in DE 3543806 A, which is achieved inter alia by providing steady rest arms with a greater length and providing each outer steady rest arm with two cam rollers cooperating with two associated cam surfaces on the middle steady rest arm.

There is a constant strive of improving conventional steady rests, especially by increasing the grip area thereof. At the same time, the housing of the steady rests should be as compact, i.e. take up as little space, as possible to be able to fit in different machining tools. Other important factors are of course the performance of the steady rest, namely the ability of the steady rest to firmly support and hold a workpiece, as well as the cost and complexity of producing the steady rest. SUMMARY OF THE INVENTION

The object of the present invention is to provide a steady rest of the type defined in the introduction that is improved in at least some aspect as compared to previously known steady rests.

According to the invention, this object is achieved by means of a steady rest having the features defined in claim 1. The steady rest of the present invention comprises:

- a stationary housing,

- a middle steady rest arm arranged in the housing,

- a power means configured to move the middle steady rest arm with respect to the housing in an axial direction of the middle steady rest arm towards an elongated workpiece to be supported,

- two outer steady rest arms pivotally connected to the housing around a respective pivot axis that is perpendicular to said axial direction and each having a lever rigidly connected thereto, and

- an arrangement configured to provide a separate driving connection for each of the outer steady rest arms with the middle steady rest arm by acting on said lever, each driving connection comprising two rollers configured to roll along an associated cam acting as a guide track as the middle steady rest arm is moved in the axial direction for pivoting the outer steady rest arms towards each other and towards the workpiece, wherein the two rollers of each driving connection are arranged to roll on the associated cam for pivoting the outer steady rest arm associated with the driving connection in separate consecutive portions of the movement of the middle steady rest arm towards the workpiece.

The middle steady rest arm has two lateral extensions, each of which having said two rollers of one of the driving connections arranged thereon. Each driving connection has two cams acting as guide tracks arranged on the lever of the outer steady rest arm associated with the driving connection, wherein a first one of the two rollers of the driving connection is configured to roll along a first one of the two cams of the driving connection in a first portion of the movement of the middle steady rest arm in said axial direction towards the workpiece and a second one of the two rollers of the driving connection is configured to roll along a second one of the two cams of the driving connection in a second portion of said movement following upon the first portion.

Such driving connections between the middle steady rest arm and the outer steady rest arms enable increased grip area of the steady rest as compared to that of previously known steady rests, while maintaining the compactness of the steady rest, i.e. without increasing the outer dimensions of the housing of the steady rest. Alternatively, the housing dimensions may be reduced, i.e. the steady rest may be made more compact, while maintaining the grip area thereof. This is achieved by the effective gearing of the driving connections provided by the two rollers of each driving connection enabling a great leverage and mobility of the outer steady rest arms while only requiring a small free space in the housing.

A steady rest with an increased grip area enables a reduction of the number of steady rests of different sizes needed at for instance a component manufacturer, as the total dimension span needed can be covered by a smaller number of steady rests. By increasing the grip area, workpieces of a broader variety of dimensions can also be handled by smaller steady rests, which means that the machining possibilities in smaller machining tools with room only for smaller steady rests can be expanded. From a production economics perspective, also the availability of the machining tool can be increased if the performance of the steady rest is improved. This is due to the fact that fewer replacements of steady rests are required as a result of the increased grip area, i.e. set-up times can be reduced between different production series. According to an embodiment of the invention, the first and second cams of each driving connection are arranged on the lever of the outer steady rest arm associated with the driving connection such that the first cam of the driving connection is closer to the middle steady rest arm than the second cam of the same driving connection, at least at an outer end of the lever remote from the pivot axis of the outer steady rest arm and preferably along the entire extensions of the guide tracks of the cams. According to another embodiment of the invention, the first roller of each driving connection is arranged closer to a centre axis of the middle steady rest arm than the second roller of the same driving connection. According to another embodiment of the invention, the smallest distance between the axis of rotation of the second roller and a centre axis of the middle steady rest arm exceeds the smallest distance between the axis of rotation of the first roller and said centre axis by at least 10% or at least 20% or at least 30% or at least 40%.

According to another embodiment of the invention, the first roller of each driving connection is arranged at a distance from and before the second roller of the same driving connection as seen in said axial direction of movement of the middle steady rest arm.

According to another embodiment of the invention, the distance between the axis of rotation of the first roller and the axis of rotation of the second roller as seen in said axial direction of movement of the middle steady rest arm exceeds 5%, or 10%, of the total length of the middle steady rest arm in said axial direction.

According to another embodiment of the invention, the first and second rollers of each driving connection are arranged on the respective lateral extension mutually offset in the direction of the extension of their axes of rotation, wherein the first and second cams of the same driving connection are arranged on the associated lever correspondingly offset in said direction and configured to be contacted by the first roller and the second roller, respectively, by movement of the middle steady rest arm in the axial direction.

According to another embodiment of the invention, the two lateral extensions of the middle steady rest arm are integral parts of the middle steady rest arm, i.e. formed in one piece with the remaining part of the middle steady rest arm.

According to another embodiment of the invention, each one of the middle and outer steady rest arms is provided with a roller at its outer free end configured to abut against a workpiece when the workpiece is firmly supported by the steady rest.

According to another embodiment of the invention, the power means comprises a pneumatic or hydraulic cylinder operable to move the middle steady rest arm in the axial direction of the middle steady rest arm.

The invention also relates to a machining tool provided with a steady rest according to the invention and use of such a steady rest.

Further advantages as well as advantageous features of the invention will appear from the description following below. BRIEF DESCRIPTION OF THE DRAWINGS

With reference to the appended drawings, below follows a specific description of an embodiment of the invention cited as an example.

In the drawings: Fig 1 is perspective view of a steady rest according to an embodiment of the invention

Fig 2 is perspective view from above of the steady rest of Fig 1 shown with a front housing wall removed and with the middle steady rest arm in a fully retracted position,

Fig 3 is a perspective view from above of the middle steady rest arm and one of the outer steady rest arms of the steady rest shown in Fig 1 ,

Fig 4 is a view of the steady rest corresponding to Fig 2 with the middle steady rest arm in a fully advanced position, Fig 5 is a front view of the steady rest of Fig 1 shown with the front housing wall removed and with the middle steady rest arm close to a fully retracted position while clamping and supporting a workpiece with a large diameter,

Fig 6 is a view corresponding to Fig 5 with the middle steady rest arm moved towards a workpiece with a slightly smaller diameter for clamping and supporting this workpiece by the steady rest,

Fig 7 is a view corresponding to Fig 6 with the middle steady rest arm moved further towards a workpiece with an even smaller diameter for clamping and supporting this workpiece by the steady rest,

Fig 8 is a view corresponding to Fig 7 with the middle steady rest arm moved further towards a workpiece with an even smaller diameter for clamping and supporting this workpiece by the steady rest, Fig 9 is a view corresponding to Fig 8 with the middle steady rest arm moved further towards a workpiece with an even smaller diameter for clamping and supporting this workpiece by the steady rest,

Fig 10 is a view corresponding to Fig 9 with the middle steady rest arm moved further towards a workpiece with an even smaller diameter for clamping and supporting this workpiece by the steady rest, and

Fig 11 is a view corresponding to Fig 10 with the middle steady rest arm in a fully advanced position while clamping and supporting a workpiece with a small diameter. DETAILED DESCRIPTION OF AN EMBODIMENT OF THE INVENTION

A steady rest 1 according to an embodiment of the invention is illustrated in the appended figures 1-11 and will now be described while at the same time referring to all these figures.

The steady rest 1 is intended to be mounted on a machining tool, such as a lathe, for clamping and firmly supporting and centering an elongated workpiece 2 during machining thereof in the tool. Such an elongated workpiece may for example be a steel rod or shaft to be rotated by the lathe while material is removed by a non-rotary tool bit which is brought into contact with the rotating workpiece. Although the typical workpiece of this type is long and circular cylindrical, the steady rest according to the invention may also be used to hold shorter rod-like workpieces as well as non- cylindrical ones, such as a hexagonal cylinder.

The steady rest 1 comprises a housing 3 formed by two interconnected housing parts 3a, 3b. In Figs 2-11 , the steady rest 1 is shown with one of the housing parts removed. The housing part 3b that has been omitted in Figs 2-11 constitutes a detachable front wall of the housing 3. The housing 3 is configured to be fixedly mounted on the lathe in a position in which the steady rest 1 is centered with the lathe, i.e. the steady rest is arranged in a position in which the centre of the gripping area thereof is aligned with the centre of the workpiece support arrangement, including chuck and support stud, of the lathe.

The steady rest 1 comprises a middle steady rest arm 4 (in the following referred to as middle arm) and two outer steady rest arms 5, 6 (in the following referred to as outer arms) arranged in the housing 3. Each one of the middle and outer arms 4, 5, 6 is at its outer free end provided with a freely rotatable support roller 4a, 5a, 6a configured to abut against the workpiece when the workpiece is firmly supported by the steady rest. The steady rest 1 is configured to grip the workpiece 2 by the three rollers 4a, 5a,

6a and hold it with its centre in a fixed position while allowing it to rotate by rolling against the rollers 4a, 5a, 6a during a machining operation. The steady rest 1 further comprises a power means configured to move the middle arm 4 with respect to the housing 3 in an axial direction of the middle arm 4 towards a workpiece to be gripped, i.e. in the longitudinal direction of the middle arm 4. In the illustrated embodiment, the power means comprises a pneumatic or hydraulic cylinder 8 and a fluid pressure amplifier 7, wherein pressurized fluid is feed to the pneumatic or hydraulic cylinder 8 via the fluid pressure amplifier 7 in order to effect a movement of the middle arm 4 in its axial direction. The cylinder 8 comprises an actuation piston, which is moveable in the axial direction of the cylinder 8 and connected to the middle arm 4 via a piston rod. Thus, the middle arm 4 is moveable under the effect of the cylinder 8 in a movement direction corresponding to the axial direction of the middle arm. The two outer arms 5, 6 are pivotally connected to the housing 3 through a respective hinge member 5b, 6b and thereby allowed to pivotally move around pivot axes that are perpendicular to said axial direction. The outer arms 5, 6 are arranged on opposite sides of the middle arm 4, wherein a first one 5 of the outer arms is pivotable in relation to the middle arm 4 about a first pivot axis located on a first side of the middle arm 4 and the other outer arm 6 is pivotable in relation to the middle arm 4 about a second pivot axis located on an opposite second side of the middle arm 4. Said first pivot axis is parallel to said second pivot axis. Each outer arm 5, 6 has a lever 5c, 6c, which is rigidly connected to the associated outer arm 5, 6 and extends from the hinge member 5b, 6b of the associated outer arm 5, 6 away from the workpiece supporting part of the associated outer arm 5, 6.

The steady rest 1 further comprises an arrangement configured to provide a separate driving connection for each one of the outer arms 5, 6 with the middle arm 4 by acting on the respective lever 5c, 6c of the outer arms. The arrangement comprises for each driving connection a first roller 9a, 10a and a second roller 9b, 10b arranged on a lateral extension 11a, 11 b of the middle arm 4. Thus, the first and second rollers 9a, 9b of a first one of the driving connections are arranged on a first one 11 a of the lateral extensions and the first and second rollers 10a, 10b of the other driving connection are arranged on the other lateral extension 11 b. The lateral extensions 11a, 11 b are arranged opposite each other on opposite sides of a centre axis of the middle arm 4. In the example shown in the drawings, the lateral extensions 11a, 11 b are integral parts of the middle arm 4. However, the lateral extensions could as an alternative be separate parts or parts of the same separate body rigidly secured to the remaining part of the middle arm. The arrangement further comprises for each driving connection a first cam 12a, 13a and a second cam 12b, 13b with guide tracks/cam surfaces associated with the first roller 9a, 10a and the second roller 9b, 10b, respectively, wherein the first and second cams of each driving connection are arranged on the lever 5c, 6c of a respective one the outer arms 5, 6. The first and second rollers 9a, 10a, 9b, 10b of each driving connection are arranged on the associated lateral extension 11a, 11 b mutually offset in the direction of the extension of their axes of rotation and the first and second cams 12a, 13a, 12b, 13b of the same driving connection are arranged on the associated lever 5c, 6c correspondingly offset in said direction, i.e. aligned in depth with the first roller and the second roller, respectively.

The first cam 12a, 12b of each driving connection is arranged on the associated lever 5c, 6c to be closer to the middle arm 4 than the second cam 13a, 13b of the same driving connection at an outer end thereof remote from the pivot axis of the respective outer arm and along the entire extensions of the guide tracks of the cams 12a, 12b, 13a, 13b.

Each driving connection has the first roller 9a, 10a arranged closer to the centre axis of the middle arm 4 than the second roller 9b, 10b, preferably such that the smallest distance between the axis of rotation of the second roller 9b, 10b and the centre axis of the middle arm 4 exceeds the smallest distance between the axis of rotation of the first roller 9a, 10a and said centre axis by at least 10%, at least 20%, at least 30% or at least 40% and preferably by between 40 and 50%. Moreover, each driving connection has the first roller 9a, 10a arranged at a distance from and before the second roller 9b, 10b as seen in said axial direction of movement of the middle arm 4, preferably such that the distance between the axis of rotation of the first roller 9a, 10a and the axis of rotation of the second roller 9b, 10b as seen in said axial direction of movement of the middle arm 4 exceeds 5%, or exceeds 10%, and is preferably between 10 and 20%, more preferably between 10 and 15%, of the total length of the middle arm 4 in said axial direction. The above-mentioned arrangement converts the axial movement of the middle arm 4 into pivoting movements of the outer arms 5, 6 towards each other and towards a workpiece 2 to be gripped and supported by the steady rest 1 by the rollers 9a, 9b, 10a, 10b on the middle arm 4 contacting and rolling along the cams 12a, 12b, 13a, 13b on the respective lever 5c, 6c when the middle arm 4 is moved in the axial direction towards the workpiece 2, which will push the levers 5c, 6c of the outer arms 5, 6 away from each other and thereby move the rollers 5a, 6a at the outer ends of the outer arms towards each other. More specifically, the two rollers 9a, 9b, 10a, 10b of each driving connection are arranged to roll on a respective cam 12a, 12b, 13a, 13b for pivoting the associated outer arm 5, 6 in separate consecutive portions of the movement of the middle arm 4 towards the workpiece 2, wherein the first roller 9a, 10a is configured to roll along a first cam 12a, 12b in a first portion of the movement of the middle arm 4 in said axial direction towards the workpiece 2 and the second roller 9b, 10b is configured to roll along a second cam 13a, 13b in a second portion of said movement following upon the first portion so that the respective lever 5c, 6c is at first pushed by the first roller 9a, 10a in the first portion of the movement (see Figs 5-9) of the middle arm 4 towards the workpiece and then by the second roller 9b, 10b in the second portion of said movement (see Figs 7-11). As is seen in and understood from Figs 5-11 these two portions of the movement may partly overlap each other and both the first roller 9a, 10a and the second roller 9b, 10b of each driving connection may be in contact with and roll along the associated cam 12a, 12b, 13a, 13b over a large part of the movement of the middle arm.

Figs 5-11 illustrate a closing operation of the steady rest 1 , i.e. an operation of moving the three arms 4, 5, 6 of the steady rest towards a workpiece 2 to be gripped and firmly held by the steady rest. Even though workpieces of different diameters are shown in these drawings, one could imagine that the arms 4, 5, 6 of the steady rest are moved from an open position (see Figs 2 and 5) to a closed position for gripping a workpiece with a very small diameter (see Fig 11 ). From the open position shown in Figs 2 and 5, the movement of the middle arm 4 in the axial direction towards the workpiece is initiated and the first rollers 9a, 10a on the middle arm 4 roll along the first cams 12a, 12b on the levers 5c, 6c while pushing the levers away from each other and thereby moving the rollers 5a, 6a at the free ends of the outer arms 5, 6 towards each other (see Fig 6). By further movement of the middle arm 4 in said axial direction, the second rollers 9b, 10b will come into contact with the associated second cams 13a, 13b (see Fig 7) and roll along these cams so that each lever 5c, 6c is pushed by both rollers 9a, 9b, 10a, 10b of the associated driving connection in a middle portion of the movement (see Figs 7-9). In the last portion of the movement of the middle arm 4 in said direction, the first rollers 9a, 10a have moved past an end of the associated first cams 12a, 12b and only the second rollers 9b, 10b are in contact with the levers 5c, 6c (see Figs 10-11 ) and push the levers towards the end position and then hold them in the end position. In the end position, the levers 5c, 6c are held as far away from each other as possible and thereby the rollers 5a, 6a at the free ends of the outer arms 5, 6 are held close to each other for gripping and supporting a workpiece 2 with a very small diameter (see Fig 11). An opening operation of the steady rest 1 may be imagined by looking at the figures from Fig 11 to Fig 5 and is effected by retracting the power driven middle arm 4 under the effect of the pneumatic or hydraulic cylinder 8 and thereby pulling the levers 5c, 6c towards each other. By pulling the levers 5c, 6c towards each other, the rollers 5a, 6a at the free ends of the outer arms 5, 6 are pivoted away from each other. The retracting movement of the middle arm 4 is, in a conventional manner, converted into a pivoting movement of the levers 5c, 6c about the pivot axis of the respective outer arm 5, 6 through two connection elements 20 (see Figs 2 and 4). In the illustrated embodiment, the connection elements 20 are at a first end pivotally connected to a respective one of the lateral extensions 11a, 11 b on the middle arm 4, wherein each lever 5c, 6c is provided with a pin 21 that is fixed to the lever and slidably received in a guide groove 22 in the connection element 20 associated with the lever 5c, 6c. The connections elements 20 have been omitted in Fig 3 and in Figs 5-11.

The arrangement with two rollers 9a, 9b, 10a, 10b and two cams 12a, 12b, 13a, 13b for each driving connection between the middle arm 4 and the outer arms 5, 6 enables a reduction of the length of the levers 5c, 6c of the outer arms and thereby a reduction of the dimensions of the housing 3, while maintaining the length over which the middle arm 4 impacts the levers 5c, 6c of the outer arms 5, 6 and thereby maintaining the grip area of the more compact steady rest 1. Conversely, this arrangement also enables an increased grip area while maintaining the outer dimension of the housing 3.

Hence, a steady rest 1 with a more compact design and/or an increased grip area as compared to previously known steady rests of this type is provided by the present invention, and especially by having the two rollers 9a, 9b, 10a, 10b of each driving connection arranged on the associated lateral extension 11a, 11 b on the middle arm 4 in such a way that the first roller 9a, 10a is located as near the axis of rotation of the associated outer arm 5, 6 as possible in the fully retracted position of the middle arm 4 (without hitting the housing 3 in the fully advanced position of the middle arm 4) to start acting on the first cam 12a, 12b as soon as the movement of the middle arm in the axial direction towards the workpiece is initiated and by having the second roller 9b, 10b positioned at a significant distance from the first roller 9a, 10a (without hitting the housing 3 in the fully retracted position of the middle arm 4) so as to achieve a good force distribution in and thereby leverage on the associated outer arm 5, 6. The invention is of course not in any way restricted to the embodiments described above. On the contrary, many possibilities to modifications thereof will be apparent to a person with ordinary skill in the art without departing from the scope of the invention as defined in the appended claims.

A component being “pivotally connected to” another component means that there is some type of hinge arrangement directly or indirectly interconnecting these components.

Where it is stated that a component is “connected” to or “interconnected” with another component, this is to be interpreted such that the components are interconnected directly, or indirectly by an intermediate component, unless otherwise stated.