Traction head for metal bar cropping benches

The present invention relates to a traction head for metal bar cropping benches according to the preamble of claim 1.

Conventionally, in the field of building, cropping benches are used which automatically crop to size the metal bars used to form reinforcement frames and the like. In particular, cropping benches are preferably used, because of their greater versatility, if it is necessary to meet different production orders, i.e., to treat bars of different sizes, as an alternative to conventional cropping lines, which are more powerful but more limited from the functional point of view.

Cropping benches are provided, at one end, with a traction head for the metal bars. The bars are usually advanced by pairs of grooved wheels, which are actuated along axes which are transverse to the advancement direction and between which said bars are clamped.

The traction head is provided with means which measure the advancement of the bars to be cut, actuating the cropping elements.

According to a known solution, the means for measuring the advancement of the bars to be cropped include a sensor of the type commonly known as encoder, associated with fixed dimensional checking elements which correct any errors in the measurement performed up to that point.

This solution provides for great precision in measurement but is relatively complicated to implement and is therefore expensive.

Another known solution provides for locators movable along the measurement axis. The locators are positioned by mechanical elements, such as chains and the like; the dimension is measured by sensors such as encoders and the like. This solution, too, achieves high precision but is very complicated and expensive and has the drawback of requiring a certain amount of time to pass from one dimension to the next.

A further known solution which is more widespread in practice provides for the use of an encoder associated with a measurement wheel which works in series with said traction wheels. However, this solution does not ensure precise measurement of the advancement of the bars, particularly in the case of bars having ridges such as those commonly used for reinforced concrete.

The ridges in fact cause vibrations in the measurement wheel which cause loss of grip, with a consequent measurement error of the encoder. This problem is obviously increased in the case of large-diameter bars fed at high speed.

A device having features as comprised in the preamble of the claims 1 and 6, is known from the document EP-A-0 326 001.

A principal aim of the present invention is to solve the above problem by providing a traction head for cropping benches which allows to precisely and continuously control the advancement of metal bars to be cropped.

Within the scope of this aim, an object of the present invention is to provide a traction head which is simple in concept, safely reliable in operation, versatile in use, and relatively inexpensive.

This aim and this object and others which will become apparent hereinafter are achieved, according to the present invention, by a traction head and bar advancement measuring means which have the features set forth in claims 1 and 6.

A method, according to the invention, for measuring bar lenghts, is characterized by the steps set forth in claim 10.

The features of the invention will become apparent from the following detailed description of a preferred embodiment of the traction head, illustrated only by way of non-limitative example in the accompanying drawings, wherein: <ul id="ul0001" list-style="none" compact="compact"><li>figure 1 is a longitudinal vertical sectional view of the traction head according to the present invention;</li><li>figure 2 is a horizontal sectional view of the measurement wheels of the traction head, taken along the plane II-II of figure 1.</li></ul>

With particular reference to the above figures, the reference numeral 1 generally designates the traction head, which is arranged at one end of a metal bar cropping bench, not illustrated in the drawing.

The head 1 has traction means for causing the advancement of the metal bars to be cropped, the traction means having a plurality of pairs of wheels actuated along axes which are transverse to the advancement direction A; the metal bars to be cropped are clamped between said pairs of wheels.

More specifically, the traction means comprise two first pairs of wheels 2, 4 and 3, 5 respectively referenced as lower and upper pairs. The lower wheels 2 and 4 are rotatably supported by a fixed frame 6 and are rotationally actuated so as to subject the metal bars to traction. The upper wheels 3 and 5 ensure an adequate clamping pressure and are supported, so that they can rotate freely, by a supporting frame 7 oscillatable about a pivot 28 and pivoted to a lever arm 8. The lever arm 8 is articulated, on a vertical plane lying longitudinally with respect to the direction A, about a pivot 9 through the actuation of an actuator 10 which is in turn pivoted to the frame 6.

In practice, the lower wheels 2 and 4 are driving wheels, whilst the upper wheels 3 and 5 act as abutments.

Downstream of the traction wheels 2, 3 and 4, 5 along the advancement direction A, there are provided two further pairs of wheels 11, 13 and 12, 14, referenced to as lower and upper wheels respectively. The lower wheels 11 and 13 are rotatably supported by the fixed frame 6, are arranged in series on the same horizontal plane as the traction wheels 2 and 4, and are actuated so as to be driving wheels like wheels 2 and 4. The wheels 2, 4 and 11, 13 are in fact connected to driving elements, not shown, by adapted transmission elements.

The upper wheels 12 and 14, meant to measure the advancement of the bar to be cropped, are supported so that they can rotate freely by a supporting frame 15 oscillatable about a pivot 29 and pivoted to a lever arm 16 which is substantially mirror-symmetrical with respect to lever 8; the lever 16 is articulated, on a vertical plane lying longitudinally with respect to the direction A, about a pivot 17 through the actuation of an actuator 18, which is in turn pivoted to the frame 6.

The measurement wheels 12 and 14, made of metallic materials, are appropriately knurled so as to prevent slippage of the bars to be cropped, compromising the measurement.

As shown in detail in figure 2, the first measurement wheel 12 is supported at the end of a shaft 19 which is mounted so that it can rotate freely, by means of rolling bearings 20, 21, and 27, in appropriate seats formed in the supporting frame 15. A rigid radial ball bearing 21, adapted to detect the advancement of the bars to be cropped, as provided for example by the company SKF as part number 6206/VU1028, and provided with a resolution of 64 pulses per turn, or other sensors such as encoders and the like, is associated with the shaft 19.

The second measurement wheel 14 is in turn supported at the end of a shaft 22 which is mounted, so that it can rotate freely by means of rolling bearings 23, 30 in a corresponding seat formed in the frame 15, with an axis which is parallel to the shaft 19 of the first measurement wheel 12.

Shafts 19 and 22 of the measurement wheels 12 and 14 are connected one another by means of a transmission chain or belt 24 appropriately provided with teeth and winding around respective pulleys 25 and 26 which are keyed on shafts 19 and 22. The pulleys 25 and 26 have the same diameter, so as to provide a unit transmission ratio.

The operation of the traction head can be easily desumed from the above description.

The metal bars to be cut are inserted in the traction head 1 above the driving wheels 2, 4 and 11, 13 and then clamped elastically by the contrast wheels 3, 5 and by the measurement wheels 12, 14 through the actuation of the corresponding actuators 10, 18; preferably, actuators 10, 18 are constituted by pneumatic cylinders adapted to ensure an elastic clamping.

The traction wheels actuate the advancement of the metal bars to be cropped in the direction A; the measurement wheels 12 and 14, turned by the advancement of said metal bars, measure the advancement of the bars, actuating, at the appropriate time, the cropping elements of the bench.

The measurement is in fact provided by the bearing 21 which senses the advancement of the bars to be cropped, which is mounted on the shaft 19 of the first measurement wheel 12. The sensor bearing 21, however, also responds to the rotation of the second measurement wheel 14, since the shaft 22 of the second measurement wheel is connected to shaft 19 by the belt transmission 24.

In practice, this allows to double the bar advancement reading points, thus preventing any loss of grip which might occur on one of the measurement wheels from affecting the reading of the sensor bearing 21, thus compromising the precision of the measurement.

In other words, if the first measurement wheel 12 loses grip on the bar, traction of the shaft 19 whereon the sensor bearing 21 is mounted is in any case ensured by the second measurement wheel 14, which is connected to shaft 19 by the belt transmission 24.

The traction head according to the invention therefore allows to continuously control the advancement of the metal bars, even if the bars have large ridges, ensuring very precise operation.

The traction head is capable, in particular, of ensuring a high operating speed without compromising bar measurement precision.

The traction head is also provided in a manner which is constructively simple, so as to achieve a proportional reduction in production and operation costs.

In the practical embodiment of the invention, the materials employed, as well as the shapes and the dimensions, may be any according to requirements.

Where technical features mentioned in any claim are followed by reference signs, those reference signs have been included for the sole purpose of increasing the intelligibility of the claims and accordingly, such reference signs do not have any limiting effect on the interpretation of each element identified by way of example by such reference signs.