This invention relates to a gripper feeder for metal strip.

Metal strip feeders are known for those presses and machines in which the strip is subjected to particular predetermined operations.

A known type of feeder comprises a pair of grippers for engaging the metal strip to be advanced, members for moving the grippers in a direction parallel to the axis of said strip and in the opposite direction, and means for independently operating said grippers such that while the gripper which moves in the direction of advancement of the strip is activated, that which moves in the opposite direction is deactivated.

In particular the mover members consist of a bar presenting two portions threaded in opposite directions which engage a threaded bush provided on a gripper of each pair, a motor being provided, powered alternately in the two directions of rotation.

These known feeders have however the drawback of advancing the strip intermittently. This intermittent advancement is due on the one hand to the advancement pitch of the grippers and on the other hand to the operation pitch. In this respect, on the basis of an advancement pitch of 1 m and an operation pitch of 2.5 m, the advancement of the strip has to be halted every metre to allow"gripper changeover"and enable the strip to be halted every 2. 5 m as required by the operating cycle.

According to the invention, this drawback is eliminated by a gripper feeder for metal strip as described in claim 1.

A preferred and a modified embodiment of the invention are described in detail hereinafter with reference to the accompanying drawings, in which :

Figure 1 is a side view of a first embodiment of a gripper feeder according to the invention, Figure 2 is a cross-section therethrough on the line ll-ll of figure 1, Figure 3 is a plan view thereof, Figure 4 is a plan view of a second embodiment, Figure 5 is a side view thereof.

As can be seen from the figures, the gripper feeder for metal strip according to the invention comprises, in the embodiment shown in Figures 1 to 3, a base 2 on which two linear motors 4, 4'are mounted. Each linear motor 4,4'comprises a stator 6, 6'and a carriage 8,8'supporting a gripper 10,10'.

A single stator could also be used, on which the two carriages slide independently.

Each gripper 10,10'comprises a fixed jaw 12,12'rigid with the carriage 8,8', and a movable jaw 14,14'moved relative to the corresponding fixed jaw 12, 12'by a pneumatic actuator 16,16'of vertical axis.

On the base there are also mounted transverse guides 16, along which carriages 20 slide supporting rollers 22 of vertical axis having in their lateral surface a groove for engaging and guiding the longitudinal edge of the metal strip to be advanced.

The carriages 20 are moved along the respective guides by operating handwheels 26.

The invention also comprises a control centre for controlling the various constituent elements of the feeder, such as the pneumatic jaw actuator, the linear motors etc.

The operation of the feeder in this embodiment is as follows :

the machine is firstly adjusted to adapt it to the width of strip to be fed; this adjustment involves operating the actuators which control the distance between the grippers, and then the actuators which control the distance between the rollers 22.

Having undergone this preliminary adjustment, the feeder is ready to operate, assuming that the initial configuration is that in which the carriages 8, 8'are as close together as possible, with the carriage 8 moving in the strip advancement direction, the jaws 12 and 14 closed to grip the strip, the carriage 8'moving in the opposite direction to the strip advancement direction, and the jaws 12', 14'open (see Figure 3). Following activation of the stator 6 the carriage 8 moves in the direction indicated by the arrow 27 in figure 3 with the carriage 8'moving at the same time in the direction indicated by the arrow 28 in the same figure, following activation of the stator 6'.

Because of the presence of the two separate motors 4,4'and the particular operating cycle set by the control centre, the two carriages can be advanced not only with different speeds but also with variable speed, so that while the carriage 8 always moves at constant speed towards its front end-of- travel position, the other carriage 8'moves at greater speed than the carriage 8 to reach its rear end-of travel position, then reverses its direction and attains the same advancement speed as the other carriage 8, then before this reaches its front end-of-travel position, i. e. before the jaws 12,14 loosen their grip, it intervenes with its jaws 12', 14'to grip the metal strip and continue to advance it in a virtually continuous manner.

The carriage 8'operates in a like manner, in that after reaching its front end-of-travel position, it reverses its travel direction, attains the speed of the other carriage 8 and arranges its jaws to grip the metal strip.

From the aforegoing it is apparent that the feeder of the invention presents numerous advantages, and in particular: - it achieves high operating speed by eliminating the pause time for gripper changeover, - it is more reliable because of the presence of the linear motors, which result not only in a quiet machine but also in simpler construction as those guides which were previously required for carriage advancement are now incorporated into the motor.

In another embodiment (not shown in the drawings) two pairs of linear motors positioned side by side on each section are provided. This embodiment, of so-called"electric tree"type, is particularly advantageous for very wide strip.

In the embodiment shown in figure 4 the feeder comprises two electric motors 30,30', the shafts of which are rigidly connected to two threaded rods 32,32'engaging threaded bushes 34,34'provided on carriages 36,36' supporting the grippers 38, 38'.

The carriages are rigid with two slides 40,40'slidable along longitudinal guide rails 42,42'.

The operation of the feeder of this embodiment is substantially similar to the preceding in that with the electric motors separately powered, one pair of grippers can be driven in one direction and the other pair of grippers in the other direction, as in the aforedescribed case.