BRAKING DEVICE POSITIONABLE ON TEST BENCHES OF CORRECT OPERATION OF INDUSTRIAL SCREWDRIVERS

Abstract

Braking device inserted in a test bench (2) for checking the correct operation of industrial screwdrivers, wherein the braking simulates a tightening operation of such screwdriver, comprising a container body (1) on the top of which a coupling (11) protrudes, suitable for coupling with the head (3) of the screwdriver to be tested, said coupling (11) being connected, by means of a shaft (12), to a braking unit (13), an electronic torque and angle detector (14) of the shaft rotation (12). Such braking unit (13) comprises a plate (14), rotated by the screwdriver, which is braked by suitable friction surfaces (15) moved towards the plate by the movement of an actuator; the movement of such actuator is performed by means of at least one electronically controlled piezoelectric element (17).

Claims

1. Braking device provided in a bench (2) to check the correct operation of industrial screwdrivers, wherein the braking simulates a tightening operation of said screwdriver, comprising a container body (1) on the top of which a coupling (11) protrudes, suitable for coupling with the head (3) of the screwdriver to be tested, said coupling (11) being connected, by means of a shaft (12), to a braking unit (13), an electronic torque and angle detector (14) of the shaft rotation (12), said braking unit (13) comprises a plate (14), rotated by the screwdriver, which is braked by suitable friction surfaces (15) moved towards the plate by the movement of an actuator, characterized in that the movement of said actuator is realized by at least one electronically controlled piezoelectric element (17).

2. Braking device according to claim 1, wherein the actuator is placed below the plate and pushes upwards the friction surfaces (15) to the lower surface of said plate, while on the upper surface of the plate contrast surfaces (16) are provided, which cooperate with the friction ones to brake the plate.

3. Braking device according to claim 1, wherein the piezoelectric element is placed in a housing and expands itself when subjected to an electric current, thus lifting upwards a lifting plate (18) which in turn pushes such friction surfaces, said plate moving along guides located on the inner surfaces of the container body (1).

4. Braking device according to claim 1, wherein the top of the actuator (17) lifts a cap (19), abutting the lower surface of the lifting plate (18) in a single point of contact.

5. Braking device according to claim 1, wherein the actuator comprises a plurality of piezoelectric elements placed one on the other, so as to increase the total stroke of the actuator, adding up the effects of each element.

6. Braking device according to claim 2, comprising means for compensating the clearance due to production tolerances and consumption of the lining of the friction surfaces positioned near the base of the container body (1) and including a rotating plate (20) moved by a suitable motor and a disk (21), coupled each other, said disk moving vertically and going to abut with its flat upper surface on the base of the actuator, the upper surface of the plate and the bottom of the disk being shaped in such a way that when the rotary plate driven by the motor inclined surfaces of the plate and of the disc coming into contact each other, they lift said disc upwards, thus raising the actuator upwards.

7. Braking device according to claim 6, wherein the plate is provided, on the upper surface, with two cams shaped as annular sectors (22) opposed each other.

8. Braking device according to claim 7, wherein said means on the lower surface of the disk (21) have a flat central part (23) corresponding to a similarly flat central part (24) of the plate (20) positioned between the two cams and the two inclined annular sectors (25) corresponding with the two cams (22) of the plate.

9. Bench for testing industrial screwdrivers comprising a plurality of braking devices according to claim 1, to which an industrial screwdriver can be associated, which are suitably controlled by a bench electronic control board, the electronic braking torque and angle detectors being controlled by said electronic board, determining the choice of a set braking program, once the operator has chosen the brake to be used for testing the screwdriver (A).

Description

[0013] The characteristics and advantages of the present invention will be clearer and evident from the following illustrative and non-limiting description of an embodiment, with reference to the attached figures which illustrate respectively:

[0014] FIG. 1 shows a first type of test bench for verifying industrial screwdrivers;

[0015] FIG. 2 shows a second type of test bench for verifying industrial screwdrivers;

[0016] FIG. 3 presents a schematic view of the braking device according to the present invention;

[0017] FIG. 4 illustrates a sectional view of such braking device according to the present invention;

[0018] FIG. 5 illustrates a brake calibration plate;

[0019] FIG. 6 illustrates a rotating abutment calibration base for such plate of FIG. 5.

[0020] With reference to the mentioned figures the bench or verification system according to the present invention comprises a plurality of brakes with which the screwdriver is associated, appropriately controlled by an electronic control board from the bench which controls such brakes.

[0021] Each brake is provided with external measurement transducers, connected to the electronic board that determines the choice of a driver program, once the brake to be used for testing the screwdriver A has been chosen by the operator. Such program appropriately controls an actuator present in the brake which is able to modulate the braking capacity of the brakes.

[0022] A braking device according to the present invention is inserted in a test bench, generally indicated with reference number 2. From the surface of the bench the upper part of a preferably cylindrical container body 1 of the device protrudes and in particular a known coupling 11 protrudes, suitable for coupling with the head 3 of a screwdriver to be tested.

[0023] The coupling 11 is connected, by means of a shaft 12, to a braking unit 13 with the interposition of an electronic torque and angle detector 14 of the shaft 12 rotation.

[0024] The detector is controlled by the electronic board that controls the test bench of a screwdriver as a whole. Such electronic board S appropriately controls the braking unit 13 and detects, through the detector 14, the characteristics of the screwdriver for establishing the correspondence thereof with previously established test parameters.

[0025] Such measurements and verifications are known in themselves to a person skilled in the art and therefore shall not be further described or shown herein. The braking unit 15 comprises a plate 16, placed in rotation by the screwdriver, which is braked by appropriate friction surfaces 17 moved towards the plate by the movement of an actuator.

[0026] The actuator is preferably placed below the plate and pushes upwards the friction surfaces 15 on the lower surface of such plate. On the upper surface of the plate contrast surfaces 18 are provided, which cooperate with the friction surfaces to brake the plate.

[0027] The movement of said actuator is provided by at least one piezoelectric element 19.

[0028] Piezoelectricity is a natural characteristic of some crystals that produce an electric field if they are subjected to a mechanical action. The electric field in these crystals is the result of the deformation of the crystal lattice that constitutes them: the crystal is no longer electrically neutral, rather it is polarized. Such transformation is completely reversible.

[0029] Therefore, the appearance of an electric field due to a mechanical action takes the name of direct piezoelectric effect. There is also the opposite phenomenon, the action of an external electric field causes the deformation of the crystal (inverse piezoelectric effect). Because of these two principles both (direct effect) sensors and (inverse effect) actuators can be constructed.

[0030] In the present invention the piezoelectric element is placed in a housing and expands when stimulated by an electric current, raising a lifting plate 20 upwards which in turn pushes such friction surfaces. Such plate moves in guides placed on the internal surfaces of the container body 1.

[0031] The actuator preferably comprises a plurality of piezoelectric elements placed one on the other, so as to increase the total stroke of the actuator, adding up the effects of each element. Such type of actuator is known as a piezoelectric “stack”.

[0032] Such stack is present as a cylinder that increases its height when stimulated by an appropriately driven electric current. In the specific case such actuator reaches strokes of about 0.10 mm.

[0033] The top of the actuator 19 lifts a cap 21, abutting the lower surface of the lifting plate 20 in a single point of contact. In this way, there is a single point of contact between the plate and the cap, preventing any not perfectly vertical movements of the plate. Clearly, the desired braking level can be reached with precision only if such mechanical parts guarantee uniform action of the friction surfaces on the plate.

[0034] According to a further characteristic of the present invention, the device has a means for compensating for any clearance due to tolerances and processing uncertainties and consumption of the brake lining of the friction surfaces.

[0035] In fact, the production tolerances could lead to imperfect contact between the cap 21 and the lower surface of the lifting plate 20, with consequent loss of effectiveness of the action of the piezoelectric actuator, because of the reduced stroke thereof.

[0036] Furthermore, after braking a significant number of times, the braking surfaces can become worn and cause an increase in the stroke required of the actuator with respect to previous analogous braking. In that case it is necessary to make the actuator move slightly upwards so that it always maintains a position of the lifting plate and the friction surfaces brushing against the plate.

[0037] Such compensation means is positioned in proximity to the base of the container body 1 and of the actuator and comprises a rotating plate 21 moved by a relevant motor (not shown) and a disk 22 coupled between them. Such disk can move vertically abutting the base of the actuator with its flat upper surface. The upper surface of the plate and the lower surface of the disk are shaped so that when the plate rotates activated by the motor, the inclined surfaces of the plate and of the disk coming into contact with each other lift such disk upwards, in turn lifting the actuator upwards.

[0038] By controlling the activation of the motor, it is always possible to keep the friction surfaces 17 of the plate 16 at the same distance.

[0039] Preferably, the plate is provided on the upper surface with at least one cam 23 which is raised with respect to the surface of the plate and inclined with respect thereto. Even more preferably, the cams are both shaped like opposing annular sectors. Furthermore, such means on the lower surface of the disk 22 has a flat central part 24 that corresponds with a similarly flat central part 25 of the plate 20 positioned between the two cams. There are also two inclined annular sectors 26 on such disk that correspond to the two cams 23 of the plate.