Movable suspended scaffolds are well known and employed for any maintenance or repair services on a vertical plane, as for instance at a façade, the hull of a ship and other points of external access at a higher level. Individual scaffolds-also called"cadeirinhas" (little chairs/lift)-are composed of a winch with a main steel cable that supports a seat where the worker sits. The Brazilian rules require a secondary cable, also called additional safety cable, along which a locking device runs with a lever on which the worker fixes his own safety-belt by means of a hook. The lever is actuated by the worker having two end positions, one corresponding to the free displacement and the other corresponding to the locking position. Although the cable is clasped by the device, the locking action results from the incidence of the jaw in a single direction on the cable determined by the location of the lever against the guide surface of the device on the side opposite to the jaw, that is to say, the clasping force is lateral, rather than being diametrically opposite.

In fact, this is a safety device; however, the reliability of the operation of the de- vice is determined by its capacity of twisting the cable, by the due precautions of the worker and the working of the movable parts, which depending on the working conditions are sub- ject to wear. One limitation of some of these devices, is that once actuated in the event of free fall, remain unserviceable and not all of them are suitable for collective scaffolds.

For personal use, a self-jamming device is known from US Pat 5,076,400, pub- lished on December 31,1991. The device is formed by two pulleys, one of which is fixed and

the other mounted on a pivoting plate, the device being responsive to acceleration above a limit value during the descent. Although the device has autonomous action, its application is restricted to ropes, since a torsion has to be applied with two reversed curves on the same plane of the support element, for which reason it is not applicable to steel cables of commer- cial size.

Collective scaffolds-also called a rocker-are composed of a horizontal platform of work with supporting winches at each one of the ends of this platform, where one end of the main steel cable of the assembly is wounded the other end being fixed at the top of the buildings or construction sites.

The locking and safety devices used specifically in this type of scaffold are known since long ago, as disclosed in the following patents: US 3,968,865, published on July 13,1976; US 3,980,161, published on September 14,1996; and US 3,991,979, published on November 16,1976.

The device of US Pat. 3,968,865 in the name of Cable Climber Safety Devices Inc. is fixed to the hoisting mechanism and employs a speed-sensing element for detecting any acceleration, even if the motor is switched off. The device actuates on the support cable of the scaffold itself in a progressive manner, by friction, until the scaffold is halted. The locking action employs an ajustable precision mechanism with a great number of parts.

Although the device actuates upon occurrence of an acceleration of the scaffold, its com- plexity and inefficacy in the event of loosening of the fixation of the cable or its breaking are strong limiting factors for its acceptation.

The device of US Pat 3,980.161 in the name of Hi-Lo Powered Stirrups, Inces Inc. is fixed to the scaffolds at a height above the winch mechanism and, as can be inferred from column 2 of this document, it is intended for guaranteeing an instantaneous locking, instead of the progressive locking of the device of US Pat 3,968,865. The support cable also runs through this device, the latter having guide portions for assisting in leading the support cable into and out of the locking device and the scaffold winch during vertical movement.

The device is actuated by the centrifugal force of masses arranged for rotation, upon occur- rence of acceleration or free fall of the scaffold. The limitations of the cited prior art still sub- sist in this device, since the loosening or breaking of the support cable is out of the control of the device.

Due to the possibility of loosening and breaking of one of the support cables, the Brazilian rules require the use of an additional cable or secondary cable, also called addi- tional safety cable, on which the locking device can be mounted and acts upon occurrence of any of the aforementioned conditions while it freely runs as long as it is not active.

The object of the present invention is to overcome the drawbacks of the devices of the prior art and the risks involved in the vertical hoisting of loads by means of a locking device which is guided on an auxiliary cable parallel to the support cable. The locking device of the invention has fewer parts and above all offering a self acting operation, that is, without the interference of any actuating element or of the worker who is protected by the device.

Another object of the present invention is to improve the reliability of the sus- pended system. Scaffolds bearing the devices of the prior art offer a reliability serial, since the loosening or breaking of the support cable leads to the free fall of the object. However the use of the device of the invention, while running on an auxiliary cable and preventing from falling the object which is suspended by the support cable, offers a reliability parallel, since, for the object to drop the loosening and/or breaking of both cables, the main one and the auxiliary one, has to occur simultaneously and on the same side.

The auxiliary or secondary safety cable, in this case, in the same way as with in- dividual scaffolds, is fixed at one end to the top and hangs parallel to the main or support cable, the other end remaining free. Upon occurrence of any of the failures, that is, a failure of one of the winches, the breaking of the main cable or acceleration, the device locks the auxiliary cable autonomously, thus preventing the platform from inclining or tumbling thereby preventing workers and material from falling.

Another objective of the present invention is to provide a self-acting locking de- vice substantially free from maintenance and which is reusable after its locking actuation.

A further objective is to provide a device bringing together in a single construc- tion properties which are specific of each of the devices of the prior art.

Therefore, the present invention refers to a locking device to prevent free fall and uncontrolled acceleration of a suspended body to which it is fixed, formed by a casing hav- ing an upper and a lower side which has a bore along its length and which, by means of an elastic element placed on the upper side, houses in a retractable manner a passage section for the auxiliary cable, the passage section bearing at least one pair of jaws arranged on the same horizontal plane and converging to the cable to be bitten into, the jaws being ar-

ranged in the lower region of the casing. These bodies form a system of intemal forces in balance. While in normal or controlled movement, the jaws are maintained in a shaped cavity region of the casing close to one of the ends of said passage section, at which the jaws are kept away from the auxiliary cable. Upon occurrence of loosening or breaking of any of the support cables, an external acceleration or free-fall force is exerted on the system of inner forces in balance of the locking device. This causes the elastic element to react independ- ently, retracting the passage segment bearing the jaws into a region of the bell-shaped cav- ity where the jaws are assisted by the internal wall of the bell-shaped cavity thereby the jaws converging to bite into the auxiliary cable.

Although the locking device of the invention is fixed to the suspended body, the only element which actuates the locking device is the acceleration force, there being no in- terference by any mechanical component, such as a lever, auxiliary spring, or cam, which actuates the devices of the prior art. The locking occurs as a reaction of the internal elastic element itself, which supports the passage segment in a retractable manner inside the cas- ing of the device, as will be described below.

Preferably, the elastic element is a spring with an elasticity coefficient responsive to the external force of acceleration of the suspended body and the masses of the casing and the passage segment being chosen as a function of the application.

The components of the locking device can be housed in a capsule with a cap for protecting the device, when the working conditions so require.

Brief description of the figures The objectives and advantages of the present invention will become apparent from the detailed description, given by way of example with reference to the accompanying figures, in which: -figure 1 is a longitudinal cross section of a preferred embodiment of the locking device running free along the auxiliary cable in a first mode of operation; -figure 2 is a transversal cross section aiong line 2-2 of the device of figure 1; -figure 3 is a longitudinal cross section shows when locking on the auxiliary ca- ble;

-figure 4 is a transversal cross section of the device according to figure 3; and -figure 5 shows a front view of a scaffold with the device of the invention fixed at both ends thereof and showing the two modes of operation along the secondary cable re- spectively.

Detailed description With reference to the figures, a locking device for preventing falls, according to a preferred embodiment of the invention, is applied to a scaffold, as shown in figure 5. The locking device 10 shown in the longitudinal section view of figure 1 can be sealed inside a capsule 31. The locking device 10 basically comprises four parts, which are a casing 11, a passage segment 12, a spring 15 and a pair of jaws 19 guided in cavities on the wall of the passage segment 12 within capsule 31.

The casing 11 is made of a thick-wall steel tube with a cavity 16,17 at each separate end and in communication by a channel 18 for conduction of the auxiliary cable 13.

The upper cavity 16 is defined by a cylindrical wall 32 and a lower circular shoulder 14. The lower cavity 17 has a conical inner face 33 and a straight outer face 20 with a diameter smaller than that of the casing body 11, forming a bell 21, with a larger cross-section region 29 and a smaller cross-section region 30, adjacent the channel 18. The cavities 16 and 17 are open in respective upper and lower ends of the device.

The passage segment 12 is formed by a tube with a straight wall 24 and pro- vided with a shoulder 23 at the upper end. The shoulder 23 and the straight wall 24 cooper- ate with the inner face 19 of the upper cavity 16 and with the wall of the channel 18, respec- tively, for the sliding of the passage segment 12 through the inside of the casing 11. In the bell region 21, the passage segment 12 has two radial cavities 25 facing each other for cas- ing in a movable manner two respective jaws 19, the surfaces of which compress the auxil- iary cable 13 as long as to bite into it when the support cable breaks or loosens, at which moment body is supported by the locking device on the auxiliary cable 13, as will be ex- plained below. In the sealed configuration, the passage segment 12 has a weight 27 at its opposite end region, imparting to the body of the segment 12 a mass different from that of the casing 11, to provide a greater stability to the assembly, the weight 27 having a skirt 28, the inner face of which slides in vertical movement on the straight outer face 20 of the cavity 11.

The passage segment 12 is inserted into the casing 11 and in the channel 18 with retractable movement between the end stroke positions of the passage segment 12 by an axial spring 15 housed in the cavity 16, between a seat formed by the lower shoulder 14 and the counter-support formed by the shoulder 23 of the upper end of the passage segment 12.

As can be seen from figure 1, with the spring 15 compressed and the passage segment 12 inserted more deeply into the casing 11, the jaws 19 are maintained in the larger cross-section region 29 of the bell portion 17. In this position, the region of the channel 18 is left free for the displacement of the device 10 along the auxiliary cable 13. In this condition, the body suspended on the support cable displaces in normal conditions of operation, and the locking device intervenes only as a guide device.

The transversal cross section view of the device according to figure 2 shows the jaws 19 in a region of the bell 17 at which they are away from the cable 13.

The longitudinal cross section view according to figure 3 corresponds to the act- ing mode of operation, that is to say, jaws 19 biting into secondary cable 13 when the device acts to a force of acceleration or free fall, due to the breaking of the support cable or loos- ening of a body from the cable to which it is fixed. In this condition and as shown in the fig- ure, the spring 15 reacts to the impulsion which overcomes its compressive force in the ex- panding reaction. The passage segment 12 is compelled from an initial position of insertion in casing 11 to a final position of retraction with respect to the casing 11, leading the jaws 19 to the upper bell-shaped region of smaller cross-section 30, the jaws 19 being compelled by the conical inner wall 33 of the bell converging onto the cable 13, compressing and biting into it.

The arrows in the transverse cross section view of figure 4 indicate jaws 19 bit- ing into the cable 13, closed channel 18, that is, in the upper bell-shaped region where cross section 30 is of smaller diameter than region 29.

Figure 5 shows one field of application of the locking device of the invention. Ac- cording thereto the body protected by the locking device is a collective scaffold 40, sus- pended at its longitudinal ends by respective support cable or main cable 41. Reference 13 indicates the auxiliary cable along which the locking device 10 runs, hanging free and par- allel to main cable 41. Locking device 10 is coupled to scaffold 40. Locking device 10 as already described forms a system of internal forces in balance. In this way, upon occurrence

of an unbalancing of the scaffold, be it by loosening or by breaking of any of the main cables 41,41' the acceleration force resulted therefrom is sensed by the locking device 10 which acts by stopping the scaffold thereby maintaining the same in balance at the height at which it is at that moment. In this way, the locking device prevents the tumbling and failing to ground of workers and materials on the scaffold.

Instead of a scaffold, the suspended body may be a freight-elevator, maintaining the auxiliary cable always close to the support cable, and with an adequate sizing of the spring and the masses.

The mode of operation of the locking device of the present invention is based on Newton's laws and on the momentum conservation principle of classic physics. The casing 11, the passage segment 12 with the jaws 19, and the spring 15, create internal forces act- ing between the referred-to bodies, forming a system isolated from external forces, or if any, said external forces are not strong enough when compared to the internal forces thereby the external actions are considered negligible. Thus, the amount of movement of the system of bodies which form the locking device 10, isolated from external forces, remains constant when the device is led by the suspended body to the support cable, with a rectilinear uniform movement while descending or ascending or at rest. In this situation, the jaws are in the po- sition illustrated in figures 1 and 2, away from the auxiliary cable 13.

Upon occurrence of an acceleration of this movement or free fall, be it by break- ing of the support cable or by loosening of the body from the cable, an external force of ac- celeration or free fall actuates on the assembly in internal balance formed by components of the casing 11/segment 12 of the locking device, the device of the invention reacting by means of an internal spring 15 with an equivalent force, but in an opposite direction, accord- ing to Newton's 3rd Law. The reaction force of the internal spring 15 impels the passage segment 12 to retraction from its initial rest position in the cavity 11, bringing the jaws 19 to the channel 18 to bite into the cable 13, whereby the body in free fall remains locked against free fall on the auxiliary cable 13. This situation is represented in figures 3 and 4, with the jaws 19 bitten into the cable 13, keeping the body suspended in a condition of firm locking.

Advantageously, the relative motion of the passage segment 12, from its initial position inserted into the casing 11 to its position retracted from casing 11 can be remotely signalized by a usually open electric contact, connected by a pair of wires to a relay of the SPDT or SPST type, for interlocking of a motor, a sound or light signal at a remote panel.

The electric commutation occurs when the passage segment 12 reaches the final retracted position, signaling the locking of the jaws 19 onto the auxiliary cable 13, to warn of a failure situation.

The constructive simplicity and the materials of the components make the device suitable for its reuse in other successive applications, it being free from wear.

The invention has been described with reference only to a specific application.

However, it is evident that the inventive concept can be applied to other suspended objects, referred-to in the beginning, in which one desires to avoid uncontrolled acceleration of the object in motion along a support cable or rope in free fall, provided that there exists an aux- iliary cable parallel to the support cable, and provided that the device is fixed close to the point of fastening the object. It will also be understood that the inventive concept relates to a device in which there is no mechanical component for actuating the locking in connection with the suspended body or with the support cable of the suspended body, but rather with a system of internal forces in balance among the bodies which compose the device responsive to a gravitational force of free fall or acceleration, sufficient to impose the relative inner dis- placement between the casing component and segment with the locking elements.

The scope of the invention, therefore, does not limit itself to the embodiment il- lustrated and described herein, but rather to the terms defined in the accompanying claims and their equivalents.