The object of the invention is an apparatus for balancing an object to be reciprocated in a vertical plane along a circular orbit, or along some other closed trajectory, as defined in the preamble of claim 1.

The variable-moment balancing apparatus according to the invention is suited to many different applications. It can be e.g. a balancing machinery of a traffic boom or it can just as well be suitably applied in balancing a trajectory in essentially the vertical plane of any object whatsoever that is fixed at one of its ends or at its edge in a hinged manner, wherein the center of mass of the object moves along an essentially closed circular orbit. These types of objects are, in addition to booms, skylight windows, hatches, tip-up doors, automobile hoods, tail gates, levers that function as parts of a machine and the masses connected to them, as well as also drawbridges and corresponding structures.

Among other things, a counterweight is known in the art as a balancer of the trajectory of an object that is to be moved in the vertical plane and is hinged at one of its ends or at its edge, the moment produced by which counterweight corresponds to the variable moment produced by the position of the object to be moved. One problem of a counterweight, however, is its weight and the space that it requires. A counterweight cannot in general be used e.g. for balancing the trunks and tailgates of automobiles, because the structures of an automobile do not contain space for a counterweight. Likewise, the ends of traffic booms or corresponding booms do not generally comprise space for such a large counterweight that the solution would require. For this reason boom solutions based on a counterweight are not generally used nowadays.

European patent no. EP0438364 Bl and US patent no. US 4,848,175 present solutions for balancing the movement of a traffic boom. Both patent publications present a complex apparatus based on levers and springs, which apparatus comprises _, a large number of different small parts. A problem in these is, among other things, the large number of parts, which detracts from the reliability of operation and raises costs. In addition, there are many different sizes and variations of booms, in which case each size and variation must have its own parts dimensioned for it. This considerably increases the number of parts needed, in which case also storage costs, among others, increase. The object of the present invention is to eliminate the aforementioned drawbacks and to achieve an inexpensive, operationally reliable and energy-saving apparatus for balancing an object to be reciprocated along a closed trajectory. The apparatus according to the invention is charac- terized by what is disclosed in the characterization part of claim 1. Other embodiments of the invention are characterized by what is disclosed in the other claims.

An advantage of the apparatus according to the invention is its simple, lightweight construction that is inexpensive in costs, fits into a small space and does not comprise a lot of moving parts. For this reason the operation of the apparatus is reliable, and also servicing and repairs do not need to be performed often. Another advantage is that owing to the balancing construction of the apparatus, in e.g. re- mote-controlled apparatuses very low-power power units, such as electric motors, can be used for driving the apparatus. This saves very much energy compared to prior-art apparatuses. Another advantage is that in the apparatus ac- cording to the invention the object to be turned, such as a traffic boom or automobile hood, etc., is balanced in all positions and the downward movement is against a spring force. In this case the object to be turned is safe, be- cause is not able to drop downwards unexpectedly and does not produce any hazards caused by this. A further advantage is that the balancing apparatus according to the invention can be built at the factory as a subassembly that comprises only the balancing machinery part. In this case a small ma- chinery part is an easily packed, lightweight and small- sized product, which can easily be transported for sale to anywhere in the world whatsoever. On site the apparatus is just fixed to its base and the object to be turned, such as a traffic boom, is fixed to the pivot shaft of the appara- tus, which object to be turned can be procured from elsewhere than from the manufacturer of the balancing apparatus .

In the following, the invention will be described in greater detail by the aid of some embodiments and by refer- ring to the attached simplified drawings, wherein

Fig. 1 presents a diagrammatic and simplified side view of one apparatus according to the invention applied for turning a traffic boom and with the front plate of the frame part removed. Fig. 2 presents a top view of a partial section of the apparatus according to Fig. 1 and

Fig. 3 presents a diagrammatic and simplified side view of the operation of the apparatus according to Fig. 1 in a situation in which the boom has turned 45 degrees.

Fig. 1 presents a diagrammatic and simplified side view of one apparatus according to the invention applied for turn- ing an object 1, such as a traffic boom, and with the center part of the front plate 2a of the frame part cut away as well as with other parts that are at the front removed. In the viewing direction from the front of the apparatus, the boom 1 is presented with dot-and-dash lines, so that it does not cover the parts of the apparatus behind it. Correspondingly, Fig. 2 presents a simplified and partially sectioned top view of the apparatus according to the invention.

The apparatus presented in Figs. 1 and 2 comprises at least a casing-type frame part 2, which comprises a front plate 2a and a rear plate 2b, which plates 2a and 2b are essentially similar plates that correspond to each other, which function as a frame of the apparatus and as a support for the bearings of the shafts, and which are fixed to each other e.g. with fastening means 13 such that a space remains between the plates 2a and 2b for the balancing machinery 3. The balancing machinery comprises at least a transmission means 4, with a transmission shaft 5, along with which the transmission means 4 turns. The transmission shaft 5 is mounted on bearings onto the frame part 2 by means of the bearings 5a. In addition, the balancing machinery 3 comprises a compensating means 9, such as a pretensioned torsion spring, that balances the changing force exerted by the weight of the object 1 to be moved, the first end 9a of which compensating means is fixed to a flange 5b on the transmission shaft 5, the position of which first end is adjustable and which flange rotates along with the transmission shaft. Thus the flange 5b transmits the spring force of the torsion spring 9 to the transmission shaft 5. The second end 9b of the torsion spring 9 is fixed to the front plate 2a of the frame part. The balancing machinery 3 further comprises a turning means 7, which is fixed to the pivot shaft 8 and is fitted to turn along with the pivot shaft 8 and also to function as a converter of the transmission ratio. The transmission shaft 8 is mounted on bearings onto the frame part 2 by means of the bearings 8a. The object 1, e.g. a traffic boom, is fixed to the first end of the pivot shaft 8, which object the balancing machinery 3 is fitted to balance. The center of mass of the boom 1 fixed at one of its ends moves as the boom turns along a closed circular orbit and the moment produced by the weight of the boom 1 on the pivot shaft 8 changes as a function of the cosine of the turning angle of the boom. Correspondingly the pretensioned moment of the torsion spring 9 changes linearly. The balancing machinery 3 is arranged to match the linearly changing moment of the torsion spring 9 with the moment produced by the boom 1 that changes as a function of the cosine of the turning angle such that the forces caused on the belt 6 by the aforementioned moments are in all angular positions of the boom 1 of equal magnitude to each other but in opposite directions.

The balancing machinery 3 further comprises a power means 12, such as an electric motor, fastened to the rear plate 2b of the frame part at the second end of the pivot shaft 8, which power means is fitted to turn, if necessary, the pivot shaft 8, e.g. in connection with automatic control. In addition, the balancing machinery 3 comprises a traction means 6, such as a belt, a cable, a chain or corresponding, which is fixed at its first end to the transmission means 4 with a fastening means 10 and at its second end to a turning means 7 with a fastening means 11 and is tightened to a suitable tautness before fixing with an adjustment means of tightening that is in connection with the fastening means 11. The power means 12 is needed to overcome friction and any possible external forces in all the positions of the boom 1 and to keep the traction means 6 always sufficiently taut.

In the situation according to figures 1 and 2, the boom 1 is in its horizontal position and the moment produced by the weight of the boom 1 is at its maximum. Likewise, the moment of the pretensioned torsion spring 9 that is on the transmission shaft 5 of the transmission means 4 is at its maximum, in which case the torsion spring 9 attempts to push the boom 1 upwards with its maximum force. Correspondingly the weight of the boom 1 attempts to push the boom 1 downwards all of the time. When the boom 1 is in the horizontal position, the forces of the boom 1 and of the torsion spring 9 are transmitted to the belt 6 via the contact points 14 and 15, and when the boom is in the vertical position the forces are transmitted to the belt 6 via the contact points 14n and 15n, which contact points are not however presented in the figures.

The transmission means 4, the turning means 7 and the tαr- sion spring 9 are dimensioned with respect to the boom 1 according to the case so that the forces in the belt 6 are in each turning position of the boom 1 as great as each other, in which case the boom 1 is in balance in all its turning positions. In this case the force acting on the belt 6 is as great both in the contact point 14...14n of the belt 6 and the turning means 7 as well as in the contact point 15...15n of the belt 6 and the transmission means 4. The force acting on the contact point 14...14n is determined by the moment produced by the boom 1 to be turned and by the radius of the contact point 14...14n, i.e. by the distance of the contact point 14...14n to the center line of the pivot shaft 8. This distance is described later with the term contact radius R7. Correspond- ingly, the force acting on the contact point 15...15n is determined by the moment of the torsion spring 9 exerted on the transmission shaft 5 and by the distance of the contact point 15...15n to the centerline of the transmission shaft 5. This distance is described later with the term contact radius R4.

The torsion spring acts as a renewable energy storage, giving up energy when the boom 1 is lifted and collecting energy when the boom 1 is lowered downwards.

Fig. 3 presents a diagrammatic and simplified side view of the operating principle of one apparatus according to the invention. In the example situation according to Fig. 3, the boom 1 has turned upwards to an angle of 45° from the bottom position upwards or from the top position downwards. In this case also the turning means 7 fixed to the pivot shaft 8 has turned 45°, i.e. the amount of the angle B, but the transmission means, owing to its shape and to the dimensioning between the turning means 7 and the transmission means 4, has turned the angle A, which is greater than the angle B, and the length of the contact surface 4a on the transmission means 4 corresponding to which angle A corresponds to the length of the belt 6 released from the turning means 7. In this embodiment the dimensioning of the transmission means 4, the turning means 7 and the torsion spring 9 is such that when the boom 1 turns 90° the transmission means 4 turns approx. 276°.

The turning means 7 comprises a contact surface 7a of the belt 6, which contact surface is at least of the length of the circular curve S corresponding to a 90° circular seg- ment, the radius of which curve S is R7. In practice the contact surface 7a continues for some distance on both sides of the curve S, but the contact surface 7a in this area outside the curve does not necessarily need to be shaped as a circular curve. The angle C of the circular segment is in this case 90°, but depending on the application it can also be other than 90°. Viewed from the side, the shape of the turning means 7 is reminiscent of a circu- lar segment that is the shape of a quarter-circle, which comprises two essentially straight sides and a curved surface between them. In addition, a hole for the pivot shaft 8 is disposed near the point of convergence of the straight sides such that the contact radius R7 of the turning means 7 at least in the area of the circular segment of the angle C is essentially constant. The contact radius R7 refers in this context to the curve S, i.e. the length of the radius in the area of the contact surface 7a from the center axis of the pivot shaft 8. The contact radius R7 can also be continuously variable instead of constant.

The contact surface 4a of the belt 6 of the transmission means 4 is determined such that the contact radius R4 of the transmission means 4 is continuously changing according to the turning angle of the transmission means 4. In this case the magnitude of the contact radius R4 in each turning position of the transmission means 4 is selected to be such that essentially the same force acts on the belt 6 at the contact point 15a of the belt 6 and the contact surface 4a of the transmission means 4 as that which remains in the torsion spring 9 at that moment and which is the same magnitude as the force exerted on the belt 6 by the moment of the boom 1, but in the opposite direction. In this case the contact radius R4 of the transmission means 4 at each particular time is dimensioned to correspond to the moment of the torsion spring 9 at that time and to be such that the length of the contact radius R4 is at its greatest when the force caused by the moment produced by the weight of the boom 1 is at its greatest, i.e. when the boom 1 is in the horizontal position. When the boom 1 is turned upwards, the moment exerted on the pivot shaft 8 by the boom 1 decreases as a function of the cosine of the turning angle and the moment of the torsion spring 9 decreases as the pretensioning of the spring decreases. At the same time also the contact radius R4 of the transmission means 4 changes at the contact point of the belt 6 and the contact surface 4a such that the force produced by the moment of the spring 9 is the magnitude of the force produced by the moment of the boom 1, but in the opposite direction, in which case the boom 1 is in balance. When the boom 1 is in the vertical position, both moments are essentially zero.

When, on the other hand, the boom 1 descends towards its horizontal position, the moment produced by the boom 1 on the pivot shaft 8 increases as a function of the cosine of the turning angle and the torsion spring 9 tightens. At the same time also the contact radius R4 of the transmission means 4 at the contact point of the belt 6 and the contact surface 4a changes such that the force produced by the mo- ment of the spring 9 is the magnitude of the force produced by the moment of the boom 1, but in the opposite direction, in which case the boom 1 is in balance. The contact radius R4 that functions as a torque arm is the distance between the contact point 15, 15a...15n of the belt 6 and the transmission means 4 and the center axis of the transmission shaft 5, which thus changes as a function of the turning angle both of the transmission means 4 and of the boom 1. Since the turning angle of the boom 1 also affects the turning angle of the transmission means 4 via the belt 6, the turning angle of the transmission means 4 changes, and at the same time also the contact radius R4, as a function of the turning angle of the boom 1. The pretensioning of the torsion spring 9 and the contact radius R7 of the turning means as well as the contact radius R4 of the transmission means are dimensioned such that the force produced by the moment that changes according to the position of the turning angle of the boom 1 on the transmission means 4 via the pivot shaft 8 acts all the time on the belt 6 at the contact point 14, 14a...14n and 15, 15a...15n of the belt and the transmission means 4.

When the boom 1 and at the same time the pivot shaft 8 is turned e.g. 10° upwards, a certain amount of belt 6 is released from the turning means 7. The transmission means 4 must be turned so much that exactly the same amount of belt 6 wraps around the transmission means 4. Otherwise the belt 6 remains loose or breaks. After the boom 1 has left the horizontal position in the case according to this embodiment, when the turning angle of the boom is 10° the turning angle of the transmission means 4 is approx. 24°, but because the contact radius R4 of the transmission means 4 changes to become smaller all the time, the next 10° turn- ing angles of the turning means correspond to an ever larger and larger turning angle on the transmission means. Fi- nally, when the turning means 7 has turned 90°, the transmission means 4 has turned approx. 276°.

What is essential to the solution according to the inven- tion is that the apparatus comprises two pieces to be turned according to a different center point, i.e. a turning means 7 rotating around the center point of the pivot shaft 8, and a transmission means 4 rotating around the center point of the transmission shaft 5. Of the pieces 4 and 7, the moment produced by the weight of the object 1 to be moved is acting on one, i.e. on the piece 7, and the moment produced by the torsion spring 9 acting in the opposite direction with relation to the moment produced by the weight of the object 1 to be moved is exerted on the other, i.e. the piece 4. A traction means 6 is fixed at its ends to the outer rim of both the pieces 4 and 7 such that each of the pieces 4 and 7 always moves when the other moves and the pieces 4 and 7 are shaped such that forces of the same magnitude as each other are exerted on the traction means 6 at both its ends in all positions of the object 1.

It is obvious to the person skilled in the art that different embodiments of the invention are not limited to the ex- ample described above, but that they may be varied within the scope of the claims presented below. Thus, for example, instead of the belt that functions as a traction means, also a steel rope, a chain or some other corresponding means for transmitting force and that is suited to the purpose can be the traction means.

It is also obvious that the shape and the contact surface of the transmission means can be such that the transmission means turns e.g. only 180° instead of an angle of 276° when the boom or other object to be turned in a vertical plane turns 90°. In this case, however, a more rigid torsion, spring is needed.

It is also obvious that the shape and the contact surface of the transmission means can be such that the transmission means rotates a number of revolutions, i.e. over 360°, when the boom or other object turning in a vertical plane turns 90°.

It is further obvious that the spring structure can also be made with nested springs, in which case there is the possibility to achieve a very competitive solution.

Furthermore, it is also obvious that in the examples presented, the torsion spring structure that functions as a compensating means can be replaced with some other means of force, with which it is possible to bring about a counter- force resisting the weight of the boom.