This invention relates to a portable self-levelling measurement device with laser ray emissions.
Numerous manual self-levelling devices exist which, utilizing the force of gravity, project laser rays able for example to define horizontal and/or vertical alignments or levelling even if the device lies on a surface inclined by a few degrees to the horizontal or the device is in an inclined position on a horizontal surface.
U.S. Pat. No. 3,771,876 describes a device of the said type comprising a pendulum consisting of a moving assembly carrying a vertically positioned laser ray generator. This assembly is suspended by a wire from a hollow case within which it can swing until it reaches its equilibrium position by virtue of the damping action provided by the presence of magnets which generate parasitic currents. Within this device, the vertical ray generated by the laser is projected against a lens (pentaprism) which deviates this ray through 90xc2x0, to hence obtain a horizontal ray which leaves the said hollow case or housing. By rotating the pentaprism, driven by a small electric motor, the ray can be projected horizontally through 360xc2x0.
Other known devices are described in U.S. Pat. No. 5,724,744 and U.S. Pat. No. 5,782,003. In these documents, a pendulum containing a laser diode, positioned such as to project a horizontal laser ray when the pendulum is at rest, is coupled to a cross fixed to the inside of the case. With the pendulum in its equilibrium position, on rotating the case which is connected to a base via a ball bearing, the horizontal ray leaving this case generates a flat horizontal laser beam. A mechanical damping system which grazes the bottom of the pendulum shortens the time required for attaining the equilibrium position.
A further known device, described in U.S. Pat. No. 5,680,208, comprises a pendulum connected to a hooking point within the hollow housing by an element of flexible synthetic material, for example in the form of a band or strip (known commercially as mylar) which replaces the cross used in U.S. Pat. No. 5,782,003 or U.S. Pat. No. 5,724,744.
In general, the described devices are of rather complex construction and often suffer from intrinsic manufacturing limits. For example, the use of the cross as a suspension means for the pendulum requires the use of four mechanical decoupling members or bearings, and requires a pendulum of fairly large weight to overcome the friction of the various (numerous) bearings to enable the pendulum to always halt in its correct equilibrium position.
In contrast, the use of the element of thin flexible material (for example mylar) as the suspension member has an intrinsic limit deriving from the nature of the material itself and difficulty of enabling sensitivity, elasticity and torsional inertia to coexist within such an element, which is for example in the form of a thin strip.
An object of the invention is to improve the known solutions with a view to decreasing their currently high cost, deriving from their complicated construction because of the number of their component parts, their complicated assembly and the complexity of their mechanical damping system, while at the same time overcoming those problems of friction, torsion during rotation and overall size which have been highlighted in the aforegoing description of the state of the art.
Hence an object of the invention is to provide a self-levelling device of simple construction and reliable use, which comprises a small number of easily constructed and assembled mechanical parts, and is able to project in a visible and stable manner an always horizontal laser ray (or vertical by deviation through 90xc2x0) even if the device is inclined by a few degrees, for example xc2x15xc2x0.
A further object is to provide a device of the stated type which enables a laser ray to be projected through 360xc2x0 always horizontally even if the device is resting on a surface inclined by a few degrees.
A further object is to provide a lightweight device of small dimensions which is extremely competitive and economical, besides being robust, reliable and accurate.
These and further objects which will be apparent to the expert of the art are attained by a self-levelling device in accordance with the accompanying claims.