Servo-controlled automatic level and plumb tool

Details Servo-controlled automatic level and plumb tool Servo-controlled automatic level and plumb tool

2001-12-04

2003-09-30

Gutierrez, Diego (Department: 2859)

Geometrical instruments

Straight-line light ray type

Alignment device

C033S290000, C033S291000, C033SDIG002, C033S282000, C033S27500R, C033S283000, C033S285000, C033S292000, C033S381000, C033S382000, C033S391000, C033S397000, C356S148000, C356S249000

Reexamination Certificate

active

06625895

ABSTRACT:

TECHNICAL FIELD
The invention described herein relates generally to alignment tools that generate optical alignment beams. More particularly, improved leveling mechanisms for automatically leveling the outputted beam(s) are described.
BACKGROUND
A variety of survey and carpentry tools have previously employed lasers. The first laser alignment tools were manually leveled as in U.S. Pat. No. 3,897,637 and U.S. Pat. No. 3,279,070. Subsequently, self-leveling instruments were employed to improve accuracy and reliability.
In one type of leveling instrument, an entire laser is suspended by a pendulum and leveled by gravity. For example, in U.S. Pat. No. 3,771,876 a He—Ne laser and chassis are hung by a flexible support to create a plumb beam which is subsequently directed in the horizontal plane using a pentaprism.
FIG. 1
herein shows that system, with the laser
4
hung by a wire
2
over a pentaprism
10
. The beam exits by a window
14
, while the pentaprism
10
is rotated by a motor
16
. The pendulous oscillation of the laser
4
is damped out by a magnet
12
. Alternative approaches have used viscous fluids to damp the oscillations.
Another laser leveling system is described in U.S. Pat. No. 5,184,406 and is shown in
FIG. 2. A
laser diode assembly
22
is mounted on a float
26
, which is supported by a liquid
28
in a vessel
24
. The laser beam remains plumb in spite of the tilt of the vessel. In another approach shown in
FIG. 3
, U.S. Pat. No. 5,144,487 uses a ball bearing pendulum. Platform
23
is suspended by a ball bearing pivot
25
within a housing
29
. An optical assembly within the platform
23
generates multiple collimated laser beams
21
for alignment purposes. The platform motion is damped by eddy currents induced by a magnet
27
. The use of several ball bearings makes the instrument expensive, large, and of limited accuracy and ruggedness.
In another distinct approach, a laser is rigidly mounted to a housing of the unit and a compensation means (typically, lensing devices) is used to correct for the tilt of the housing. For example, in U.S. Pat. No. 3,684,381, a thin film of oil
36
is contained by an upper window
34
and a housing
35
(shown in FIG.
4
). This thin film of oil
36
is used to create a correcting prism which directs the downwardly directed laser beam
32
toward the plumb direction. The oil prism is formed by the upper level of the oil
36
which is level and a lower window
38
which is tilted. A laser source is mounted in a laser housing
30
. This system is accurate only when two cells with oil of index of refraction 1.5000 are used. This system has proven inadequate due to the absence of a fluid having the desired properties over the normal temperature range. In addition, the meniscus of the oil film
36
at the edges of the chamber contributes to wave front errors. In the system of
FIG. 4
, a pentaprism
40
(which is typically spinning) directs the plumb beam into a horizontal plane.
Several methods have been developed to tilt compensate a laser beam using wires. For example, in U.S. Pat. No. 4,221,483 a pendulous lens hangs below a laser diode. As the housing is tilted, the lens motion under gravity is proportional to the tilt angle, which steers the laser beam to the plumb position. A pentaprism again converts the plumb beam to the horizontal plane. In a system described in U.S. Pat. Nos. 4,852,265 and 4,912,851 and shown in
FIG. 5
, a laser beam
41
is reflected from a mirror
43
on a platform
46
which is suspended from a single wire
44
. The reflected laser beam
42
is compensated by the tilt of the platform under the force of gravity. The length and diameter of the wire are chosen so that when the housing of the unit is tilted exactly one degree, the platform tilts exactly one half of one degree. Because of the two-to-one relationship between mirror tilt and beam correction, the laser beam is restored to its plumb direction after being tilted. These patents also show laser diodes mounted on cantilevers which respond to housing tilt to correct the output beam.
Each of the foregoing laser leveling techniques and apparatuses suffers from accuracy limitations, ruggedness concerns, and/or the expense of the components. In particular, devices requiring pendulums require expensive low-friction joints to allow free motion of the laser. These low friction pendulums are subject to oscillations (at the slightest touch) that require a long time to settle. As a result, such pendulum devices require expensive, difficult to perfect damping mechanisms to overcome the oscillation problems. What is needed is a method and apparatus for overcoming these and other difficulties in a relatively low-cost laser level device.
SUMMARY OF THE INVENTION
In accordance with the principles of the present invention, an apparatus and method for achieving automatic beam leveling are disclosed.
In one embodiment, an optical level comprises an optical assembly for generating a light beam and a platform that supports the optical assembly. The embodiment includes a slip-stick mechanism that pivotably supports the platform for rotation in at least one degree of freedom. The slip-stick mechanism provides sufficient stiction to hold the platform in place even when the platform is tilted somewhat relative to level. The slip-stick mechanism also permits the platform to pivot with relatively lower friction when the stiction is overcome. The embodiment includes an actuator arranged to cause motion of the platform by supplying sufficient force to the platform to overcome stiction from the slip-stick mechanism.
Yet another optical level embodiment comprises an optical assembly for generating an output light beam and a platform that supports the optical assembly. As with the foregoing embodiment, a slip-stick mechanism and an actuator are included. The embodiment includes a sensor for providing signals that may be used to determine whether the platform is level. The sensor includes a detector light source, a position sensitive light detector, and a two-axis bubble level. The two-axis bubble level is positioned with respect to the detector light source and the position sensitive light detector, such that detector light produced by the detector light source is projected through the two-axis bubble level onto the position sensitive light detector. Because the two-axis bubble level is aligned with the output beam, the detector can determine whether the two-axis bubble level is leveled and thereby whether the output beam is leveled.
Yet another embodiment comprises a leveling assembly that includes a pivotably mounted platform capable of rotation in at least one degree of freedom. The platform also including an actuator arranged to cause motion of the platform by supplying sufficient force to tilt the platform. The platform also includes a sensor for providing signals that may be used to determine whether the platform is level.
In a related embodiment, the sensor comprises a detector light source for producing detector light and a position sensitive light detector that is sensitive to the detector light. A two-axis bubble level is aligned with the platform, such that when the two-axis bubble level is leveled, the platform is also level. The light source is positioned so that it projects the detector light through the two-axis bubble level onto the position sensitive light detector so that the detector can determine whether the platform is leveled.
In yet another related embodiment, the leveling assembly further comprises a slip-stick mechanism providing sufficient stiction to hold the platform in place even when the platform is tilted somewhat relative to level, while permitting the platform to pivot with relatively lower friction when the stiction is overcome; and, wherein, the actuator can cause motion of the platform by supplying sufficient force to the platform to overcome stiction from the slip-stick mechanism.
In another embodiment, the apparatus comprises a beam projecting element tiltably mounted such that the optical assembly can tilt about two axes and ho

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