Abstract:
Rotating construction laser device with a grade mechanism, including a code element and a position detection device for providing and detecting a feedback position information, and a leveling mechanism, which supports a lens barrel tiltably and is designed to tilt the lens barrel in order to have the level position detected by a tilt sensor and therewith to level the grade arm, the code element or the position detection device is arranged directly on the grade arm, and the feedback position information directly depends on the position of a reference point on the grade arm, the reference point being defined by the code element or the position detection device, respectively, thus allowing to deduce a position of the grade arm directly from the feedback position information, and/or to calculate a tilting angle of the grade arm with respect to the lens barrel directly from the feedback position information.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a feedback sensor, in particular a home sensor, for a grade mechanism of a tiltable laser optical system, particularly of a tiltable rotating construction laser, and a method for determining a position of a grade arm of this grade mechanism. 
     BACKGROUND 
     Construction lasers with a rotatable laser beam are used primarily in the constructional industry as an auxiliary means for tracing horizontal and vertical lines on floors, ceilings and walls or to mark points or objects, to fix paths or reference lines, or to determine horizontal or vertical planes, or planes at defined inclinations on walls, ceilings and floors, which helps with the orientation or positioning along objects. Rotating construction lasers can be used, e.g. for aligning walls, windows or door frames and for the determination of the course of plumbing or electrical installations. 
     A conventional prior art rotational constructional laser comprises a laser unit located in a housing, an emitted laser beam of which being deflected by about 90° by a deflection device. The housing usually comprises optically transparent windows or cut-outs, which enable the laser to be emitted to the outside. The deflection device rotates about an axis that in general is coincident with the optical axis. Upon rotation of the deflection device, the laser beam, which, as a result of its deflection, propagates transverse to the rotational axis of the deflection device, describes a plane in such a way that a visible or detectable path or line is generated on a surface. 
     To enable an alignment of the path according to predefined or given settings the laser unit generally is mounted tiltably in two mutually perpendicular directions in relation to a housing that encloses the laser unit. It is well known from prior art that rotating construction lasers can be levelled with the help of a reference vial, in particular two orthogonally aligned reference vials, comprising sensor means for the determination of an absolute grade of the optical core module. 
     Conventionally, for controlling the grade of a rotating construction laser and its horizontal alignment a grade mechanism is used, which comprises a tilt sensor, e.g. a reference vial, that is mounted on a tiltable grade arm, respectively two orthogonally aligned tilt sensors on one grade arm or platform. Alternatively, the European patent application EP 09177262.4 describes the use of two tilt sensors on two orthogonally aligned grade arms. 
     In prior art there are various documents available that generally disclose a rotational laser, the inclination of which can be adjusted by a grade mechanism of this design—for instance the document U.S. Pat. No. 5,485,266. It is further known from this document that the tilting of the grade arm is run by a motor, in particular a stepper motor, which rotatably drives a lead screw that is connected with the grade arm by means of a nut. The grade mechanism employs an encoder, either in its lead screw mechanism to detect a rotation speed of the lead screw mechanism, or in its driving motor, which rotatably drives the lead screw. In case of a stepper motor the number of steps performed by the stepper motor corresponds to a certain change in the tilting angle of the grade arm. In order to be able to return the grade arm to the home position the number of steps performed by the stepper motor into a certain direction is counted and in particular memorized. 
     As a result of an accumulated error due to repetitive use of the lead screw mechanism, or a wear of a part of the mechanism due to repetitive use, or a deterioration of a part of the mechanism, errors can occur and cause general deviations in angle setting, so that tilting accuracy cannot be guaranteed any longer. Also, the stepper motor can lose count of the steps performed, e.g. if the device falls to the ground or through other circumstances receives a shock. As a consequence the grade mechanism would not be capable of returning the grade arm to the correct home position any longer. In following applications of the construction laser this would then lead to an incorrect inclination and would make a recalibration necessary. 
     With a feedback sensor that measures the tilt of the grade arm in at least one position, preferably the home position, it would always be possible to reference back to the original position. None of the solutions for rotational lasers of the above-mentioned prior art documents has a form of feedback-control that allows to confirm a set grade or to show an error or deviation. A feedback sensor of this type is already known from the European patent application EP 1 901 034 A2. This document discloses a feedback sensor system with a light emitting diode (LED) and a pattern plate that are mounted on the nut of the lead screw, together casting a light pattern onto an image reception surface of a charge-coupled device (CCD) array scanner mounted on the lens barrel. This solution, though, has some disadvantages: first of all there is still the possibility that the nut and particularly the connection of the nut with the grade arm might become imprecise. This, unfortunately, reduces the reliability of the feedback sensor. Another disadvantage arises from its complex, and therefore relatively pricey, setup with a pattern plate and a CCD. 
     SUMMARY 
     It is an object of the present invention to provide a high accuracy home and narrow range grade sensor system for a grade mechanism that precisely and reliably allows returning to the home position, in this manner also correcting for deviations occurring in the connection between the nut and the grade arm. Moreover, it is a particular object of the invention to provide this solution with simple means and at reduced production cost. At least one of these objects is achieved by the home sensor system. 
     A grade mechanism of a rotating construction laser according to an embodiment of the present invention includes: a lens barrel in which a laser optical system is disposed, a levelling mechanism which supports the lens barrel tiltably, a frame structure fixed to the lens barrel and provided with a grade arm and a tilting mechanism, which tilts the grade arm relative to a horizontal plane, a tilt sensor, which is provided at the grade arm and is configured to detect a preset reference position of the grade arm, and a feedback sensor system, which is configured to detect a position of the grade arm and/or to calculate a tilting angle based on the position of the grade arm. 
     The levelling mechanism, which supports the lens barrel tiltably, is designed to tilt the lens barrel so as to detect the reference position by the tilt sensor on the grade arm and then to level the grade arm by tilting the lens barrel. 
     The grade arm is tiltable in at least one of an XZ-plane and a YZ-plane, where the XZ-plane has an X-axis and a Z-axis, the YZ-plane has a Y-axis and a Z-axis, the Z-axis is, or coincides with, an optical axis of the laser optical system, and the X-axis and the Y-axis are perpendicular to each other in a plane perpendicular to the Z-axis. In case of a preferred embodiment with two grade arms, one grade arm is tiltable in an XZ-plane, and the other one in a YZ-plane. 
     The tilting mechanism comprises a lead screw, which is rotatably driven by a driving motor, and a nut, which is reciprocated by the lead screw and engages with the grade arm and tilts the grade arm relative to the reference position. 
     According to the feedback sensor system of the present invention, and in contrast to the solution of EP 1 901 034 A2, the light source and the shadow casting object are mounted directly on the grade arm and not on the nut, therefore the feedback sensor system according to the present invention also corrects for deviations caused by errors in the nut and its connection with the grade arm, which is important for overall instrument accuracy. 
     Although the inclination of a construction laser can actually be raised up to 25%, for a normal use situation it is sufficient to have highly precise feedback accuracy within a range of +/−4% of the grade setting. The feedback sensor according to the present invention is designed for that purpose. It is a highly efficient solution, as only very simple components are required, which in particularly is interesting for cost-effective production. 
     For the feedback sensor system of the present invention there is only a simple and low cost pin required, instead of an aperture with an absolute pattern plate as disclosed in EP 1 901 034 A2. Instead of a CCD array sensor a simple optical linear sensor is sufficient, as there are no complex patterns to be evaluated but only a simple shadow, the position of which easily can be recognized by a one-dimensional sensor. Additionally, with the use of a pin and a linear sensor, no complex calculations have to be implemented to evaluate an absolute light pattern. Thus, also a separate computing unit is dispensable. Moreover, there is no gluing process required for the pin as compared to other solutions with a plastic or glass disc encoder. The pin can be produced directly as a part of the grade arm component to reduce production costs, e.g. the grade arm and the pin could be produced as a single injection moulded part or an aluminium casting. 
     Alternatively, instead of a set-up with LED, pin and optical linear detector as feedback-sensor means, also other approaches are imaginable: For instance, a digital code and an encoder sensor can be used, one of them placed on the grade arm, and the other one on the frame structure, thus detecting an absolute position of the grade arm. 
     To further decrease production costs, the supporting bearing of the grade arm can be in the form of a “V-joint”. The upper half of the bearing bushing, resting on two linear supports, is supported by a supporting pin and, like the shadow casting pin, can be produced as an integral part of the grade arm. This reduces the production costs of the single components and facilitates assembly. A lower part of the bearing bushing is attached to the bottom of the grade arm and prevents that the grade arm jumps off the supporting pin. The grade arm can also be shaped in such a way that there are more than one bearing bushings of this kind. Particularly, a version with two bearing bushings on both sides of the supporting pin can be useful. The lower part then has to be shaped accordingly to the shape of the grade arm, or there is one lower part for every bearing bushing. 
     Another advantage of the “V-joint” is enhanced repeatability, as, in contrast to a ball bearing, only two bearing parts—one inner and one outer bearing part—keep returning into the initial position. Because of two linear supports there is no geometrical over-determination as in the case of a bush bearing. Through free definition of the length of the sliding surfaces and the axial preloading the guidance can be controlled. 
     In a preferred embodiment of the invention the grade mechanism comprises two orthogonally aligned grade sensor devices with the home sensor according to the invention to measure the grade both in an X-axis and a Y-axis. The use of two independent grade arms, as described in the European patent application EP 09177262.4, circumvents the problems with inaccuracy arising from roll errors when a common grade arm with two tilt sensors is used. It is also possible to use only one single grade mechanism for this purpose. The grade mechanism then has to be mounted pivotably on the lens barrel. By being pivoted around the Z-axis, it can measure the grade sequentially in the two directions. 
     The grade mechanism of the present invention can also be used with a double grade arm, on which two tilt sensors are mounted measuring the tilt in an XZ-plane and a YZ-plane at the same time. In this case the use of optical array detectors, e.g. CCD array sensors, is advantageous in order to minimize or exclude roll errors, which occur when the double grade arm is supported by a single supporting pin and tilted independently by two tilting mechanisms. Thus, even if the grade arm is tilted only in the XZ-plane by one of the tilting mechanisms, also the position and inclination of the shadow casting object is changed. As this also affects the shadow that is cast by the shadow casting object, a linear detector eventually could detect only part of the shadow or no shadow at all. The array detector can detect a two-dimensional shadow silhouette of the shadow-casting object. In case of a cubical or cylindrical pin a rectangular shadow would be cast on the array detector. The array detector correctly detects the silhouette of the shadow, even if it is tilted due to the rolling of the grade arm, and can deduce a position of the shadow casting object. 
     It is even possible to use only one array detector for the determination of the tilt of the grade arm in both directions: The array detector then not only detects the position of the shadow but also its tilt and from the position of the shadow deduces a tilt of the grade arm in an XZ-plane and from the tilt of the shadow deduces a tilt of the grade arm in a YZ-plane. 
     An array detector can also be useful for embodiments with two independent grade arms. The array detector for instance can be used to detect lateral fluctuations—e.g. fluttering—of the shadow during the tilting process that could be due to a deterioration of the tilting mechanism. In this case a warning could be provided to the operator that maintenance service is needed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention in the following will be described in detail by referring to exemplary embodiments that are accompanied by figures, in which: 
         FIG. 1  shows a schematic representation of a tiltable rotational construction laser comprising a grade mechanism according to the invention; 
         FIG. 2   a  shows a schematic representation of a first embodiment of the grade mechanism with a sensor system according to the invention; 
         FIG. 2   b  shows a schematic representation of the embodiment of  FIG. 2   a  in a tilted state; 
         FIG. 3  shows a schematic representation of a second embodiment of the grade mechanism with a sensor system according to the invention; 
         FIG. 4  shows a diagram of exemplary light intensity received by the optical linear sensor and the corresponding angle derived from these values; 
         FIG. 5   a  shows a schematic representation of a third embodiment of the grade mechanism with a sensor system according to the invention with a digital code and an encoder sensor; 
         FIG. 5   b  shows a schematic representation of a fourth embodiment of the grade mechanism with a sensor system according to the invention with a digital code and an encoder sensor; 
         FIG. 6  shows a schematic representation of a fifth embodiment of the sensor system according to the invention; 
         FIG. 7  shows a schematic representation of a V-joint for the tiltably supporting the grade arm on the frame structure; 
         FIG. 8  shows a schematic representation of the rotational construction laser of  FIG. 1  without a frame structure, the components of the grade mechanism being mounted directly on the lens barrel; 
         FIG. 9  shows a schematic representation of sixth embodiment the grade mechanism with a sensor system according to the invention having a double grade arm; 
         FIG. 10   a - c  show three schematic representations of an array sensor with a shadow; 
         FIG. 11  shows a flow diagram that schematically illustrates the working principle of the cooperation between the tilt sensor, the levelling mechanism, the grade mechanism and the home sensor system. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  is a schematic representation of a tiltable rotating construction laser device  28  comprising the grade mechanism  1  according to the invention. The grade mechanism  1  is mounted on the lens barrel  21 , which comprises a laser optical system  20  and is tiltably supported by the levelling mechanism  23 . The laser optical system  20  emits a laser beam  24  in the direction of the optical axis  25 . The laser beam  24  is deflected by about 90° by a deflection device  26 , which rotates about the optical axis  25 . Upon rotation of the deflection device  26 , the laser beam  24 , which, as a result of its deflection, propagates transverse to the rotational axis of the deflection device, describes a plane  27 . 
       FIG. 2   a  shows the grade mechanism  1  with the home sensor system according to the invention, comprising a frame structure  8 , which is fixed to the lens barrel  21  of a laser optical system  20  (not illustrated), and a tilting mechanism  22 , which is provided at the frame structure  8  and comprises a lead screw  5 , a stepper motor  9  driving the lead screw  5  by means of a train of gears  6 , and a nut  7 , which is reciprocated by the lead screw  5 . The grade mechanism  1  further comprises a grade arm  2 , which is tiltably supported on the frame structure  8  and engages with the nut  7  of the tilting mechanism  22  by engagement means  17  of the nut  7 . A tilt sensor  10  is fixed on the grade arm  2 . In a home position the grade arm  2  is aligned in an output angle β with regard to the frame structure  8 . In this schematic representation an exemplary output angle β of 90° is shown. 
     The home sensor system according to the invention is a feedback sensor for this grade mechanism  1  to achieve acceptable repeatability within +/−4% from the true level of the instrument, i.e. the home position of the grade arm  2 . The home sensor system comprises an LED  11  (or an alternative light emitter) and a pin  12 ′, which are mounted on the grade arm and aligned in such a way that a shadow  14  is cast from the pin to a home sensor  13 , when the LED  11  emits a light towards the pin  12 ′. The home sensor  13  comprises an optical linear detector and is mounted on the cast structure  8 . 
     The pin  12 ′ is mounted on a reference point of the moveable grade arm  2  in such a way that in a home position of the grade arm  2  it is situated just in front of the centre of the home sensor  13 . The LED  11  illuminates the pin  12 ′, which consequently casts a shadow  14  onto the photosensitive surface of the optical linear detector. From the position of the shadow  14  on the surface of the linear detector a vertical position of the pin  12 ′ can be calculated relative to the longitudinal axis of the home sensor  13 . From the vertical position of the pin the absolute position of the grade mechanism, respectively the angle β 1  between the grade arm  2  and the frame structure  8 , can be determined by the home sensor  13 . Alternatively, a separate calculation unit  15  can be provided as an additional feature for this purpose. 
     Also multiple pins or other objects such as a simple hole can be used instead of the pin  12 ′, as long as this object casts a shadow  14  that can be recognized by the optical linear detector of the home sensor  13  and from which a vertical position of this object can be deduced. 
       FIG. 2   b  shows the same grade mechanism  1  for the case in which the laser plane generated by the rotating construction laser is levelled to a horizontal axis. After the tilting mechanism  22  had tilted the grade arm  2  upwards to an angle β 1 , the tilt sensor  10  on the grade arm  2  reported a tilt that consequently was compensated by a tilt of the lens barrel  21  (not illustrated), to which the frame structure  8  is fixed, and the optical axis  25 , until the tilt sensor  10  reported to be aligned horizontally again. 
     In a second embodiment of the invention, which is illustrated in  FIG. 3 , the LED  11  emits light not in a direction parallel to the grade arm  2 , but orthogonally to this. The shadow casting pin  12 ′ is mounted on a lateral extension  2   a  of the grade arm  2  in such a way that a shadow  14  is cast on the surface of the optical linear detector of the home sensor  13 , which is mounted on the frame structure  8 . Theoretically, the light can be emitted in any direction that lies within the plane in which the grade arm  2  is tilted by the tilting mechanism  21 . In  FIG. 3  a situation is shown after the grade arm  2  has been tilted by the tilting mechanism  22 , but before the levelling mechanism  23  subsequently has tilted the lens barrel  21  to level the grade arm  2 . 
       FIG. 4  is a diagram, which illustrates the working principle of the optical linear detector of the home sensor  13 . The detector measures the light intensity on its surface in a one-dimensional, linear resolution. The shadow  14  of the pin  12 ′ results in a sudden decrease of light intensity in a certain area of the photosensitive surface of the detector. The local minimum value of light intensity corresponds to a vertical position of the pin  12 ′ and an angle β 1  of the grade arm  2 . When the grade arm  2  has been returned to its home position by the tilting mechanism  22  the angle β 1  should equal the predefined output angle β. Here, a difference of around 0.3° between the measured angle β 1  and the output angle β is shown. This difference can occur if the stepper motor  9  loses count of the steps performed, or a part of the tilting mechanism  22 , e.g. the train of gears  6  or the nut  7  or the engagement means  17 , have become imprecise from deterioration. The tilt of the grade arm  2  then can be corrected by the tilting mechanism  22  until the grade arm  2  reaches its true home position at the output angle β. 
     As illustrated in  FIG. 5   a , the home sensor system can also consist of or comprise a linear or rotary encoder with an encoder sensor  16  that is mounted on the frame structure and designed for scanning a digital code  12 ″ on the surface of an angular or linear scale that is mounted on the grade arm  2 . The digital code  12 ″ contains the encoded absolute position of the grade arm  2  and can be provided by various means, such as optical, magnetic, inductive or capacitive means. The encoder sensor  16  detects a part of the code  12 ″ and from this part deduces an absolute position of the grade arm  2 . The encoder can also be placed on a lateral extension  2   a  of the grade arm  2 , as shown in  FIG. 5   b.    
     A further exemplary embodiment of the grade mechanism  1 , having certain distinct feature designs but in general the same working principle as the embodiments described above, is illustrated in  FIG. 6 . As shown here, it is also possible that a separate calculation unit  15  is provided, the motor  9  can drive the lead screw  5  without a gear ratio adaptation by a train of gears  6 , the position of LED  11  and shadow casting pin  12 ′ may vary as well as the design of the tiltable support  4  on the frame structure  8 . Also, there are different designs of the engagement means  17  for the engagement of the nut  7  and the grade arm  2  thinkable. 
       FIG. 7  shows an embodiment of the end of the grade arm  2  that is supported tiltably on the frame structure  8  with a V-shaped joint. The tiltable support  4 , which holds the end of the grade arm  2 , here is a simple pin, particularly made of steel. At this end the grade arm  2  has a lower part  3 , which is attached to the grade arm. Both the grade arm  2  and the lower part  3  have a V-shaped notch. When the grade arm  2  and the lower part  3  are put together, these V-shaped notches form a common opening. Thus, the grade arm  2 , respectively the upper half of the bearing bushing, rests on the supporting pin  4  by two linear supports  19 . The lower part  3 , respectively the lower half of the bearing bushing, prevents that the grade arm  2  jumps off the supporting pin  4 . Here, an embodiment with two bearing bushings and one supporting pin  4  is illustrated, but there are also various alternative embodiments with one or more than two bearing bushings and more than one supporting pin  4  thinkable. 
     The frame structure  8  of the grade mechanism  1  can be mounted to the lens barrel  21  in various ways, e.g. it can be glued or bolted to the surface of the lens barrel  21 . It also can be produced as an integral part of this. In another alternative embodiment, the frame structure  8  of the grade mechanism  1  is totally dispensable. This is shown in  FIG. 8 . All components of the grade mechanism  1  that in the embodiments described above are mounted to the frame structure  8  can also be mounted directly to the lens barrel  21 . The lens barrel  21  could also be produced in such a way that its surface comprises the necessary mountings for these components. 
       FIG. 9  schematically shows a sixth embodiment of the invention in a top view. In this embodiment a grade mechanism  1 ″ with a double grade arm  2 XY is used. Of the grade arm  2 XY one part is aligned in the direction of the X-axis  27  and the other in the direction of the Y-axis  29 . Both parts of the grade arm  2 XY each have the features of the first embodiment: a light emitter  11 X/ 11 Y, a shadow casting object  12 X/ 12 Y and a tilt sensor  10 X/ 10 Y (not shown). The double grade arm  2 XY is supported by a pin  4 ″ and can be tilted in an XZ-plane by a first tilting mechanism  22 X and in a YZ-plane by a second tilting mechanism  22 Y. 
     With this grade mechanism  1 ″ it is possible to measure the tilt of the grade arm  2 XY relative to the X-axis  27  and the Y-axis  29  at the same time. In  FIG. 9  the sensor means to receive and detect the shadows  14 X/ 14 Y cast by the shadow casting objects  12 X/ 12 Y are area array detectors  13 X/ 13 Y, which detect the shadows  14 X/ 14 Y two-dimensionally. 
       FIGS. 10   a ,  10   b  and  10   c  schematically show the surface of an array detector  13 X with a representation of a rectangular shadow  14 X. In  FIG. 10   a  the position of the shadow  14 X represents the home position of the grade arm  2 XY in the XZ-plane, e.g. a tilting angle β of 0°. As the shadow  14 X stands upright, there is also no tilt in the YZ-plane. In  FIG. 10   b  the position of the shadow  14 X is elevated. This position represents an upward tilt of the grade arm  2 XY in the XZ-plane. Also in this figure the shadow  14 X stands upright, showing that there is no tilt in the YZ-plane with respect to the Y-axis  29 . In  FIG. 10   c  the shadow  14 X is tilted to the left, which indicates a rolling of the grade arm  2 XY due to a downward tilt in the YZ-plane. 
     As the vertical position of the shadow  14 X represents a tilt of the grade arm in the XZ-plane, and from the tilt of the shadow  14 X a tilt of the grade arm  2 XY in the YZ-plane can be deduced, it is also possible to use only a single array detector  13 X for the detection of the home position in both directions. 
     In  FIG. 11  a flow diagram is shown that schematically illustrates the working principle of the interaction of the tilt sensor  10 , the levelling mechanism  23 , the tilting mechanism  22  and the home sensor system: When the rotating construction laser device is set-up and switched on, and the operator inputs that a horizontal plane shall be projected, the home sensor verifies whether the position of the grade arm  2  is the home position. In case that there is a deviation, the tilting mechanism  22  readjusts the tilt of the grade arm  2  until the home sensor verifies that the grade arm  2  has reached its home position. If the grade arm  2  is in its home position the levelling mechanism  23  levels the lens barrel  21  according to information provided by the tilt sensor  10  on the grade arm  2 . 
     When the operator of the device selects an inclination grade the tilting mechanism  22  tilts the grade arm  2  accordingly, e.g. by counting steps of the stepper motor  9 . As the tilt sensor  10  is mounted on the grade arm  2 , it is then no longer levelled. Thus, the levelling mechanism  23  tilts the lens barrel  21  until the grade arm  2  and the tilt sensor  10  are levelled again. The lens barrel  21  and the laser plane generated by the rotating construction laser then have the desired inclination. This is repeated as long as the operator selects a different inclination and until the device is switched off. 
     Optionally, after the use of the device the tilting mechanism  22  returns the grade arm  2  to the (assumed) home position, and the home sensor verifies whether the position of the grade arm  2  is the home position. This option in  FIG. 9  is represented by broken lines. It is advantageous especially in the case that the tilt of the grade arm  2  exceeds the perception angle of the home sensor. 
     An optional additional function of the home sensor is the possibility to verify any tilting angle β 1  of the grade arm  2  within a range that is perceptible by the sensor means. The range depends on the dimensions of the linear or array detector and should reach at least 4°, in particular at least 10°, in both directions. 
     Although the invention is illustrated above, partly with reference to some preferred embodiments, it must be understood that numerous modifications and combinations of different features of the embodiments can be made. All of these modifications lie within the scope of the appended claims.