Method and apparatus for machine element control

A method of monitoring the location, and the orientation of a machine element, and apparatus for monitoring and controlling the operation of the machine include a robotic total station and a plurality of targets in known positions relative to the machine element. The total station, located at a known location near the machine element, repeatedly, successively determines the location of each target. Acquisition and re-acquisition of the targets is aided by stored data regarding the prior locations and movements of the targets. Further, active targets may be used to facilitate re-acquisition. The operation of the machine is controlled based upon the location and orientation of the machine element.

CROSS-REFERENCE TO RELATED APPLICATIONS

Not applicable.

Not applicable

BACKGROUND OF THE INVENTION

This invention relates generally to machine control methods and systems for machines having machine elements, such as for example construction machines such as graders, milling machines, pavers, and slip-forming machines. More particularly, the present invention relates to a machine control method and system using a stationary tracking station that determines the location and orientation of the machine element, and transmits this information to the machine for use in controlling the operation of the machine element.

It is desirable to monitor the position and movement of various types of relatively slow-moving machines, such as for example construction machinery including graders, pavers, and slip-forming, as well as the position, orientation and movement of machine elements associated with such machines. This information can then be used to control the operation of the monitored machines.

While in the past, machine operators have relied on physical references set by surveyors at a job site when operating equipment of this type, automatic machine control systems have also been developed that provide an optical reference, such as a reference beam of laser light, to specify elevation. In such a system, a laser receiver mounted on the grader senses the laser beam and provides an elevation reference. The sensed elevation of the reference laser beam is compared to a set point, either by a machine operator or by an automatic control. The movement of the machine element is then controlled based on this information, either manually by an operator or automatically by an automated control. The set point, that is, the desired vertical position, may be adjusted depending upon the x and y location of the machine at the work site, with this machine location being determined in any of a number of ways.

Total stations have been used both for surveying and for machine control. In a typical surveying application, a total station, positioned at a known location, directs a beam of laser light to a target positioned by a surveyor at a point to be surveyed. The target includes retroreflectors which reflect the beam back to the total station. By measuring the time of flight of the beam, the distance between the total station and the target is determined. By also measuring the direction of the beam from the total station to the target, i.e., the altitude and azimuth angles that define a vector from the total station to the target, the location of the target is precisely determined.

Robotic total stations have been developed that are capable of locating and tracking a target without being attended by an operator. With a robotic total station, the surveyor moves the target around the work site. Servo motors in the robotic total station cause it to rotate toward the target, providing precise angular and distance measurements as the surveyor moves to various locations at the work site. The total station automatically tracks the remote target as it moves, thus providing real-time position data for the target.

Robotic total stations have also been used for machine control. They typically use a single robotic station with single target per machine. The position information is communicated to the machine control system remotely where the control software calculates the machine element position relative to the job plan. Multiple targets on a single machine element have required multiple robotic stations. Such arrangements have been somewhat complicated. There is, therefore, a need for a simplified system using a single total station.

SUMMARY OF THE INVENTION

This need is met by a method of monitoring the location, and the orientation of a machine element according to the present invention. The method includes the steps of: providing a plurality of targets in known positions relative to the machine element; providing a total station at a known location near the machine element; repeatedly, successively determining the location of each target using the total station; and determining the orientation of the machine element based on the locations of the targets.

The step of repeatedly, alternately determining the location of each target using the total station comprises the step of directing a beam of laser light from the total station repeatedly, successively to the targets, and measuring the distances from the total station to each of the targets and the directions to each of the targets.

The step of repeatedly, successively determining the location of each target using the total station comprises the step of directing a beam of laser light from the total station successively to the targets by successively acquiring the targets.

The step of successively acquiring the targets may comprise the step of storing the detected locations of each of the targets and the movement history of each of the targets, and predicting the locations of each of the pair of targets as the laser beam is directed successively to the targets, whereby the reacquisition of the targets is facilitated. This may be done at the robotic station itself or by the machine control system and the predicted position communicated back to the robotic station.

The step of providing a plurality of targets in known positions with respect to the machine element may comprise the step of providing a pair of targets that are fixed in known positions on the machine element and moveable with the machine element.

The step of providing a pair of targets that are fixed in known positions on the machine element and moveable with the machine element may comprise the step of providing a pair of targets that are fixed in position with respect to the machine element.

A method of controlling the movement of a machine element, comprises the steps of: providing a plurality of targets in known positions with respect to a moving machine element; providing a total station at a known location near the moving machine element; repeatedly, successively determining the location of each target using the total station; transmitting the location of each target determined by the total station from the total station to the machine; at the machine, determining the orientation of the machine element based on the locations of the targets; and, at the machine, controlling the movement of the machine element in response to the determined locations of the targets and the determined orientation of the machine element.

The step of repeatedly, successively determining the location of each target using the total station comprises the step of directing a beam of laser light from the total station repeatedly in succession to each of the plurality of targets, and measuring the distances from the total station to each of the plurality of targets and the directions to each of the pair of targets.

The step of repeatedly, successively determining the location of each target using the total station comprises directing a beam of laser light from the total station to the targets by alternately acquiring the targets in succession.

The step of acquiring the targets in succession comprises the step of storing the detected locations of each of the targets and the movement history of each of the targets, and predicting the locations of each of the targets as the laser beam is directed repeatedly in succession to each of targets, whereby the reacquisition of the targets is facilitated.

The step of providing a plurality of targets in known positions with respect to the machine element comprises the step of providing a pair of targets that are fixed in known positions on the machine element and moveable with the machine element.

The step of providing a pair of targets fixed in known positions on the machine element and moveable with the machine element comprises the step of providing a pair of targets that are fixed in position with respect to the machine element.

A system for controlling the movement of a machine element on a machine, comprises: a control on the machine for control of the machine element; a plurality of targets mounted in known positions with respect to a moving machine element; and a total station positioned at a known location near the moving machine element. The total station includes a laser light source for providing a beam of laser light on the targets, a target prediction unit for predicting the locations of each of the targets based on previous locations and movement of the targets, a beam control for directing the beam of laser light on the targets and repeatedly, successively determining the location of each target, and a transmitter for transmitting the locations of each of the targets to the control on the machine. The measured locations of the targets can be used to control the location, orientation, and movement of the machine element.

The total station may further include a measurement unit for measuring the distances from the total station to each of the targets, and for determining the directions to each of the targets. The plurality of targets may comprise a pair of targets.

Accordingly, It is an object of the present invention to provide an improved system and method for controlling a machine and machine element. Other objects and advantages of the invention will be apparent from the following description, the accompanying drawings, and the appended claims.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Reference is made toFIGS. 1–3, which illustrate the apparatus and method of the present invention for monitoring the location and orientation of a machine element, and controlling the movement of the machine element.FIG. 1depicts a robotic total station10, which is comprised of a base portion12, a rotational alidade portion14, and an electronic distance-measuring portion16. Rotational alidade portion14rotates on base portion12about a vertical axis, with a full 360-degree range of rotation. Electronic distance-measuring portion16similarly rotates within rotational alidade portion14about a horizontal axis. With this arrangement, it is possible for the distance-measuring portion16to be oriented toward a target in virtually any direction so that the distance can be measured from the total station10to the target.

The electronic distance-measuring portion16transmits a beam of laser light through lens18toward a target20. As seen inFIG. 2, target20includes a plurality of retroreflective elements22which are positioned circumferentially therearound. Retroreflective elements22may be retroreflective cubes or other reflectors which have the property of reflecting received light back in the direction from which it originated. Target20also includes an LED strobe24which directs a strobe light upward onto inverted conical reflector26. The light is reflected outward from the reflector26in all directions and provides a means of assisting the robotic total station in acquiring or in reacquiring the target20. The frequency of the strobe light or its frequency of pulsation may be set to differ from that of other targets, thereby permitting a total station to distinguish among targets.

A beam of laser light transmitted by the total station10ofFIG. 1to the target20is reflected back from the target20, and is then received by the electronic distance-measuring portion16through lens18. The laser light may, in other total station arrangements, however, be received through a separate lens. Preferably, the beam of laser light is pulsed, facilitating the measurement of the time required for the light to travel from the total station10to the target20and return. Given an accurate time-of-flight measurement, the distance between the total station and the target can be computed directly. The azimuth, angle and altitude angle measurements, in conjunction with the computed distance between the total station10and the target20, then provide the polar coordinates of the location of the target20with respect to the total station10.

The robotic total station10includes a control28, having a keypad30and display32. The robotic total station10includes a servo mechanism (not shown) which orients the electronic distance-measuring portion16, by controlling its rotation around the horizontal axis, and controlling the rotation of alidade portion14about a vertical axis. The robotic total station10further includes a radio transmitter (not shown) and antenna34which permit communication of location and measurement data to a remote location.

Reference is made toFIG. 3, which illustrates diagrammatically a system for controlling the movement of a machine element36on a machine38. The machine element is shown as a blade36that is moved on machine38by hydraulic cylinders40. A control42on the machine38controls the operation of the machine38, including the movement of the blade36by cylinders40. A pair of targets44and46are mounted in known positions with respect to the machine element36, by means of masts48and50. An inclinometer45provides an indication of the angular pitch of the machine element36.

Total station10is positioned at a known location near the machine38and machine element36. The total station10includes a laser light source for providing a beam of laser light from lens18that can be directed to either of the targets44and46. The control28in the total station10includes a target prediction unit for predicting the locations of each of the pair of targets44and46based on previous locations and movement of the targets or alternatively the predicted position information is calculated by control42and transmitted back to the total station10. The control28includes a beam control that directs the beam of laser light on the targets44and46, and repeatedly, alternately determines the location of each target. The path of the beam to target44is labeled as52and the path of the beam to target46is labeled as52′. The transmitter in the total station10transmits the locations of each of the targets44and46via antenna34and antenna54on the machine38to the control42on the machine38.

It will be appreciated that the measured locations of the targets44and46can be used to determine the desired location, orientation, and movement of the machine element36relative to the total station10. This information can then be used by control42to operate the machine38.

The location and the orientation of machine element36is monitored by the total station10and this information is provided to the machine38where it can be used for automatic or manual control of the element36. The pair of targets44and46are provided in known positions relative to the machine element. InFIG. 3, arrangement is illustrated, for example, in which the targets are mounted symmetrically on masts48and50at each end of the machine element36. The total station10is providing at a known location near the machine element36. In the method of the present invention, the location of each of the targets44and46is repeatedly, alternately determined using the robotic total station10. The location and orientation of the machine element36can then be determined by the control42based on the locations of the pair of targets44and46. It will be appreciated that a plurality of targets, such as three or four targets, may be used, with the total station repeatedly, successively determining the position of each of the plurality of targets. Such an arrangement may provide greater accuracy and may also facilitate operation of the system if the total station is unable to acquire one of the targets.

The beam of laser light is directed alternately to one and then to the other of the pair of targets44and46along paths52and52′ in relatively rapid fashion. The targets are alternately acquired by the robotic total station10with the help of strobed pulses of light reflected outward in all directions from conical mirrors56and58. The measured locations of the targets are stored in the control28or alternatively control42. This provides the movement history of each of the targets, and permits the further locations of each of the targets to be predicted by a target prediction unit in control28or transmitted back to it from control42. This, in turn, facilitates their acquisition as the laser beam is directed alternately to one and then to the other of the pair of targets, or to each of the targets in succession in the event that more than two targets are used. It will be appreciated that, based on the locations measured for targets44and46, the orientation of the machine element36may also be determined by control42. Control42may also be responsive to inclinometer45which provides an indication of the orientation of the element36from one end to the other. The frequency with which the total station switches between the two targets will vary, depending upon the speed with which the machine element36and targets44and46are to be moved.

If desired, the pair of targets44and46may be fixed in symmetrical positions with respect to the machine element36, although this is not required. All that is needed is that the targets be in a known, fixed relationship with regard to the element36. If the position of the targets is known, the position of the machine element is also known. It will be further appreciated that although the description is of an arrangement having two targets, a system employing three or more targets may also be utilized.

It will be appreciated that once the locations of the targets are determined, this information can then be used to control the movement of the machine element. The location information is transmitted to the machine38and the orientation of the machine element36is determined by the control42. For example, a desired worksite contour may be stored in computer60and used by the control42to control element36to achieve this contour. The desired surface configuration of an area to be paved may be stored in the computer60, for example, if a paver is being controlled. The movement of the machine element36is controlled by control40, either automatically or manually, so that the machine element36moves along a desired path.

While certain representative embodiments and details have been shown for purposes of illustrating the invention, it will be apparent to those skilled in the art that various changes in the invention disclosed herein may be made without departing from the scope of the invention, which is defined in the appended claims.