A position control arrangement, especially for a surveying instrument, and a surveying instrument

SWEDEN (12) PATENT WRITING (13) C2 (11) 524 329

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2004-07-27

2004-03-21

2002-09-20

2002-09-20 (19) SE ₍₅₁₎

International class ⁷G01C 15/00, 1/02

PATENT AND REGISTRATION (45) (41) (22) (24) (62) (86) (86) (83)

Patent filed Application widely available The patent application was submitted on expiration date

Tribal application number

International filing date Filing date for European patent application Deposit of microorganism (21) Patent application number 0202793-6

Application received as:

ΡΠ Swedish patent application completed international patent application with number □ converted European patent application with number (30) Priority information (73) (72) (74) (54) (56) (57)

Assignee

INVENTOR

AGENT

NAME

Trimble AB, Box 64 182 11 Danderyd SE

Magnus Westermark, Enskede SE, Mikael Hertzman, Sollentuna SE, Ulf Berg, Stockholm SE, Thomas Klang, Sollentuna SE Albihns Stockholm AB

A position control arrangement, especially for a geodetic instrument, and a geodetic instrument

CALLED PUBLICATIONS:

JP A 11 311 517 (G01C 15/00), US Ä 5 852 493 (uc 33/291) SUMMARY: A position control arrangement (30) for controlling the rotational position of a moving unit (2), geodetic instrument, including an electric motor ( 12) for rotating said movable unit (2) around a predetermined axis of rotation (9), and wherein guide means (31-34, 17) are provided for controlling motor operation in response to a designated rotational position of the movable unit. The motor is a direct-driven motor whose drive shaft constitutes the axis of rotation of the movable unit and the motor is adapted to selectively operate in either a first normal operating mode of rotation of the moving unit to a desired position or in a second friction operating mode to provide resistance to a forced rotation of the moving unit during a rotation from a predetermined position to a new position. A control unit (36) is provided to detect a forced rotation of the movable unit. The control unit (36) is arranged to disengage the controller (34) from the motor (12) and automatically change the mode of operation accordingly. A geodetic instrument is also included, which exhibits such characteristics.

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The numbers in brackets indicate international identification code, INID code. Letters in clamps indicate international document code.

Summary

A position control arrangement (30) for controlling the rotational position of a movable unit (2), geodetic instrument, comprising an electric motor (12) for rotating said movable unit (2) around a predetermined rotation axis (9), and wherein control means (31) are provided. -34, 17) for controlling the engine's drive in response to an intended rotational position of the moving unit. The motor is a direct-driven motor whose drive shaft constitutes the axis of rotation of the moving unit and the motor is arranged to selectively operate in either a first normal operating mode of rotation of the moving unit to a desired position or in a second friction operating mode to provide resistance to a forced rotation of the moving unit during a rotation from a predetermined position to a new position. A control unit (36) is provided to detect a forced rotation of the movable unit. The control unit (36) is arranged to disengage the controller (34) from the motor (12) and automatically change the mode of operation accordingly. A geodetic instrument is also included, which exhibits such characteristics.

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Field of the Invention

The present invention relates to a position control arrangement, in particular for a geodetic instrument as defined in the preamble of claim 1, and also a geodetic instrument defined by the preamble of claim 8.

Background of the invention

In geodetic instruments, especially so-called total stations, the setting of a moving unit in the instrument is required around a horizontal and a vertical axis by rotating the moving part of the instrument around the required axes. The rotation about an axis is preferably done by means of a gearshift either by hand for a manual instrument or by the use of an electric motor connected to the gear unit of an automatic instrument intended to automatically move from one position to another, e.g. . using a target tracking arrangement. Such gear arrangements must exhibit very high precision to serve their purpose and, as a result, are expensive. In addition, in order to meet strict precision requirements, a preload of the gear arrangement is required. Due to the resulting deadlock and hysteresis in the gear arrangement, there is a need for an automated instrument to have angular sensors on both the motor and on the moving unit to obtain a sufficiently stable and accurate servoloop to control the motor.

The presence of a gear arrangement between the motor and the moving unit prevents forced movement by the hand of the moving unit to a new position, since the gears will block such movement. However, in order to allow a forced movement by the hand of the movable unit to a new position, it has been customary to provide a frictional coupling between a gear arrangement and the movable unit, thereby allowing the movable unit to be moved while the gear arrangement remains in position.

By using a gear arrangement and two angle sensors as well as a friction clutch on each shaft around which the moving unit is to be moved by means of a motor, the geodemeter instrument becomes relatively complicated and expensive. There is therefore a need for an improved design in these respects.

With respect to the general rotation of a moving unit in a geode meter instrument, it is previously known by US 2002/0005944 A1 to provide an optical transmitter in which a main unit is rotated about a vertical axis using an electric direct-driven motor and where there are means for delivering light signals to a remote receiver at a particular rotation position of the main unit. However, in an arrangement of this kind, there is no need or intention to stop the main unit in a special rotational position. There is also no need to make a forced rotation of the main unit.

The object of the invention

An object of the invention is to provide an improved position control arrangement which is simpler and which is cheaper to manufacture. A further object is to provide a position control arrangement which is highly precise in use, yet easy to use. A further object is to provide an arrangement that requires less space. A further object is to provide an improved geodetic instrument.

Summary of the Invention

According to the invention, there is provided a control arrangement as defined in claim 1 and also a geodetic instrument as defined in claim 8.

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By providing a direct-driven electric motor, the need for a clutch arrangement is eliminated and by enabling selective operation of the motor in a normal mode or in a friction mode, the need for a conventional friction clutch is eliminated to allow for forced rotation of the movable unit.

By providing means for automatically switching between the modes of operation of the engine in response to the presence of an external force affecting the moving unit, a simple mode of operation is made possible because the operator need not worry about choosing a mode of operation.

In a further embodiment, a friction control unit is adapted to control, in the friction mode, the magnitude of the resistance to forced rotation, and preferably said friction control unit is arranged so that the resistance is limited to a selected value. In this way, good precision can be obtained when manually moving the position of the moving unit.

The elimination of the coupling arrangement provides a faster and calmer operation as the moving unit moves from one position to another.

Further objects, features and advantages of the invention will become apparent from the description below of a preferred embodiment with reference to the accompanying drawings.

Brief description of the drawings

Fig. 1 is a front view of a geodetic instrument utilizing the invention; Fig. 2 is a schematic sectional view of a motor arrangement used in a position control arrangement according to the invention; and Fig. 3 is a block diagram illustrating a position control arrangement according to the invention.

Description of a preferred embodiment

Fig. 1 is a front view of a geodetic instrument 1 of the type commonly referred to as a total station. A movable unit 2, comprising optical equipment of the total station represented by a lens 3, is carried in a housing 4 in such a way that it can be pivoted relative to the housing 4 around a substantially horizontal axis 5 indicated by a double arrow 6. The housing 4 comprises a base 7 by means of which it is supported on a frame 8 in such a way that it is rotatable relative to the frame 8 around a substantially vertical axis 9 shown by a double arrow 10. Thus, by rotating the movable unit 2 around the two axes 5 and 9, the movable unit 2 can be oriented in any desired position for the purpose of performing a intended measurement operation. For movement of the movable unit 2 around the shaft 5, there is a motor arrangement 11 in the housing 4 and for movement of the housing 4 and the movable unit 2 around the shaft 9, a similar motor is arranged 12 in the frame 8. Each of the two motor arrangements 11, 12 are included in a position control arrangement related to respective axes 5 and 9 and will be described below. The geodetic instrument 1 is intended to be supported via the stand 8 on a tripod or similar equipment in a conventional conventional manner.

The two motor arrangements 11 and 12 are similar in appearance and for simplicity only the motor arrangement 12 will now be described, with reference to Fig. 2, where parts of the frame 8 have been excluded for the sake of clarity. A drive shaft 13 of the motor is rotatably supported by a bearing 14 which is secured to an upper part of the frame 8 and engages the non-rotatable base 7 of the housing 4 so that the base 7 can be rotated using the drive shaft 13 to indirectly rotating the movable unit 2 around the shaft 9. The rotor 15 of the motor is supported in a non-rotatable manner by the drive shaft 13 while the stand 8 supports the stator 16 of the motor in a non-rotatable manner.

In order to be able to determine the rotational position of the drive shaft 13, and thus indirectly of the moving unit 2, a position detecting arrangement 17 is provided, it is arranged to detect the relative position between the stator 16 and the rotor 15 in the embodiment shown, the position detecting arrangement 17 comprises two detecting units 18 and 19 which are diametrically opposed to each other around the drive shaft 13. These two detecting units 18, 19 are of substantially similar design. In each of them, a light emitter 20 fixed to the stator 16 emits intermittent light to a reflector 21 attached to the drive shaft, from said reflector light is reflected on a sensor 22 attached to the stator 16. On its way from the reflector 21 to the sensor 22, the light passes through a transparent disk 23 which is non-rotatably fixed to the drive shaft 13 and which is provided with a pattern that causes specific position signals generated in the sensor 22 as the drive shaft 13 rotates. By using signal production at a high rate, a high degree of precision can be obtained by the position detecting arrangement 17.

The two detecting units 18, 19 may conveniently be arranged so that their reflected light passes through radially different regions with mutually different patterns on the transparent disk 23 to allow an improved accuracy in the positioning arrangement 17.

It should be noted in Fig. 2 that the two detecting units 18 and 19 of the position detecting arrangement 17 are arranged in a substantially closed environment within the motor arrangement 12 and for that reason are well protected. The number of detecting units 18,19 as well as their location and their performance can, of course, be varied as desired.

In order to control the motor arrangements 11 and 12 to obtain a desired position of the moving unit 2, a position control arrangement is provided for each of the two motor arrangements. These position control arrangements are similar to perform η Λ

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Fig. 3 schematically shows in block diagram form a position control arrangement 30 according to the invention related to the motor arrangement 12. Input means 31, through which the position control arrangement 30 receives information about the transmitted position or position of the moving unit 2 driven by the motor arrangement 12. Such intended position information can be provided to the input means. by input from an operator, e.g. via a joystick or by other means, or automatically by one or more units in the measurement system. As an example, the measurement system may include a target tracking arrangement to enable the moving unit to automatically follow a target. Several other similar applications are known in the past and need not be described in further detail herein. Signals from the input means 31 are, during normal operation, fed to a filter unit 32 and thence to an adding unit 33, the signal of which is fed to a regulator 34 which controls the current to the motor 12. In response to the transmit input, the motor 12 causes a movement of the movable the unit 2 (in this case via the housing 4 and around the shaft 9), which in turn causes the corresponding position detecting arrangement 17 to generate a position signal. In a connection between the position detecting arrangement 17 and the adding unit 33, a character change unit 35 is arranged which changes the sign of the position signal which is fed to the adding unit

33rd In this way, a control loop is provided for guiding the motor 12 to a designated rotation position. As long as there is a difference between the signals received in the adding unit 33 from the filter unit 32 and the character change unit 35, the controller 34 will receive a signal causing the motor 12 to operate, but as soon as the difference is zero, the controller 34 will not receive any signal and the motor will stop automatically.

A control unit 36 ​​is also provided which contains inputs from the input means 31, the location detecting arrangement 17 and the adding unit 33.

329 On the basis of these signals, the control unit 36 ​​can determine whether the directional control arrangement is to operate in the normal manner as shown above, or in a friction operation, which will be described below. To accomplish this, the control unit 36 ​​controls a switching arrangement 37 comprising two switches 38 and 39 and included in the position control arrangement. The switch 38 is located between the input means and the filter unit 32 and can connect the filter unit 32 either with the input means 31 (normal operation, shown in solid line) or with the position detecting arrangement 17 (friction operation, shown in dashed line). The switch 39 is located between the controller 34 and the motor 12 and can connect the motor 12 either to the controller 34 (normal operation, shown with a solid line) or with the character change unit 35 via a friction control unit 40 (friction operation, shown with a dashed line).

If, during normal operation, an operator wishes to quickly adjust the moving unit 2 to a new angle or position, the operator can, according to the invention, grasp the moving unit 2 and manually turn it to the desired angle and at the same time experience a certain force which counteracts movement. When the operator grasps the moving unit 2 in such a way, the position detecting arrangement 17 will detect a large and rapid change in the position of the moving unit 2. This will cause a large difference between the signals received by the adding unit 33 and this large difference will be noticed by the control unit 36, which now determines that the operating mode is no longer normal and therefore influences the switches 38 and 39 to change from the normal mode of operation. , represented by solid lines, to the friction mode, represented by dashed lines. As a result, the filter unit 32 will now receive input signals directly from the position detecting arrangement 17 to obtain information on the current position of the moving unit

2nd In addition, the motor 12 will be connected to the friction controller 40 rather than to the controller 34.

In response to the forced movement detected by the moving unit 2, the friction control unit 40 causes the motor 12 to produce a torque that resists the forced movement. The magnitude of this torque is preferably determined as a function of the temporary acceleration and velocity of the forced movement, to adjust the magnitude of the torque to the type of motion being performed. It is to be understood that the nature of the resistance torque can be selected in many ways and can be easily altered by software changes in the friction controller 40. In order to protect the motor 12, it is preferred to limit the size of the torque allowed by the friction controller 40.

When the forced movement of the moving unit 2 ceases, on the basis of the position information received from the position detecting arrangement 17, the control unit 36 ​​will note that the velocity change of the position has become relatively small and therefore decide, on the basis of this analysis and other information received. , that the position control arrangement 30 should now be operated in normal operation. As a result, switches 38 and 39 will be operated to reset arrangement 30 from friction mode to normal mode (shown in solid lines in Fig. 3).

The friction controller 40 may include a derivation module 41 for determining the velocity change in the angular position of the movable unit 2, a proportioning module 42 for calculating the required torque needed, and a limiting module 43 for limiting the permissible torque. The counter-torque generated in the fiction operation is similar to a viscous friction from a conventional friction device such as a sliding clutch or similar arrangement.

It will be apparent that the position control arrangement shown for the motor arrangement 12 may exhibit some degree of commonality with a corresponding position control arrangement related to the second motor arrangement 12, in order to obtain a simpler and more compact embodiment comprising fewer parts. Thus, e.g. the control unit and other units have a channel for each of the motor arrangements.

In order to obtain good precision, it is desirable to use a sampling rate of the angular position of about 1000 Hz and to allow the light emitters to generate very short flashes of light. Each flash could last for only a few microseconds. The angular velocity of each motor arrangement 11, 12 could have a maximum value of about 1 or 2 rad / s, and the maximum angular acceleration could be around 3 rad / s². It is also desirable that the power consumption of each motor be as low as possible, since the motors will normally be battery operated to provide flexible use of the geodetic instrument.

For precise control of the engine, it is desirable to take the moment of inertia of the parts to be moved into account to control the torque so that adequate acceleration and deceleration are obtained to obtain fast and accurate positioning.

It will also be apparent that within the scope of the invention, various changes may be made in addition to those mentioned in the embodiments shown.