Classifications

• • G—PHYSICS
  • G05—CONTROLLING; REGULATING
  • G05B—CONTROL OR REGULATING SYSTEMS IN GENERAL; FUNCTIONAL ELEMENTS OF SUCH SYSTEMS; MONITORING OR TESTING ARRANGEMENTS FOR SUCH SYSTEMS OR ELEMENTS
  • G05B19/00—Programme-control systems
  • G05B19/02—Programme-control systems electric
  • G05B19/18—Numerical control [NC], i.e. automatically operating machines, in particular machine tools, e.g. in a manufacturing environment, so as to execute positioning, movement or co-ordinated operations by means of programme data in numerical form
  • G05B19/401—Numerical control [NC], i.e. automatically operating machines, in particular machine tools, e.g. in a manufacturing environment, so as to execute positioning, movement or co-ordinated operations by means of programme data in numerical form characterised by control arrangements for measuring, e.g. calibration and initialisation, measuring workpiece for machining purposes
  • G05B19/4015—Numerical control [NC], i.e. automatically operating machines, in particular machine tools, e.g. in a manufacturing environment, so as to execute positioning, movement or co-ordinated operations by means of programme data in numerical form characterised by control arrangements for measuring, e.g. calibration and initialisation, measuring workpiece for machining purposes going to a reference at the beginning of machine cycle, e.g. for calibration
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
  • G01D5/00—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable
  • G01D5/12—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means
  • G01D5/244—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means influencing characteristics of pulses or pulse trains; generating pulses or pulse trains

Definitions

• the invention relates to a method for absolute position determination on an axis of rotation and the associated device with the features in the preamble of the main method and device claim.
• absolute position measuring systems are used for absolute position determination, the measuring range of which is greater than the possible rotational path of the axis. These systems output a defined absolute position value for each axis position, which can be used directly in the machine control or elsewhere.
• Such measuring systems consist in principle of two parts, namely a cyclically absolute precision measuring system, which is used for the precise determination of the angular position of the axis of rotation. Its cycle is usually limited to one revolution of the axis. If the axis makes several revolutions, a coarse system, which is absolute over the entire measuring range, is used to determine the cycle in which the precision measuring system is located. Depending on the number of possible axis rotations, the coarse measuring device itself is divided into several stages.
• the previously known absolute position measuring system has the disadvantage that, due to its multiple stages, it requires considerable construction work, which increases with the number of axis rotations to be checked. Its area of application is limited to a certain cycle and can only be expanded through upstream reductions or additional levels in the position measuring system. Due to its size, it can not at any point Axis of rotation must be arranged, and sometimes must be housed in vulnerable places.
• the invention solves this problem with the features in the main method and device claim.
• a cyclically absolute position encoder is used, the cycle of which is smaller than the rotational range of the axis.
• the position encoder transmits an absolute position value only within its cycle.
• the absolute position values are compared and evaluated.
• the absolute position value that is ultimately available consists of a low-value part that corresponds to the position of the position encoder and a higher-value part that corresponds to the cycle in which it is located.
• the position measuring system according to the invention has an arbitrarily expandable working range and is suitable for all types of axes.
• the translatory movement can be converted into a rotary movement.
• the implementation is then considered as the axis of rotation.
• the position measuring system has a single-stage position transmitter, that is to say only one precision measuring device.
• the position encoder can also be a multi-stage cyclical absolute encoder be formed, the cycle is smaller than the measuring range.
• the position sensor can be of any design, for example as an optically scanning sensor, potentiometer, resolver or the like. It is coupled to a comparison circuit, which can be assigned to the position measuring system as an independent hardware component. However, the comparison circuit can also be integrated in the machine control, for example in the case of a manipulator or a multi-axis industrial robot. In the control, the comparison, evaluation and storage operations can be carried out via a special program part in the computer unit which is already present.
• the position transmitter can query the position values continuously or in cycles.
• continuous polling the direction of rotation and the cycle change are obtained directly from a comparison of the position values according to size and sequence.
• intermittent polling there are different variants depending on the height of the maximum possible rotational speed and acceleration of the rotary axis or the encoder axis as well as the available cycle time.
• the direction of rotation can be continuously monitored in addition to the cycle change. If the axis has higher rotational speeds and the cycle time is limited, a second option can be used. Here, the maximum speed is queried at least once per cycle, but the cycle does not go through completely between two queries. In this variant, the direction of rotation detection is only queried at a relatively low speed and then switched off. Above this threshold, the speed is like this high that changes of direction of rotation within the cycle time are not possible with the maximum acceleration available.
• the position measuring system When starting up, the position measuring system assumes a preset value. In order to register any intermittent rotations when switching off and restarting, the end and start position values are checked for equality. If they differ from one another within a specified tolerance, the system should be readjusted. To further increase safety, the position values continuously monitor whether the axis is rotating or not. The corresponding status is continuously saved and queried when restarting. If the axis was in motion when switching off, a new adjustment is also recommended.
• the position measuring system according to the invention can be used not only to determine the output position of the axis of rotation, but also to check and control a three-phase motor. This saves the position encoder required for proper field control. This has a particular impact on three-phase motors with sinus feed that require a position encoder that measures relatively precisely.
• the position measuring system it may be necessary to readjust and preset the number of cycles by carrying the number of cycles in an electrical counter in the event of malfunctions.
• the adjustment must be easy, quick and safe to carry out during the operating time, which is not possible with the known mechanical depth gauges with manual operation.
• the invention solves this additional task aspect with the subordinate method and device claim.
• the method according to the invention and the associated device can also be used successfully in connection with absolute or relative position measuring systems according to the prior art.
• position measuring system according to the invention they decisively shorten the adjustment times and enable automatic adjustment with a high degree of measurement reliability and reproducibility.
• an adjustment run can be inserted briefly before restarting the machine.
• the area of application also extends to linear axes or the mutual adjustment of any machine parts.
• Markings on the axis are used to indicate the mechanical zero position, preferably notches, humps or other clearly detectable contour changes.
• the surface of the axis and the marking is scanned mechanically or without contact by a scanning device.
• the scanning method can be carried out optically, for example with a forked light barrier and a marking in the form of a switching flag, by inductive or capacitive scanning of local field changes or the like.
• With the preferred contour scanning which can also take place mechanically or without contact, only the relative changes in height are monitored. The scanning device therefore does not have to be adjusted in relation to the axis.
• the notch base or hump vertex defining the mechanical zero point is recognized as a jump point in the height change signal and leads to storage and / or occupation of the position value of the position measuring system carried along.
• the actual position value of the precision measuring device is stored and, at the same time, the higher-value part corresponding to the cycle is newly preset. The complete actual position value is saved. If the precision measuring device is firmly adjusted, it is only sufficient to preset the number of cycles. In the case of relative systems, such as incremental counters or the like, the reference point is occupied and redefined.
• a jump point occurs when a notch or hump flank determined by a change in height merges into the base or apex or the opposite flank and the change in height changes accordingly. This change in the change in height can be detected reliably and precisely and evaluated with high reliability in terms of signal technology.
• the duration of the pending change in height signal is advisable to monitor the duration of the pending change in height signal in order to reliably distinguish the zero mark from surface defects on the axis.
• the characteristics of the marking e.g. Length of the notch flank, duration of the optical darkening, sequence of light / dark fields or the like can also be described more precisely and stored in the control. When scanning, the features found are compared with the stored ones for more precise identification of the marking. A complete comparison of types can also take place.
• the scanning device can be designed differently, for example as a contactless optical, inductive, capacitive button or the like. It preferably has a mechanical sensor that follows the surface contour of the relatively moving axis and is coupled to an electrical measuring device, for example a coil. The measuring device preferably emits a binary-coded signal, which is recommended for reporting jump locations and for further processing in modern control systems.
• Fig. 3 a scanning device for zero adjustment of an axis of rotation
• a six-axis industrial robot (10) with a rocker (11), a boom (12) and a robot hand (13) is shown.
• the various parts of the robot hand (13) are actuated via three axes (2) which are spread apart on the end of the arm (12) and driven by brushless three-phase motors (9).
• the axes of rotation (2) continue in the rotor shafts (8), at each end of which a position measuring system (1) is arranged. Both the absolute rotational position of the axes (2) and the angular position of the rotor shaft (8) with its permanent magnets with respect to the external rotating field windings are measured via the position measuring systems (1) and reported to the control of the industrial robot (10).
• the position measuring systems (1) have cyclically absolute rotary encoders (3), here in the form of resolvers, which emit an absolute signal, for example 12 bits, within one motor revolution or within a part of the motor revolution in the case of multi-pole design.
• the axes of rotation (2) can rotate as far as desired, although cyclically absolute position encoder (3), each rotational position can be determined absolutely according to the number of cycles and angular position in the last cycle.
• Figure 2 shows schematically the structure of the position measuring system (1). It consists of the aforementioned position sensor (3), which is constructed in one step and has only one precision measuring device (4), here in the form of an absolute value disc.
• the absolute disc (4) is connected to the axis of rotation (2) directly or via a gear ratio. In the direct connection shown, the cycle of the disc (4) corresponds to one revolution of the axis of rotation (2).
• the absolute value disc (4) is coded and shows 2 n different positions, for example 1024.
• the position value read optically, electrically or in some other way is fed to a comparison circuit (5) with a memory (6) and a counter (7).
• the comparison circuit (5) determines the direction of rotation of the axis (2) and the number of cycles from the measured absolute position values by comparison and evaluation and outputs a corresponding absolute position and direction signal to the robot controller.
• the comparison circuit (5) is designed in terms of hardware as a separate electronic circuit which is directly associated with the position transmitter (3) and is accommodated in its housing. In the exemplary embodiment in FIG. 1, however, the comparison circuit (5) is integrated in the robot controller and is implemented by a program part in the computing unit.
• a complete absolute position value consists of a low-value part, which corresponds to the position of the position transmitter (3) or the fine measuring device (4), and a higher-value part, which corresponds to the cycle in which the fine measuring device (4) is located.
• Position measuring system (1) the higher value part at a known position of the axis of rotation (2) is preset to the corresponding value, for example zero for axis stop. From this point on, a cycle change of the fine measuring device (4) is monitored. If there is a change in the direction defined as positive, the higher value part in counter (7) is increased by 1, with a change in the corresponding negative direction it is decreased by 1.
• the position values of the precision measuring device (4) are interrogated in cycles, temporarily stored in the comparison circuit (5) and compared with one another. There are several options for this:
• the position of the fine measuring device (4) changes with 2 n different positions per cycle (here one revolution) between two machining or query times by less than 2 n ⁇ . In other words, less than half the cycle runs between two queries.
• the polling cycle and the maximum speed of rotation of the encoder axis which is identical to the axis of rotation (2) here, are coordinated accordingly.
• a cycle change took place when the amount of the position difference of the precision measuring device values between the current position P t and P_ t _ 1 at the previous processing or query time is greater than or equal to 2 n , ie is 1/2 cycle length. Since at maximum speed of rotation of the axis (2) between two polling times only less than half of the available positions can be covered, a higher absolute value of the position difference can only be explained with a zero crossing, ie a cycle change. Conversely, an amount means Position difference of less than half of the available positions that there is no cycle change. Since only the amount of the position difference is considered, the distinction applies to both the positive and the negative axis rotation direction.
• the position of the precision measuring device (4) with 2 n positions changes by less than 2 n between two processing or query times.
• the position sensor (3) so that at least queried 'once in a cycle.
• the maximum possible position change speed b ie the acceleration of the encoder axis or axis of rotation (2), is less than n — 2 or equal to 2 between two processing times.
• the maximum speed of rotation of the encoder axis or the axis of rotation (2) can be significantly higher than in variant 1.
• the direction detection is switched off and the direction that was present at the time of departure was used as the current direction of rotation. This applies until the speed drops below the threshold again and direction detection is switched on again in accordance with variant 1.
• are recognized if the position P. of the precision measuring system at the current point in time with a recognized negative direction is greater than the position P t _ ⁇ at the last time of the query. If the positive direction is detected, however, P. is smaller than p tr
• cycle changes are recognized: t > P t _ ⁇ -> cycle change with negative direction of rotation t ⁇ P t _ 1 -> cycle change with positive direction of rotation
• the initial position values and the movements of the axis of rotation checked. This ensures that the calculated absolute actual position value matches the actual rotational position of the axis (2).
• the last position value of the position transmitter (3) is stored in the memory (6) in the comparison circuit (5) and is retained even if the position measuring system (1) is switched off or there is a power failure. If the first newly queried position value after restarting the rotary axis (2) and the position measuring system (1) varies by more than an approved tolerance value from the last saved position value, the correspondence between the rotational position of the axis (2) and the calculated actual position value is no longer guaranteed.
• the necessary tolerance results from system-specific fluctuations, for example thermal expansion and the like. If the tolerance is exceeded, the axis is readjusted and the higher-value position part, i.e. the number of cycles, preset again.
• the comparison circuit (5) continuously checks whether the measured position values change or stand still, i.e. whether the axis (2) rotates or stands. This status is saved on an ongoing basis and also remains saved when the device is switched off or in the event of a power failure.
• the status is queried when the rotary axis (2) and the position measuring system (1) are restarted. If it turns out that the axis (2) is not at a standstill when the position measuring system (1) is switched off or uncoupled, the correctness of the absolute position value can also no longer be guaranteed.
• the axis (2) is readjusted and the higher position part is preset again. Modifications to the above-described embodiments are possible in various ways.
• the position transmitter (3) can be connected to the axis of rotation (2) via a translation. According to the translation, its cycle and the position change speed change when reading.
• the cycle of the position encoder can also be smaller than a complete revolution or encoder axis revolution.
• the position transmitter (3) can also be designed in several stages, so that its cycle corresponds, for example, to 2 n revolutions of the axis, for example 512 revolutions.
• a previously known position transmitter in the working area can thus be expanded as desired beyond its cycle.
• the type of coding of the position transmitter can also vary. At extreme axis speeds, the cycle time for the queries can be shortened or the aforementioned translation can be switched between the rotary axis and the position encoder.
• FIGS. 3 and 4 show a scanning device (14), with the aid of which an axis of rotation (2) according to FIG. 3 or a linear axis (22) according to FIG. 4 can be adjusted to the mechanical zero position.
• the axis of rotation (2) is, for example, a manipulator or robot axis.
• the axes (2, 22) can be moved in relation to an axis housing or a holder (17) for the scanning device (14), the mutual distance remaining the same. They are connected to a position measuring system (not shown), preferably a system according to FIGS. 1 and 2, which indicates their position relative or absolute.
• the scanning device (14) is designed as an electronic measuring probe. It has a housing (18) from which a spring-loaded mechanical sensor (15) protrudes downwards towards the surface of the axes (2, 22) and scans this surface during the relative movement.
• the Scanning device (14) can be detachable for individual measurements or permanently connected to the axle housing or the holder (17) for continuous operation. The latter is recommended for axis and position encoder adjustment on manipulators or real axis industrial robots.
• the search is started from a marked axis position.
• the sensor (15) is immersed in a measuring notch (19) which represents the mechanical zero point of the axis (2,22).
• a survey can also serve as a marker.
• the sensor (15) moves downward on the falling notch flank during the relative movement, slides over the notch base (20) and then rises again on the other notch flank .
• a measuring device (16) is arranged in the housing (18) of the probe (14) and monitors and measures the relative height movement of the sensor (15). Parts of the measuring device (16) can also be external, e.g. be arranged in the machine control.
• the probe (14) emits a binary coded signal corresponding to the relative change in height of the sensor (15). It has two digital outputs:
• the signal from the measuring device (16) stores the current actual position value reported by the absolute precision measuring system carried along.
• the cycle value is simultaneously set to zero.
• the time in which a signal (10 or 01) indicating the change in height is present is also measured in the measuring device (16) or the machine control.
• the time represents a reference value for the flank length of the depression or elevation. Only when the signal is constant over a predetermined minimum duration approximately corresponding to the edge length is the subsequent signal change registered and evaluated, ie the actual position value is stored. Surface errors cannot falsify the adjustment result.
• the position value in the middle of the notch base (20) can be determined from the actual position value initiated by the probe (14) when entering the notch base (10 - 11 transition) and the actual position value when leaving the notch base (11 - 01 transition) ( corresponds to the mechanical zero). If there is no notch back, the actual value in the mechanical zero point is identical to the actual value at the 10 - 01 transition of the button.
• the search is carried out several times, in particular twice, whereby the direction of movement of the axis (2, 22) can remain the same or change.
• the position values stored in each run are compared with each other for a tie. Deviations outside the tolerance lead to the termination of the adjustment and require troubleshooting.

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• Engineering & Computer Science (AREA)
• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Human Computer Interaction (AREA)
• Manufacturing & Machinery (AREA)
• Automation & Control Theory (AREA)
• Length Measuring Devices With Unspecified Measuring Means (AREA)

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Citations (4)

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• 1988
  • 1988-09-23 DE DE19883832457 patent/DE3832457A1/de active Granted
• 1989
  • 1989-09-22 WO PCT/EP1989/001104 patent/WO1990003553A1/de unknown

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