Incremental measuring device

Abstract

The present invention relates to a measuring device (10) for incrementally measuring positions, travel distances or angles of travel along a displacement direction (V) taking into account the direction of movement, comprising a marking arrangement (20), a sensor arrangement (30) and a processing unit (40) which is operatively coupled to the sensor unit (30), wherein the marking arrangement (20) and the sensor arrangement (30) are displaceable relative to one another along the displacement direction (V) and the sensor arrangement (30) is configured to detect a marking state at a current relative positioning with respect to the marking arrangement (30), wherein the processing unit (40) is configured to determine a relative displacement of the marking arrangement (20) with respect to the sensor arrangement (30) on the basis of a periodic detection of the marking state.According to the invention, the marking arrangement (20) comprises at least three marking tracks (22a - 22c) extending parallel to one another in the direction of displacement (V), and the sensor arrangement (30) comprises at least three sensor units (32a - 32c) arranged next to one another with respect to the direction of displacement (V), each of which is configured to read a marking bit on the corresponding marking track (22a - 22c).

Description

The present invention relates to a measuring device for incrementally measuring positions, actuating distances or actuating angles along a displacement direction taking into account the direction of movement, comprising a marking arrangement, a sensor arrangement and a processing unit which is operatively coupled to the sensor unit, wherein the marking arrangement and the sensor arrangement are displaceable relative to one another along the displacement direction and the sensor arrangement is configured to detect a marking state in the case of a current relative positioning with respect to the marking arrangement, wherein the processing unit is configured to determine a relative displacement of the marking arrangement with respect to the sensor arrangement on the basis of a periodic detection of the marking state.It is known from the prior art to use such generic measuring devices to determine positions, travel distances and / or angle of displacement between two components of a superordinate structure, for example of an industrial truck, which can be displaced relative to one another with respect to the displacement direction during operation of the corresponding superordinate apparatus. In this case, for example, in the device known from DE 10 2004 041 391 A1, a pair of sensors is used which record an individual movable graduation track or marking track with regard to its marking state and are in this case spaced apart along the displacement direction according to a predetermined phase angle.By selecting the corresponding coding of the graduation track in a suitable manner, an incremental determination of the relative displacement between the sensors and the graduation track can be achieved by a periodic detection of the respective states of the graduation track determined by the two sensor units when a state transition is registered, wherein additional information can also be derived by varying the marking pattern of the graduation track, for example, in order to set reference marks along the accessible displacement path.However, it has been found in practice that, due to the configuration of the device known from DE 10 2004 041 391 A1 with the two sensors spaced apart along the displacement direction, an increased installation space of the device is required in this direction and consequently this device from the prior art is not suitable for certain practical applications in which limitations with respect to the available installation space are present along the displacement direction. Furthermore, in the system from the prior art just described, an adjustment of the accuracy of the system is possible only on the basis of a combined modification of the distance of the two sensors and the graduation track, which restricts the flexibility of this system with regard to an adjustment to different application scenarios.It is therefore the object of the present invention to further develop a measuring device of the generic type in such a way that, on the one hand, the restrictions with respect to the required installation space along the displacement direction, which arise in the prior art, are eliminated, as a result of which the flexibility of the measuring device with respect to different application scenarios is increased, and, on the other hand, the resolution of the system can be adapted and increased in a simplified manner.To solve this problem and to eliminate the above-discussed disadvantages of the prior art, it is accordingly proposed according to the invention that, in the generic measuring device described at the beginning, the marking arrangement should comprise at least three marking tracks extending parallel to one another in accordance with the displacement direction and the sensor arrangement should comprise at least three sensor units arranged next to one another with respect to the displacement direction, which are each configured to read a marking bit on the corresponding marking track.Accordingly, it is proposed according to the invention that the plurality of sensor units of the sensor arrangement no longer be arranged spaced apart with respect to the displacement direction between the marking arrangement and the sensor arrangement at a predetermined phase spacing with respect to only one marking track, but rather to provide at least three marking tracks provided with a corresponding phase spacing next to one another parallel and aligned with the displacement direction. In the same way, the at least three sensor units of the sensor arrangement are likewise placed next to one another perpendicularly to the displacement direction, where they record the mutually phase-shifted marker bits of the individual marker tracks and pass corresponding outputs on to the processing unit for further data processing. An arrangement of the individual sensor units which is completely perpendicular to the displacement direction is preferred here, but according to the invention these can also be offset with respect to one another by a certain amount along the displacement direction as long as sufficient installation space is present in this direction in the corresponding application and the correspondingly occurring offset is mapped or taken into account in the marking tracks.Accordingly, according to the present invention, the marking state is composed of the individual marking bits, zeros and ones on the individual marking tracks being represented phase-shifted with respect to one another in a suitable manner for this purpose and depending on the sensor type used in each case. In this case, the marking bits determine the resolution of the measuring device according to the invention at the same time with respect to their dimensions and are generally equally spaced apart with the exception of reference marks still discussed further below and phase-shifted with respect to the respective other marking tracks, wherein the basic periodicity of the marking tracks is identical without any reference marks. By the individual sensor units reading out respective marking bits in this way, a total of 2 3= 8 states can be implemented in the example of three marking tracks and three sensor units, on the basis of the coded sequence of which the actual incremental measuring process can be carried out by the processing unit, both with regard to a direction of the relative movement between the marking arrangement and the sensor arrangement and also the distance covered. The unique sequence of states enables unique error detection and identification of the direction of movement. Only the change of an individual state bit is provided in each case and, in addition, the state sequence is known, so that a measurement or sensor error can be deduced if a plurality of bits are changed or if a state sequence is not provided. Also, on the basis of the known state sequence, the direction of movement can be unambiguously recognized from the change between two states.Accordingly, in one example of use of the measuring device according to the invention, one of the two components, the marking arrangement and the sensor arrangement, can be fixedly installed on a vehicle body of an industrial truck and the respective other component can be installed on that part which is movable with respect to the vehicle body and the displacement of which is to be detected, that is to say, for example, on a lifting device which is provided for receiving a load and is installed so as to be vertically displaceable, or else a pivotable device, the angular movement of which is converted in a suitable manner into a relative displacement of the marking arrangement with respect to the sensor arrangement.It should also be noted that the periodic detection of the marking state by the processing unit can take place in cooperation with the sensor units at a relatively high clock frequency, since the data volumes to be processed are small on the basis of the pure detection of marking bits and, in particular, sensor types with a low intrinsic inertia can be used. For example, it could be envisioned to provide a processing unit acquisition period on the order of about one millisecond, thereby enabling a precise and error-resistant measurement of the displacement between the marker assembly and the sensor assembly.In a possible specific embodiment, the marking arrangement can accordingly be embodied as a metal sheet or metal rail and the marking tracks can be formed by recesses therein, while the sensor units are each formed by inductive sensors. In this case, it can be considered in particular to implement the sensor units as eddy current sensors which are distinguished by high reliability and good spatial resolution and simple availability.The mode of operation of inductive sensors is based here on the fact that different values are output by the corresponding sensor units depending on whether or not a metallic section lies opposite them within a predetermined distance, so that, for example, the corresponding recesses in a metal sheet or a metal rail can be identified as 0-bit, while a 1-bit can be output in the case of a corresponding metallic surface being present. Of course, however, alternative embodiments of sensor units are also conceivable here; optical sensors could be considered here, for example, such as, in particular, light barriers, which can likewise determine the presence or absence of a surface, or, for example, also photo sensors, which can distinguish between bright and dark surfaces in order to code marking bits in each case in this way.In this case, it should be pointed out in particular that in various of the aforementioned embodiments of the sensor units, the recesses in the marking arrangement can each be configured as individual holes for each of the marking tracks, but such an embodiment of the recesses is disadvantageous, in particular when eddy current sensors are used, to the effect that eddy currents can occur in the material around the corresponding holes themselves, which eddy currents can impair the precision and resolution of the detection. Accordingly, generally speaking, the marking arrangement can be designed as a planar component and the marking tracks can be formed by recesses therein, wherein the recesses of the marking tracks can each be connected in such a way that continuous recesses are formed across the marking tracks. Thus, in such a configuration of the marking arrangement, recesses of adjacent marking tracks are formed continuously without continuous webs or the like therebetween, whereby the phase shifts between the adjacent marking tracks result in each case in staircase-shaped profiles of the recesses and also in the material sections or webs provided between the recesses in the displacement direction.In this case, the ratio of recesses to material of correspondingly designed marking arrangements can be adapted to different properties of the system; for example, the tolerance or hysteresis of the sensor type used can be taken into account. It is evident here that, in order to take account of the so-called "electrical duty cycle" of certain sensor types and in this case in particular of inductive sensors, the ratio of recesses to material of the marking arrangement in the region of the marking tracks should in the optimum case be greater than 1, in order to be able to ensure optimum resolution and functionality of the measuring device, since a signal ratio as close as possible to 1:1 can be achieved as a result. On the other hand, for example in the case of optical sensors, the ratio between material and recesses can be substantially already 1:1, since with such sensor types switching is effected at material edges in a practically delay-free manner.As already indicated further above, the marking arrangement can furthermore comprise at least one reference mark, which can preferably be formed in such a way that the ratio of recesses to material of the marking arrangement is increased or decreased at points in the region of the marking tracks. Accordingly, in the region of this at least one reference mark, a deviating behavior of the sensor arrangement with respect to the transition between individual possible marking states is expected, as a result of which, for example, the detection of specific predefined positions of the relative displacement between the marking arrangement and the sensor arrangement is made possible, or in particular also of the direction of movement.In this case, the marking arrangement can comprise in particular two types of reference marks, which preferably differ in the ratio of recesses to material of the marking arrangement in the region of the marking tracks. Such a configuration makes it possible, in particular in the example already discussed above of providing three sensor units and consequently providing a total of 8 possible marking states, to provide a state with three 0-bits or three 1-bits only in the region of the reference marks, while outside the reference marks along the marking tracks only states with in each case at least one 1-bit and at least one 0-bit can be provided in order to be able to detect and intercept undesired or faulty states or faulty measurements of the sensor arrangement in a simplified manner at an early stage. In a similar manner, however, it would also be conceivable to completely dispense with states having three 0-bits or three 1-bits in the marking arrangement, since an adequate coding of information is also already made possible by the remaining six possible states.For a similar purpose, the marking arrangement can be designed such that, in the event of a change in the marking state along the displacement direction, always only one of the marking tracks has a transition between a recess and material of the marking arrangement or vice versa, that is to say that during a relative movement between the marking arrangement and the sensor arrangement along the displacement direction at a predefined point, in each case at most one of the sensor units can be subjected to a transition between the two corresponding states of the respective marking track and will output a bit transition.In this connection, the processing unit can be configured in particular to increase or decrease an increment counter, which represents an amount of displacement of the marking arrangement relative to the sensor arrangement, in the event of a change in the marking state. This increase or decrease of the increment counter can furthermore comprise a plausibility check of the corresponding change in the flag state in order to count only allowed or provided changes or transitions. Examples of impermissible changes or transitions could in this case consist, inter alia, in the example already addressed, in that more than one of the sensor units reports a bit transition from a detection of the marking state to a next detection or a transition between two marking states is detected, which are not provided in this sequence in the corresponding marking arrangement.One possibility for implementing the incremental determination of the displacement between the marking arrangement and the sensor arrangement may in particular consist in the processing unit being configured to act as a state machine in order to classify changes in the marking state, in particular with regard to a direction of the relative displacement of the marking arrangement with respect to the sensor arrangement and / or reaching or sweeping over a reference mark.In this case, a state machine is distinguished in that only a finite set of states of the data to be processed can be taken, that is to say in the present case the marking state composed of individual sensor bits, and predefined state transitions can occur between these specific states, according to which state transitions a transition from a current state to a new state takes place. By the processing unit evaluating the corresponding state transitions on the basis of the supplied marker states, the incremental measurement can consequently take place on the basis of an evaluation of the state transitions, wherein, in the case of a corresponding suitable processing of the state transitions specifically taking place, not only the displacement quantity but also the displacement direction can be derived, provided that the marker arrangement is coded in a suitable manner.Furthermore, the processing unit can be configured to register an error in the event of an unexpected change in the flag state, wherein, in particular in the example of a state machine just addressed, unexpected changes or errors can be intercepted on the basis of an expected sequence of the states, on the basis of which, for example, a message can be output to a human operator. In this connection, reference is again made to the example of the transition of more than one bit at the same time, which has already been discussed several times above, which can indicate, for example, a malfunction of one of the sensor units, which can make manual intervention by an operator necessary for eliminating it.While the measuring device according to the invention can in principle be used in different application cases, it is, however, particularly suitable for use in industrial trucks because of its construction, so that the present invention relates according to a further aspect to an industrial truck and in particular a low-lift vehicle, which comprises a vehicle body and a load-receiving device which can be displaced with respect to the vehicle body, and a measuring device of the type according to the invention just described, wherein one of the measuring arrangement and the sensor arrangement is intended to be associated with the vehicle body and the other is intended to be associated with the load-receiving device.In this case, the case described above is applicable in particular in the example of a low-lift vehicle addressed, in which the installation space for the sensor arrangement is limited in the displacement direction between the marking arrangement and the sensor arrangement and, consequently, the use of a corresponding measuring device is made possible at all by the arrangement of the sensor units, which arrangement is rotated by preferably 90 degrees in comparison with the prior art, with respect to one another and with respect to the marking arrangement.According to a further aspect, the present invention relates to a method for operating a measuring device of the type just described, comprising the steps of periodically detecting the marking state and, in the event of a change in the marking state, determining a relative displacement of the marking arrangement with respect to the sensor arrangement. It should be pointed out here that the method steps to be carried out and specific implementations described further above in connection with the measuring device are to be claimed in the same way in connection with the method according to the invention and that this can comprise the determination of a direction of movement, for example, in the manner described above. It should also be noted that the determination of an initial state in the method according to the invention is possible without any problems due to the design when the measuring device is put into operation, since an initial determination of the state of the marking can be carried out easily in any conceivable alignment between the marking arrangement and the sensor arrangement.It should also be pointed out that the method according to the invention can comprise checking the change in the marking state on the basis of at least one predetermined condition before determining a relative displacement, wherein it should be pointed out again that, depending on the configuration of the measuring device, only certain transitions between marking states can be allowed, wherein, in the case of determinations of other transitions, the respectively detected data can be discarded or registered as an error.Further features and advantages of the present invention will become more apparent from the following description of an embodiment thereof when taken in conjunction with the accompanying drawings. These show in detail: FIG. 1 is an isometric view of a measuring device according to the invention, and FIG. 2 shows a schematic illustration of the marking arrangement and of the sensor arrangement of the measuring device from FIG. 1 and of signals of the sensor arrangement output during a method according to the invention.FIG. 1 shows, firstly in an isometric and partially schematic view, a measuring device 10 according to the invention for incrementally measuring positions, adjustment paths or adjustment angles along a displacement direction V which runs vertically in the illustration from FIG. 1. In this case, relative movements both vertically upward and downward are conceivable along the displacement direction, which is expressed by a corresponding movement direction in the positive or negative displacement direction.The corresponding displacement takes place between a marking arrangement 20 and a sensor arrangement 30, which are each attached to components of a superordinate structure, not shown in any more detail, for example an industrial truck, which are movable relative to one another. Furthermore, the measuring device 10 comprises a processing unit 40, which is illustrated only schematically and is operatively coupled to the sensor unit and is configured for processing the data supplied by the sensor arrangement 30. Here, the processing unit 40 can be embodied by electronic means known per se, such as a microcomputer or a microcontroller, which are each provided with an assigned memory and software means coded thereon.It is likewise conceivable to provide the processing unit 40 integrated or coupled with a central control unit of the superordinate structure; thus, for example, the central control unit of an industrial truck equipped with the measuring device 10 could be coupled with the sensor arrangement 30 and carry out the corresponding data processing, or a separate processing unit 40 could be provided, which however, by means of a suitable data connection, in turn delivers an output to the central control unit for further processing.In the embodiment of FIG. 1, the marking arrangement 20 is designed as a metal sheet which comprises parallel marking tracks 22 ato 22 c, which are aligned in the displacement direction V and are each formed as recesses 24 connected to one another across the marking tracks 22 ato 22 c. Metallic webs 26 are thus provided between the corresponding recesses 24, wherein a step-shaped embodiment of both the recesses 24 and of the webs 26 is achieved by a phase shift between the individual marking tracks 22 ato 22 c.While the recesses 24 and the webs 26 are designed in constant widths over a large part of the extent of the marking tracks 22 ato 22 calong the displacement direction V in order to achieve a regular pattern, it should be pointed out, however, that in the embodiment from FIG. 1 two reference marks 28 are furthermore provided, in the region of which the ratio of recesses 24 to webs 26 in the region of the marking tracks 22 ato 22 cis reduced or increased at points.The sensor arrangement 30 schematically illustrated in FIG. 1 comprises, in alignment with the three marking tracks 22 ato 22 c, three sensor units 32 ato 32 c, which are situated next to one another perpendicularly to the displacement direction V and are each embodied in an identical manner by eddy current sensors. A corresponding bit value is output by each of the sensor units 32 ato 32 cdepending on whether a section of the metal sheet of the marking arrangement 20, that is to say in particular one of the webs 26, or one of the recesses 24 is located directly in front of it. To illustrate this mode of operation of the sensor arrangement 30, reference is also made to FIG. 2, in which both the respective orientation of the sensor units 32 ato 32 cto the marking tracks 32 ato 32 cand the corresponding outputs during a relative movement along the displacement direction V or over the time t are illustrated. In principle, a total of 8 marking states (P0=000) to (P7=111) are acceptable in the usual manner in binary representation, which can be derived by a combination of the sensor outputs.In particular, in each case in the case of a transition between a recess 24 and a web 26, a corresponding change of the bit state and thus of the signal of the corresponding sensor unit 32 ato 32 cfrom 0 to 1 occurs in the event of a relative displacement of the marking arrangement 20 with respect to the sensor arrangement 30, wherein the three marking bits supplied by the individual sensor units 32 ato 32 cform overall the marking state just explained. In the embodiment shown here, the corresponding processing of the sensor bits supplied by the sensor units 32 ato 32 cis carried out by the processing unit 40, which carries out, inter alia, an incremental counting of the transitions between the marking states determined in this way and, if appropriate, the detection of faulty or impermissible transitions.However, it should be noted here that the state P0 (000) is not assumed in the embodiment discussed here, since only states in which at least one of the sensor units 32a to 32c outputs a 1-bit are provided in the region of the marking tracks 22a to 22c. These seven states actually provided are already sufficient to ensure the desired functioning of the device. Accordingly, upon detection of the state P0in this embodiment, a fault may be detected in any case which could be attributed to both a mechanical fault and an electrical or electronic fault.However, in that the state transitions between the states in FIG. 2 are evaluated by the processing unit 40 during a regular operation by periodic detection of the corresponding marking states during a relative displacement between the marking arrangement 20 and the sensor arrangement 30, the relative direction of movement with respect to the displacement direction V can be determined on the one hand by the corresponding known sequence of states and accordingly an increase or a decrease of an increment counter can be carried out in each case, which can be converted into a displacement path.On the other hand, it is also possible to evaluate impermissible or provided transitions between marker states as errors, for example if a plurality of marker bits have a change at the same time, which is not provided in the embodiment shown here, or if the state P 0 discussed above is registered. Accordingly, on the basis of an evaluation of the signal output illustrated here, in the embodiment of a measuring device 10 shown in FIG. 1, a determination of the relative displacement amount in the case of a displacement along the displacement direction V can be achieved in a reliable manner, taking into account the corresponding movement direction, in the case of a configuration of the sensor arrangement 30 which is particularly compact in the displacement direction V.References included in the specificationThis list of documents cited by the applicant has been produced in an automated manner and is only included for the better information of the reader. The list is not part of the German patent application or utility model application. The DPMA does not take any adhesion for any faults or omissions.Patent Literature citedDE 10 2004 041 391 A1 [0002, 0004]

Claims

Measuring device (10) for incrementally measuring positions, adjustment paths or adjustment angles along a displacement direction (V) taking into account the movement direction, comprising: - a marking arrangement (20); - a sensor arrangement (30); and - a processing unit (40), which is operatively coupled to the sensor unit (30); wherein the marking arrangement (20) and the sensor arrangement (30) are displaceable relative to one another along the displacement direction (V) and the sensor arrangement (30) is configured to detect a marking state in the case of a momentary relative positioning with respect to the marking arrangement (30), wherein the processing unit (40) is configured to determine a relative displacement of the marking arrangement (20) with respect to the sensor arrangement (30) on the basis of a periodic detection of the marking state, characterized in that the marking arrangement (20) comprises at least three marking tracks (22a-22c) extending parallel to one another according to the displacement direction (V), and the sensor arrangement (30) comprises at least three sensor units (32a-32c) arranged next to one another with respect to the displacement direction (V), which are each configured to read a marking bit on the corresponding marking track (22a-22c).The measuring device (10) according to claim 1, wherein the marking arrangement (20) is formed as a metal sheet or metal rail and the marking tracks (22a - 22c) are formed by recesses (24) therein; and the sensor units (32a - 32c) are each formed as inductive sensors.The measuring device (10) according to any one of the preceding claims, wherein the marking arrangement (20) is formed as a planar component and the marking tracks (22a - 22c) are formed by recesses (24) therein; and the recesses (24) of the marking tracks (22a - 22c) are each connected in such a way as to form continuous recesses (24) beyond the marking tracks (22a - 22c).Measuring device (10) according to Claim 2 or 3, wherein the ratio of recesses (24) to material of the marking arrangement (20) in the region of the marking tracks (22a - 22c) is greater than 1.Measuring device (10) according to one of the preceding claims, wherein the marking arrangement (20) comprises at least one reference mark (28), which is preferably formed in such a way that the ratio of recesses (24) to material of the marking arrangement (20) is increased or decreased at points in the region of the marking tracks (22a - 22c).Measuring device (10) according to claim 5, wherein the marking arrangement (20) comprises two types of reference marks (28), which preferably differ in the ratio of recesses (24) to material of the marking arrangement (20) in the region of the marking tracks (22a - 22c).Measuring device (10) according to one of the preceding claims, wherein the marking arrangement (20) is designed in such a way that, in the event of a change in the marking state along the displacement direction (V), only one of the marking tracks (22a - 22c) always has a transition between a recess (24) and material of the marking arrangement (20).Measuring device (10) according to one of the preceding claims, wherein the processing unit (40) is configured to increase or decrease an increment counter which represents an amount of displacement of the marking arrangement (20) with respect to the sensor arrangement (30) in the event of a change in the marking state.Measuring device (10) according to one of the preceding claims, wherein the processing unit (40) is configured to act as a state machine in order to classify changes in the marking state, in particular with regard to a direction of the relative displacement of the marking arrangement (20) with respect to the sensor arrangement (30) and / or reaching or sweeping over a reference mark (28).Measuring device (10) according to one of the preceding claims, wherein the processing unit (40) is further configured to register an error in the event of an unexpected change in the marking state.Industrial truck, in particular a low-lift vehicle, comprising: - a vehicle body and a load-receiving device which can be displaced with respect to the vehicle body, and - a measuring device (10) according to one of the preceding claims, wherein one of the marking arrangement (20) and the sensor arrangement (30) is assigned to the vehicle body and the other is assigned to the load-receiving device.Method for operating a measuring device according to one of Claims 1 to 10, comprising the steps of: - periodically detecting the marking state; - in the event of a change in the marking state, determining a relative displacement of the marking arrangement (20) with respect to the sensor arrangement (30).Method according to the preceding claim, further comprising, before determining the relative displacement: - checking the change of the marker state on the basis of at least one predetermined condition.

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