DE102018217564A1 - Procedure for determining the preload loss of finite traction devices - Google Patents

Abstract

Method for determining the loss of preload of finite traction means made of elastomeric material within a linear drive, the traction means having strength members or reinforcing elements embedded in the longitudinal direction in the traction element body, the actual position within each after a running-in phase of the linear drive for each position of the translationally moved object linear travel path is determined and compared to a target position of the translationally moved object, calculated from the movement data of the drive motor, within the linear travel path, a theoretical initial length L of the traction device being determined and stored for the position approached for each position, whereby in the subsequent operating phase, a theoretical current status length L of the traction device is determined from the ratio of the currently measured actual and target positions and with the traction Lengths L is compared, a warning signal being given after a predetermined threshold value for the differences has been exceeded, or an exchange of the traction means being requested.

Description

The invention relates to a method for determining the preload loss of finite traction means made of elastomeric material within a linear drive, in which the traction means rotates via deflection or drive rollers and is connected at the end to a driven object that is translationally moved via a predetermined, essentially linear travel path, the Has traction means in its longitudinal direction embedded in the traction body strength members or reinforcing elements, preferably formed as twisted or struck cords made of filaments. The invention also relates to a linear drive which is designed to carry out the method.

Linear drives are known in a variety of applications today. For example, slides of machine tools as well as reading heads in copiers, printing devices in printers and also transport and lifting devices in high-bay warehouses are moved by linear drives. All of these linear drives must have high positioning accuracy so that e.g. Workpieces with the smallest tolerances can be machined and transport goods can be placed in their place with millimeter precision.

In a conventional linear drive, a finite traction means, as a rule made of elastomeric material, is connected with its two ends to the object which is moved in translation, that is to say to the tool slide or lifting devices mentioned. The traction means is driven and then moves the moving object over a predetermined, essentially linear travel path, the traction means rotating around deflection or drive rollers (), so that a back and forth movement is made possible.

In the case of traction devices made of elastomeric materials, the required high positioning accuracy can of course only be achieved if the tension in the traction devices is defined and closely monitored. Any decrease in tension or even "sagging" of the traction means that the specified positions can no longer be approached with the required accuracy.

Toothed belts made of elastomeric material are often used as traction devices in such linear drives. Here, installed timing belt lengths of up to 80 m are no longer uncommon. In closed systems, the traction means / toothed belts are connected at the ends to one another or to the translationally moved object, as already described above.

In linear drives, a distinction is made between a tensile load side (load strand) and an empty side (empty strand). With increasing load on the load strand, this area is stretched elastically, which in turn means that the empty strand loses tension and becomes "limp". If this elongation becomes too large or it manifests itself as permanent elongation, not only can the specified positions no longer be approached with the required accuracy, it can also happen that the toothed belt no longer meshes with the toothed pulley with sufficient accuracy, i.e. no longer properly toothed in the toothed disc. The result can be massive application damage.

In order to be able to move loads of different sizes in a linear drive, toothed belts are pretensioned in the elastic range, so that excessive stretching is counteracted by such pretensioning. Such a pretension therefore causes the toothed belt to run into the toothed pulley safely and within acceptable tolerances.

This preload must of course be checked periodically. This usually takes place when the drive is stopped. The pretension is set via the natural frequency of the belt strand. The belt strand is excited to a forced oscillation and its change depending on the tensile force in the belt strand is calculated using the known formulas, namely through the relationship $$F_{\mathrm{e.g.}uG}=\mathrm{4th}m{L}_{Trum}^{\mathrm{2nd}}{f}_{eiGen}^{\mathrm{2nd}}$$

f_eigen = Eigenfrequenz [Hz]Here is
F = _train traction in the run of a linear actuator
L _strand = free partial length (strand length) [m]
m = weight per meter of the traction device $\left[\frac{kG}{m}\right]$

f _eigen = natural frequency [Hz]

The values for the clamping or tensile forces generally have to be checked regularly by manual measurements and are often only to be carried out with very limited installation space. As soon as the tensile forces due to permanent expansion of the elastomeric material and the reinforcing elements are no longer sufficient to e.g. To ensure safe meshing with the toothed lock washer and precise positioning, it must be re-tensioned and the traction device must be replaced at the end

The object of the invention was therefore to provide a method which makes it easier to determine the drop in the pretensioning of traction means in linear drives and which involves only a relatively small outlay in terms of apparatus / construction for the associated devices.

This task is solved by the features of the main claim. Further advantageous developments are disclosed in the subclaims. A linear drive designed in an inventive manner is also claimed.

After a running-in phase of the linear drive, the actual position of the translationally moved object within the linear travel path is determined for each approached position and is related to a target calculated from the movement data of the drive motor, preferably the revolutions of the drive roller of the linear drive -Position of the translationally moved object within the linear travel path, a theoretical starting length L _{beginning (Pos 1-n) of} the traction device being determined from the ratio of the two positions and the geometric dimensions of the linear drive and in the form of a base quantity or base curve of Zugmittellängen is stored, wherein in the run-in subsequent operating phase from the ratio of the respectively currently measured actual and desired positions of a theoretical current status _Currently length L _{(Pos 1-n)} of the traction means and determines nd is compared with the traction means length L _{beginning (item 1-n) of} the base quantity or base curve, whereby after exceeding predetermined threshold values for the differences ΔL _{(item 1-n)} = L _{beginning (item 1-n)} - L _{current (item 1 -n)} between the theoretical initial lengths and the theoretical current status lengths of the traction devices, a warning signal is given or the traction device is requested to be replaced. The drop in pre-stress can thus be automatically determined, documented and classified using threshold values. A precautionary and limited use of the traction device within the linear drive, i.e. predetermined replacement intervals that are defined from the outset, is then no longer necessary, since the loss of preload due to wear or aging can be determined permanently or as required.

The change and aging of such drive belts used as traction means for linear drives, in particular also toothed belts, is particularly evident in the permanent elongation or elongation of the traction means, which changes over time.

One reason for this are the signs of wear that occur in the traction device and in the strength members / traction members of the traction device as a result of the load collective of a traction device in the course of the service life. If you look at the interplay between the tensile stress on the traction device and the number of bends on the deflection pulleys and drive pulleys, a typical wear pattern results that reduces the tensile strength of the suspension device to such an extent that there is permanent elongation / elongation. This reduction in tensile strength essentially results from a reduction in the load-bearing cross-section as a result of the friction / wear of the individual filaments against one another, the so-called “fretting”. A reduction in the load-bearing cross-section can also occur due to brittle fractures of individual filaments as a result of the constant bending load.

These processes and a geometric change in the individual traction elements within the polymer matrix result in a change in the length of the traction means. The geometric change of the individual tension members / tension elements arises, for example, from the fact that friction / wear of the filaments twisted together / twisted, i.e. through movement of the individual filaments relative to one another during operation, that is to say through the aforementioned fretting, a change in shape and the position of the individual filaments and strands of a tension member results. This creates a change in diameter within the tension member and thus an elongation of the traction means or toothed belt, which is detectable. The change in length is thus a measure of the change in the tensile / elongation behavior of the traction means, i.e. for the aging of the traction device. With the corresponding correlation between the elongation of the traction device or traction belt on the one hand and the aging or remaining residual load-bearing capacity of the traction device on the other hand, the method according to the invention enables reliable and unambiguous control of the prestressing capacity of the traction device and can determine the time of replacement with good accuracy. The determination of the remaining belt elongation for a toothed belt also allows a statement to be made as to when the tooth pitch of the belt no longer matches the - unchangeable - tooth pitch of the pulley and a change must be made.

Of course, a certain number of load cycles or a certain operating time can also be specified, after which the ratio of the originally measured length and the corresponding length of the suspension element then present is measured.

The elongation and thus the loss of the pretension can be determined practically by, for example, determining the exact position of the tool slide or the lifting device in the high-bay warehouse by using position encoders on deflection disks, a separate position or Provides height copying, which detects the respective actual position of the translationally moved object.

In addition, the drive pulley or motor data must be able to determine which theoretical path the belt travels. This can be done by determining the number of rotations of a drive motor - with knowledge of the gear ratios - or by measuring the movement of a linear motor. Rotation sensors, Hall sensors, encoders in the drive motor or encoders on the drive pulley are suitable for this.

In this way, each actually reached "real position" of the translationally moved object is determined as the actual position of the translationally moved object within the linear travel path and is related to a position "calculated" from the movement data of the drive motor, namely the target position of the translationally moving object within the linear path. From the ratio of the two positions and the geometrical dimensions of the linear drive, a theoretical initial length L _{beginning (item 1-n) of} the traction device is determined for each position approached and stored in the form of a basic quantity or curve of traction device lengths.

Such a coupling of the two measured values (real position / calculated position) can be used to determine a theoretical belt length for each position approached. During commissioning, a base curve for the respective theoretical belt lengths is recorded, which can be compared with the corresponding status curve at subsequent times. Over time, the current belt length will continue to deviate from the base curve. After reaching a defined deviation from the initial state, a signal is given as an indication of retensioning the toothed belt.

The term "running-in phase", also "run-in new condition" means the condition of the traction device / toothed belt that has arisen after a series of several hundred load cycles due to settlement and running-in of the system. A load cycle is to be understood here as a complete linear movement of the translationally moving object via the available travel path or an upward or downward stroke of the lifting device in a high-bay warehouse. With regard to the traction device, the connection between the strength members or the tensile members and the polymer or rubber matrix and the running into the deflection and drive rollers has become so great that significant changes in state with regard to the pretension only develop after a much longer period of time. The change in length of the traction device then serves as an indicator of the aging or reduction of the pretension.

As already described above, the load collectives of a suspension element present in the course of their lifetime lead to signs of wear in the tension element and in the tension members, which have an influence on the shape, the tensile strength and the pretension of the tension element and e.g. a reduction in the load-bearing cross-sections due to friction / wear of the individual filaments can cause each other. Such changes in shape and strength, ie also due to permanent expansions and constrictions of the strength members of a traction means, also change its elastic behavior, namely the elastic and the permanent expansion during operation.

An advantageous development consists in that the actual positions of the translationally moving object are determined by position sensors arranged within the linear travel path and detecting the position of the translationally moving object. This provides a cost-effective way to determine the actual position within the travel path using simple measuring sensors.

An advantageous development consists in that the actual positions of the translationally moved object are determined on the deflection disks by position encoders or rotary encoders. Here, too, known and proven sensors can be used to determine the actual position, especially since this can be the same type of sensor that is also used to determine the desired positions of the translationally moving object by means of position encoders or rotary encoders on the drive disk .

An advantageous further development consists in that the target positions of the translationally moved object are determined by position encoders in the drive motor. This is particularly useful when the drive is made by a linear motor.

A further advantageous embodiment consists of the fact that the theoretical current status length L _{current (item 1-n) of} the traction device and the comparison with the traction device lengths L _{beginning (item 1-n) of} the basic quantity determined from the ratio of the currently measured actual and target positions or base curve based on threshold values for the differences ΔL _{(item 1-n)} = L _{start (item 1-n)} - L _{current (item 1-n) in} such a way that the threshold values are learned using methods of artificial intelligence based on relations between Preloading of the traction devices and positioning accuracy of a linear drive. As a decision criterion for the admission of a threshold value, a just allowed relation between preload and positioning accuracy can be preselected, the reaching or exceeding of which is checked again in the course of the operating time and saved as a learning curve for certain timing belts and drive constellations.

A linear drive with an object driven by finite traction means made of elastomeric material and translationally moved over a predetermined, essentially linear travel path is particularly suitable for the application of such a method, in which the traction means rotates around deflection or drive rollers and is connected at the end to the translationally moving object , wherein the traction device has in its longitudinal direction embedded in the traction element strength members or reinforcing elements, preferably designed as twisted or beaten cords from filaments, the linear drive on the one hand having position measuring devices arranged within the linear travel path for each actual position of the translationally moved object, the Linear drive, on the other hand, has measuring devices arranged within the drive elements and recording the movement data of the drive elements, preferably measuring devices in ei nem drive motor or in a drive roller of the linear drive, the linear drive further comprising a control and arithmetic unit which compares the first measured values of the position measuring devices with second measured values, which are determined by calculation from the movement data of the drive elements and from the ratio of the first and second measured values and A theoretical length L of the traction device is determined from further geometric dimensions of the linear drive for each position of the moving object that is approached, is continuously stored over an operating period, and changes in the stored theoretical lengths are detected and evaluated on the basis of threshold values.

Claims (7)

Method for determining the preload loss of finite traction means () made of elastomeric material within a linear drive, in which the traction means rotates via deflection or drive rollers and is connected at the end to a driven object that is translationally moved via a predetermined, essentially linear travel path, the traction means in its longitudinal direction has strength members or reinforcing elements embedded in the traction element body, preferably designed as cords twisted or beaten from filaments, characterized in that after a running-in phase of the linear drive, the actual position of the translationally moved object within the linear travel path for each position of the translationally moved object that is approached is determined and related to a target position of the transl. calculated from the movement data of the drive motor, preferably the revolutions of the drive roller of the linear drive atorically moving object within the linear travel path, a theoretical initial length L _{beginning (item 1-n) of} the traction device being determined from the ratio of the two positions and the geometric dimensions of the linear drive for each position approached, and stored in the form of a basic quantity or base curve of traction device lengths , in the operating phase that follows the running-in phase, a theoretical current status length L _{current (item 1-n) of} the traction device is determined from the ratio of the currently measured actual and target positions and with the traction device lengths L _{start (item 1-n) of} the base quantity or Base curve is compared, and after exceeding predetermined threshold values for the differences ΔL _{(item 1-n)} = L _{start (item 1-n)} - L _{current (item 1-n)} between the theoretical initial lengths and the theoretical current status lengths of the traction devices, a warning signal is given or to replace the traction device. Procedure according to Claim 1 , in which the actual positions of the translationally moving object are determined by position sensors arranged within the linear travel path and detecting the position of the translationally moving object. Procedure according to Claim 1 , in which the actual positions of the translationally moved object are determined by position encoders or rotary encoders on the deflection disks. Procedure according to one of the Claims 1 to 3rd , in which the target positions of the translationally moved object are determined by position encoders in the drive motor. Procedure according to one of the Claims 1 to 3rd , in which the target positions of the translationally moved object are determined by position encoders or rotary encoders on the drive disk. Procedure according to one of the Claims 1 to 5 , in which the theoretical current status length L _{current (item 1-n) of} the traction device and the comparison with the traction device lengths L _{beginning (item 1-n) of} the base quantity or base curve based on threshold values determined from the ratio of the currently measured actual and target positions for the differences ΔL _{(item 1-n)} = L _{start (item 1-n)} - L _{current (item 1-n) in} such a way that the threshold values are learned using methods of artificial intelligence based on the relationships between the pre-tensioning of the traction means and the positioning accuracy a linear actuator. Linear drive with an object which is driven by finite traction means made of elastomeric material and which is translationally moved over a predetermined essentially linear travel path, in which the traction means rotates around deflection or drive rollers and is connected at the end to the translationally moved object, the traction means being embedded in the traction element body in its longitudinal direction Has strength members or reinforcing elements, preferably designed as twisted or beaten cords, the linear drive on the one hand has position measuring devices arranged within the linear travel path for each actual position of the translationally moved object, the linear drive on the other hand arranged within the drive elements and the movement data of the Measuring devices receiving drive elements, preferably measuring devices in a drive motor or in a drive roller of the linear drive, wobe i the linear drive also has a control and arithmetic unit which compares the first measured values of the position measuring devices with second measured values, which are determined by calculation from the movement data of the drive elements and from the ratio of the first and second measured values and from further geometric dimensions of the linear drive for each approached Position of the moving object, a theoretical length L of the traction device is determined, continuously stored over an operating period, and changes in the stored theoretical lengths are detected and evaluated on the basis of threshold values according to the method steps Claim 1 to 6 .