AU2020273297A1

AU2020273297A1 - Method and Device for Measuring an Axial Displaceability of a Rotatably Mounted Shaft

Info

Publication number: AU2020273297A1
Application number: AU2020273297A
Authority: AU
Inventors: Tim Fritsch; Eric Kratzsch; Robert Schneider
Original assignee: Brandenburgische Technische Universitaet Cottbus
Current assignee: Brandenburgische Technische Universitaet Cottbus
Priority date: 2019-12-20
Filing date: 2020-11-19
Publication date: 2021-07-08
Also published as: EP3839463A1; DE102019135385A1

Abstract

The invention preferably concerns a method for measuring an axial displaceability of a shaft rotatably mounted in a casing, characterised in that the casing with the rotatably mounted shaft is clamped horizontally in a clamping device. After setting the force application directions to the 5 central axis of the shaft, a first force is initially applied along a first force application direction until a first test force is reached, and a second force is subsequently applied in an opposite direction along a second force application direction until a second test force is reached. During the operation, the measuring instrument measures the shaft's axial change in position relative to the casing in order to determine the shaft's displaceability in relation to the casing. Another aspect of 0 the invention concerns a device for measuring an axial displaceability of a shaft rotatably mounted in a casing, preferably by means of the method according to the invention. 20 Fig. I 21 21

Description

Fig. I

21

METHOD AND DEVICE FOR MEASURING AN AXIAL DISPLACEABILITY OF A ROTATABLY MOUNTED SHAFT

Field of the Invention

The invention relates to a method for measuring axial displaceability of a shaft rotatably mounted in a casing, characterised in that the casing with the rotatably mounted shaft is clamped horizontally in a clamping device. After setting a force application direction to the central axis of the shaft, a first force is initially applied along a first force application direction until a first test force is reached, and a second force is subsequently applied in an opposite direction along a second force application direction until a second test force is reached. During the operation the measuring instrument measures the shaft's axial change in position relative to the casing in order to determine the shaft's displaceability in relation to the casing. Another aspect concerns a device and a method for measuring an axial displaceability of a shaft rotatably mounted in a casing.

Background of the invention

Shafts and axles are widely used wherever component parts need to perform rotational movements. Possible applications include, for example, transmissions, conveying systems, hoisting gear, tooling machines, engines and processing machines, motors, motor vehicles, turbines, textile machines, construction machinery, etc. For these purposes, shafts and axles are manufactured from rods or forged blanks. The choice of material depends on the intended application.

A suitable casing is essential for the relative rotational movement between a shaft (or axle) and the rotating surface of a machine element rotating relative to the shaft (or axle). Bearings have the purpose of transferring forces with the smallest possible wear and tear and minimal friction. This can only be achieved by separating the surfaces which come into contact. This is achieved .5 by using roller bearings or hydrodynamic or hydrostatic slide bearings.

The axial displaceability of the bearing is highly relevant for the design of a bearing for the particular requirements of a specific field of application. Using an inappropriate bearing -with excessive or insufficient axial displaceability - can lead to extensive damage to machine parts. Such a bearing must therefore be monitored regularly for its axial displacement before its installation and during its operational phase. The axial displacement is determined by means of measurement methods.

A frequently applied design of a shaft rotatably mounted in a casing is a support roller as is known to a person skilled in the art. According to the prior art, the axial displaceability of support rollers is usually determined according to DIN 22112-3. With the relevant method, the end faces of a support roller are vertically clamped into a testing device. With this method, only the casing is clamped. A 500 N load is alternately applied to the mounted shaft via a lower and an upper lever. Another lever is provided between the lower lever and the front face of the shaft end, and said lever transmits the extent of axial displacement to a dial gauge. The vertical position of the support roller is disadvantageous for this test method, because the mass of the shaft influences the applied test force through the force of its weight. When measuring the axial displaceability according to the DIN standard, the applied test force is excessive, having a detrimental effect, if it is applied in the direction of the weight force of the shaft. On the other hand, if it is applied in the opposite direction to the weight force of the shaft, it is insufficient, also with a detrimental effect. Consequently, the measurement result may be distorted. Support rollers can have different dimensions or embodiments. While the device allows an adequately flexible setting, the adjustment effort and time required are, however, detrimentally large. Further, the design of the measuring device according to DIN 22112-3 is detrimental to the accuracy of measurement, since the application of the test force results in a deformation of the frame, which is also recorded by a dial gauge.

Problem addressed by the invention

The problem addressed by the invention is thus to avoid the disadvantages of the prior art and to provide a method as well as a device for obtaining precise measurement results for determining an axial displacement of a shaft rotatably mounted in a casing, wherein its handling or execution respectively are also to be simplified.

Abstract of the invention

The problem according to the invention is solved by the features of the independent claims. Advantageous embodiments of the invention are described in the dependent claims.

A first aspect of the invention preferably concerns a method for measuring an axial displaceability of a shaft rotatably mounted in a casing, characterised in that:

a) the casing with the rotatably mounted shaft is clamped horizontally in a clamping device, with a measuring instrument being provided to measure the axial position of the shaft relative to the casing;

b) means for applying a first and an opposite second force in a direction along the longitudinal shaft axis are adjusted relative to the central axis of the shaft depending on the casing diameter;

c) a first force is applied at a first end of the shaft along a first force application direction until a first test force is reached and

d) a second force is subsequently applied in a second force application direction, opposite to the first force application direction, until a second test force is reached;

wherein a measuring instrument measures the axial position change of the shaft relative to the casing in order to determine the axial displaceability of the shaft relative to the casing.

The advantage of such a method is that the test force or the applied force respectively is not influenced by the weight force of the shaft, and consequently better measurement results are achieved. Additionally, the shaft can be advantageously and easily applied in a device for carrying out the above-mentioned method, wherein a special advantage lies in the fact that extremely heavy, large and unwieldy shafts can be used. Another advantage is that the deformation of the shaft and frame of the testing device does not impact on the measurement method.

A shaft is an elongated, round cylindrical machine element that is used for transmitting rotational movements and torques of parts firmly connected by the shaft (i.e. co-rotating parts). Its rotatable mounting occurs mostly in two places along its design. According to the invention, the shaft is preferably rotatably mounted around its axial length.

In contrast to shafts, axles do not transmit rotational movements. They do not turn but are fixed. However, components may be rotatably mounted around an axle. According to the invention, a shaft can therefore likewise be designed as an axle. Accordingly, a casing can be rotatably mounted around an axle, while the axle is firmly attached. A person skilled in the art knows that there may be axial displaceability between two components which are rotatably mounted relative to each other, making the method of the invention relevant to both shafts and axles.

According to the invention, the horizontal direction is vertical to the perpendicular direction, which preferably coincides with the direction of gravity. The horizontal direction as well as the perpendicular direction are terms understood by the average person skilled in the art. As the shaft is aligned horizontally for the measurement of axial displaceability according to the invention, the weight force of the shaft does not influence the application of the test force. This advantageously leads to better measurement results.

The axial displaceability of a shaft in a casing is preferably defined as the shaft's axial displacement relative to its casing, wherein the axial direction corresponds to the direction of the shaft's longitudinal axis. A person skilled in the art is aware of this. The axial displaceability is also referred to as 'axial play' in the prior art. The shaft's longitudinal axis runs in a horizontal direction in particular in this case.

According to the invention, the axial displacement of the shaft is preferably measured relative to the casing via a measuring instrument. This measuring instrument is preferably a displacement gauge. This instrument is also known as a distance or length gauge to a person skilled in the art. As the names suggest, these measuring instruments serve to measure travel, distance or length. In this specification, the term 'measuring instrument' generally refers to a measuring instrument for measuring travel, distance or length as referred to in this paragraph. Any other measuring instruments referred to are specified differently, for example the force gauge referred to below.

A shaft casing is likewise known to a person skilled in the art and can be variously embodied. According to the invention, such shaft/casing designs are preferably referred to as "support rollers". These are used as support or guiding elements in conveyor belt systems, for example. Shaft/casing designs are not, however, limited to support rollers. For practical purposes, similarly designed machine elements may also be referred to as shaft/casing designs in addition to support rollers, for example electrical motors with a mounted rotor in a stator. According to the invention, a casing is preferably a component which envelops the shaft, with the casing comprising an interior surface, which faces the shaft, and an exterior surface, which faces away from the shaft. The shape of the exterior surface may differ from that of the interior surface. The rotatably mounted shaft and its casing are also referred to as test piece in this document.

The exterior shaft casing is preferably designed as a round cylinder, with the exterior shape of the casing comprising a shell surface and two end faces. The two end faces define the two side surfaces or the base areas of the cylinder.

According to the invention, a clamping device is the preferred holding device. This is preferably designed such that it is able to hold a body firmly in position in a form-fitting and/or friction-fitting manner. The clamping device preferably clamps the casing on end faces. The advantage of having the casing clamped at end faces is that the casing is positively clamped since the test force is applied along the longitudinal axis of the test piece. Positive, form-fitting clamping has an advantageous effect in protecting the material compared to friction-fitting clamping.

In a further preferred embodiment, the shaft of the test piece features at least one axle journal. An axle journal is a section of the shaft which is designed as a step on one end of the shaft. The shaft may also include two journals, with one provided at each of the two ends. The journal has a smaller diameter than the rest of the shaft. In the prior art, axle journals are also referred to as axle stubs. A step serves advantageously as an axial stop for sliding components or as an assembly stop for inner rings of roller bearings.

A force application direction according to the invention is the direction in which a force acting on a body applies to the body. Additionally, the force application direction according to the invention can be set via means, wherein the particularly preferred force application direction runs parallel to or in the direction of the longitudinal axis of the shaft. Advantageously, this results in only an axial load applied to the bearings, which permits more precise measurement results to be obtained and causes less wear in the test piece. An axial load is a term known to a person skilled in the art.

The force application direction is preferably set such that the applied force acts precisely on the symmetrical axis or central axis of the journal in the longitudinal direction of the shaft. The height position of the central axis of a test piece depends on its dimensions, in particular the design of the casing. Therefore, the force application direction is preferably set dependent on the casing diameter according to the invention.

According to the invention, the means for applying the first and the opposite second force in the first and second opposite force directions can be any force-transmitting components known to a person skilled in the art that set a defined direction, such as a rod or bar, a spring, cable or chain. Preferably, rods or bars and/or tension or compression springs are used for the design of the means defining the force application direction. A bar has the advantage of being able to transmit a force along its longitudinal axis (both tensile and compressive forces). Depending on its design, the spring may also exhibit such advantageous behaviour. A coil spring can, for example, be placed under both tensile and compressive loads.

According to the invention, the test force is preferably a predefined force. This test force is essentially the same for each embodiment of the method according to the invention and corresponds preferably to 100 N to 1000 N, preferably to 300 N to 800 N and particularly preferably to 400 N to 600 N. A test force that is essentially the same every time it is applied advantageously permits different test pieces to be compared. A predefined test force also has the advantage of ensuring that the applied forces do not exceed a threshold. Exceeding the test force or a threshold level respectively could potentially cause damage to the test piece.

The applied first and second forces are preferably measured using a force gauge and compared to the predefined test force via a control unit. According to the invention, the force gauge is preferably a load cell or a force transducer. A force transducer serves to measure a force acting on a sensor. Most of the time, both tensile and compressive forces can be measured by means of elastic deformation. A force transducer is preferably selected from a group of tools including spring body force transducers, piezo force transducers, force transducers with oscillating elements, electro-dynamic force transducers, resistive force transducers. A person skilled in the art is familiar with the above-mentioned load cells. The advantage of such force gauges is that they are very compact and thereby enable precise measurements.

Terms such as 'essentially, approximately, about' etc. preferably describe a tolerance range of less than +/-40%, preferably +/-20%, and particularly preferably +/-10%, and even more particularly preferably less than +/-5%, and above all less than +/-1% and at all times include the exact value. The term 'similar' describes parameters which are approximately the same. The term 'partially' preferably describes at least 5%, particularly preferably at least 10% and even more particularly preferably at least 20%, in some instances at least 40%.

In a further preferred embodiment of the invention, the method is characterised in that the first and second test force have the same value. The repeatability and comparability of measurements of axial displacement is advantageously better achieved by using a defined test force that is always the same.

An average person skilled in the art here understands that the expression 'the same value' can be interpreted to mean that the value of the forces is essentially the same.

In a further preferred embodiment of the invention, the method is characterised in that the measuring instrument is zeroed to the given axial position of the shaft relative to the casing when the first test force is reached and the axial displaceability of the shaft relative to the casing is ascertained as an absolute value by the measuring instrument based on the change in axial position by the time the second test force is reached. Advantageously, the zeroing of the measuring instrument ensures that no calculations or differences between the measured values need to be made or ascertained. The zeroing step allows the axial displaceability to be ascertained as an absolute measurement relative to the zero point.

According to the invention, the zeroing of a measuring instrument is defined as the measuring instrument being readjusted and being reset to zero. In doing so a new reference point is defined for the measuring instrument.

In a further preferred embodiment of the invention, the method is characterised in that the axial displaceability of the shaft relative to the casing is ascertained from the difference between the axial position change of the shaft relative to the casing on reaching the first test force and the axial position change of the shaft relative to the casing on reaching the second test force. In this case, the measuring instrument does not need to be zeroed, which has the advantage of saving time where measuring instruments are used which are difficult to access. This embodiment also substantially reduces additional effort in case of measuring instruments which require several method steps for zeroing.

According to the invention, the value measured for the position change as the first test force is reached is recorded and subsequently compared with the value measured as the second test force is reached. The axial displacement is then determined from the difference between the two values. The measured values can be recorded manually by a user or automatically by being stored in a storage device.

In a further preferred embodiment of the invention, the method is characterised in that the shaft is mounted inside the casing by at least one roller bearing. Roller bearings have the advantage of less (start-up) friction. Roller bearings also have the advantage of being available as standardised units which allow for easy installation and easy selection in keeping with applicable loads. A further advantage is the high degree of precision of roller bearings as well as their easy lubrication and the surprisingly small quantities of lubricant they require. Roller bearings are additionally advantageous as they are also suitable for mixed friction operation and generate little heat.

According to the invention, roller bearings are preferably a ready-to-install machine element. A roller bearing consists preferably of an outer ring, an inner ring and rolling bodies which are guided inside a cage. Loads can be transmitted radially, axially or diagonally (radially and axially). The roller bearing designs according to the invention are preferably selected from a group consisting of radial ball bearings, angular ball bearings, self-aligning ball bearings, cylindrical roller bearings, needle roller bearings, tapered roller bearings, spherical roller bearings, self aligning roller bearings. All of the above roller bearings are known to a person skilled in the art.

The shaft can be preferably mounted inside the casing via at least one bearing. The shaft is particularly preferably mounted in the casing via two bearings. However, the maximum number of bearings is not limited.

In a further preferred embodiment of the invention, the shaft is rotatably mounted in a casing via at least one slide bearing. With slide bearings, the two parts moving relative to each other slide against each other against the resistance caused by the gliding friction. This resistance can be minimised by choosing a low-friction pairing of materials, by lubrication or by creating a lubricating film (full lubrication) to separate the two contact surfaces from one another. Slide bearings offer the advantage of being low-maintenance. Additionally, slide bearings have the advantage of generating little noise; they are also not susceptible to the entry of dust and vibrations and highly suitable for high rotation speeds.

In a further preferred embodiment of the invention, the method is characterised in that the measuring instrument is a dial gauge, preferably with a stand which is attached to the casing. Dial gauges have the advantage of being inexpensive, robust and nevertheless very precise.

A dial gauge is a mechanical measuring instrument for measuring lengths or length differences. They are used for comparative, planarity, position or concentricity measurements, for example. The function and design of a dial gauge are preferably standardised by DIN Regulation 878 and are known to a person skilled in the art.

The stand for the dial gauge is preferably attached by fixtures to the casing. The fixtures can preferably include bonded connections, rivet connections or screw/bolt connections. Particularly preferred are fixtures based on a magnet. The force applied by the magnet ensures that the stand is firmly attached to the casing of the test piece. The magnet can preferably be switched on and off. The dial gauge and stand can advantageously be attached or removed without requiring tools and without causing damage.

In a further embodiment, the measuring instrument is selected from a group including incremental encoders, fibre-optic path sensors, video extensometers and laser distance meters.

In a further preferred embodiment, the measuring instrument and/or its attachment is located at a distance from the test piece or casing respectively and thus not attached to the casing of the test piece. The advantage of such an embodiment is that the measuring instrument can remain at the same position even if the test piece is changed. The measuring instrument does not need to be recalibrated and advantageously also does not need to be reattached or removed when the test piece is changed.

In a further preferred embodiment of the invention, the method is characterised in that the first and/or second force is applied mechanically, hydraulically, magnetically, electrically and/or pneumatically.

According to the invention, the mechanical application of a force preferably takes the form of a transfer of movements, forces and torques via rigid components (bars, joint rods). The advantage of a mechanical introduction of forces is the non-complex and simple design of the components. The mechanical application of forces is known to a person skilled in the art.

With a hydraulic system, power is transmitted via a hydraulic fluid. The preferred fluid is a mineral oil. With hydraulically applied forces, mechanical power is preferably converted into hydraulic power via a pump. This power is subsequently transformed into mechanical power again. Such a principle is known to a person skilled in the art. The advantage of such a hydraulic arrangement is that substantially higher forces can be transmitted, and very even and precise force movements are possible, as the compression of the hydraulic fluid is very small.

In a further preferred alternative, compressed air is used instead of a hydraulic fluid. A person skilled in the art understands this to mean the introduction of pneumatic forces and is familiar with such an arrangement. This arrangement has the advantage of permitting the holding of a constant force without power. This arrangement has the further advantage of being robust against overload and not susceptible to fluctuations in temperature.

In a further embodiment of the invention, the force is preferably applied magnetically. According to the invention, a ferromagnetic shaft end can, for example, be attracted by a magnet attached to a frame. Advantageously, a force acts on the shaft end in the force application direction without the shaft being in contact with a component, except for the mounting.

In another variant of magnetically applied forces, the shaft end is equipped with a permanent magnet. The frame next to it features an electromagnet. Depending on the polarisation of the electromagnet, the shaft end is then attracted or repelled. The advantage of such a design is the contactless application of a force as well as the fact that the force is preferably only applied to the test piece from one side of the shaft. Permanent magnets and electromagnets are known to a person skilled in the art.

In a further embodiment of the invention, a force is preferably applied electrically. Preferably a generator produces electricity, which is converted into a mechanical form of motion, causing a force to act on the shaft in the force application direction. The form of motion can, for example, be converted via an electrical motor or an electromagnet.

In a further preferred embodiment of the invention, the method is characterised in that the first and second force application directions are determined by a connection of the first end of the shaft to a frame, wherein the casing in the clamping device can be moved along the longitudinal axis of the shaft by means of a positioning device and the first test force and second test force are applied by the casing being moved relative to the frame, causing corresponding tensile and compressive forces at the first end of the shaft. Such an arrangement can advantageously be designed to be very compact, as the test piece only needs to be connected to the frame on one side of the test piece. As is described in detail below, the reverse of the method is also conceivable and feasible, i.e. with the shaft being moved and the casing being fixed in place. The described embodiment avoids deformation of the frame and the associated measurement error.

According to the invention, the connection of a first end of the shaft to a frame is preferably rigid or stiff, preferably via a rod or bar. A bar has the advantage of having highly wear-resistant properties. A bar is also advantageously able to absorb compressive and tensile forces. The connection of a shaft end to a frame preferably defines the force application direction.

A connection thereby preferably allows two force application directions to be defined. A rigid bar can therefore absorb both compressive and tensile forces, with these two forces acting in opposite directions.

In a further preferred embodiment, the connection to the frame is designed elastically. According to the invention, an elastic element is preferably defined as an element, preferably a body or a material, which changes its form when acted upon by a force and which returns to its original form as the action of the force is removed.

By using an elastic element, the force is increased by moving the casing relative to the frame; this is done in a linear manner as the distance increases until the desired test force is set. The spring constant of the elastic element can preferably be selected to ensure a test force with a desired travel distance. For example, to ensure a test force of 100 N to 1000 N with a displacement of 1 mm, an elastic element with a spring constant between 100 and 1000 N/mm can preferably be selected. If the same test forces are to be reached with a longer travel distance of 10 mm, it may be preferable to select an elastic element with a correspondingly smaller spring constant of 10 and 100 N/mm, i.e. a reduction by a factor of 10. Elastic elements thus permit a (preferably longer) travel distance to be set precisely, thus improving the sensitivity or measuring accuracy respectively.

The elastic properties of the elastic element can be preferably ensured by a relevant choice of form, structure and/or material. For example, the elastic element may include a spring structure or be made fully or partially out of elastic materials.

In a preferred embodiment, the elastic element is designed as a block-shaped elastomer. According to the invention, an elastomer refers preferably to a synthetic material whose special property is its rubber elasticity. A person skilled in the art knows that this would be a synthetic material whose glass transition temperature is below the operating temperature. An elastomer therefore retains its shape but is advantageously elastic and returns into its original form after any deformation. Examples include natural or synthetic rubber, although a person skilled in the art would be familiar with a large range of further elastomers.

In a further preferred embodiment, the elastic element is designed as a spring. The rigidity of a spring can advantageously be calculated very well. In a preferred embodiment of the spring, the spring is a tension and/or compression spring selected from a group consisting of coil springs, zigzag springs and/or plate springs. The spring is particularly preferably designed as a coil spring. An average person skilled in the art is aware of various forms of springs.

In a preferred alternative of the connection, it is designed as a combination of described elastic elements and stiff or rigid design elements such as a bar. According to the invention, these elements are preferably connected in a series one behind another.

In a further preferred embodiment, the connection between the test piece and the frame includes a load cell. This has the advantage of allowing the applied force to be measured.

In a further preferred embodiment, the connection can preferably include a force- or energy producing component such as a motor or generator in addition to a force-transmitting component.

In a preferred embodiment the journal at the shaft ends features a cross hole. The connecting element between the test piece and the frame, however, features a so-called fork at one end. The fork of the connection likewise features holes so that a bolt can be inserted through the holes as the fork and journal engage, thereby providing a positive connection. A bolt connection of this type as well as a fork referred to in this context are known to a person skilled in the art. Such a connection has the advantage of being able to be released with little effort so that different test pieces can be changed quickly.

The connection between the shaft and frame can also be attached to the shaft by other forms of attachment. The attachment can, for example, take the form of bonded connections, rivet connections, screw/bolt connections or a clamping device.

According to the invention, a positioning device preferably features a slide block and rails. In a preferred embodiment, the clamping device is moveably mounted on the rails of the positioning device via the slide block, allowing a degree of movement. The slide block can move relative to the rails. In one preferred embodiment, the slide block on which the clamping device is mounted preferably moves along the rails.

In a preferred embodiment, the movement of the slide block is caused by a linear drive. The linear drive advantageously produces an even, precise movement so that the test force of the arrangement is never exceeded.

In a preferred embodiment of the invention, the movement is provided by a humanly applied force, in particular by hand. This advantageously allows to do without a structural component such as the linear motor described above and therefore reduces costs.

Because the clamping device only clamps the casing of the test piece and the shaft is firmly connected or fixed to the frame, for example via a bolt connection, a tensile or compressive load is generated at the end of the shaft or at the connecting element respectively, depending on the direction of travel of the slide block relative to the rails. The advantage of such an arrangement resides in the fact that two force application directions are applied between the frame and test piece via a single connecting element. As a result, the measuring array can advantageously be designed very compactly.

In a preferred embodiment, the load is preferably measured by the integrated load cell. In this case, the travel continues until the compressive or tensile load reaches the test force. The travel is preferably across a distance of 0.1 mm and 10 mm, preferably across a distance of 0.5 mm and 10 mm, and particularly preferably across a distance of 1 mm and 5 mm.

In another preferred embodiment of the invention, the method is characterised in that the first force application direction is determined via a central axial connection between the first end of the o shaft and a first force application point of a frame, and the second force application direction is determined via a central axial connection between the second end of the shaft and a second force application point of the frame, with the casing being able to be fixed relative to the frame in the clamping device, and both the first test force and the second test force are applied by the test force being introduced via the respective force application points of the frame. This offers the advantage that no slide block or rails are necessary so that the test force can be applied more precisely.

The forces applied to the respective ends of the shaft preferably take the form of compressive forces. Compressive forces can advantageously be applied more easily to the shaft.

According to the invention, the force application point is the point where the connection to the frame is firmly fixed and supported. According to Newton's law, a force then also acts on the device frame, if a force is applied to the test piece. This force is transmitted to the frame as a counterforce at the force application point.

According to the invention, a central axial connection is designed such that the connection between the frame and shaft attaches to the symmetrical or central axis of the shaft. The connection may preferably include a force-producing component such as a motor in addition to a force-transmitting component. Force conversion results in the force being correspondingly applied to the test piece via the connection by mechanical, hydraulic or pneumatic means. A counterforce is correspondingly applied to the frame at the force application point.

In a preferred embodiment of the invention, the clamping device can be fixed relative to the frame. A clamping device is rigidly attached to the frame via a fixed bearing. The application of a force at the first and second shaft end leads to an axial displacement of the shaft relative to the casing.

In a further preferred embodiment of the invention, the method is characterised in that the first and/or second force are applied via a lever mechanism. The advantage of a lever mechanism is its straightforward design and the easy calculation of the applied force.

A lever mechanism according to the invention is preferably a mechanical transmission. Mechanical transmissions transmit movements, forces and torques via rigid components such as gearwheels, chains, belts or joint rods. According to the invention, the preferred lever mechanism is joint rods, with each rod being defined as a transmission link. In particular, a lever mechanism causes a force to be deflected such that the force applied to the test piece follows the preferred force application direction (parallel to the longitudinal axis of the test piece).

In a further aspect, the invention preferably concerns a device for measuring an axial displaceability of a shaft rotatably mounted in a casing, preferably for performing the described method, characterised in that the device features a clamping device for horizontally supporting the casing with the rotatably mounted shaft and a measuring instrument for determining the axial position of the shaft relative to the casing, wherein the device includes means for applying a force in a first application direction and a force in an opposite, second application direction along the central axis of the shaft, with both forces being adjustable depending on the casing diameter.

The device has the advantage of compactness and is nevertheless suitable for use with a variety of differently designed shaft or casing sizes. The above-mentioned methods can be advantageously applied to the device, or the device can advantageously be used in the method respectively. In particular, the measurement of the deformation in the preferred device is deliberately avoided by its design, since the deformation would be included in the overall result as a measurement error.

The measurement of the axial displaceability must be distinguished from measurements of the axial stiffness (deformation). When measuring axial stiffness, a rotational movement is usually applied to the object to be measured (e.g. a shaft or spindle), which results in dynamic effects within the bearing arrangement. These are caused in particular by a lubricant necessary for operation and its viscosity. In addition, running tolerances within the bearing of the shaft are usually included in the measurement of the dynamic stiffness and output in the overall result. For the device according to the invention, however, these differences recorded in the result due to the lubricant film and running tolerance represent an absolutely avoidable measuring error and are undesirable and should be avoided.

According to the invention, the clamping device is preferably designed such that a shaft rotatably mounted in a casing is firmly clamped, via the casing, at each end face by a clamping jaw. The advantage of having the casing clamped at the end face is that the casing is positively clamped since the forces are applied along the longitudinal axis of the test piece. The described clamping device is not a simple "manual" measure, but decisive for achieving the desired measuring results.

In a preferred embodiment, the test piece is clamped in place in a friction-fitting manner using tension belts running across the long side of the test piece. In a further preferred embodiment, a magnet generates the necessary holding force so that the casing of the test piece is connected to a frame in a friction-fitting manner. Both friction-fitting connections have the advantage of being able to be designed very quickly and without a lot of outlay.

In a further preferred embodiment, the device includes a control unit and a load cell. The control unit preferably has a microcontroller. The load cell is used to measure the force applied to the test piece and to compare it preferably continuously to the test force by means of the control unit. As soon as the test force or a threshold value is reached, the control unit performs the next method step. The next method step is preferably the application of a second force in the opposite direction to the previously applied first force. Preferably the control unit has a light (preferably an LED means of illumination) which lights up when the test force is reached so that a user can see that a test force has been reached.

In a further embodiment, the test force is applied by the casing being displaced relative to the shaft and the resulting tensile and compressive load applying to the first shaft end. Once the first test force has been reached, the travel movement of the casing is terminated and a light signals that the test force has been reached. The measuring instrument is then 'zeroed'. In a next step, o the casing is moved in the opposite direction relative to the shaft until the second test force is reached. A light signal again indicates that the second test force has been reached. A load cell allows the applied force to be continuously measured, with the force being compared against a threshold value via a control unit comprising a microcontroller. Once the threshold value (test force) has been reached, the light is switched on by the control unit.

In a further preferred embodiment, the control unit controls and/or regulates the application of the force, allowing it to control and/or regulate the linear drive, for example. This has the advantage that any human influence is minimised, allowing more precise measurement results to be achieved. Another advantage lies in the fact that tests are consistently performed under the same conditions, ensuring particularly good comparability of tests.

In a further preferred embodiment of the invention, the device is characterised in that the clamping device can be adjusted to the length and diameter of the casing. This advantageously allows a force to be applied to the centre of the longitudinal axis of the shaft. The device thereby has the advantage of being able to provide a method for measuring axial displacement for variously dimensioned test pieces.

The clamping device according to the invention is preferably designed such that a clamping jaw guided along rails is adjustable relative to a fixed clamping jaw which acts as a counterpart. The counterpart can also be designed as a wall-like structure. By adjusting the clamping jaw guided along rails, the clamping device can advantageously be adjusted to the casing length of the test piece.

In a further embodiment, both clamping jaws are adjustable and guided along rails of the clamping device.

In a preferred embodiment, the device has at least one screw clamp. The screw clamp serves to secure the movable clamping jaw between the casing and the screw clamp in place. In one embodiment, the screw clamp is firmly attached to the rails of the clamping device. In a further embodiment, the screw clamp is movably mounted on the rails of the clamping device, allowing a degree of movement.

In a further preferred embodiment, clamping jaws can be replaced such that they can be advantageously adapted to the casing diameter of a test piece.

In a further preferred embodiment of the invention, the device is characterised in that the measuring instrument is a dial gauge, preferably with a stand which can be attached to the casing. The use of a dial gauge in the device has the advantage of being very economical.

In a further preferred embodiment of the invention, the device is characterised in that the clamping device is mounted on a positioning device, allowing a degree of movement, such that it can be displaced in a horizontal direction. The provision of a positioning device has the advantage of applying a first and second force from only one side of the shaft.

In a further preferred embodiment of the invention, the device is characterised in that the device includes a frame with a force application point and a connection means to a first end of the shaft which is vertically adjustable relative to the diameter of the casing and can thus be adjusted to the vertical position of the central axis of the shaft. This adjustment advantageously aligns the force application direction with the axial direction such that only one axial load acts on the test piece.

In a further preferred embodiment of the invention, the device is characterised in that the device includes a frame with a first and a second force application point and connection means for a central axial connection with the first and second end of the shaft, with the force application points and connection means being vertically adjustable relative to the diameter of the casing and thus being able to be adjusted to the vertical position of the central axis of the shaft. This adjustment also advantageously aligns the force application directions with the axial direction such that only one axial load acts on the test piece.

The connection means between the force application points of the frame and shaft ends, which are vertically adjusted relative to the casing diameter, define the force application direction. In other words, the force application directions always run parallel to or in the direction of the longitudinal axis of the shaft, with vertical adjustability allowing central axial alignment with various diameters of shafts rotatably mounted in a casing for testing.

In a further preferred embodiment of the invention, the device is characterised in that the device for applying a central axial force to the first and second end of the shaft features a lever mechanism each, comprising a swivel joint and two bars. A lever mechanism allows the force to be applied to be provided in a particularly simple form. It is preferably possible to use a weight force only for applying the force, with a lever mechanism being extremely energy-efficient.

FIGURES

In the following, the embodiments of the invention are explained in more detail using figures, without limiting the invention to these embodiments.

Brief description of the figures

Fig. 1 Schematic representation of a shaft rotatably mounted in a casing, with the shaft being clamped in a clamping device connected to a frame on one side.

Fig. 2 Schematic representation of a shaft rotatably mounted in a casing, with the shaft being clamped in a clamping device and a force being applied to the test piece on both sides via a lever mechanism on each side.

Fig. 3 Schematic representation of a shaft rotatably mounted in a casing, with the shaft being clamped in a clamping device and a force being applied to the test piece on both sides (without lever mechanism).

Fig. 4 Embodiment of a test device for measuring the axial displaceability of shafts rotatably mounted in a casing

Fig. 5 Test device and test piece for measuring axial displaceability

Detailed description of the figures

Fig. 1 is a schematic representation of a shaft 2 rotatably mounted in a casing 4, with the shaft being clamped in a clamping device comprising two clamping jaws 10 and being connected to a frame 12 on one side. The clamping device is mounted with a degree of freedom on a slide block on rails and is adjustable to the casing length. A stand 6 is attached to the casing 4 for measuring the axial displaceability. The stand 6 is preferably attached to the casing via a magnet 7. The stand 6 represents a bracket for a dial gauge 8. At one end of the shaft 2 a connection 24 is provided to the frame 12. The connection 24 engages with one end of the shaft 2 and the force application point 14 of the frame 12. The figure also shows the direction of movement 15 of the slide block. Depending on the movement of the slide block, a tensile or compressive force is applied to the end of the shaft 2. The movement is continued until a predefined test force is reached. A movement is then performed in the opposite movement direction 15 until a predefined test force is again reached. In the process, the dial gauge 8 measures the relative axial displacement of the shaft 2 relative to its casing 4.

Fig. 2 is a schematic representation of a further preferred embodiment of the invention. The shaft 2 rotatably mounted in a casing 4 is clamped in a clamping device, with a force being applied to the test piece 1 on both sides via a lever mechanism 26 each. The clamping jaws 10 in the clamping device are firmly fixed to a frame 12 and hence immoveable, with the clamping device being adjustable to the casing length. The necessary lever force is generated via a weight 18. The lever mechanism 26 deflects the force of the weight such that the force can act in a preferred force application direction (parallel to or in the direction of the longitudinal axis of the shaft) at each shaft end. A stand 6 comprising a magnet 7 serves to hold a dial gauge 8. The stand 6 is attached to the casing 8, and the dial gauge 8 measures the axial displacement, with the shaft 2 moving inside the casing 4 in this embodiment.

Fig. 3 is a schematic representation of a further preferred embodiment of the invention. A shaft 2 rotatably mounted in a casing 4 is firmly clamped in a clamping device, with the clamping jaws 10 of the clamping device being firmly mounted to a frame 12. As with the previous embodiments, the clamping device can be adjusted to the casing length. A dial gauge 8 is held by a stand 6, which is attached to the casing 4 via a magnet 7. The dial gauge 8 serves to determine the axial displacement. A force is applied to both shaft ends in a force application direction at staggered intervals until a predefined test force is reached. As in the embodiment shown in Fig. 2 the shaft 2 moves inside the firmly mounted casing 4.

Fig. 4 shows an embodiment of a test device for measuring the axial displaceability of shaft 2 rotatably mounted in casing 4. The device has a clamping device with two clamping jaws 10. The connecting element 24 for connecting the shaft 2 and the frame 12 is designed to have a load cell, an elastic element and a rigid fork. The connecting element engages with the force application point 14 of the frame 4 and is ready to receive a shaft end. A linear drive 22 enables the movement of a slide block 17 on rails 16. Two screw clamps 20 allow the clamping jaw 10 to be fixed to the casing 4 of the test piece, with the screw clamps 20 and the attached clamping jaw 10 being guided along the rails 11 of the clamping device.

Fig. 5 shows the test device shown in Fig. 4 with a clamped test piece 1 for measuring its axial displaceability. The end faces of the casing 4 of the test piece are clamped between the clamping jaws 10. Two screw clamps 20 hold one of the two clamping jaws 10 in place on the casing 4. The linear drive 22 sets the slide block 17, which supports the test piece 1, in motion along the rails 16. In the process, a force is applied to the connecting element 24, which can be measured via a load cell. List of reference signs

1 Test piece

2 Shaft

4 Casing

6 Stand

7 Stand magnet

8 Dial gauge

10 Clamping jaw

11 Rails of the clamping device

12 Frame

14 Force application point to the frame

15 Direction of movement of the slide block

16 Rails of the positioning device

17 Slide block of the positioning device

18 Weight

20 Screw clamp

22 Linear drive

24 Connecting element

26 Lever mechanism

Interpretation

The appended claims are to be considered as incorporated into the above description.

Throughout this specification, reference to any advantages, promises, objects or the like should not be regarded as cumulative, composite and/or collective and should be regarded as preferable or desirable rather than stated as a warranty.

Throughout this specification, unless otherwise indicated, "comprise," "comprises," and "comprising," (and variants thereof) or related terms such as "includes" (and variants thereof)," are used inclusively rather than exclusively, so that a stated integer or group of integers may include one or more other non-stated integers or groups of integers.

When any number or range is described herein, unless clearly stated otherwise, that number or range is approximate. Recitation of ranges of values herein are intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value and each separate subrange defined by such separate values is incorporated into the specification as if it were individually recited herein.

Words indicating direction or orientation, such as "front", "rear", "back", etc, are used for convenience. The inventor(s) envisages that various embodiments can be used in a non operative configuration, such as when presented for sale. Thus, such words are to be regarded as illustrative in nature, and not as restrictive.

The term "and/or", e.g., "A and/or B" shall be understood to mean either "A and B" or "A or B" and shall be taken to provide explicit support for both meanings or for either meaning.

It is to be understood that the terminology employed above is for the purpose of description and should not be regarded as limiting. The described embodiments are intended to be illustrative of the invention, without limiting the scope thereof. The invention is capable of being practised with various modifications and additions as will readily occur to those skilled in the art.

Claims

Patent claims

1. Method for measuring an axial displaceabilityof a shaft rotatably mounted in a casing characterised in that

c) the first force is applied at a first end of the shaft along a first force application direction until a first test force is reached; and

d) the second force is subsequently applied in the opposite direction along a second force application direction until a second test force is reached;

wherein the measuring instrument measures the axial position change of the shaft relative to the casing in order to determine the axial displaceability of the shaft relative to the casing.

2. Method according to the previous claim, characterised in that the first and second test force have the same value.

3. Method according to any one of the previous claims, characterised in that the measuring instrument is zeroed to a given axial position of the shaft relative to the casing when the first test force is reached and the axial displaceability of the shaft relative to the casing is ascertained as an absolute value by the measuring instrument based on the change in axial position by the time the second test force is reached.

4. Method according to any one of the previous claims, characterised in that the axial displaceability of the shaft relative to the casing is ascertained from the difference between the axial position change of the shaft relative to the casing on reaching the first test force and the axial position change of the shaft relative to the casing on reaching the second test force.

5. Method according to any one of the previous claims, characterised in that the shaft is mounted inside the casing via at least one roller bearing.

6. Method according to any one of the previous claims, characterised in that the measuring instrument is a dial gauge, preferably with a stand which is attached to the casing.

7. Method according to any one of the previous claims, characterised in that the first and second force application directions are determined by a connection of the first end of the shaft to a frame, wherein the casing in the clamping device can be moved along the longitudinal axis of the shaft by means of a positioning device; and the first test force and the second test force are applied by the casing being moved relative to the frame, causing corresponding tensile and compressive forces at the first end of the shaft.

8. Method according to any one of claims 1 to 6, characterised in that the first force application direction is determined via a central axial connection between the first end of the shaft and a first force application point of a frame, and the second force application direction is determined via a central axial connection between the second end of the shaft and a second force application point of the frame, with the casing being able to be fixed relative to the frame in the clamping device; and both the first test force and the second test force are applied by the test force being introduced via the respective force application points of the frame.

9. Method according to any one of claims 1 to 6, characterised in that the first and/or second force are applied via a lever mechanism.

10. Device for measuring an axial displaceability of a shaft rotatably mounted in a casing, preferably for a method according to one of the previous claims, characterised in that the device features a clamping device for horizontally supporting the casing with the rotatably mounted shaft and a measuring instrument for determining the axial position of the shaft relative to the casing, wherein the device includes means for applying a first force in one application direction and a second force in an opposite application direction along the central axis of the shaft, with both forces being adjustable depending on the casing diameter.

11. Device according to the previous claim, characterised in that the clamping device can be adjusted to the length and/or diameter of the casing.

12. Device according to any one of the previous claims 10 or 11, characterised in that the clamping device is mounted on a positioning device, allowing a degree of movement, such that it can be displaced in a horizontal direction.

13. Device according to anyone of the previous claims 10 to 12, characterised in that the device includes a frame with a force application point and a connection means to a first end of the shaft which is vertically adjustable relative to the diameter of the casing and can thus be adjusted to the vertical position of the central axis of the shaft.

14. Device according to any one of the previous claims 10 to 12, characterised in that the device includes a frame with a first and a second force application point and connection means for a central axial connection with the first and second end of the shaft, with the force application points and connection means being vertically adjustable relative to the diameter of the casing and thus being able to be adjusted to the vertical position of the central axis of the shaft.

15. Device according to any one of the previous claims 11 to 14, characterised in that the device for applying a central axial force to the first and second end of the shaft features a lever mechanism each, comprising a swivel joint and two bars.

Fig. 1

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7 4 2

22 26 26

2

10

Fig. 3

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7 4

2 14

23 14 12 12 10 10

24

19 Nov 2020 14 Fig. 4

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12

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Fig. 5

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20 16 11 22