Coaxial transmission having an integrated measurement sensor system

Abstract

The invention relates to a coaxial transmission (1) comprising: - a piston set (5) having at least three pistons (10a-10p), the pistons each having, on a first end face (11), a toothing (12) having at least one tooth (13); - a hollow shaft (30) having an internal toothing (31), the pistons being arranged within the hollow shaft (30); - a guiding unit (8), the pistons being arranged spaced apart from one another in the guiding unit (8) in the circumferential direction (7) by means of guiding bridging portions (9) and being able to be moved back and forth in a linearly guided manner in the radial direction (15); - a piston drive (3) for the linearly guided movement of the pistons, - wherein the toothings (12, 13) of the first end faces (11) of the pistons can be brought into engagement with the internal toothing (31) and into a state in which they are released from the internal toothing (31), in order to rotate the hollow shaft (30) or the guiding unit (9) further about the rotational axis (2) during the particular engagement, wherein - at least one strain gauge (40, 41, 42) is fastened to at least one of the pistons.

Description

[0001]COAXIAL GEARBOX WITH INTEGRATED SENSORS SCOPE OF INVENTION The present invention relates to a coaxial gearbox comprising: - at least one piston set with at least three pistons, wherein each piston has a toothing with at least one tooth on a first end face pointing away from the axis of rotation; - a hollow shaft with internal toothing, wherein, viewed in a plane perpendicular to the axis of rotation, the pistons are arranged inside the hollow shaft; - a guide unit, wherein the pistons of each piston set are arranged in the guide unit spaced apart from one another in a circumferential direction pointing around the axis of rotation by guide webs and are linearly guided and movable back and forth parallel to a radial direction perpendicular to the axis of rotation; - a piston drive for the linearly guided movement of the pistons, - wherein the toothing of the first end faces of the pistons, in particular successively,The teeth can be brought into engagement with the internal teeth and into a state detached from the internal teeth in order to rotate the hollow shaft or the guide unit further about the axis of rotation during the respective engagement, preferably with surface contact between the respective teeth and the internal teeth. Furthermore, a coaxial drive according to the invention with an evaluation device for acquiring and evaluating measurement data is specified within the scope of the invention. PRIORITY OF THE ART Numerous different designs of coaxial drives of the aforementioned type are already known. For example, single-stage planetary gears that operate coaxially, as well as multi-stage planetary gears, are also coaxial drives. Likewise, shaft drives,Spur gear drives and eccentric or cycloidal gear drives can be designed as coaxial drives. By definition, in coaxial drives, a drive shaft and an output shaft of the drive lie on a common axis of rotation. For example, a wave gear with a ring element is known from US 4,713,985 A. The ring element is arranged around the outer circumference of a cam element. A rotational movement of the cam element does not generate a rotary driving force, but forces the drive rollers of the ring element into a cyclic and radial movement. In one embodiment, a piezoelectric component is installed as an actuator in a central section of a multi-part connecting element of a drive roller of the ring element, whereby the actuator's length can be changed. A strain gauge detects the change in length of the multi-part connecting element.which can also be used as a drive for the wave gear. However, a disadvantage is that the use of such a length-adjustable connecting element reduces the stiffness and strength of the entire wave gear. A piston drive for a piston set with multiple pistons, each guided linearly in the radial direction, is lacking in the wave gear described in US 4,713,985 A. Coaxial gears, which include a piston drive for the linearly guided movement of the pistons of at least one piston set, encompass both gears without connecting rods, in which the piston drive is effected, for example, by means of a rotatable circular disk, elliptical disk, or polygonal disk, or by means of a piezoelectric drive, and gear designs in which the piston drive is effected by a crankshaft with at least one connecting rod bearing. In these designs of coaxial gears with crankshafts, at least one connecting rod is provided.wherein at least one connecting rod is coupled to one or more pistons of at least one piston set and to at least one connecting rod bearing. Various embodiments of coaxial drives with crankshafts are already known from EP 4207717 B1 and EP 4004406 B1 of the applicant. In these embodiments, the crankshaft thus constitutes a drive element or can be described as a drive element. The hollow shaft is preferably rotatably mounted about the axis of rotation and can function as an output element. Alternatively, if the hollow shaft is fixed, the guide unit can function as the output element, for which the guide unit must be rotatably mounted. High torques can be advantageously transmitted with such coaxial drives, which are also referred to as crankshaft drives, in a compact and small design.This enables a high transmission ratio as well as high accuracy and backlash-free operation with the coaxial drives in question. While EP 4004406 B1 refers to a coaxial drive in which at least three or more pistons are connected to the at least one connecting rod bearing by means of their own connecting rod, EP 4207717 B1 takes a different approach. WO 2023 / 088656 A1 corresponds to EP 4207717 B1. In the embodiment disclosed in EP 4207717 B1, a coaxial drive is provided in which a common, star-shaped connecting rod is used to connect the pistons of the respective piston set to the at least one connecting rod bearing or crankpin. By using a common "star connecting rod" for the pistons of a piston set, both the number of components and, consequently, the complexity and size of this coaxial drive can be further reduced. With such coaxial drives, the number of pistons,The engagement or partial engagement of the internal teeth of the hollow shaft can be varied as desired to adjust the transmission ratio and the amount of transmissible torque according to requirements. At least three pistons ensure that the next piston, whose first end face presses against the internal teeth, particularly across its entire surface, does not rotate the hollow shaft or, if applicable, the guide unit back in the opposite direction, resulting only in a reciprocating motion of the hollow shaft or guide unit around its axis of rotation. Depending on the design of the piston drive, the engagement of the first end faces of the pistons with the internal teeth of the hollow shaft can occur sequentially, for example, if a crankshaft is used as the piston drive. In the case of a piston drive using a cam, for example,In the case of an elliptical or polygonal disk, the teeth of two or more pistons can also engage simultaneously with the internal teeth of the hollow shaft. Such designs for piston drives are also included in the invention. The toothing of the first end faces of the pistons means that each piston can also be described as a "tooth element." The guide unit, which guides the pistons of each piston set linearly at a distance from one another by means of guide webs, can be constructed as a single piece or composed of several elements. The pistons are thus arranged distributed in the circumferential direction. In the case that a coaxial drive is equipped with two or more piston sets, it is also conceivable that the pistons of different piston sets only move axially, i.e., in the direction parallel to the axis of rotation.are spaced apart from each other. Due to the aforementioned advantages, these coaxial gearboxes are used in a wide variety of applications. However, particularly in applications where such coaxial gearboxes are subjected to especially high mechanical and / or thermal loads, currently known coaxial gearboxes of this type offer insufficient possibilities for easily and reliably acquiring measurement data on loads during operation. This is of particular importance, for example, when using such coaxial gearboxes in wind turbines, as the high forces caused by wind gusts, turbulence, or tower vibrations, as well as the high thermal loads to which coaxial gearboxes are subjected, can lead to premature material fatigue and high wear, even to the point of material delamination and breakout of the gearboxes. Further applications include,Examples of applications where coaxial gearboxes are subjected to particularly high loads include gearboxes in electric vehicles, where high load-change forces occur, especially during recuperation, resulting in high mechanical and thermal stress on the coaxial gearboxes. Similarly, coaxial gearboxes used to drive actuators and positioning devices can also be subjected to such high loads.They are subject to high mechanical loads. Monitoring a coaxial gearbox during operation has so far only been possible with complex methods using external sensors. Particularly for the reliable monitoring of robot drives, the continuous recording of operating parameters, such as the rotation angle of the drive and the output of the coaxial gearbox, is essential. However, for monitoring conventional coaxial gearboxes, this requires an additional shaft to be routed through the hollow drive shaft, with the additional shaft mounted at the gearbox output. While this makes it possible to record both the drive and output rotation angles on the drive side using one or more encoders, it negatively reduces the inner diameter of the hollow shaft.This requires additional components and places high demands on complex assembly. Furthermore, with such an additional shaft, monitoring of the gearbox is only possible with a time delay due to the inertia of the encoders. Encoders are measuring devices or input devices that detect the current position of a shaft or drive unit and output it as an electrical signal. Encoders thus convert a movement into an electrical signal that can be read by a control unit in a motion control system, such as a programmable logic controller (PLC). The encoder sends a feedback signal that can be used to determine position, number, speed, or direction. For example, if a tooth breakage in the coaxial gearbox causes the two measured rotation angle values ​​to deviate too much from each other,For example, a safety stop can be triggered by a control system. However, installing an additional shaft in the coaxial gearbox to measure the rotation angles of the input and output shafts is structurally complex, cannot be retrofitted to existing coaxial gearboxes, and typically increases the overall length of the gearbox. Furthermore, a disadvantage of this conventional monitoring method is that it cannot detect potential deviations from setpoints, such as rising temperature or above-average friction, during operation. Therefore, there is a pressing need for a simple way to monitor coaxial gearboxes, especially those subjected to heavy loads, during operation to assess the mechanical and / or thermal stresses to which the gearbox is exposed.to detect wear and tear early and thereby assess the condition of the gearbox and schedule necessary maintenance work in a timely manner. OBJECTIVE OF THE INVENTION The objective of the present invention is to provide an improved coaxial gearbox that overcomes the aforementioned disadvantages. A further objective of the invention is to provide an improved coaxial gearbox including an evaluation device for acquiring and evaluating measurement data during operation. DESCRIPTION OF THE INVENTION To solve the aforementioned objective, a coaxial gearbox comprising: - at least one piston assembly with at least three pistons, wherein each piston has a toothed section with at least one tooth on a first end face pointing away from an axis of rotation; - a hollow shaft with internal teeth,wherein, viewed in a plane perpendicular to the axis of rotation, the pistons are arranged inside the hollow shaft; - a guide unit, wherein the pistons of the respective piston set are arranged in the guide unit spaced apart from one another in a circumferential direction pointing around the axis of rotation by guide webs, and are guided linearly and movable back and forth parallel to a radial direction perpendicular to the axis of rotation; - a piston drive for the linearly guided movement of the pistons, - wherein the teeth of the first end faces of the pistons can be brought into engagement with the internal teeth, in particular successively, and into a state disengaged from the internal teeth, in order to rotate the hollow shaft or the guide unit further around the axis of rotation during the respective engagement, preferably with planar contact between the respective teeth and the internal teeth, as provided according to the invention.that at least one strain gauge is attached to at least one of the pistons. Strain gauges, or SGFs for short, are measuring devices for detecting tensile and compressive deformations on the surface of components. Strain gauges can also be described as passive ohmic sensors or resistance elements. When a component, in this case a piston, on which at least one strain gauge is attached, is stretched or compressed, the initial length l of the SGF changes by a difference length Δl, and the initial resistance R of the SGF (in ohms) changes by a difference resistance ΔR. The change in resistance ΔR / R is greater the greater the strain ε = Δl / l. With the present invention, it is possible toDeviations in operating parameters during the operation of the coaxial gearbox can be detected early by acquiring and monitoring signals from at least one strain gauge. For example, if the stress profiles of two consecutive periods of a strain gauge differ too significantly, this can have various causes, each of which triggers an operational shutdown of the coaxial gearbox. For instance, the engagement of the gear teeth on the piston may have shifted relative to the internal gearing, material breakage may have occurred on the piston or gear teeth, foreign objects may have entered the interior of the coaxial gearbox, or the drive shaft may have broken. Detecting deviations during operation is significantly faster and more precise using one or more strain gauges directly attached to at least one piston than with conventional encoder systems.This is because, on the one hand, the inertia of strain gauges is very low, and on the other hand, the strains and compressions of the piston are measured directly in situ at the point of force transmission and not via a kinematic chain. The acquisition and evaluation of the resistance changes of the at least one strain gauge will be discussed in detail below. Currently, the input power in the drive motor is measured to monitor the torque. If this exceeds a certain value, a safety stop is initiated. With the sensor system shown here, the reaction time for overload detection is significantly reduced by providing early warning of an overload due to voltage spikes in the strain gauge with short transmission times. A further advantage of the coaxial transmission according to the invention is that...that attaching one or more strain gauges to at least one of the pistons does not affect or change the overall length of the coaxial gearbox. Therefore, it is advantageous to retrofit existing coaxial gearboxes with one or more strain gauges attached to at least one of the pistons. A further advantage of such retrofits is that no additional installation space needs to be provided within the coaxial gearbox for the measuring sensor of the at least one strain gauge. Depending on the design, for operation of the coaxial gearbox with integrated measuring sensor technology, either the guide rails adjacent to the respective pistons equipped with at least one strain gauge can be modified,The strain gauges can be fixed in place. In this design, one or more strain gauges can each be connected to a downstream evaluation unit for measurement data via signal lines for detecting resistance changes. The connecting cables or signal lines can be routed without twisting through bores in the guide webs or the guide unit to the evaluation unit. The signal lines are advantageously designed as flexible connecting cables that can withstand the linear stroke of the respective piston. Preferably, the connecting cables are assembled with an interference fit so that the relevant cable connections are not mechanically stressed or stretched, even at maximum piston stroke. Alternatively, the ring gear can be fixed in place for operation of the coaxial drive with integrated measuring sensors.wherein the signal transmission of the resistance changes of each strain gauge to a downstream evaluation unit is carried out by means of sliding contacts or by means of radio contacts. As will be explained in detail below, the coaxial drive according to the invention can be used to determine both the current rotational speed and the current angle of rotation based on the signals acquired from the at least one strain gauge,as well as the current direction of rotation. The coaxial drive according to the invention can be connected in a particularly flexible manner to a wide variety of drive units or drive motors and used for a wide variety of applications. For example, for safety reasons, the piston drive of a coaxial drive according to the invention with integrated measuring sensors can also be operated by means of a belt drive or an explosion-proof drive. Further advantageous embodiments of the invention are set out in the dependent claims and in the following description. Furthermore, the positional specifications used for components or parts, such as the terms "top", "bottom", "above", "below", "front", "back", "sideways", "inside", "outside", "in the axial direction", "in the radial direction", and the like, serve primarily to improve the understanding of the invention.especially in conjunction with the following drawings. The positional references used may refer to specific positions of individual components or parts of the coaxial drive according to the invention, or to individual views in the figures. In any case, such positional references are familiar to those skilled in the art. In a preferred embodiment of the invention, at least one strain gauge can be attached to each of at least three pistons of a coaxial drive, preferably arranged circumferentially, and particularly preferably evenly. As already mentioned at the outset, at least three pistons ensure that the next piston, which presses against the internal teeth, particularly over a surface, with the toothing of its first end face,The hollow shaft or, if applicable, the guide unit does not rotate back in the opposite direction, and only a back-and-forth oscillation of the hollow shaft or the guide unit occurs around the axis of rotation. By arranging at least one strain gauge on each of at least three pistons, which are preferably distributed circumferentially, it is ensured that at least two pistons or toothed elements with their respective teeth are at least partially engaged with the internal teeth of the hollow shaft. With this arrangement, the applied torque can be determined. In the case of a piston drive, for example, using a cam, it would even be conceivable to implement such a coaxial drive with only two pistons. To ensure the most uniform possible distribution of the pistons, each equipped with one or more strain gauges, in the circumferential direction,In a coaxial drive according to the invention, the at least one piston set can comprise an even number of at least six pistons, with at least one strain gauge attached to at least every second piston. For example, a piston set can comprise sixteen pistons, with at least one strain gauge arranged on every second piston, thus providing a total of at least eight strain gauges. Particularly precise, high-resolution monitoring of the ongoing operation of a coaxial drive according to the invention can be achieved if at least one strain gauge is attached to each piston. In order to attach the at least one strain gauge to the respective piston in a coaxial drive according to the invention in such a way that it lies outside the force flow caused by the transmitted torque from the ring gear to the guide web,At least one strain gauge can be arranged in a first piston segment on the respective piston, wherein the first piston segment forms an outer surface section of the respective piston and is positioned radially parallel to a longitudinal axis of the piston and at least partially perpendicular to an orientation direction of at least one tooth of the respective piston. If only one strain gauge is arranged per piston or per tooth element, a so-called Wheatstone quarter bridge with three additional resistors is used to evaluate the resistance change of the strain gauge. Temperature compensation is required to determine the resistance change as independently as possible from temperature influences. The temperature compensation can either be performed directly in the circuit,or are taken into account during signal evaluation. In an advantageous embodiment of the invention, at least two strain gauges can be attached to at least one, preferably at least three, pistons arranged circumferentially in a coaxial gearbox. The use of at least two strain gauges on one and the same piston offers the advantage that the second strain gauge can either serve as a half-bridge circuit for temperature compensation or can be used as a redundant measuring device, which further improves the reliability and fault tolerance of the measuring sensor system if the first strain gauge is defective. For example, if there is sufficient space on a large-dimensioned coaxial gearbox with large pistons to attach four strain gauges to one and the same piston,The four strain gauges can be connected as a full bridge. In this configuration, common-mode rejection, for example of interference on the sensor line, can be achieved to obtain particularly precise measurement signals. In the case where four strain gauges are mounted on the same side of a piston, this arrangement can also be used to detect and evaluate the bending forces acting on the piston during operation of the gearbox. In a further preferred embodiment of the invention, in a coaxial gearbox, a first strain gauge can be arranged in a first piston segment and a second strain gauge can be arranged in a second piston segment opposite the first on the same piston.wherein the first piston segment and the second piston segment each form an outer surface section on the respective piston and are each positioned radially parallel to a longitudinal axis of the piston and at least partially perpendicular to an orientation direction of at least one tooth of the respective piston. Advantageously, in this arrangement, two strain gauges are attached to opposing piston segments on the respective piston in such a way that they are each located outside the force flow caused by the transmitted torque from the ring gear to the guide web. In order to protect the strain gauges on the respective piston as much as possible from mechanical damage, in a further advantageous embodiment of the invention, a first piston segment and / or a second piston segment are each designed as a chamfered outer surface section on the respective piston in a coaxial transmission.wherein preferably a chamfer width of the first piston segment and / or a chamfer width of the second piston segment is / are each greater than or equal to the width of a strain gauge. By chamfering one or two outer surface sections on the piston, sufficient space or clearance is created to attach one or more strain gauges to the respective piston segment without the strain gauges rubbing against the adjacent guide webs of the guide unit. Alternatively or additionally to one or more chamfered outer surface sections on the respective piston, the invention further provides that a web recess can be arranged on the respective adjacent guide web of the guide unit, corresponding to the position of a first piston segment and / or corresponding to the position of a second piston segment of the respective piston.wherein the respective web recess extends radially parallel to the longitudinal axis of the piston in question and the at least one strain gauge is arranged at least partially in the web recess, wherein the respective web recess preferably has a recess width which is greater than or equal to the width of a strain gauge. In this embodiment, the web recess in the guide web forms the necessary clearance for the strain gauge on the adjacent piston to prevent the strain gauge from rubbing against the guide web. In order to provide a coaxial drive according to the invention that is as versatile and flexible as possible for a wide variety of applications, the at least one strain gauge can be selected from the group comprising or consisting of: foil strain gauges, semiconductor strain gauges, rosette strain gauges,Wire strain gauges. Foil strain gauges are typically laminated onto a thin plastic substrate and firmly bonded to the substrate, in this case, the respective piston. The combination of several strain gauges on a substrate in a partially overlapping arrangement is referred to as a rosette strain gauge or strain gauge rosette. Semiconductor strain gauges offer the advantage of relatively high k-factors, i.e., high sensitivities, and particularly compact sizes due to a piezoresistive effect. Wire strain gauges offer the advantage of being usable even at high operating temperatures. In a preferred embodiment of the invention, the piston drive of a coaxial transmission can comprise a crankshaft rotatable about the axis of rotation with at least one connecting rod bearing, wherein at least one connecting rod is provided.which connecting rod is coupled to one or more pistons of the at least one piston set and to the at least one connecting rod bearing. Such coaxial drives, also known as crankshaft drives, advantageously transmit high torques in a compact, small design, enabling a high transmission ratio as well as high accuracy and backlash-free operation. Alternatively, in a further preferred embodiment of the coaxial drive according to the invention, the piston drive may comprise at least one cam disk rotatable about the axis of rotation, or piezoelectric elements, or linear motors. In order to provide a particularly compact design for a coaxial drive, in a further embodiment according to the invention, a common connecting rod can be used to connect the pistons of the respective piston set to the at least one connecting rod bearing.A star-shaped connecting rod, to which the pistons of the respective piston set are coupled, is provided. For coupling the pistons of the respective piston set to the associated star-shaped connecting rod, elongated holes can be provided in the pistons, the elongated holes extending transversely to the radial direction. In this embodiment, coupling bolts are attached to the star-shaped connecting rod, which engage with the elongated holes. Alternatively, a separate connecting rod can be provided for each piston of the respective piston set to connect it to the at least one connecting rod bearing. The aforementioned problem is also solved with a system according to the invention comprising a coaxial drive and an evaluation unit for acquiring and evaluating measurement data, wherein the evaluation unit comprises a measurement data acquisition unit and a measurement data analysis unit, and wherein the measurement data acquisition unit is connected to the at least onepreferably connected to at least three, particularly preferably all, strain gauges of the coaxial drive via a signal connection, and the measurement data acquisition unit is configured to detect resistance changes of each strain gauge by means of at least one bridge circuit and outputs corresponding voltage signals, and wherein the measurement data analysis unit is configured to determine, based on the voltage signals output by the measurement data acquisition unit of each strain gauge, at least one actual value signal of a current rotational speed and / or a current angular position and / or direction of rotation and / or a current torque and / or a current temperature and / or a current acting force, and preferably output to a control device and / or to an external data monitoring device. Depending on the number,The positioning and configuration of the strain gauges used can be determined with the data acquisition unit, encompassing several or all of the aforementioned operating parameters: current rotational speed, current angular position, current direction of rotation, current torque, current temperature, and / or current force. Regarding the current force, it is hereby clarified that each strain gauge detects the mechanical stress acting on the piston to which it is attached, i.e., the piston's expansion or compression. Thus, strictly speaking, each strain gauge determines the force or torque acting on the respective piston.which acts on the coaxial gearbox. A coaxial gearbox according to the invention, including an associated evaluation unit for acquiring and evaluating measurement data, can be used in a particularly flexible manner for a wide variety of applications. As already mentioned at the outset, in principle any drive motor can be connected to and coupled with the coaxial gearbox. Advantageously, the evaluation unit is also configured to be "manufacturer-independent" and can process the measurement signals or voltage signals from different strain gauges regardless of the respective manufacturer of the strain gauges. In addition to at least one bridge circuit for detecting resistance changes of each of the strain gauges, and at least one measuring amplifier to output corresponding voltage signals, the measurement data acquisition unit can includeThe system must include at least one or more of the following electronic components for signal calibration or signal normalization: an additional signal amplifier, an analog-to-digital converter (ADC), an electronic component for signal normalization, an electronic component for zero-value normalization, an electronic component for signal normalization including signal adjustment via signal offset, a voltage limiter, and / or a digital-to-analog converter (DAC). The at least one measuring amplifier may be configured to provide a DC voltage for applying to the strain gauges. The measurement data analysis unit may, for example, include a CPU (processor), main memory, a data storage device including a configuration data memory for storing configuration data,and include a signal converter. Advantageously, the system according to the invention can be used, for example, to determine the rotational speed of the hollow shaft or the guide unit, wherein the evaluation device is configured to determine at least one actual value signal of a current rotational speed. A method for determining a current rotational speed using the system according to the invention comprises the following steps: - Acquiring and evaluating the voltage signals of at least one strain gauge, preferably all strain gauges,During operation of the coaxial gearbox; - Determining a period P as the time interval between two corresponding voltage peaks of the voltage signal of the relevant strain gauge; - Converting the period P, taking into account the number L of gaps in the internal gearing of the hollow shaft, into a current rotational speed ^=(2^ / L) / P. To determine the current rotational speed of the hollow shaft or the guide unit of the coaxial gearbox,The period P is evaluated as the time interval t–t between two corresponding voltage peaks of the voltage signal of the strain gauge in question. The angle of rotation corresponding to one period P is Φ² / L, where L denotes the number of gaps in the internal gearing of the hollow shaft. The rotational speed Φ / P = (2 / L) / P is given in rad / s. To determine the rotational speed, the period is also evaluated as the time interval between two corresponding voltage peaks of the voltage signal of the strain gauge in question. The period is directly proportional to the rotational speed. For example, with a gear reduction of 100:1, 100 piston strokes are required to achieve one revolution of the hollow shaft or the guide unit of the coaxial gearbox. In this case, the distance between two corresponding voltage peaks thus corresponds to an angle of rotation. 3.6°. The period defines the rotational speed. To determine the direction of rotation, the sequence of incoming voltage signals from at least two strain gauges attached to different pistons must be evaluated. For example, a signal sequence of the incoming voltage signals from the strain gauges first at the first piston and, with a time delay, at the second piston is the opposite of a signal sequence of the incoming voltage signals from the strain gauges first at the second piston and subsequently, or with a time delay, at the first piston. In order to determine the current angular position of the hollow shaft or the guide unit with the system according to the invention, the evaluation device is configured to determine at least one actual value signal of a current angular position. A method for determining a current angular position using the system according to the invention comprises the following steps: - Acquiring and evaluating theVoltage signals of at least one strain gauge, preferably all strain gauges, during operation of the coaxial drive; - Determining the respective times of voltage peaks of the respective strain gauge; - Assigning the respective times of voltage peaks, taking into account the number of gaps L of the internal gearing of the hollow shaft as an increment of the current angular position of the respective strain gauge. If the times t, t, ..., t are corresponding voltage peaks, then n is the number of periods P or gaps L or recesses in the internal gearing into which the respective piston has engaged. In the time interval from time t=0 to time t, the hollow shaft or the guide unit of the coaxial drive has therefore rotated further by a differential angle ΔΦ=n² / L. The current angular position is then Φ=Φ+ΔΦ, where Φ is a known angle of rotation at time t=0. To determine theTo determine the angular position, the respective times of stress peaks are assigned as increments of the current angular position of the corresponding strain gauge, taking into account the number of gaps L of the internal gearing of the hollow shaft. The pulse of a stress peak can, for example, be interpreted as an increment for an angular position Φ of 3.6° (corresponding to the example above). The more pistons or "gear elements" are equipped with strain gauges, the higher the resolution of the overall system. In a coaxial gearbox, for example, where 16 pistons are equipped with strain gauges, this results in 16 measurement pulses per 3.6° angular position. This allows the angular position to be resolved with an accuracy of 0.225° angular increments. If the characteristics of the measurement signals are also considered, three (or more) distinct, corresponding stress peaks can be evaluated per tooth engagement.For example, the corresponding voltage peaks at the moment the teeth engage, at the moment of the highest load during tooth engagement, and / or at the moment of disengagement can be detected. This allows the resolution of the angular position to be further increased, and the angular position can be specified, for example, with an accuracy of 0.225° / 3, i.e., in 0.075° angular increments. Further signal analysis can increase the accuracy of the angular position determination even further. The system according to the invention can also be used to determine the current torque of the coaxial gearbox. The evaluation unit is designed to determine at least one actual value signal of the current torque. A method for determining a current torque using the system according to the invention comprises the following steps: - Acquiring and evaluating the voltage signalsat least one strain gauge, preferably all strain gauges, during operation of the coaxial gearbox; - Calibration of the at least one strain gauge, preferably all strain gauges, at predefined torques and assignment of the respective voltage amplitudes of voltage peaks of the respective strain gauge to a calibrated torque value; - Comparison of the respective current voltage amplitudes of voltage peaks of the respective strain gauge during operation of the coaxial gearbox with the calibrated torque values ​​and determination of a current torque. The step of calibrating the at least one strain gauge or all strain gauges is generally only required once at the beginning of the measurements. The torque is determined by evaluating the voltage amplitude. The signal for different torques in the assembled gearbox is then...The state of the coaxial gearbox is recorded, and the system is calibrated accordingly. A specific voltage amplitude is assigned to a calibrated torque value. Due to the numerous influences from friction or manufacturing deviations during actual operation of the coaxial gearbox, a mathematical calculation is difficult to solve analytically. Numerical methods can be used to determine a factor k, which depends on the rotational speed, temperature, and material properties of the respective strain gauge. Since each strain gauge has individual material properties according to its data sheet, these must be taken into account during calibration. The respective torque M can therefore be determined as a function of the factor and the resulting force F: M = k ⋅ F. The system according to the invention can also be used to determine the current temperature within the coaxial gearbox or at the location of the respective strain gauge.For this purpose, the evaluation unit is configured to determine at least one actual value signal of a current temperature. A method for determining a current temperature using the system according to the invention comprises the following steps: - Acquiring and evaluating the voltage signals of at least one strain gauge, preferably all strain gauges, during operation of the coaxial gearbox; - Calibrating the at least one strain gauge, preferably all strain gauges, at predefined temperatures and assigning an offset of the respective voltage signal of the strain gauge in question to a known temperature value prevailing during calibration; - Determining corresponding voltage peaks of the voltage signal of the strain gauge in question over time and determining the slope S of a signal drift; - Calculating a relative temperature change ^T by multiplying S by aThe following steps are required: - Determining an initial temperature T based on the offset of the voltage signal in an initial time range; - Determining the current temperature T by adding T and ^T. The slope S of the signal drift indicates the relative temperature change. As the operating temperature increases, the voltage signal shifts to higher voltage values. The signal range (e.g., 0-10 V) must lie within the temperature range expected during operation of the coaxial gearbox. The temperature behavior characteristic of the strain gauge can be determined from its temperature coefficient (TGC), i.e., a material constant according to the strain gauge's datasheet. This allows the measuring range of the voltage signals to be adjusted according to the expected temperature range during operation.coaxial drive. BRIEF DESCRIPTION OF THE FIGURES The invention will now be explained in more detail with reference to exemplary embodiments. The schematic drawings are each exemplary and are intended to illustrate the concept of the invention. They show: Fig. 1 in a schematic sectional view a first embodiment of a coaxial drive according to the invention; Fig. 2 in an isometric oblique side view a piston of a coaxial drive according to the invention with a strain gauge attached to it; Fig. 3 in a partially cut-out isometric view a piston of a coaxial drive according to the invention with two strain gauges attached to it; Fig. 4 in a partial top sectional view the piston shown in Fig. 3 with chamfered piston segments for receiving the strain gauges within a guide unit; Fig. 5 in a partial top sectional view a piston of a coaxial drive according to the invention.with two strain gauges attached thereto within a guide unit with web recesses; Fig. 6 the first embodiment of a coaxial drive according to the invention shown in Fig. 1 with further details; Fig. 7 the coaxial drive shown in Fig. 6 in a sectional view from the side according to the section plane AA shown in Fig. 6; Fig. 8 in a schematic sectional view of a second embodiment of a coaxial drive according to the invention; Fig. 9 the coaxial drive shown in Fig. 8 in a sectional view from the side according to the section plane BB shown in Fig. 8; Fig. 10 a schematic signal flow diagram of a system of a coaxial drive according to the invention with an evaluation device for the acquisition and evaluation of measurement data; Fig. 11 a schematic circuit diagram of a Wheatstone bridge circuit of a quarter bridge; Fig. 12 a schematic signal flow diagram of an embodiment of a measurement signal acquisition according to the invention;Fig. 13 shows a diagram illustrating the voltage profile of a measurement signal over time. WAYS TO IMPLEMENT THE INVENTION Fig. 1 shows a coaxial transmission 1 according to the invention in a schematic section view perpendicular to a rotational axis 2. The coaxial transmission 1 comprises a piston drive 3, which here, for example, includes a crankshaft 3a rotatable about the rotational axis with at least one connecting rod bearing 4, wherein in the present embodiment exactly one connecting rod bearing 4 or exactly one crank pin or connecting rod journal is provided. Details of the piston drive 3 will be discussed below. The coaxial transmission 1 of the first embodiment further comprises a piston assembly 5 with sixteen pistons 10, which are designated in Fig. 1, in clockwise order, as pistons 10a-10p. The piston drive 3 serves for the linearly guided movement of the pistons 10a-10p. Each piston 10a-10p has a toothing 12 with at least one tooth 13 on a first end face 11 pointing away from the axis of rotation.The pistons 10a-10p of each piston set 5 are arranged in a guide unit 8 in a circumferential direction 7 pointing around the axis of rotation 2, spaced apart from one another by guide webs 9. The guide unit 8, or the guide webs 9 between adjacent pistons 10, serve to guide the pistons 10a-10p linearly, so that the pistons 10a-10p can be moved back and forth parallel to a radial direction perpendicular to the axis of rotation 2. The circumferential direction 7 is symbolized by a double arrow 7. Furthermore, the coaxial drive 1 shown comprises a hollow shaft 30 with internal teeth 31, wherein, viewed in a plane perpendicular to the axis of rotation 2, the pistons 10a-10p are arranged inside the hollow shaft 30. The internal teeth 31 have a plurality of gaps 32 or recesses. The teeth 12,13 of the first end faces 11 of the pistons 10a-10p can be brought into engagement with the internal teeth 31, particularly one after the other, and canThe hollow shaft 30 or the guide unit 9 can also be brought into a state detached from the internal toothing 31 in order to rotate the hollow shaft 30 or the guide unit 9 further about the axis of rotation 2 during the respective engagement of one or more teeth 13 in corresponding gaps 32 or recesses of the internal toothing 31, preferably with planar contact between the respective toothing 12, 13 and the internal toothing 31. According to the invention, at least one strain gauge 40 is attached to at least one of the pistons 10a-10p. In the first embodiment shown in Fig. 1, a strain gauge 40 is attached alternately to each second piston 10a, 10c, 10e, 10g, 10i, 10k, 10m, 10o. The strain gauges 40 shown here are, for example, designed as foil strain gauges 41, in particular as semiconductor strain gauges 42, and offer the advantage of exhibiting high k-values ​​with high sensitivities and having particularly compact dimensions. For the unambiguous assignment of the individualStrain gauges 40 for the respective pistons 10a, 10c, 10e, 10g, 10i, 10k, 10m, 10o, on which they are attached, are designated clockwise by reference numerals 41a-41h. Within the scope of the invention, one or more of the strain gauges can also be designed as wire strain gauges or arranged in a rosette shape. Fig. 2 shows an isometric view of such a piston 10 by way of example, for instance the piston 10a shown in Fig. 1. The tooth 13 has a first tooth flank 13a, a second tooth flank 13b, a tooth width 13c, an orientation direction 13d of the tooth 13, which is symbolized by a double arrow 13d, and a tooth height 13e. The piston 10, 10a has a longitudinal axis 14. The piston longitudinal axis 14 corresponds to the radial direction 15 symbolized by a double arrow 15, in which the piston 10, 10a can be moved back and forth. The piston 10, 10a shown has a bore 16 for a [missing information] (not shown).The piston pin has a longitudinal axis direction 17. Furthermore, a recess 20 is provided for a connecting rod connection. The strain gauge 40, 41, 42 is arranged in a first piston segment 18 on the piston 10, 10a, wherein the first piston segment 18 forms an outer surface section on the piston 10a and is positioned in the radial direction 15 parallel to the piston longitudinal axis 14 and at least partially normal to the orientation direction 13d of the tooth 13. The first piston segment 18 is designed here as a chamfered outer surface section with a chamfer width 18a. The chamfer width 18a is chosen here, for example, to be larger than the width 40a of the strain gauge 40 in question. Opposite the first piston segment 18 in the orientation direction 13d of the tooth 13, a second piston segment 19 is formed, the second piston segment 19 also forming an outer surface section on the piston 10a and extending in the radial direction 15 parallel to the longitudinal axis 14 of the piston.and is positioned at least partially perpendicular to the orientation direction 13d of the tooth 13. For example, the second piston segment 19 can also be chamfered. In the following, identical or comparable parts and components of different embodiments are each designated by the same reference numerals. Fig. 3 shows, in a partially cut-away view, a piston 10 of a coaxial drive 1 according to the invention with two strain gauges 40 attached to it. Fig. 4 shows, in a partial sectional view from above, the piston 10 shown in Fig. 3 with chamfered piston segments 18, 19 for receiving the strain gauges 40 within a guide unit 9. The following description applies equally to both figures, Fig. 3 and Fig. 4. On the piston 10, a first piston segment 18 and a second piston segment 19 are each formed as a chamfered outer surface section, wherein a chamfer width 18a of the first piston segment is defined.The first piston segment 18 and the second piston segment 19 each have a chamfer width 19a of at least the same size as the width 40a of a strain gauge 40, 41, 42. The first piston segment 18 and the second piston segment 19 each form an outer surface section on the piston 10 and are each positioned in the radial direction 15 parallel to the longitudinal axis 14 of the piston and at least partially perpendicular to an orientation direction 13d of the tooth 13 of the respective piston 10. Figure 3 also shows a connecting rod 6, a piston pin 21, which is inserted in the longitudinal axis direction 17 within the bore 16 of the piston 10 and enables a pivotal coupling of the piston 10 with the connecting rod 6, as well as sections of the guide unit 8 and the guide webs 9 adjacent to the piston 10. The tooth 13 on the first end face 11 of the piston 10 engages in corresponding gaps 32 or recesses of the internal teeth 31, which are arranged on the inside of the hollow shaft 30. Fig.Figure 5 shows a partial sectional view from above of a piston 10 of a coaxial drive 1 according to the invention with two strain gauges 40 attached to it within a guide unit 8 with web recesses 29. Corresponding to the position of a first piston segment 18 and corresponding to the position of a second piston segment 19 of the respective piston 10 on the respective adjacent guide web 9 of the guide unit 8, a web recess 29 is arranged here, wherein the respective web recess 29 extends in the radial direction 15 parallel to the longitudinal axis 14 of the respective piston 10. The two strain gauges 40, 41, 42 are attached to the piston 10 such that they are arranged here in the web recess 29, wherein the respective web recess 29 has a recess width 29a that is greater than or equal to the width 40a of the respective strain gauge 40, 41, 42. Fig. 6 shows again the first embodiment already shown in Fig. 1 of aThe coaxial drive according to the invention. For the basic operating principle of the coaxial drive 1, reference is made to the above. Since the specific design of the respective piston drive 3 is only of secondary importance in the present invention, further details regarding the piston drive 3 with a crankshaft 3a can be found in Fig. 6 – in addition to Fig. 1. In this embodiment, the pistons 10a-10p of the piston assembly 5 are coupled to the connecting rod 6, which here is designed as a star-shaped connecting rod 60, by means of intermediate elements 22. The intermediate elements 22 are essentially rigid, with each intermediate element 22 being pivotally connected on one side to the respective piston 10a-10p by means of guide pins 23 and on the other side pivotally connected to the star-shaped connecting rod 60 by means of connecting pins 25. The connecting pins 25 define pivot joints 27, the axes of rotation of which are parallel to the axis of rotation 2. The strain gauges 40In this view, the strain gauges 40 are attached to the respective piston 10 in such a way that they are located outside the force flow caused by the transmitted torque from the ring gear 30 to the guide web 9 of the guide unit 8. Fig. 7 is a sectional view of the coaxial drive 1 from the side according to the section plane AA shown in Fig. 6. In this side view, the strain gauges 40 attached to the pistons 10 are not visible. Fig. 8 shows a second embodiment of a coaxial drive 1 according to the invention in a schematic sectional view. The coaxial drive 1 comprises a piston drive 3 with a crankshaft 3a rotatable about the axis of rotation 2 and with at least one connecting rod bearing 4, wherein in the illustrated embodiment exactly one connecting rod bearing 4 or exactly one crankpin or connecting rod journal is provided. Three pistons 10a, 10b, 10c are connected to the connecting rod bearing 4 in a manner known per se, or the pistons 10a, 10b, 10c are movably mounted on the connecting rod bearing 4.For example, a split connecting rod eye of each connecting rod 6a, 6b, 6c is attached to the connecting rod bearing 4 by means of screws, and pistons 10a, 10b, 10c are connected to further connecting rod eyes of connecting rods 6a, 6b, 6c via piston pins 21. In the embodiment shown in Fig. 8, a total of five pistons 10 are provided, although only three pistons 10a, 10b, 10c are visible. Piston 10a is connected to the crankshaft 3a or the connecting rod bearing 4 via connecting rod 6a, piston 10b via connecting rod 6b, and piston 10c via connecting rod 6c. All pistons 10a, 10b, 10c each have a first end face 11 pointing away from the axis of rotation 2 with an embossed toothing 12, wherein each toothing 12 in the illustrated embodiment has exactly one tooth 13. In the illustrated embodiment, the crankshaft 3a is hollow along the axis of rotation 2, which, for example, allows cables (not shown) to be routed without twisting. Furthermore, in theA coaxial transmission 1 provides a hollow shaft 30 which has internal teeth 31. In the plane of Fig. 8, which is perpendicular to the axis of rotation 2, the pistons 10a, 10b, 10c – and at least partially the crankshaft 3a – are arranged inside the hollow shaft 30. This also applies to a guide unit 8 in which the pistons 10a, 10b, 10c are each guided linearly and can be moved back and forth parallel to a radial direction 15 perpendicular to the axis of rotation 2. For this purpose, the guide unit 9 in the illustrated embodiment has guide webs 9 in the form of hollow cylinders, which function as linear guides for the pistons 10a, 10b, 10c. By moving the pistons 10a, 10b, 10c back and forth, the teeth 12 on the first end faces 11 of the pistons 10a, 10b, 10c are successively brought into engagement with the internal teeth 31 and into a state disengaged from the internal teeth 31, whereby due to the linear movement of the pistons 10a, 10b, 10c during the respectiveThe engagement ensures a full-surface contact between the respective teeth 12, 13 and the internal teeth 31. The respective teeth 12, 13 are pressed against the internal teeth 31 of the hollow shaft 30 over a full-surface area. This rotates the hollow shaft 30 a further distance around the axis of rotation 2 if the guide unit 9 is fixed relative to the axis of rotation 2, or if the guide unit 8 is rotatable around the axis of rotation 2 but braked. Conversely, if the hollow shaft 30 is fixed or immovable relative to the axis of rotation 2, or braked, the guide unit 8, which is rotatable around the axis of rotation 2, is rotated a further distance. Due to the full-surface engagement or pressing action, very high torques can be transmitted from the crankshaft 3a to the hollow shaft 30 or, if applicable, to the guide unit 9. Each of the five pistons 10 (of which three pistons 10a, 10b, 10c are visible) has a strain gauge 40 attached, thus there areThis coaxial drive 1 is provided with a total of five strain gauges 40. Fig. 9 shows the coaxial drive 1 shown in Fig. 8 in a sectional view from the side according to the section plane BB shown in Fig. 8. In Fig. 9, a fourth piston 10c' and an associated connecting rod 6c', as well as a connecting rod 6a' of a fifth piston (not shown; this piston is located behind the elements shown in Fig. 8 when viewed in the direction of the drawing plane of Fig. 8, or is the last piston when viewed along the axis of rotation 2, with piston 10a being the first), are also visible. The strain gauges 40 attached to the pistons 10 are not visible in this side view. Fig. 10 shows a schematic signal flow diagram of a system of a coaxial drive 1 according to the invention with an evaluation unit 100 for acquiring and evaluating measurement data. The evaluation unit 100 comprises a measurement data acquisition unit 110 and a measurement data analysis unit 130.The measurement data acquisition unit 110 is connected to at least one, preferably at least three, and, as illustrated in Fig. 10, particularly preferably all, strain gauges 40, 41a-41h of the coaxial drive 1 by means of signal lines 90. The signal lines 90 serve as connecting cables for transmitting the resistance changes. Alternatively, the signal transmission between the strain gauges 40, 41a-41h and the evaluation unit 100 can be carried out, for example, wirelessly. However, this requires a power supply to the strain gauges 40, 41a-41h, for example, by means of slip ring contacts or conventional connecting cables. In Fig. 10, the measurement data acquisition unit 110 includes at least a bridge circuit 111, a first measuring amplifier 112, and optionally an A / D converter 113. The measurement data acquisition unit 110 is for recording changes in resistance or diagonal voltages 81The measurement data analysis unit 130 is configured to determine, based on the voltage signals 121 output by the measurement data acquisition unit 110, at least one actual value signal 140 of a current rotational speed and / or a current angular position and / or direction of rotation and / or a current torque and / or a current temperature and / or a current acting force, and preferably output to a control device 150 and / or to an external data monitoring device 160. The measurement data analysis unit comprises, for example, a CPU processing unit 131, a working memory 132, a data storage device 135 including a configuration data memory 136 for storing configuration data, and aSignal converter 140. Fig. 11 shows a schematic circuit diagram of a quarter-bridge Wheatstone bridge circuit 111. The Wheatstone measuring bridge 70 shown here comprises a total of four resistors: a first resistor 71, a second resistor 72, a third resistor 73, and a fourth resistor 74. One of the resistors 71-74 is the strain gauge 40. A voltage 80 is applied. The change in the resistance of the strain gauge 40 is detected by the bridge circuit 111 as a diagonal voltage 81 and fed into a measuring amplifier 112 as a voltage signal 81 or 81a, 81b, as symbolized in Fig. 10. Fig. 12 shows a schematic signal flow diagram of an embodiment of a measurement signal acquisition according to the invention. Essentially, Fig. 12 illustrates the measurement signal acquisition within the measurement data acquisition unit 110 in further detail. The measurement data acquisition unit 110 shown here includes, in addition to at leasta bridge circuit 111 for detecting resistance changes of each of the strain gauges 40, and a measuring amplifier 112 to output corresponding voltage signals, the following additional electronic components for signal calibration or signal normalization: an A / D converter 113 (analog-to-digital converter), an electronic component 114 for signal value normalization, an electronic component 115 for zero-value normalization, another signal value amplifier 116, an electronic component 117 for signal value normalization including signal value adjustment by means of signal offset, a first voltage limiter 118, a D / A converter 119 (digital-to-analog converter), and a second voltage limiter 120. The measuring amplifier 112 only amplifies the voltage signal 81. The provision of an applied voltage 80, preferably a DC voltage, for applying voltage to the strain gauges 40 is carried out separately. The voltage 80 is supplied separately to the strain gauges 40.The resistance change measured by the strain gauge 40 is recorded as a diagonal voltage 81 in the bridge circuit 111 and initially amplified in the measuring amplifier 112. The amplified (or increased) voltage 82 is then converted in the A / D converter 113. A raw signal 82a obtained in this process is normalized in a signal normalization unit 114. The normalized signal 82b is then set to zero in a subsequent zero-value normalization unit 115, thereby compensating for any signal deviations and inaccuracies. For normalization, the measurement signal of the strain gauge 40 is recorded and normalized in its unloaded resting state. This normalization step is typically performed only once at the beginning of the measurements. The normalized zero-value signal 82c obtained in this way serves to calibrate an output signal 82d, which is amplified in a further signal amplifier 116 to a normalized digital signal 83. Since this signal 83 alsoSince negative voltage values ​​can occur when the respective strain gauge 40 or the associated piston 10 is subjected to tension rather than compression and records tensile forces, the signal 83 is amplified in the device 117 for signal value normalization and adjustment by means of a signal offset by combining it with an offset signal 84, resulting in a processed output signal 85. To protect the measuring sensors and electronics, a first voltage limiter 118 upstream of the D / A converter 119 serves to limit the voltage, for example, to a maximum of 10 V. A correspondingly limited output signal 86 is converted in the D / A converter 119 into an analog signal 87, which, after passing through a second voltage limiter 120, is output as a voltage signal 121 by the measurement data acquisition unit 110. Fig. 13 shows a diagram illustrating the voltage profile of a measurement signal over time. The abscissa represents time t in milliseconds [ms]The voltage U in volts [V] is plotted on the ordinate. A voltage amplitude A is also shown as an arrow A in the ordinate direction. The voltage curve shown is a sequence of recorded voltage peaks from a strain gauge during the tooth engagement of the respective piston, which is equipped with the respective strain gauge. Index 1 denotes the first tooth engagement, index 2 denotes the second tooth engagement, and so on. Starting from the left, a comparatively low voltage peak E can be observed at the beginning of the first tooth engagement, followed by a maximum voltage peak S at maximum load during the first tooth engagement, and then a lower voltage peak L when the first tooth engagement is released. These signals essentially repeat themselves periodically with each subsequent tooth engagement. A signal sequence is again observed during the second tooth engagement.A comparatively low voltage peak E is detected at the beginning of the second tooth engagement, followed by a maximum voltage peak S at the highest load during the second tooth engagement, and then by a lower voltage peak L upon disengagement of the second tooth engagement. A period P can be determined as the time interval tt between two corresponding voltage peaks S,S at the highest load during tooth engagement, or between two corresponding voltage peaks E,E at the beginning of tooth engagement, or between two corresponding voltage peaks L,L upon disengagement of the tooth engagement. Furthermore, Fig. 13 illustrates an increase in the detected voltage signals as a signal drift to higher voltage values ​​with a slope S = ^y / ^x. The slope S indicates the relative temperature change. With increasing temperature, the signal migrates to higher voltage values. Referring to the figures,Particularly with reference to Fig. 13, the functioning of the invention is explained below with reference to the determination of the rotational speed, the angular position, the torque, and the determination of a temperature change during the measurement of resistance signals from the strain gauges 40. Furthermore, the determination of the direction of rotation is also explained with reference to two strain gauges 40 attached to spaced-apart pistons 10a, 10b. FUNCTIONAL METHODS OF THE INVENTION A) Determination of the Rotational Speed ​​The system according to the invention can determine the rotational speed of the hollow shaft 30 or the guide unit 8, wherein the evaluation device 100 is configured to determine at least one actual value signal of a current rotational speed, the determination comprising the following steps: - Acquiring and evaluating the voltage signals 121 of at least one strain gauge 40, preferably all strain gauges 40, during operation of theCoaxial gear 1; - Determining a period P as a time interval tt between two corresponding voltage peaks S,S; E,E; L,L of the voltage signal 121 of the respective strain gauge 40; - Converting the period P, taking into account the number L of gaps 32 of the internal gearing 31 of the hollow shaft 30, into a current rotational speed ^=(2^ / L) / P. To determine the current rotational speed ^^ of the hollow shaft 30 or the guide unit 8 of the coaxial gear 1, the period P is evaluated as a time interval t–t between two corresponding voltage peaks of the voltage signal of the respective strain gauge. The rotational angle Φ^^^2^ / L corresponding to a period P. The rotational speed ^^^Φ / P=(2^ / L) / P is given in [rad / s]. To determine the rotational speed, the period P is also used as the time interval between two corresponding voltage peaks S,S; E,E; L,L of the voltage signal of the strain gauge in question.evaluated. The period P is directly proportional to the rotational speed. B) Determination of the angular position With the system according to the invention, the current angular position of the hollow shaft 30 or the guide unit 8 can be determined. The evaluation device 100 is configured to determine at least one actual value signal of a current angular position, the determination comprising the following steps: - Acquiring and evaluating the voltage signals 121 of at least one strain gauge 40, preferably all strain gauges 40, during operation of the coaxial drive 1; - Determining the respective times t,t of voltage peaks S,S; E,E; L,L of the respective strain gauge 40; - Assigning the respective times t,t of voltage peaks S,S; E,E; L,L taking into account the number L of gaps 32 of the internal gearing 31 of the hollow shaft 30 as an increment of a current angular position of the respective strain gauge 40. If theSince the time points t, t, ..., t correspond to stress peaks, then n is the number of periods P or gaps L or recesses in the internal gearing into which the respective piston has engaged. In the time interval from time t=0 to time t, the hollow shaft 30 or the guide unit 8 of the coaxial drive 1 has therefore rotated further by a differential angle of rotation ΔΦ=n² / L. The current angle of rotation is then Φ=Φ+ΔΦ, where Φ is a known angle of rotation at time t=0. C) Determination of the torque The current torque of the coaxial drive 1 can also be determined using the system according to the invention. The evaluation device 100 is configured to determine at least one actual value signal of a current torque, the determination comprising the following steps: - Acquiring and evaluating the voltage signals 121 of at least one strain gauge 40, preferably all strain gauges 40, during the operation of the coaxial gearbox 1;- Calibrating at least one strain gauge 40, preferably all strain gauges 40, at predefined torques and assigning the respective voltage amplitudes U,U of voltage peaks S,S; E,E; L,L of the respective strain gauge 40 to a calibrated torque value; - Comparing the respective current voltage amplitudes U,U of voltage peaks S,S; E,E; L,L of the respective strain gauge 40 during operation of the coaxial gearbox 1 with the calibrated torque values ​​and determining a current torque. The step of calibrating the at least one strain gauge 40 or all strain gauges 40 is generally only required once at the beginning of the measurements. D) Determining the temperature change. The system according to the invention can also be used to determine the current temperature within the coaxial gearbox 1 or at the location of the respective strain gauge 40. For this purpose,The evaluation unit 100 is configured to determine at least one actual value signal of a current temperature, the determination comprising the following steps: - Acquiring and evaluating the voltage signals 121 of at least one strain gauge 40, preferably all strain gauges 40, during operation of the coaxial drive 1; - Calibrating the at least one strain gauge 40, preferably all strain gauges 40, at predefined temperatures and assigning an offset of the respective voltage signal 121 of the strain gauge 40 to a known temperature value prevailing during calibration; - Determining corresponding voltage peaks S,S; E,E; L,L of the voltage signal 121 of the strain gauge 40 over time and determining the slope S of a signal drift; - Calculating a relative temperature change ^T by multiplying S by a corresponding known material constant of theThe relevant strain gauge 40; - Determining an initial temperature T based on the offset of the voltage signal 121 in an initial time range; - Determining the current temperature T by adding T and ^T. The slope S of the signal drift indicates the relative temperature change. As the operating temperature increases, the voltage signal migrates to higher voltage values. The signal range (e.g., 0-10 V) must accordingly lie within the temperature range expected during operation of the coaxial gearbox. The characteristic of the temperature behavior of the relevant strain gauge can be determined from its temperature coefficient (Temperature Coefficient of Gauge Factor), i.e., a material constant according to the strain gauge's datasheet. This allows the measuring range of the voltage signals to be set according to an expected temperature range during operation of the coaxial gearbox. E) DeterminationThe direction of rotation can also be determined with the system according to the invention, the direction of rotation of the hollow shaft 30 or the guide unit 8, wherein the evaluation device 100 is configured to determine at least one actual value signal of a current direction of rotation, the determination comprising the following steps: - Acquiring and evaluating at least one first voltage signal 81a, 121 of a first strain gauge 40, 41a, which is arranged on a first piston 10a, and at least one second voltage signal 81b, 121 of a second strain gauge 40, 41b, which is arranged on a second piston 10b spaced apart from the first piston 10a, during the operation of the coaxial drive 1; - Determining at least one time t of the incoming first voltage signal 81a, 121, and at least one time t of the incoming second voltage signal 81b, 121, preferably taking into account the respective corresponding voltage peaks S, S; E, E; L,L of the firstThe voltage signal 81a,121 of the first strain gauge 40,41a and the second voltage signal 81b,121 of the second strain gauge 40,41b are determined. The temporal sequence tt of a signal sequence of the first voltage signal 81a,121 of the first strain gauge 40,41a and the second voltage signal 81b,121 of the second strain gauge 40,41b is determined. The index 1 denotes the time t of the arrival of the first voltage signal 81a,121 of the first strain gauge 40,41a at the first piston 10a. The index 2 denotes the arrival of the second voltage signal 81b,121 of the second strain gauge 40,41b at the second piston 10b. To determine the direction of rotation, the sequence of the incoming voltage signals from at least two strain gauges 40 and 41a, 41b, respectively, which are attached to different pistons 10a, 10b, is required.to evaluate. Preferably, the corresponding voltage peaks S,S; E,E; L,L of the incoming voltage signals 81a,81b, 121 should also be taken into account. For example, a temporal sequence tt of the signal sequence of the incoming voltage signals 81a,121 of the first strain gauge 40,41a first at the first piston 10a and time-shifted to the later arriving voltage signals 81b,121 of the second strain gauge 40,41b at the second piston 10b, opposite in direction of rotation to a temporal sequence tt of the signal sequence of the incoming voltage signals 81b,121 of the second strain gauge 40,41b first at the second piston 10b and subsequently or time-shifted to the later arriving voltage signals 81a,121 of the first strain gauge 40,41a at the first piston 10a. By appropriately defining the temporal sequence of the incoming voltage signals to a first direction of rotation, a rotation direction corresponding to the first direction of rotation can also be achieved.The opposing second direction of rotation determines the current direction of rotation. REFERENCE SYMBOL LIST 1 Coaxial gear 2 Axis of rotation 3 Piston drive 3a Crankshaft 4 Connecting rod bearing; connecting rod journal; 5 Crankpin 6 Piston assembly 7 Connecting rod (or 6a, 6a', 6b, 6b', 6c, 6c') 8 Circumferential direction (double arrow) 9 Guide unit 10 Piston (or 10a-10p) 11 First end face of the piston 12 Toothing 13 Tooth 13a First tooth flank 13b Second tooth flank 13c Tooth width 13d Orientation direction of the tooth (double arrow) 13e Tooth height 14 Piston longitudinal axis 15 Radial direction (double arrow) 16 Bore for piston pin 17 Longitudinal axis direction of the piston pin bore 18 First piston segment 18a Chamfer width of the first piston segment 19 Second piston segment 19a Chamfer width of the second piston segment 20 Recess for connecting rod connection 21 Piston pin; Coupling bolt REFERENCE SYMBOL LIST (continued) 22 Intermediate link 23 Guide bolt 25 Connecting bolt 27 Swivel joint 29 Web recess 29a Width of the30 Hollow shaft 31 Internal toothing of the hollow shaft 32 Gap or recess of the internal toothing 40 Strain gauge; 40a Width of the strain gauge; 41 Foil strain gauge; (or 41a-41h) 42 Semiconductor strain gauge; Semiconductor strain gauge 60 Star-shaped connecting rod 70 Wheatstone bridge 71 First resistor 72 Second resistor 73 Third resistor 74 Fourth resistor 80 Applied voltage 81 Diagonal voltage 81a, 81b Diagonal voltage of a single strain gauge 82 Amplified (increased) voltage 82a Raw signal 82b Normalized signal 82c Normalized zero-value signal 82d Output signal 83 Normalized digital signal 84 Offset signal 85 Processed output signal 86 Limited output signal 87 Analog signal 90 Signal line for resistance change; connecting cable 100 Evaluation unit for measurement data REFERENCE SYMBOL LIST (continued) 110 Measurement data acquisition unit 111 Bridge circuit 112 (First) measuring amplifier 113 A / D converter 114Signal value normalization 115 Zero value normalization 116 (Second) measuring amplifier; signal value amplifier 117 Signal offset 118 Voltage limiter 119 D / A converter 120 Voltage limiter 121 Output voltage signal 130 Measurement data analysis unit 131 CPU processing unit 132 Main memory 135 Data storage device 136 Configuration data storage 138 Signal converter; I / O link 140 Actual value signal 150 PLC control device 160 External data monitoring device A Amplitude E,E Voltage peak at the beginning of tooth engagement L,L Voltage peak when tooth engagement disengages P Period S,S,S Voltage peak at maximum load during tooth engagement t,t,t Time

Claims

PATENT CLAIMS 1. Coaxial gear (1), comprising: - at least one piston assembly (5) with at least three pistons (10a-10p), wherein the pistons (10a-10p) each have a toothing (12) with at least one tooth (13) on a first end face (11) pointing away from an axis of rotation (2); - a hollow shaft (30) with internal toothing (31), wherein, viewed in a plane normal to the axis of rotation (2), the pistons (10a-10p) are arranged inside the hollow shaft (30); - a guide unit (8), wherein the pistons (10a-10p) of the respective piston assembly (5) are each arranged in the guide unit (8) spaced apart from one another in a circumferential direction (7) pointing about the axis of rotation (2) by guide webs (9), and are guided linearly and are movable back and forth parallel to a radial direction (15) normal to the axis of rotation (2);- a piston drive (3) for the linearly guided movement of the pistons (10a-10p), - wherein the teeth (12,13) ​​of the first end faces (11) of the pistons (10a-10p), in particular successively, can be brought into engagement with the internal teeth (31) and into a state detached from the internal teeth (31) in order to further rotate the hollow shaft (30) or the guide unit (9) about the axis of rotation (2) during the respective engagement, preferably with planar contact between the respective teeth (12,13) ​​and the internal teeth (31), characterized in that at least one strain gauge (40,41,42) is attached to at least one of the pistons (10a,10c,10e,10g,10i,10k,10m,10o).

2. Coaxial gear unit (1) according to claim 1, characterized in that at least three pistons are arranged, preferably in the circumferential direction (7), and particularly preferably evenly distributed; (10a, 10c, 10e, 10g, 10i, 10k, 10m, 10o) at least one strain gauge (40, 41, 42) is attached to each.

3. Coaxial gear (1) according to claim 1 or 2, characterized in that the at least one piston set (5) comprises an even number of at least six pistons (10a-10p), wherein at least one strain gauge (40, 41, 42) is attached to at least every second piston (10a, 10c, 10e, 10g, 10i, 10k, 10m, 10o).

4. Coaxial gear (1) according to any one of claims 1 to 3, characterized in that at least one strain gauge (40, 41, 42) is attached to each piston (10a-10p). 5.Coaxial gear (1) according to one of claims 1 to 4, characterized in that the at least one strain gauge (40, 41, 42) is arranged in a first piston segment (18) on the respective piston (10a-10p), wherein the first piston segment (18) forms an outer surface section on the respective piston (10a-10p) and is positioned in the radial direction (15) parallel to a piston longitudinal axis (14) and at least partially normal to an orientation direction (13d) of the at least one tooth (13) of the respective piston (10a-10p).

6. Coaxial gear (1) according to any one of claims 1 to 5, characterized in that at least two strain gauges (40, 41, 42) are attached to at least one, preferably at least three pistons (10a, 10c, 10e, 10g, 10i, 10k, 10m, 10o) arranged distributed in the circumferential direction (7). 7.Coaxial gear (1) according to claim 6, characterized in that a first strain gauge (40, 41, 42) is arranged in a first piston segment (18) and a second strain gauge (40, 41, 42) is arranged in a second piston segment (19) opposite the first piston segment (18) on the same piston (10a-10p), wherein the first piston segment (18) and the second piston segment (19) each have an outer surface section on the respective piston (10a-. 10p) and are each positioned in the radial direction (15) parallel to a piston longitudinal axis (14) and at least partially normal to an orientation direction (13d) of the at least one tooth (13) of the respective piston (10a-10p).

8. Coaxial gear (1) according to one of claims 5 to 7, characterized in that a first piston segment (18) and / or a second piston segment (19) is / are each formed as a chamfered outer surface section on the respective piston (10a-10p), wherein preferably a chamfer width (18a) of the first piston segment (18) and / or a chamfer width (19a) of the second piston segment (19) is / are each greater than or equal to a width (40a) of a strain gauge (40, 41, 42). 9.Coaxial gear unit (1) according to one of claims 5 to 8, characterized in that a recess (29) is arranged on the respective adjacent guide web (9) of the guide unit (8) corresponding to the position of a first piston segment (18) and / or corresponding to the position of a second piston segment (19) of the respective piston (10a-10p), wherein the respective recess (29) extends in the radial direction (15) parallel to the longitudinal axis (14) of the piston (10a-10p) in question, and the at least one strain gauge (40, 41, 42) is arranged at least partially in the recess (29), wherein the respective recess (29) preferably has a recess width (29a) which recess width (29a) is greater than or equal to the width (40a) of a strain gauge (40, 41, 42).Coaxial gear (1) according to one of claims 1 to 9, characterized in that the at least one strain gauge (40) is selected from the group comprising: foil strain gauges (41), semiconductor strain gauges (42), rosette strain gauges, wire strain gauges.

11. Coaxial transmission (1) according to one of claims 1 to 10, characterized in that the piston drive (3) comprises a crankshaft (3a) rotatable about the axis of rotation (2) with at least one connecting rod bearing (4), wherein at least one connecting rod (6) is provided, which connecting rod (6) is coupled to one or more pistons (10a-10p) of the at least one piston set (5) and to the at least one connecting rod bearing (4).

12. Coaxial transmission (1) according to claim 11, characterized in that a common, star-shaped connecting rod (60) is provided for connecting the pistons (10a-10p) of the respective piston set (5) to the at least one connecting rod bearing (4), with which the pistons (10a-10p) of the respective piston set (5) are coupled, or that a separate connecting rod (61a-61p) is provided for connecting each piston (10a-10p) of the respective piston set (5) to the at least one connecting rod bearing (4). 13.System comprising a coaxial gearbox (1) according to any one of claims 1 to 12 and an evaluation device (100) for acquiring and evaluating measurement data, wherein the evaluation device (100) comprises a measurement data acquisition unit (110) and a measurement data analysis unit (130), wherein the measurement data acquisition unit (110) is connected (90) to at least one, preferably at least three, particularly preferably all, strain gauges (40, 41a-41h, 42) of the coaxial gearbox (1) by means of a signal (90), and the measurement data acquisition unit (110) is configured to detect resistance changes of each of the strain gauges (40, 41a-41h) by means of at least one bridge circuit (111) and outputs corresponding voltage signals (121), and wherein the measurement data analysis unit (130) is configured to use the measurement data acquisition unit (110) to determine the resistance changes of each of the strain gauges (40, 41a-41h) by means of at least one bridge circuit (111) and outputs corresponding voltage signals (121), and wherein the measurement data analysis unit (130) is configured to use the voltage signals output by the measurement data acquisition unit (110) to determine the resistance changes of each of the strain gauges (40, 41a-41h) by means of at least one bridge circuit (111). Voltage signals (121) of each of the strain gauges (40,41a-41h,42) at least one actual value.to determine signal (140) of a current rotational speed and / or a current angular position and / or direction of rotation and / or a current torque and / or a current temperature and / or a current acting force, and preferably to output it to a control device (150) and / or to an external data monitoring device (160). 14.Method for determining a current rotational speed using a system according to claim 13, wherein the evaluation device (100) is configured to determine at least one actual value signal (140) of a current rotational speed, comprising the following steps: - Acquiring and evaluating the voltage signals (121) of at least one strain gauge (40, 41, 42), preferably all strain gauges (40, 41, 42), during operation of the coaxial drive (1); - Determining a period P as a time interval (t – t) between two corresponding voltage peaks (S,S; E,E; L,L) of the voltage signal (121) of the respective strain gauge (40, 41, 42); - Converting the period P, taking into account the number L of gaps of the internal gearing (31) of the hollow shaft (30), into a current rotational speed ^^=(2^ / L) / P. 15.Method for determining a current angular position using a system according to claim 13, wherein the evaluation device (100) is configured to determine at least one actual value signal (140) of a current angular position, comprising the following steps: - Acquiring and evaluating the voltage signals (121) of at least one strain gauge (40, 41, 42), preferably all strain gauges (40, 41, 42), during operation of the coaxial drive (1); - Determining the respective times (t, t) of voltage peaks (S, S; E, E; L, L) of the respective strain gauge (40, 41, 42);. - Assigning the respective time points (t,t) of voltage peaks (S,S; E,E; L,L) taking into account the number L of gaps of the internal gearing (31) of the hollow shaft (30) as an increment of a current angular position of the respective strain gauge (40,41,42).

16. Method for determining a current torque using a system according to claim 13, wherein the evaluation device (100) is configured to determine at least one actual value signal (140) of a current torque, comprising the following steps: - Acquiring and evaluating the voltage signals (121) of at least one strain gauge (40,41,42), preferably all strain gauges (40,41,42), during the operation of the coaxial gearbox (1); - Calibrating at least one strain gauge (40,41,42), preferably all strain gauges (40,41,42), at predefined torques and assigning the respective stress amplitudes (U,U) of stress peaks (S,S; E,E;L,L) of the respective strain gauge (40, 41, 42) each with a calibrated torque value; - Comparing the respective current voltage amplitudes (U,U) of voltage peaks (S,S; E,E; L,L) of the respective strain gauge (40, 41, 42) during operation of the coaxial drive (1) with the calibrated torque values ​​and determining a current torque.

17. Method for determining a current temperature using a system according to claim 13, wherein the evaluation device (100) is configured to determine at least one actual value signal (140) of a current temperature, comprising the following steps: - Acquiring and evaluating the voltage signals (121) of at least one strain gauge (40, 41, 42), preferably all strain gauges (40, 41, 42), during operation of the coaxial drive (1); - Calibrating at least one strain gauge (40, 41, 42), preferably all strain gauges (40, 41, 42), at predefined temperatures and assigning an offset of the respective voltage signal (121) of the strain gauge (40, 41, 42) to a known temperature value prevailing during calibration; - Determining corresponding voltage peaks (S,S; E,E; L,L) of the voltage signal (121) of the strain gauge (40, 41, 42) over time (t) and determining the slope S of a signal drift; - Calculating a relative temperature change ^T by multiplying S by a corresponding known material constant of the strain gauge (40, 41, 42); - Determining an initial temperature T based on the offset of the voltage signal (121) in an initial time range; - Determining the current temperature T by adding T and ^T.

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