Patent Application
20200061832
The invention relates to a drive system, in particular that of a machine tool, of a robot or of a production machine, and to a method for the assessment of the drive system.
The operation of a machine, such as a machine tool, a production machine or a robot, is subject to various general conditions. Depending on those conditions, a load on the machine (e.g.: a lathe, milling machine, grinding machine, drill, robot, etc.) is produced. In order to machine a workpiece using a machine tool, a part program is executed in a controller of the machine tool, for example, which controls the motion sequences of a tool in particular with pinpoint accuracy. The part program comprises a large number of program instructions that can trigger various actions by the controller or machine tool. For example, there are program instructions that directly effect a relative movement of the tool vis-à-vis the workpiece along a predetermined path with pinpoint accuracy. However there are also program instructions that call a subprogram, an auxiliary movement, or a cycle, for example. In these latter cases, parameters, by means of which a machining process or a movement to be executed by the machine tool is specified more precisely, are generally transferred as well. For example, parameters are provided to the controller by the part program when a pocket milling cycle is called, which determine the exact position and size of the pocket to be milled. The program instruction “mill pocket” in conjunction with the corresponding parameters causes the controller automatically to generate the necessary path data for the movement of the tool relative to the workpiece. Calling an auxiliary movement is another example of a program instruction. Here, only the start and end point are specified to the controller, and the controller generates corresponding path data for the auxiliary movement so that the tool not engaging with the workpiece is moved in a collision-free manner from the start point to the end point.
In series production it can be important for the motion sequences executed by the machine tool to be optimized, since non-optimized motion sequences can represent a significant time and therefore cost factor in the manufacture of a workpiece. In order to raise machine productivity, it can therefore be worthwhile—especially in series production—to use optimized motion sequences, or to optimize the load on hardware. Hardware refers to the drive system, for example. The machine's axes can represent part of the hardware, for example. An axis has for example an electric motor and/or a current converter. The calculation of optimized motion sequences takes place offline, for example, i.e. outside of the controller, as this requires a large amount of computing power and is very time-consuming. In this approach, changes to the part program carried out directly on the machine can be integrated into the optimization of motion sequences only with difficulty. This represents an impediment to the generation of time-optimized motion sequences and usually restricts their use to large-scale series production.
In a simplified approach, motors or drives can be dimensioned by specifying a load change. Here, the dimensioning of the motor, the mains power supply, the power modules, the regulation components and/or the position detection function is performed on the basis of the required torque, the required rotational speed and/or the required power.
The dimensioning of the motor is performed for example with regard to:
The variables drawn upon, especially masses and rated power, depend to a very large extent on the design of the machine and are perhaps not yet known at the time of motor configuration. The dimensioning is therefore then based on assumptions by the customer, for example, and involves safety factors.
A simulation tool and an analysis tool for a mechatronic system are known from US 2010/0082314 A1. The behavior of a drive system can be predicted on the basis of a configuration by a user.
A dimensioning program can be used to dimension a drive, which can have a combination of a motor and current converter, for example.
The dimensioning of one or more drives then becomes complex in particular if multi-axis machines are involved, as may be the case for example with machine tools and robots, if the movement of one axis changes the position of another axis. A mechanical interaction between the axes is then produced.
In some cases the data about motor/drive dimensioning is imprecise. This affects the dimensioning of applications with linear and torque motors, for example. However the limits of feasibility for an application may have to be approached with these direct drives in particular. In the past, motors or drives were often overdimensioned unnecessarily (safety margin). This situation can be improved through a better dimensioning method. In this way, the following problems can be overcome, by way of examples:
An object of the invention is to improve the drive system of a machine. The dimensioning of the motor and/or of a downstream component can then be made more precise. In this way, incorrect dimensioning can be avoided in particular. This refers to e.g. overdimensioning of the drive or underdimensioning of the drive.
One solution to this object is provided in accordance with a method having the features as claimed in claim 1 and with a drive system having the features as claimed in claim 14. Further embodiments are provided in accordance with claims 2 to 13 and 15 to 17, by way of examples.
In a method for the assessment of a drive system of a machine tool or of a production machine, the drive system having an axis, a load of the drive system is simulated. The drive system has in particular three or more axes. A drive profile is used for the simulation, wherein actual values of the drive system are simulated, wherein the simulated actual values are correlated with comparative values. The load can be determined or calculated for example on the basis of a maximum torque Mmax, a maximum current Imax, a rated torque Mnenn, a maximum rotational speed Nmax, a thermal load I2t and/or a standardized operating mode such as S1, S2, S3, etc. In this way, during the operation and/or development of a machine for example, the load of the machine axes (axes) can be determined and/or optimized, for example. This refers in particular to a given application that could be optimized. In particular, the optimization is performed automatically.
In one embodiment of the method the drive profile is based on a part program. The part program is known for example from the programming of machine tools.
In one embodiment of the method, the part program is traveled along in order to determine the load in a machine with a part program, and using measurement data it is checked whether the machine is producing the dynamics set. If the desired machining time is not achieved, then the dynamics requirement is gradually increased. In this way, either the target is achieved, or the drives' limits are reached (e.g. current, torque, power, rotational speed). This then allows a limiting component to be determined and replaced with a higher-powered component, for example.
In one embodiment of the method a virtual machine is used. This virtual machine has components such as a numerical controller (NC), a drive and a machine model, for example. These components can be simulated in three successive stages, for example:
This simulation can be carried out for customer applications as part of a virtual production using a mechatronic model of the machine. Added to this is the application for motor/drive dimensioning. Detailed conclusions can be reached regarding the motor dimensioning, especially in combination with a particular NC program or motion sequence for the customer. Here, the specific characteristics of the algorithms for motion control in the NC and the regulated drives are considered. This then allows dynamic and thermal aspects to be examined. During dimensioning, the customer's specific application is already examined by means of the virtual machine. The motor load is calculated for the typical application, for example, and not for a theoretical load cycle alone. Through simulation with a virtual machine in different configurations as well, the dimensioning of the motor/regulated drive is refined in respect of static, dynamic and thermal aspects. A virtual production can be drawn upon for the motor/drive dimensioning.
In one embodiment of the method the drive system has at least five axes. In machine tools that allow five-axis machining, the interaction of the different axes while also taking account of various part programs is complex, and consequently advance processing of the drive system allows it to be improved. So, for example, before the construction of the machine tool or a robot or a production machine, with a large number of axes the mechanics of the machine tool or robot or production machine can be adjusted depending on the processing of the drive system. Mechanics refers e.g. to its rigidity, elasticity, the bearing capacity of bearings, etc. In one embodiment of the method the load of at least one of the axes is consequently used for dimensioning of the machine tool or robot or production machine.
In one embodiment of the method a cycle of a machine, in particular of a machine tool, a robot or a production machine, is simulated, wherein the simulated actual value is an average value, wherein the dimensioning of the machine is changed depending on the average value. A cycle refers in particular to a recurring motion sequence of the axes of the machine. The average value refers for example to a torque of a drive of an axis. The average value allows in particular a thermal evaluation of the cycle.
In one embodiment of the method a typical NC program for production of an object is specified, from which it is then possible to specify the drive needed in order to perform the machining described in the NC program faster on a new machine. In addition, the quality of the production or machining can also be considered depending on the speed.
In one embodiment of the method an acceleration curve can be checked or calculated for a production cycle in order to draw conclusions from this regarding motor heating in an axis e.g. in the x-axis.
In one embodiment of the method a machining of spectacle lenses using linear direct drives can be examined, for example, in order through simulation to calculate the required acceleration or the jerk, in order therefrom to draw conclusions about the motor.
For example, also in the case of a gantry-type milling machine or a contour milling machine, with conventional dimensioning, the max. acceleration data assumed in the motor configuration cannot be achieved operationally (this affects the load) as a result of significant jerk limits in the axes (this affects the drive profile, as the virtual machine can be reflected there). The simulation of the virtual machine allows the max. achievable jerk values to be calculated and considered in the motor dimensioning. Saving motor power and cooling power creates great potential to save costs.
For example, machining on a milling machine with direct drives can result in the linear motors overheating and consequently in the failure of the drives in the x-axis. With the aid of the virtualization of the production or production machine (in this case the milling machine) using virtualization of the direct drives, it is possible to check whether the specified motion profile of the part program, which can be represented by a drive profile, caused the overheating. One or many of the following steps can be performed for this purpose:
In one embodiment of the method simulated actual values are used to change the drive profile. The drive profile or a production can be adjusted e.g. for existing hardware (e.g. motor and/or current converter). Here, an adjustment for the possibilities or power limits of existing hardware can be performed e.g. by reducing an acceleration, in particular so that a drive's current limit is not exceeded.
In one embodiment of the method the drive system has a large number of axes. The drive system refers to a numerically controlled machine tool with multiple axes (e.g. with three, four, five or more axes), for example. The simulation and any adjustments that may be necessary can avoid, for example, an axis dimensioned too weakly reducing the performance of a whole drive system.
In one embodiment of the method a load of at least one axis is simulated. The axis has at least one motor or at least one motor-current converter combination.
By means of digitalization, simulation, or the provision of a digital twin, it is possible to determine and optimize the drive load for typical applications. Before the development of a new machine, the load of the axes can also be simulated in this way for a typical application. With this, the drive dimensioning and kinematic properties of the machines can be optimized.
In one embodiment of the method machine parameters are used for the simulation. By way of example, this is a transmission ratio for a transmission and/or an axis pitch, etc. The simulation is improved as a result.
In one embodiment of the method mechanical properties are used for the simulation. By way of example, this is a friction, a friction coefficient and/or a temperature coefficient, etc. The simulation is improved as a result.
In one embodiment of the method a machine parameter and a mechanical property are used for the simulation. This also improves the simulation.
In one embodiment of the method the comparative value is a maximum torque, a maximum rotational speed, a maximum power, a maximum current and/or a motor characteristic curve.
In one embodiment of the method a cycle is simulated, wherein the cycle undergoes thermal evaluation in particular. The cycle is, for example, a machining cycle, a production cycle, a load cycle, etc. By examining a cycle or by examining cycles it is possible to achieve an optimization of the load. During the drive dimensioning of a new machine, for example, a load cycle is estimated that is expected to represent the greatest load for one or more drives. It is now possible to perform the dimensioning using a part program and the machine-specific kinematic components. In 5-axis or 6-axis machining in particular, the highly dynamic compensating motions that occur make it difficult to estimate an appropriate load cycle.
In one embodiment of the method it is determined by means of the simulation which axis and which dynamic variable is having a limiting effect on dynamics during the sequence of the part program. The axis in question is changed in order to overcome the limit.
In one embodiment of the method it is possible to examine the extent to which a limit determined, or a large number thereof, is a decisive factor for the productivity of the machine. Simulation makes it possible to establish how extending the current limits would positively affect the manufacturing quality or the duration of the manufacturing process. If, for example, the acceleration limit in one axis could be increased by just a few percent, this can have a significant effect on the total machining time. This will then be implemented through machine construction and technical control measures. Here one step is, for example, identifying the relevant limit and establishing the relationship. This is made possible by means of the examinations shown. For example, it would be possible to proceed as follows:
In one embodiment of the method a torque-rotational speed diagram is created for a machine tool with five or more interpolated axes. From this it is possible to determine which axis is having a limiting effect.
In one embodiment of the method a histogram of dynamic limits is created. From this it is possible to determine what is limiting the dynamics, and countermeasures can be taken. For example, a higher-powered motor can be used.
In one embodiment of the method the drive dimensioning, the motor dimensioning, kinematic parameters and/or the clamping situation is optimized. As a result it is possible to raise efficiency.
In one embodiment of the method the limiting axis and/or a limiting variable are determined for a large number of axes. The limiting axis or the limiting variable can subsequently be analyzed and parts of the machine adjusted so that the limit identified no longer occurs.
In one embodiment of the method the drive load for a specific part program can be determined automatically using the parameters of the machine, by means of a simulation. In this case, exclusively the load due to the reference variables is examined in particular (disturbance variables such as e.g. machining forces and friction are disregarded). This result can represent a good approximation of the real total load.
In one embodiment of the method a load cycle is compared on a drive-by-drive basis with the characteristic curves and limits of the power section and motor. This refers, for example, to:
In one embodiment of the method a value for productivity and/or a value for manufacturing quality are determined. In the case of a robot as well as a machine tool, raising productivity can refer to an increase in the maximum possible speed of a motion system with multiple axes. In the case of a machine tool, manufacturing quality can refer to, for example, the surface quality of a workpiece being machined by means of a tool. As such, an increase in speed can cause a deterioration in manufacturing quality.
In one embodiment of the method it is possible to examine the extent to which the limits determined, in particular on axes or their drives, are a decisive factor for the productivity of the machine. Simulation makes it possible to trial how extending the current limits would positively or negatively affect the manufacturing quality or the duration of the manufacturing process. If, for example, the acceleration limit in one axis could be increased by just a few percent, this can have a significant effect on the total machining time. This can then be implemented through machine construction and/or technical control measures. In one step before optimizing (improving) the machine (machine tool, robot, production machine, etc.) the relevant limit is identified and the relationship is established. This is made possible by means of the examinations or simulations shown.
The trialing process can be automated. This means that iteration steps for optimization can be or are automated. In particular, for this purpose the manufacture of a workpiece is also simulated. The simulation considers which tool is intended for machining of the workpiece (e.g. type of milling head, type of drill bit, wear on the tool, etc.).
A drive system, which is a machine tool or a production machine in particular, has at least one axis, wherein a simulated load of the drive system is correlated with comparative values on the basis of a drive profile. Overloads and/or deficiencies, for example, can be identified in this way.
In one embodiment of the drive system, the drive system can be operated in accordance with the method described.
In one embodiment of the drive system, the drive system has a simulation computer that is linked by data connection via the internet to the machine tool or production machine. Computing work involving considerable effort can then be carried out remotely so as not to influence the machine's performance impermissibly.
In one embodiment of the drive system, the drive system has a large number of simulation computers, wherein one computer is provided in order to link up simulation data of the large number of simulation computers. This network structure allows the efficiency of the simulation to be improved.
The invention is explained in more detail below with reference to exemplary embodiments. In the drawings:
Continuing on from
| Number | Date | Country | Kind |
|---|---|---|---|
| 17158480.8 | Feb 2017 | EP | regional |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2018/054643 | 2/26/2018 | WO | 00 |
