# US 10,481,578 B2 · Determining the rigidity of a drivetrain of a machine, in particular a machine tool or production machine

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- Number: US 10,481,578 B2
- Document ID: US10481578B2
- Status: Granted
- Kind: B2
- Application number: 15/780,547
- Filed: 2016-11-24
- Published: 2019-01-17
- Granted: 2019-11-19
- Earliest claimed: 2015-12-02
- Assignees: Siemens Aktiengesellschaft
- Applicants: Siemens Aktiengesellschaft
- Inventors: David Bitterolf; Gerhard Forster; Elmar Schäfers; Torsten Schür
- Web page: https://patentgrep.com/patent/US10481578B2

## CPC

- G05B 19/404: characterised by control arrangements for compensation, e.g. for backlash, overshoot, tool offset, tool wear, temperature, machine construction errors, load, inertia (G05B19/19, G05B19/41 take precedence)
- G05B 19/401: characterised by control arrangements for measuring, e.g. calibration and initialisation, measuring workpiece for machining purposes (G05B19/19 takes precedence)
- G05B 19/4065: Monitoring tool breakage, life or condition
- G05B 2219/41057: Stiffness, deformation of slide, drive
- G05B: CONTROL OR REGULATING SYSTEMS IN GENERAL; FUNCTIONAL ELEMENTS OF SUCH SYSTEMS; MONITORING OR TESTING ARRANGEMENTS FOR SUCH SYSTEMS OR ELEMENTS (systems for controlling or regulating non-electric variables G05D; systems for regulating electric or magnetic variables G05F; control devices or systems insofar as characterised by mechanical features only G05G)

## Abstract

A drivetrain for linear movement of a machine component along a linear guide of a machine includes a motor with a motor-measuring system. A length-measuring system is assigned to the linear guide for determining a position of the machine component. To determine rigidity of the drivetrain, a constant acceleration for the machine component is predetermined by a numerical controller for performing closed-loop control of the movement of the machine component. The numerical controller determines a difference between a position of the machine component derived from the motor-measuring system and a position of the machine component measured at the same time by the length-measuring system during the acceleration phase, and the difference is assigned to the acceleration or to a force required for the acceleration and storage in the numerical controller of the pair of values established in this way and/or of a rigidity value emanating from the pair of values.

## Claims

### Claim 1

A method for determining a rigidity of a drivetrain having a screw drive for moving a machine component along a linear guide of a machine, said method comprising the steps of:
under control of a numerical controller, imparting during an acceleration phase on a rotary motor having a first position sensor and being operatively connected to the linear screw drive a constant acceleration for the machine component;
measuring during the acceleration phase with the first position sensor a first position of the machine component;
measuring simultaneously during the acceleration phase with a length-measuring system operably connected to the linear guide a second position of the machine component along the linear guide;
determining a difference between the first position and the second position; associating the difference with the constant acceleration or with a force producing the constant acceleration; and
storing in the numerical controller a value pair composed of the determined difference and the constant acceleration or a rigidity value derived from the value pair.

### Claim 2 (depends on 1)

The method of claim 1, wherein the machine is a machine tool or a production machine.

### Claim 3 (depends on 1)

The method of claim 1, further comprising repeating the method steps for different machine components and/or for different constant accelerations until an abort criterion is reached.

### Claim 4 (depends on 3)

The method of claim 3, further comprising determining a characteristic curve from the value pairs established for different constant accelerations, and storing the characteristic curve in the numerical controller.

### Claim 5 (depends on 1)

The method of claim 1, further comprising determining a friction force to be overcome for moving the machine component, and compensating the friction force.

### Claim 6 (depends on 5)

The method of claim 5, wherein the friction force is determined from a plurality of measurements of a power consumption of the motor, during which the machine component is moved at different constant speeds.

### Claim 7 (depends on 5)

The method of claim 5, further comprising establishing a Stribeck curve using measurement technology for determining the friction force as a function of a speed with which the machine component is moved.

### Claim 8 (depends on 7)

The method of claim 7, further comprising determining a plurality of Stribeck curves as a function of the position of the machine component in relation to the linear guide.

### Claim 9 (depends on 1)

The method of claim 1, further comprising specifying to the numerical controller a mass of the machine component.

### Claim 10 (depends on 9)

The method of claim 9, wherein the mass of the machine component is derived by the numerical controller from the force producing the constant acceleration.

### Claim 11 (depends on 1)

The method of claim 1, further comprising determining the rigidity of the drivetrain at different points in time, and inferring from a comparison between the rigidity determined at different points in time characteristic properties of the drivetrain.

### Claim 12 (depends on 1)

The method of claim 1, further comprising determining the rigidity of a number of drivetrains of identical design installed at a number of machines, and inferring from a comparison of the rigidities established for the drivetrains of the identical design characteristic properties of the respective drivetrains.

### Claim 13 (depends on 11)

The method of claim 11, wherein the numerical controller carries out predetermined functions depending on the characteristic properties of the drivetrain.

### Claim 14 (depends on 12)

The method of claim 12, wherein the numerical controller carries out predetermined functions depending on the characteristic properties of the respective drivetrains.

### Claim 15

A numerical controller for closed-loop control of a movement of a machine component of a machine moving along a linear guide, said numerical controller being configured to
impart during an acceleration phase on a rotary motor having a first position sensor and being operatively connected to a linear screw drive which moves the machine component a constant acceleration on the machine component;
measure during the acceleration phase with the first position sensor on the motor a first position of the machine component;
measure simultaneously during the acceleration phase with a length-measuring system operably connected to the linear guide a second position of the machine component along the linear guide;
determine a difference between the first position and the second, postion;
form a value pair composed of the determined difference and the constant acceleration or a force producing the constant acceleration; and
store the value pair and/or a rigidity value derived from the value pair.

### Claim 16

A machine, comprising:
a machine bed;
a machine table;
a linear guide secured to the machine bed and guiding the machine table along the machine table;
a length-measuring system operably connected to the linear guide for measuring a first position of the machine component relative to the machine bed;
a drivetrain comprising a screw drive which converts a rotational movement of a rotating motor into a translational movement of the machine table; a motor-measuring system comprising a motor sensor which determines from a known transmission ratio of transmission elements of the drive train a second position of the machine table in relation to the machine bed; and
a numerical controller configured to impart during an acceleration phase a constant acceleration on the machine component along the linear, measure during the acceleration phase simultaneously the first position and the second position, and determine a difference between the measured first position and second position, associated the difference with the constant, acceleration or with a force producing the constant acceleration, and store a value pair composed of the determined difference and the constant acceleration or and/or a rigidity value derived from the value pair.