Hi mechatronics fans!

Welcome to this new post in our Sinadrives blog.

February 2022

In today’s instalment we’ll be discussing the machine tool and why it’s so precise.

Note: By “machine tool” we mean all machinery whose purpose is the machining of metal and non-metal parts by means of removing shavings; that is, machinery such as lathes, milling machines, grinding machines, drills, etc.
The first and possibly the main difference between a machine tool and all other tools is the precision of their machining, thanks to their rigidity and great robustness.

Machine tools surely constitute the oldest industrial sector. There was a time in history when it was necessary to machine the first screw, the first base plate and the first pulley for “the first machine.” In the early days, the sector had to produce artisanal solutions in order to be able to manufacture certain parts of high geometric precision and to guarantee the tolerances of flatness, parallelism or concentricity. All of that is in the past; today we have at our disposal an extensive range of machine tools to meet the strictest demands in terms of geometric tolerances and precision.

The machine tool owes a lot of its success to the “direct position feedback” concept. This method has always been applied in machine tools. The advantage of this method consists of measuring the direct position of the trolley (5) by means of a second encoder (8) and not, as is usual, by means of the encoder (7) of the servo motor (1). The diagram below shows the principle of direct position feedback.

This type of feedback with a direct encoder significantly improves the behaviour of the axis, improves precision and repeatability, increases dynamic response, reduces the influence of thermal expansion, completely ignores the error of the spindle mechanical step (3, 4) and other mechanical elements (2) of the assembly as a whole.

Picture 1. Source: Renishaw.

It’s worth highlighting that the direct feedback method is also used in linear motor applications, torque motor applications or linear motor modules. This simple method significantly improves the behaviour of any machine, especially if it is dynamic and requires high precision.

Thanks to the direct feedback solution, linear motor modules easily achieve an absolute precision of up to ± 3 micrometres and a repeatability of +- 100 nanometres.

Here we’re referring to components such as the base, the table, the mobile trolley and the rails. The components of a machine tool are the key to ensuring the required precision. The easiest way to achieve a precision assembly is to have high-quality parts that meet the indicated tolerances and have geometric accuracy characteristics within the established margins. The quality of finishes and the geometric precision of these components are crucial factors.

Standard components include elements such as bearings, guides, CNC, drives, torque motors, encoders, etc. Nowadays, a wide range of specific components exist for this market in order to fulfil the most demanding precision requirements.
These components already meet most of the demands and requirements for the performance of machine tool applications, such as precision, repeatability, power, software, specific algorithms, compensation tables, etc.

The assembly and adjustment of a machine tool deserves a separate chapter. It’s said that even if you’ve got all the drawings of the parts and have them machined according to the required tolerances, without the right experience you won’t be able to assemble a machine that works properly.

In companies that manufacture machine tools, adjusters enjoy special status and are considered key employees of the organization.

Once the machine is assembled, the calibration stage comes into play. The linear and rotary axes are calibrated for total accuracy and the measurement errors of encoders and position sensors are corrected.

This type of calibration is used in order to reduce absolute precision error using laser calibration. The mobile trolley is taken to position 100 by means of the encoder and this position value is compared with the laser measurement. The difference between the two positions is entered in the numerical control correction table.

Picture 2. Source: Renishaw.

This type of calibration makes it possible to adjust the perpendicularity of axes. The test consists of making a circular movement and comparing it with the measurement of the Ballbar.

Picture 3. Source: Renishaw.

One of the main trends in the sector is the integration of direct drive mechanisms in machine tool applications. The rotary direct motor (or torque motor) is already a common component in milling machines or lathes. As for the linear motor, the application of this type of mechanism is increasingly used in high dynamics and precision applications.

Another component in great demand are robust linear and rotary encoders, with inductive technology. These types of encoders ensure safe operation in highly complex environmental conditions, such as those involving shavings, moisture or cutting fluids.

Picture 4. Source: Heidenhain.

You can also make the most of the advantages and experience of the machine tool. If you have an application in which you need to improve dynamics, accuracy or repeatability, we’ll be delighted to help you. Take advantage of our 15-year track record in the machinery and automation markets.

If you have an application in which you’re keen to improve the performance of your machine, be it in terms of speed, dynamics, precision or simply reducing maintenance needs, please contact us.

Our specialists in Direct Drive technology and Linear Modules with linear motor technology will be happy to advise you free of charge.

Draw your own conclusions. Decide which innovation you want to implement in your machine to be competitive. We can help you.

Your SINADRIVES Team.