RODER · Inspection · Speed and motion
Linear speed and length in motion
The speed of a moving material is a central physical quantity in process control: drive synchronisation, cutting to length, metre counting and line regulation all depend on it. In this Inspection section we examine the quantity “speed” in its various forms — surface, linear, multidimensional — and the methods for measuring it with non-contact optical speed meters and encoders.
On this page
What the measurement is for: linear speed and length in motion ↑ top
Unlike the Technologies (theory) and Applications (practical cases) sections, here we concentrate on the measured quantity: how it is defined, in which units it is expressed and which instruments determine it accurately.
Speed as a process quantity ↑ top
Speed expresses the distance covered in unit time and, in the case of materials in continuous production, it is typically measured in metres per second (m/s) or metres per minute (m/min). Knowing the real speed of the material is indispensable for many reasons: it makes it possible to derive the length by integration, to synchronise rollers and drives and to keep the process stable. Measuring it accurately, however, is not trivial, above all when the material is hot, shiny or moving at high speed.
Optical speed meters solve the problem by measuring speed without contact: the VLM500 using the spatial filter principle (up to 50 m/s, uncertainty < 0.025 %), the VLM60 using the correlation method (down to 0 m/s, bidirectional too).
The different forms of speed ↑ top
The speed of a material can be described in different ways depending on the application. Surface and linear speed concerns the running of the material along the line; material speed and length links speed to the length produced; multidimensional speed takes into account movement in several directions (x and y) with direction recognition. Each of these forms is examined in a dedicated page.
Why measure speed optically ↑ top
- Non-contact measurement: no wear and no slippage
- Accuracy down to < 0.025 % and a wide dynamic range
- Measurement down to 0 m/s and direction recognition (VLM60)
- Valid on hot, shiny, thin or delicate materials
- Encoder, analog and fieldbus outputs for integration
From the quantity to the solution ↑ top
For the instruments, the optical speed meters and encoders page brings together the ASTech range; for real cases, Applications and solutions; for the theory, Optics and LASER and Doppler and optical correlation. The closely related quantity “length” is dealt with in Continuous length.
VLM500 optical speed meters
Speeds up to 50 m/s, uncertainty < 0.025 %, CCD spatial filter.
VLM60 optical encoder
A replacement for measuring wheels, measuring down to 0 m/s.
Optical encoder speed meters
Overview of the optical speed meter and encoder family.
Rotation speed and linear speed ↑ top
Two families of speed are encountered in industrial processes: rotation speed, expressed in revolutions per minute, and linear or surface speed, expressed in metres per minute. The two are linked by the diameter of the rotating member, but they are not interchangeable: measuring the revolutions of a roller is not the same as knowing the real speed of the material, because there can be slippage between roller and material. For this reason, when the actual speed of the product is what matters, direct optical measurement on the surface is the most reliable choice.
Why the real speed matters ↑ top
Knowing the real speed of the material, and not the one estimated from a roller, is decisive for process quality. The calculated length, the synchronisation between drives and the stability of the settings all depend on it. An error in speed propagates to all these functions. Non-contact optical measurement supplies the actual speed of the product, eliminating the systematic errors typical of indirect measurements and improving line control as a whole.
Dynamics and response time ↑ top
Besides accuracy, responsiveness also counts in speed measurement. A short update time makes it possible to follow accelerations, decelerations and rapid transients while keeping control stable. Optical speed meters update the measurement in fractions of a millisecond and offer configurable filters to balance responsiveness against signal stability. They are therefore suited both to slow lines with frequent stops and to fast lines running continuously.
Speed and product quality ↑ top
An accurate speed measurement does not only improve the calculated length: it has a direct effect on product quality. In printing lines, for example, a stable speed favours correct registration; in drawing lines it helps to prevent excessive tension and breakage; in hot processes it makes it possible to calculate elongation. In all these cases, having the real speed value of the material is the prerequisite for effective process control and for a compliant product.
Robustness in an industrial environment ↑ top
The speed measurement must remain reliable in real conditions: dust, vibration, heat and surface variations. With IP 65 protection, white LED illumination and, where necessary, protective housings, optical speed meters offer high availability even in continuous operation. The absence of moving parts reduces maintenance to a minimum, keeping accuracy constant over time.
One value shared with several systems ↑ top
The speed value can be distributed simultaneously to several recipients: fast control loops through the encoder output, supervisory systems through the fieldbus and display devices through the analog output. In this way a single instrument feeds the entire control chain, simplifying the architecture of the line and reducing the number of sensors required.
Frequently asked questions ↑ top
Typically in metres per second (m/s) or metres per minute (m/min); the length is derived from the speed by integrating it over time.
With an optical speed meter that illuminates the material and analyses the reflected light: the VLM500 uses the spatial filter, the VLM60 optical correlation.
Surface or linear speed concerns running along one direction; multidimensional speed takes into account movement in x and y with direction recognition.
The VLM500 offers an uncertainty below 0.025 %; the VLM60 below 1 %, with measurement down to 0 m/s.
Yes, the VLM500 measures up to 50 m/s (3000 m/min in the extended range) while maintaining high accuracy.
The pages in this section ↑ top
The in-depth pages for this quantity: techniques, selection criteria and instrument families.
In depth
Non-contact linear speed measurement
→
Laser linear speed meters for strip, sheet metal and moving products (VLM).
In depth
Surface and linear speed
→
Surface speed (or linear speed) is the speed at which the surface of a material moves along the production line. It is the quantity that gov…
In depth
Material speed and length
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The speed and length of a moving material are two closely related quantities: by measuring the first you obtain the second, by integration over t…
In depth
Multi-dimensional speed
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Multidimensional speed describes the movement of a material along several directions, typically the x and y axes, with detection of the direction of mov…
→
Continuous length measurement concerns materials produced without interruption: strips, wires, cables, tubes, profiles, panels and fabrics. In these cases the…
The information on this page is provided for information purposes. Although it has been compiled with the greatest care, it may contain transcription errors or typos: for precise, up-to-date information please contact RODER SRL directly.
Contacts & Information
Contact for general information : info@roder.it
Machine Vision Division of RODER : www.visiotronix.com
RODER Instruments Division : www.innovacheck.com
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Note: Some images on this website have been intentionally generated using artificial intelligence (AI). This is because, for many applications and projects, photographs of the actual installation or system cannot be disclosed owing to confidentiality agreements, contractual clauses and non-disclosure agreements (NDAs).
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