Multi-dimensional speed

Multi-dimensional speed describes the movement of a material along more than one direction, typically the x and y axes, with recognition of the direction of travel. It is an important quantity in applications where the material does not simply move forward but may change direction or have transverse components of motion. Optical encoders using correlation measure this type of speed without contact and bidirectionally.

This page belongs to the Speed and rotation in motion section of the Inspection area and looks in more detail at speed measurement in several directions.

What multi-dimensional speed is

Whereas linear speed considers movement along a single direction only, multi-dimensional speed takes several components of the motion into account. In many industrial applications the material may move both in the direction of travel (x) and transversely (y), or may reverse its direction of travel. Measuring both components, and recognizing the change of direction, allows far more complete control of the process. To do so, however, requires a measuring principle capable of following movement in two dimensions.

The VLM60 uses the correlation method: by comparing successive images of the surface, it determines the displacement in the x and y directions and recognizes the change of direction. The measurement remains valid even at zero speed, with no minimum speed.

Bidirectional measurement and direction recognition

Direction recognition is essential in material handling that involves forward and backward movement, or oscillation of the material. A correlation encoder, measuring in x and y, distinguishes the direction of movement and provides correct data even when the material reverses. It is therefore suited to positioning, winding and complex handling applications, where a single-direction measurement would give ambiguous results. In start-up and stop phases, for example, the ability to measure down to 0 m/s prevents loss of count.

Advantages of multi-dimensional measurement

• Measurement of movement in the x and y directions
• Recognition of direction and of changes of direction
• Measurement down to 0 m/s, with no minimum speed
• Non-contact: no wear and no slippage
• Direct replacement for measuring wheels and rotary encoders

Further reading and products

The correlation principle underlying multi-dimensional measurement is described in detail on the Doppler and optical correlation page. For the other forms of speed, see Surface and linear speed and Material speed and length; for practical cases, see Applications and solutions.

Applications of measurement in several directions

Multi-dimensional measurement is useful in every situation where the material does not simply advance in a straight line. Examples include handling with reversal of travel, precision positioning, winding with transverse movement and measurement on surfaces that may oscillate. In these cases, knowing the x and y components of the movement, and their direction, allows accurate control that a single-direction measurement could not guarantee.

Optical correlation and robustness

The correlation method compares successive images of the surface and calculates their displacement; it is inherently bidirectional and copes well with surfaces of varying contrast. Because it uses white-light LED illumination, it does not require the safety precautions typical of laser systems and it reduces speckle. It therefore offers an excellent combination of accuracy and robustness in real factory conditions, where vibration and variations in the surface are the norm.

Integration and encoder replacement

The VLM60 provides an incremental encoder output for each direction of movement, compatible with existing counting systems, as well as an optional fieldbus interface. It can therefore directly replace measuring wheels and rotary encoders, including in multi-dimensional applications, without requiring the control system to be redesigned. RODER technical support helps define the configuration best suited to the specific application.

Zero speed and changes of direction

Many complex handling operations involve stopping, restarting and reversing. In these cases the ability to measure down to 0 m/s and to recognize the direction of movement is decisive: it prevents loss of count and provides correct data even when the material is stationary or changes direction. A single-direction measurement, by contrast, would not distinguish forward from backward travel, producing errors in the counting of position or length.

Surfaces and environment

The correlation method tolerates surfaces of varying contrast and, thanks to LED illumination, remains stable even in the presence of reflections or non-uniformity. With IP 65 protection and compact dimensions, the optical encoder is easily integrated into installations where space is limited, maintaining consistent performance over time and reducing maintenance compared with contact solutions.

Configuration and support

Defining the working distance, the mounting and any accessories depends on the specific multi-dimensional application. RODER technical support assists the customer in the choice and the integration, so as to make the best use of bidirectional measurement and direction recognition, whether replacing existing encoders or in new positioning and handling installations.

Multi-dimensional measurement and advanced automation

In automation cells and positioning systems, measuring movement in x and y with direction recognition provides a valuable reference for control. Combined with measurement down to 0 m/s, it allows start-up, stop and reversal phases to be managed precisely, contributing to accurate process control and reliable production records, requirements increasingly demanded by connected industry.

Frequently asked questions