Posted in | Position Sensors

How Do Slab Resolvers Work?

Slab resolvers are used widely in motion control applications for the feedback of velocity and rotational position. The term ‘slab resolver’ refers to a resolver with a large diameter proportionate to its axial height. Normally, slab resolvers also have a large bore to contain through shafts, hydraulic pipes, electrical cables etc.

Slab resolvers have a long track record for offering reliable position and velocity feedback as well as commutation without being restricted by the environmental restrictions imposed by other sensing methods. The vibration and shock levels encountered in military, aerospace, or heavy industrial equipment are usually within the operating envelope for many of the slab resolvers.

Operating Principles of Slab Resolvers

Whilst there are lots of variations on the theme, a typical resolver has three windings – a primary winding and two secondary windings. These windings are usually formed on the resolver’s stationary element – the stator. The primary is used as the input for an AC drive signal and each secondary is used as pick up or receive winding. In the diagram below, the rotor is made from a material such as iron or steel and is arranged relative to the windings such that it will couple varying amounts of energy in to the secondaries depending on its angle of rotation. In the diagram below, the output from the secondaries will be in the form of a sinusoid and cosinusoid. Accordingly, the ratio of signals varies in proportion to angle.

The outputs from a ‘single speed’ resolver are unique over each rotation – in other words angle can be calculated absolutely over 360o. A two-speed resolver has outputs which are unique over 180o; a three-speed resolver has outputs which are unique over 120o and so on. Typically, most resolvers are 1, 2, 4, 8, 16 or 32 speed.

Celera Motion's Zettlex Technology vs Slab Resolvers

Along with RVDTs, RVITs, synchros, and Inductosyns™, slab resolvers are considered a ‘traditional’ form of inductive position sensor, and have many disadvantages when compared with their latest equivalents. Celera Motion'sZettlex IncOders are based on the same primary physics as slab resolvers and so offer the same high levels of strength. Using laminar constructions with printed circuits as opposed to traditional large spools of wire, IncOders are less expensive, more compact and lighter, providing a most favorable solution for engineers with much greater design and integration flexibility. Celera Motion's Zettlex IncOders’ low height, large inner diameter and tolerance to misalignment make installation easy in applications such as gimbals mounts, pan and tilt pedestals, and rotary joints.

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