Is A Resolver?
When discussing RESOLVERS, people often interchange
terms such as: encoders, rotary position sensors, motion feedback
sensors, and transducer sensors. On occasion, synchros (cousin
to the resolver) are also mentioned when explaining devices
of this nature. Regardless of the names people choose to describe
resolvers, their role in the world of automation remains unparalleled.
as an analog sensor that is absolute over a single turn, the
resolver was originally developed for military applications
and has benefited from more than 50 years of continuous use
and development. It was not long before numerous industrial
segments recognized the benefits of this rotary position sensor,
engineered to withstand the punishment of a military application.
Product packaging plants and stamping press lines are perfect
examples of where you might find resolver based systems at
work. In typical applications, the resolver sensor feeds rotary
position data to a decoder stationed in a Programmable Logic
Controller (PLC) that interprets this information and executes
commands based on the machines' position.
advances in technology have enabled the integration of a resolver
and on-board electronics in one housing as an alternative
to other types of encoders. Referred to as DuraCoders, these
motion sensing devices are available with the following output
types; Absolute Parallel, Incremental Digital, Analog Current,
Analog Voltage, and DeviceNet. The Absolute Parallel and Incremental
Digital versions can also be ordered with a field programmable
option. Using simple onboard switches, technicians and engineers
can easily select the unique resolution required by the application,
thereby reducing the number of units that must be stocked.
Through the evolution of machine development, builders and
system integrators alike, agree that the ‘resolver’
transducer is unsurpassed in its ability to reliably supply
rotary position data in the harshest industrial environments.
RESOLVER CONTROL TRANSMITTER
Typical Brushless Resolver Cross Section
A resolver is a rotary transformer where the magnitude
of the energy through the resolver windings varies sinusoidally
as the shaft rotates. A resolver control transmitter has one
primary winding, the Reference Winding, and two secondary
windings, the SIN and COS Windings. (See figure 1.1,
Resolver Cross Section). The Reference Winding is located
in the rotor of the resolver, the SIN and COS Windings in
the stator. The SIN and COS Windings are mechanically displaced
90 degrees from each other. In a brushless resolver, energy
is supplied to the Reference Winding (rotor) through a rotary
transformer. This eliminates brushes and slip rings in the
resolver and the reliability problems associated with them.
Figure 1.2 Brushless
In general, in a control transmitter, the Reference Winding
is excited by an AC voltage called the Reference Voltage (Vr).
(See figure 1.2, Resolver Schematic). The
induced voltages in the SIN and COS Windings are equal to
the value of the Reference Voltage multiplied by the SIN or
COS of the angle of the input shaft from a fixed zero point.
Thus, the resolver provides two voltages whose ratio
represents the absolute position of the input shaft. (SIN
θ / COS θ = TAN θ, where θ = shaft angle.) Because the ratio
of the SIN and COS voltages is considered, any changes in
the resolvers’ characteristics, such as those caused
by aging or a change in temperature, are ignored. An additional
advantage of this SIN / COS ratio is that the shaft angle
is absolute. Even if the shaft is rotated with power removed,
the resolver will report its new position value when power
RESOLVER CONTROL TRANSFORMER
Figure 1.3 Brushless
Resolver Control Transformer Schematic
A resolver control transformer has two input stator
windings, the SIN and COS windings and one rotor output winding.
(See figure 1.3) The rotor output is proportional
to the sine of the angular difference between the electrical
input angle of the inputs and the mechanical angular position
of its shaft...in other words, the voltage induced into the
rotor is proportional to sin(),
is measured from some reference shaft position called zero.
|Figure 1.4 shows what might be
called the "classic" resolver mechanical follow-up
servomechanism. The command angle is established by the
shaft position of the control transmitter. When the servomotor
has reached the commanded position,
the control transformers output is zero and the motor
stops. Although the above description is oversimplified,
it is useful in describing a control transformer.
Figure 1.4 Typical
Electromechanical Follow-up Servo
| Both control
transmitters and control transformers are unidirectional
devices i.e. Control transmitters manufacturers specifications
are only valid when the electrical input is the rotor,
and control transformers specifications are only valid
when the electrical inputs are the stator. Although both
can be used "backwards", performance cannot
What does it all mean (to you)?
When an encoder application exists in a hot, humid, dusty,
oily, or mechanically demanding environment, the resolver-based
system is the preferred choice. Ultra reliability, coupled
with proven performance support the bulletproof reputation
this rotary position sensing device has earned.
Resolver Sensor Products: