Resolver vs. Encoder?

A couple of questions. Do you need to know where the motor is, it's speed, or how many times it's gone around? Accuracy? Are you using it in a control loop? Money?

Tom

As said abouve- more info will help pick the right device. If you need speed and direction feedback either device will work. Both will also give position data as well, however there is one important difference.

A resolver is a pure position device - it has the ability to retain it's shaft position (360 degrees) data regardless of power or software outages. Also if you power off a resolver and move the shaft, upon re-applying power it will report the new postion.

Encoders tend to work by counting pulses, and have many cases where the accumulated position data can be lost.

With that said the encoder would still probably be the best choice- If position is vital then 2 devices would be my choice.

Device 1 -encoder or resolver on motor for speed feedback and device 2- resolver on door geared 1 rev = full travel; thus providing position data that cannot be lost.

Using a motor mounted resolver for position and speed requires software to accumulate position data, thus it would no better than an encoder since accumulated position data could be lost on power up-(resolver only knows position for 360 degress of winding travel)

Another benefit of a resolver is the ability to detect feedback loss without spinning the shaft.

Why mess with positioning control stuff when you could simply use end-switches?

Just a thought....

I have used both. Encoders can be sensitive to both heat and shock. Resolvers are more robust and handle more heat. Making a decision on what to use depends on exactly what you application is. Can you be specific on how and where you want to use it?

Mike

Just out of curiosity, what kind of door? If it's a door to a room or entrance door to a building, then you probably won't need either -- it's doable otherwise.

If it's a door to something that needs to be controlled for intemediate positions, then one of the things which needs to be known by anyone who wishes to offer advice is, "How accurately do you need to control the position?"

Resolvers have essentially infinite resolution (within practical limits, of course). Incremental encoders have resolutions ranging from once per revolution to several thousand counts per revolution, +/- one increment. Absolute encoders are similar to incremental encoders in that they have discrete positional resolution, and they are similar to resolvers in that they will maintain their positional output in cases of power failure and restoration.