How to Change the Rotation of Motor

Give backward command

it is a DC motor, simply reverse the polarity of the supply to the motor and it will run backwards.

Answers #1 and #3 are both good.

Is it possible the encoder was physically installed upside down/backwards?

For example, if the encoder wheel was a slotted metal or etched/painted glass disk, flipping it over would also give you the opposite feedback.

Although, why would changing the encoder cause it run the opposite direction? When you start the motor moving by applying the proper voltage, does the encoder feedback cause the controller to reverse the voltage and keep it reversed?

Sounds odd.

"Flipping the disk" would be appropriate for an absolute encoder. As far as I can make out, an incremental encoder is used with the AC890 - in which case the disk orientation wouldn't matter.

Maybe the OP can throw more light?

If the motor connections were not changed but the direction has reversed, the drive must be relying on encoder feedback to decide which way (and how far and how fast) it's moving.

If the phases of the replacement encoder were exchanged with respect to the original, the direction in which the motor drives will reverse.

If nothing has changed except the encoder, what possible alternative explanation could there be?

John, wasn't saying your answer was incorrect, it is probably the best explanation as to why this is happening, I was merely giving the OP another option on how to skin the cat.

OP states that the motor is a DC brushless. This is from the Parker AC890 "home page":

Depends how it's configured & on the particular variant.

What type of encoder are you using? Is it a speed or position encoder?

In either case interchanging either the armature or field connections should do the trick

Think you'd better explain to the OP:

• What the difference is between a speed and position encoder, and
  
• Where the field and armature connections are for an encoder, or
• Where the field and armature connections are for a brushless DC motor.

Are you perhaps confusing an encoder with a resolver, or maybe a tachogenerator?

Lets take it one by one

Encoders serve as devices for detecting rotational and linear positions of machines such as servomotors, linear actuators, tachometers, and the like. They allow accurate positioning of such machines, and determination of such quantities as velocity and acceleration. Position encoders are used to generate an electronic signal that indicates an absolute mechanical position, or an incremental mechanical movement relative to a reference position. Rotary encoders and linear encoders are known. There are many known ways of generating a position signal, including magnetic sensors, capacitive sensors, and optical sensors. Linear and rotary type encoders are used extensively as detectors for control over feed rates and stop positions of various actuators. Classified in another way, these encoders fall into two broad types: incremental and absolute. The incremental type encoder detects and outputs increases and decreases in relative movement between coder and detector. A typical incremental encoder includes a wheel with tally marks arranged in a circular array about the wheel. A sensor detects the passage of tally marks as the orientation of the wheel is changed. Absolute position encoders provide a readout of absolute position, thereby avoiding the problem with initialization movements that plagues incremental encoders. The absolute type encoder reads the relative position between coder and detector using a fully periodic array pattern scale of the coder. The relative position, after suitable processing, is output as an absolute position. Encoders can employ different ways to detect angular or rotary motion such as mechanical means utilizing brush contacts or magnet/inductive methods. But the most common, reliable and widely used devices are non-contact optical receptors employed by optical encoders. An optical encoder comprises a light emitting unit which emits a light beam and photoelectric converting elements which are disposed behind two diffraction gratings. A photoelectric rotary encoder is a kind of a sensor that is used to detect rotation angle, rotation number, rotational speed and the like of a rotating unit as digital signals. Optical shaft encoders generally consist of an optical shutter, such as a disk or drum, which is rigidly attached to the shaft whose position is to be determined. Such encoders are used in various types of machinery and machine tools where information concerning the precise angular relationship or speed between a shaft and another component is needed.

Thank you google for this information.

Where the field and armature connections are for an encoder

There are none , encoders are meant to be part of control circuit and not be in power line.

Where the field and armature connections are for a brushless DC motor.

Oops I overlooked the BRUSHLESS part.

If you read carefully, you'll find that (in this context) your big paragraph boils down to the statement: "there is no difference between position and speed encoders - it's the way you process the signals that yields the information".

Fine, still the encoders are called by different names. aren't they? In my shop we had one particular problem when a rotary encoder was damaged , new one was relaying reverse position information though the DOR of motor was ok.Meaning when the sideguide was closing, opening info was coming and speed was also positive which should have been negative. This could be set right only after checking all the 12 bits one by one. Thus my original question came.

"Fine, still the encoders are called by different names. aren't they?"

No.

Are you sure you're not confusing incremental and absolute encoders? These may loosely be called "speed" and "position" encoders, but in fact both can provide speed and positional information.

The major difference in use is that the absolute encoder will give the correct angular position of the input shaft after cycling the power (even if the shaft was rotated while the power was off).

I wouldn't say the increment encoder can provide positional information. It will just tell you which way you are going and how fast.

If you turn off the electronics, (and to be sneaky, rotate the motor by hand), and turn the electronics back on, the absolute encoder will know the position (within a revolution), but the incremental will not have a clue, and will have to go through a re-homing process.

Rufus

"I wouldn't say the increment encoder can provide positional information. It will just tell you which way you are going and how fast."- it will also tell you how far you have gone!

Incremental encoders are frequently used for position feedback - I use them myself for such, but you may want to look at the results of this google search.

True, they need to be driven to a home or reference position before the absolute position is known. This is often the first action after powering up a CNC machine anyway, whether the encoders are incremental or absolute (as you say, the absolute encoder will not usually retentively count the number of turns of the shaft, so can only give the shaft angle).

It provides pulse and direction only, you have to count the pulses to generate positional information externally. The signals you will get at, say, position 15 degrees, are the same signals you are likely to get at 195 degrees.

If an absolute encoder is used for more than 360° of shaft rotation, the turns must be counted. Switch off the power, rotate the shaft manually through one full turn (or more) and switch on again. How well will your system be able to control its position?

Counting is very easy. Most people learn to do it when they are small children. It is a fundamental function of all control systems. Very few programmable logic controllers (and the like) do not have the ability to accept incremental encoder inputs, and derive position information from them. Many motion control systems accept input from incremental encoders for position control. It is far easier to derive position information than speed from any type of encoder (and I don't class a tachogenerator as an encoder).

What is your problem?

My problem must have been distinguishing between "derive" and "read".

(The word that was originally used was "provide")

But, really now: "Counting is very easy..." ?

Do you find counting difficult? If so, maybe you're in the wrong place.

Oh and by the way (if you're going to get picky with semantics), an "increment [sic] encoder" will not "tell you" anything.

An incremental encoder will go round and round and round (just like an absolute encoder).

Appropriate circuitry may be connected to derive the direction, relative position (and with rather more difficulty, speed) information from the output signals. The result provided may be read by the control system (or by a human, if a suitable display device is connected to the electronics).

Still have a problem?

Another problem I have is confusing intelligence with maturity level.

You are clearly very intelligent and have many good posts, and I respect you for that.

You are welcome to have the last word on this branch of the thread because this is mine.