does the gear box affecting the positioning value????

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i m connecting a servo motor to a gear box with direct coubling method. This gear box is in ratio 1 to 5. Does this ratio will affecting the value of positioning of servo motor??? I just know that the gear box will affect the result of the running speed. Thanks a lot.
 
It will depend on where your position feedback device is located.

If it's mounted on the motor, which is the case in the majority of applications, then the ratio must be figured into the calculation of encoder counts per unit of travel.

If it's mounted on the load, the gearbox ratio doesn't enter the calculation.
 
It's Saturday morning and most of my chores are done (I still have to mow the lawn). And so, I just started typing...


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The following assumes that an 8000-Count Encoder is mounted on the motor.

TAKE-OFF POINT-A:

The Gear Box and Point-A are directly coupled - the ratio is 1-to-1.
To get 1 Rev (OUT) at Point-A requires 1 Rev (IN) from the Gear Box.
To get 1 Rev (OUT) from the Gear Box requires 5 Revs (IN) from the Motor.
If the encoder is mounted at the motor...
If the motor encoder produces 8000 Counts per Rev, then it takes 5 times 8000 = 40,000 counts to move Point-A 1 Rev.
If the encoder is mounted at Point-A...
If the encoder produces 8000 Counts per Rev, then 1 Rev at Point-A produces 8000 counts.

TAKE-OFF POINT-B:

Point-A and Point-B are coupled using a 2-IN to 1-OUT ratio.
To get 1 Rev (OUT) at Point-B requires 2 Revs (IN) from Point-A.
To get 2 Revs (IN) at Point-A requires 2 Revs (OUT) from the Gear Box.
To get 2 Revs (OUT) from the Gear Box requires 10 Revs (IN) from the motor.
If the encoder is mounted at the motor...
If the motor encoder produces 8000 Counts per Rev, then it takes 10 times 8000 = 80,000 counts to move Point-B 1 Rev.
If the encoder is mounted at Point-B...
If the encoder produces 8000 Counts per Rev, then 1 Rev at Point-B produces 8000 counts.

TAKE-OFF POINT-C:

Point-B and Point-C are coupled using a 1-IN to 1-OUT ratio.
To get 1 Rev (OUT) at Point-C requires 1 Rev (IN) from Point-B.
To get 1 Rev (OUT) at Point-B requires 2 Revs (IN) from Point-A.
To get 2 Revs (IN) at Point-A requires 2 Revs (OUT) from the Gear Box.
To get 2 Revs (OUT) from the Gear Box requires 10 Revs (IN) from the motor.
If the encoder is mounted at the motor...
If the motor encoder produces 8000 Counts per Rev, then it takes 10 times 8000 = 80,000 counts to move Point-C 1 Rev.
If the encoder is mounted at Point-C...
If the encoder produces 8000 Counts per Rev, then 1 Rev at Point-C produces 8000 counts.

TAKE-OFF POINT-D:

Point-C and Point-D are coupled using a .5-IN to 1-OUT ratio (or, 1-IN to 2-OUT, if you prefer).
To get 1 Rev (OUT) at Point-D requires .5 Rev (IN) from Point-C.
To get .5 Rev (OUT) at Point-C requires .5 Rev (IN) from Point-B.
To get .5 Rev (OUT) at Point-B requires 1 Revs (IN) from Point-A.
To get 1 Revs (IN) at Point-A requires 1 Rev (OUT) from the Gear Box.
To get 1 Rev (OUT) from the Gear Box requires 5 Revs (IN) from the motor.
If the encoder is mounted at the motor...
If the motor encoder produces 8000 Counts per Rev, then it takes 5 times 8000 = 40,000 counts to move Point-D 1 Rev.
If the encoder is mounted at Point-D...
If the encoder produces 8000 Counts per Rev, then 1 Rev at Point-D produces 8000 counts.

So, now you have all of these take-off points. Any number of possiblities are available to you as far as producing motion.

In general, the output from the Servo Motor is ultimately expected to produce some kind of linear motion and/or circular motion.

This is not to say, strictly linear or circular. There are all kinds of ways to produce different kinds of motion.

Circular ->
Conveyor Belt
CAM Action
Toggle Action (Back & Forth kinda thing, like maybe a Pendulum)
etc, etc., etc....
You are limited only by your imagination and the Laws of Physics.

Position/Velocity/Acceleration at, or after, the final stage can be measured two ways: linearly and/or angularly.

Linear Position is measured in inches, feet, meters, etc.
Linear Velocity is measured in inches/sec, feet/sec, meters/sec, etc.
Linear Acceleration is measured in inches/(sec*sec), feet/(sec*sec), meters/(sec*sec), etc.

Angular Position is measured in Revs, Degrees or Radians
Angular Velocity is measured in Revs/sec, Degrees/sec or Radians/sec
Angular Acceleration is measured in Revs/(sec*sec), Degrees/(sec*sec) or Radians/(sec*sec).

I said... "...can be measured two ways: linearly and/or angularly."

This means you can indeed measure linear motion in an angular fashion as well as angular motion in a linear fashion.

For example, if a motor drives an eccentric and the eccentric is connected to a slide, then the position of the slide can be expressed in...

Linear terms (relative to full back)
full back = 0",
1/4 forward = 3",
full forward = 6",
1/4 back = 3"


Angular terms (relative to full back)
full back = 0-Degrees,
1/4 forward = 90-Degrees,
full forward = 180-Degrees,
1/4 back = 270-Degrees.

At some point, you are going to need to know the action/reaction relationship between the initial-driver and the final-driven.

Whether you should measure the motion at the driver-end (motor) or the driven-end depends on the kind of accuracy you need and the manner in which your measuring devices are measuring.

If you have a motor-mounted encoder that produces 8000 Counts per Rev, and your system requires 20 Motor Revs to get 1 Rev at the final stage, and that 1 Rev produces 3-inches of linear travel, then you get...

20 Rev * (8000 Counts/Rev) ==> 1 Rev ==> 3-Inches of linear travel

160,000 Counts / 3 Inches ==> 53,333 Counts per Inch (Actual = 53,333.333...Counts per Inch)

If you placed the same encoder at the final stage, then you would only get...

1 Rev * (8000 Counts/Rev) ==> 3-Inches of linear travel

8000 Counts / 3 Inches ==> 2,666 Counts per Inch (Actual = 2,666.666...Counts per Inch)

You could install yet another linkage from the last stage to the encoder. If the linkage was 1-IN to get 20-OUT then you would have the same precision as if you mounted the encoder on your motor.

Of course, there is always the concern that the PLC can indeed catch all of those pulses! Your PLC must have a reliable scan rate that is at least twice as fast as the pulses might occur.

Alternatively, you could use a high-speed counter. A high-speed counter also has a limit on the number of pulses it can count but the limit is quite a bit higher than the PLC can handle.

Now that the dew has evaporated off of the lawn, I better go mow it.
 
Your gear box will have some backlash (free movement as the gears need some clearance) associated with it. Precision gearboxes will give you a positioning accuracy spec. Some servo controllers will allow you to attach a secondary encoder on your load to compensate for inaccuracies.
 

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