axcontrol, Author at AX Control, Inc.

A Quick Primer on Servo Position Controllers

Servo systems are widely used in manufacturing, laser processing equipment, industrial robotics, and various robotic and motor applications. But if you’re just starting to dip your foot into the world of servos there are plenty of terms you probably have never heard of.

A servo position controller (plc servo motor kontrolü) — Servo position controller.

Here’s a short overview of some of the most common servo-related questions. Reading through these snapshots should help you understand some of the most common terms related to servos.

What is a servo system?

A servo system, or servo mechanism, includes a moving device, a sensor, and some sort of logic that can compare a desired set point to an actual point, then drive the moving device until the desired and actual match.

In real terms, this usually means the moving device is an electric motor, the sensor is an encoder, and the logic is supplied by a motion controller.

What is a motion controller?

Motion controllers create controlled motion profile sequences for other devices while monitoring and adjusting for speed and position errors. These are the brain of a motion control system and typically work as a closed circuit, comparing feedback signals to actual output so as to reduce errors to zero.

A number of different kinds of motion controllers exist. This includes autonomous controllers, PC-based controllers, and microcontrollers, or MCUs. These controllers can be open loop or closed loop systems.

What’s the difference between an open-loop and a closed-loop system?

Open loop systems are simple and cheap, but don’t rely on feedback loops for adjustment. Closed-loop systems tend to be more complex and more expensive, but can also offer more finely-tuned outputs. Here’s an example of the difference between the two.

It’s July and your air conditioner suddenly dies. You go out and buy two fans, one for your living room and one for your bedroom. The living room fan is a cheap box fan with an on/off switch, but the one for the bedroom actually has a thermostat that controls the fan.

All day long, both fans run. As night falls and the temperature begins to drop, the box fan in the living room keeps going, even though now the surrounding temperature has gotten so comfortable the moving air is too much all the time. But the bedroom fan is different. It’s cycling on and off, keeping that room at a nice temperature. If the room starts to heat back on it kicks back on for a few minutes, but otherwise, it takes a break.

That’s the difference between an open-loop (no feedback) and a closed-loop (with feedback) system.

What’s the difference between servo brushed and brushless systems?

Most motors used in servo systems tend to be brushless but from time to time you may come across a brushed permanent magnet motor. What’s the difference?

Brushed DC motors are built using wound wire coils, called an armature. These work as an an electromagnet inside the motor that work against the magnets located on the outside of the motor. A rotary switch called a commutator reverses the polarity of the armature twice per cycle. This is what creates the current running through the brushed motor.

By contrast, the brushless motor has a magnet as its external rotor. Inside it has a specialized sensor that tracks the rotor position and three phases of driving coils. These coils are activated one after another by the controller via reference signals.

Other terms to research

If you want a deeper understanding of servo position controllers, we suggest doing independent research on these terms:

Accumulated Pulse
Angular Position
Deviation Counter
Encoder
Gain Adjustment
Incremental Encoder
PID Control
Position Control
Resolution
Speed Control

Contact AX Control today for your Servo and motor needs.

Why do PLC Manufacturers Provide Derating Curves?

PLC power supply, 57c493. Power supplies like this usually include derating curves in their manuals. — Reliance Electric 57c493 Power Supply for the Automax PLC

If you’ve done any work around a PLC (programmable logic controller) or DCS (distributed control system), you’ve probably had an opportunity to see mention of derating curves. These are often included for the power supply. But why provide these little charts? What are they good for?

Derating curve example. Derating curves are used for equipment like PLC power supplies. — Source: Wikimedia Commons

Heat dissipation curves are usually part of the product manual. They can help the end-user determine the de-rated power value at the expected operating temperature. In manufacturing settings where power supplies may be enclosed, temperatures can quickly become elevated.

But increased heat can reduce output due to a loss of thermal dissipation. Frequently, this loss is due to the breakdown of conductive fillers that provide the electrical connection between a substrate and mounted components. Accordingly, if the temperature becomes too high, the conductive particles that provide electrical connections become entrapped in cured adhesive and can no longer function as they should.

PLC Derating charts offer insight into just how much heat will affect output. This offers the end-user the opportunity to consider upsizing their power supply to compensate, or to provide external cooling to reduce the amount of heat. This is often the best course of action since heat will damage and often limit the lifespan of components. With this in mind, heat control should always be part of your plan.

Need a power supply for your Reliance AutoMax system? We have many in stock, including several revisions of the Reliance 57c493 Power Supply.

Motors and Drives: Typical Repairs

Close up image of a repair in process. Motors and drives sometime need repairs. — Sometimes repairs are needed. We can help.

At AX Control we do a lot of repairs on motors and drives. Not only do we offer repair services for our customers, but we also examine every reconditioned part leaving our warehouse for defects and optimize its performance before it gets boxed up for transit. Our people get plenty of hands-on time with all sorts of drives and motors.

Skilled technicians take care of all our repair work. We back up that work with a 2-year warranty for AC/DC and Servo Drives, and a one-year warranty for Motors.

But do you know what may lead to your components needing repair? We get there’s a lot to know about industrial automation equipment. We thought we would offer up a list of the most common causes we’ve noticed, partitioned by type of drive or motor.

AC Drives

There have been many technological advances in the field of AC Drives that have brought more features to these drives even as they’ve decreased in size and cost.

AC Drive from Reliance Electric — The 15V4150 Reliance GV3000 15 HP AC Drive is one AC drive in our stock.

The primary driver of repairs in AC Drives, without a doubt, is heat. This may come from various sources, but when you get to the root of the problem heat is the cause of the damage.

Here are a few of the most common ways heat strikes:

A dusty environment. When fans aren’t cleaned on a regular basis, the drive can’t pull air through, and heat builds up. Protection is easy: maintain a regular maintenance schedule and keep fans and other heat dissipating equipment clean. Try to cut down on the amount of dust in your environment through mitigation.
Power spikes. These can come from other machines, from lightning strikes, or from your main power line. You can often limit these problems by adding a line reactor in front of your drive system to protect from transients and power surges.
Too much power draw. If a drive is attached to a poorly-maintained motor, such as one with ungreased bearings, too much bearing wear, or shaft imbalance, this can cause a mechanical overload that increases the motor’s demand on the drive. Connected systems have to be maintained together or they will die together.