The Advantages and Working of a Servo Motor

Servo control, which is known as "motion control" or "robotics" is used in industrial processes to move a specific load in a controlled fashion. These systems can utilize either pneumatic, hydraulic, or electromechanical actuation technology. The choice of the actuator type (i.e. the device that provides the power to move the load) is based on power, speed, precision, and cost requirements. Electromechanical systems are typically used in high precision, low to medium power, and high-speed applications. These systems are flexible, efficient, and cost-effective. Servo Motors are the actuators used in electromechanical systems. Through the interaction of electromagnetic fields, they generate power.

Servo Motor Advantages

Servo motors with related controls provide very precise and repeatable control of both position and velocity, and its various feedback parameters allow users to closely monitor the dispensing process and detect any abnormalities before they can become major problems. There are three main advantages to servo drive technology in adhesive and sealant dispensing equipment:

1. Servo drive motors allows you to have preset, multi-segment shot profiles, with each segment having its own material volume and flow rate, and with the ability to smoothly blend the motion of each segment into the next one in the profile.  The user can then select from among these preset profiles before initiating the dispense cycle.

2. Servo technology also allows you to continuously vary the material flow rate during the dispense cycle based upon a command reference from the process control.  This allows the user to either apply a continuous bead of material with varying bead widths, or conversely, to maintain the same bead width despite changes in the applicator's linear speed, for example when a robot slows down to negotiate a complex curve.

3.  A major advantage to servo control is its ability to reliably maintain the commanded volumetric flow rate of material despite changes in the physical conditions of the dispensing system or its environment.  Examples of these types of changes are variations in material viscosity, and therefore in the back pressure it generates during the dispense cycle, due to such things as variations in ambient temperature or differences in batches of material; variations in the plant utilities supplied to the dispensing equipment, such as air pressure or electrical voltage; and load changes due to physical wear on the dispensing equipment as it ages.  The servo drive simply increases or decreases the amount of current it supplies to the motor as required to maintain the commanded material flow rate, up to the current limits of the drive.  If those limits are ever exceeded, the drive generates a fault and stops the cycle, which prevents the customer from unknowingly making out of spec parts.

Working of a Servo Motor

Servo motors are utilized to control position and speed very precisely, but in an easy case, only position may be controlled. Mechanical position of the shaft can be sensed by using a potentiometer, which is coupled with the motor shaft through gears. The current position of the shaft is converted into electrical signal by the potentiometer, and the compared with the command input signal. In modern servo motors, electronic encoders or sensors are used to sense the position of the shaft.

Command input is given according to the required position of the shaft. If the feedback signal differs from the given input, an error signal is generated. This error signal is then amplified and applied as the input to the motor, which causes the motor to rotate. And when the shaft reaches to the required position, error signal becomes zero, and hence the motor stays standstill holding the position.

The command input is given in the form of electrical pulses. As the actual input applied to the motor is the difference between feedback signal (current position) and applied signal (required position), speed of the motor is proportional to the difference between the current position and the required position. The amount of power required by the motor is proportional to the distance it needs to travel.

Connecting a Servo Motor

Servo motors typically have three wires. The power wire, usually red, is connected to teh power rail. The ground wire, ususally black or brown, is connected to the ground rail. The third wire, usually yellow or oragne, is the signal wire and is connected directly to a digital pin on the Arduino. The Arduino can normally directly supply power to a servo motor, but when using serveral servo motors, you ned to separate the Arduino power supply to the servo power supply to avoid brown outs. Servo motors, even if they do not always act like typical motors, still have a small motor inside and can draw large amounts of current, far more than what the ATmega can deliver.



Before using servo motors, you must import the Servo library. You can do this either by importing the library. You can do this either by importing the library through the Arduino IDE menu (Sketch Import Library servo) or by manually typing:

#include (servo.h)

In your software, you must first creat a new servo object before issuing instructions. You must create one object per servo motor (or group of servo motors) to contorl.

Servo frontWheels;
Servo rearWheels;

To tell the Arduino which pins the servo motors are connected to, call attach(), specifying the pin, and optionally, specifying the minimum and maximum pulse size.

servo attach (pin)
servo attach (pin, min, max)

By default, Arduino uses 544 microseconds as the minimum pulse length (equivalent to 0 degrees) and 2,400 microseconds as the maximum pulse width (equivalent to 180 degrees.) If your servo motor has different settings for a maximum and minimum pulse, you can change the values in attch () by specifying the duration in microseconds. For example, a servo motor that uses a 1 millisecond minimum and 2 millisecond maximum can be configured like this:

servo.attach (pin, 1000, 2000);

From then on, the Arduino automatically calculates the length of the pulse according to the wanted angle but will not issue commands until a function specifically orders the servo motor to move.

How to Wire Your Stepper

A stepper motor can come with assortment of wire configurations. The type of motor you’ve selected will determine the wire setup. Most commonly stepper motors come with four, five, six, or eight wires.

To begin, if your stepper motor only has four wires, this means it can only be used with a bipolar driver. You will notice each of the two phase windings has a pair of wires, use your meter to identify the wires.

4 Wire Stepper Motors

W numerous motors make the most of 6- and 8-wire configurations, the majority of bipolar (1 winding per phase) stepper motors offer 4 wires to connect towards the motor windings. A fundamental 4-wire stepper motor is shown in Figure 1. Connecting this motor kind is extremely simple and merely demands connecting the A and A' results in the corresponding phase outputs in your motor drive.

There's not a lot detailing right here. The 4 wire stepper denotes a single feasible configuration and that's of a bipolar stepper motor. We don't have to bore us with particulars like whether or not this motor is variably reluctance, permanent magnet or hybrid as that only relates to building. What we have to understand is the fact that two wires are for PHASE A and also the other two wires are for PHASE B. Which 1 is PHASE A and which 1 is PHASE B is type of arbitrary.

If you have the motor datasheet then you know which wires represent which. But if you do not have this document, just do a quick continuity test and determine which two wires are connected together through an inductor. You can also use a simple BACK EMF test in which you short two leads together. If it is harder to move the rotor, then those two wires form one of the phases. If the rotor moves as easy as with no wires crossed over, then those two wires are not connected through a winding. Keep on going until you find both phases.

The Five Wire Stepper

This motor is also equally easy to deal with as it can only be wired as an unipolar stepper motor. There is really no way to use this motor in a bipolar configuration as all the center taps have been shorted together. Do note this motor style is quite rare. I think these motors were more common a few years ago when unipolar motors were much more cost effective. Today, however, since driving bipolar motors is not a superbly expensive endeavor, the five wire stepper motor is not as common as it used to be. Instead, the six wire stepper motor has replaced the five wire stepper motor because of what we will see next. If you do happen to get your hands on a five wire stepper motor, here is how you wire it:

The Six Wire Stepper

We can now start to complicate things. As it turns out, the six wire stepper is optimized to operate as a unipolar stepper motor but it is rather doable to use it as a bipolar stepper motor as well. The trick, however, is that there are multiple ways of wiring the motor as bipolar and it all depends on what you will want to achieve. For example, do you want speed, or do you want torque? Maybe you want both? Well, I can only promise one or the other by utilizing conventional drive technology. If you want both (torque and speed) you will need to resort to some highly advanced drive technology, which although available out there, is not in the$5.00 range.

So lets first see how to wire the six wire stepper as a unipolar motor:

A bipolar driver will require you use only one end wire and one center tap of each winding. With a five wire stepper motor the wire setup is very similar to the six wire driver, the main difference being the center taps are connected together internally, bringing it out as one wire. This will make the motor only function as a unipolar driver. Also, the windings will be impossible to identify without trial and error, the best you can do is try to identify the center tap wire since it has half the resistance.

Finally there is the eight wire stepper motor, which is much like the six wire. The difference being that the two phases are split into two separate windings. When this is done it allows for the stepper motor to be connected as a unipolar motor, as well as three different bipolar combinations.

Gearmotor selection/tech questions - DIY 3D printer

Gears, the universal symbol of productivity, have been a major cog in industry for hundreds of years. Before electromagnetic rotating machines were even a glimmer in Michael Faraday's eyes, there were gears.

Early gears had been produced from wood with cylindrical pegs for cogs. They had been frequently lubricated with animal fat, vegetable oils, as well as water. Gears had been utilized then for exactly the same factors they're now - simply because of their force multiplying properties. You’d discover them on ships (hoisting anchors), in catapults (tensioning fly arms), and on a number of machinery powered by wind and water wheels.

The choice of motor will depend largely on what software interface you plan to use. If you want to use pre-made software, then you might want to stick to the type of actuator they use/ suggest: it might be a stepper motor, servo or DC gear motor + encoder.

If you plan to make your own software interface, then using the same type of actuator throughout the machine has its advantages - and we'd suggest you again use a stepper motor.

If you really wanted to use a DC gear motor with encoder, you'd need a DC motor controller (serial or PWM) and connect the encoder output to the microcontroller. You would then need to program the microcontroller separately from the software you use to slice the part. It's quite involved. The Arduino would provide the 5V power for the encoder and read the states of the onboard IR sensors.

Gear types

There are many types of gears available today, each with specific advantages and limitations. Topping the list — at least for big jobs — are worm, spur, and helical gears.

Spur gears are compact as well as efficient, but they tend to be noisy and don’t always handle shock as well as worm gears. They can achieve about 10:1 ratio per stage.

Worm gears are relatively inexpensive, achieve high ratios in a single gear set (up to 100:1), and are available in right-angle configurations. They also run quietly and tolerate high shock loads. However, they are less efficient than other forms of gearing.

Spur gears by contrast are much more most likely to create noise, much less tolerant of shock in comparison to worm gears, and slightly much more costly. Around the plus side, they're compact, effective, and accessible in parallel-shaft arrangements. They're also simple to discover simply because numerous producers create them. Spur gear ratios are usually ten:1 per stage.

Helical gears are similar to spur gears, but they have angled teeth. Because helical gears have more tooth contact area than spur gears, pound for pound they can carry heavier loads, though not quite as efficiently. They are somewhat more expensive as well and, depending on the configuration, may produce thrust loading on the bearings. Versatility is a plus, however, as helicals can be used on non-parallel, even perpendicular, shafts, achieving a 10:1 ratio per stage.

Types of Stepper Motor and Their Significances

A stepper motor is definitely an electromechanical device that induces mechanical movements by converting electrical pulses. It's driven by digital pulses rather of constantly applied voltage, and it could step or rotate in fixed angular increments. Stepper motors are usually utilized in applications that need position manage. They're assumed to adhere to digital directions when utilized inside a stepper motor method style. They are classified as open-loop systems due to their lack of feedback to keep control of the position. Stepper motors can be classified into three basic types:

Variable reluctance stepper motor:

The VR stepper motor is characterized by the fact that there is no permanent magnet either on the rotor or the stator. The construction of a 3-phase VR stepper motor is shown in figure.

The stator is produced up of silicon steel stamping s with inward projected even or odd quantity of poles or teeth (generally the amount of poles of stator is definitely an even quantity). Every and each stator pole carries a field coil or thrilling coil. In case of even quantity of poles the thrilling coils of opposite poles are connected in series. The two coils are connected such that their MMF get added. The mixture of two coils is recognized as phase winding.

The rotor is also made up of silicon steel stamping s with outward projected poles and it does not have any electrical winding. The number rotor poles  should not be equal to the number of stator poles to have self starting capability and bi-directional rotation. The width of the rotor teeth should be equal to the width of stator teeth.

Permanent magnet stepper motor:

Permanent Magnet (PM) motors use permanent magnet rotors and are commanded by electrical pulses. They are widely used in printers, copies, and scanners, among other applications. They are also used to operate valves in household water and gas systems as well as drive actuators in automotive applications.

One of the main benefits of the PM stepper motor is that, in addition to being electronically commutated like a brushless DC motor or any other type of stepper motor, the PM stepper motor requires no “teeth” as are typically found in the variable reluctance (VR) stepper motor. This makes the permanent magnet stepper an extremely popular choice for many motor applications.

Hybrid Stepper motors:

Hybrid stepper motors provide excellent performance in areas of torque, speed, and step resolution. Typically, step angles for a hybrid stepper motor range from 200 to 400 steps per revolution. This type of motor provides a combination of the best features available on both the PM and VR types of stepper motors. Hybrid stepper motors enhance the performance in terms of torque, speed, and step resolution, so they are useful in applications that require high stepping speeds for operation. They come in step angles designed at 0.9 degrees, 1.8 degrees (commonly used), 3.6 degrees, and 4.5 degrees.

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How to Select the Right Gearmotor

Gear motors are crucial elements of any systems they drive. They're by their extremely nature the muscle that moves your machinery. That tends to make your gear motor supplier an integral a part of your provide chain. That stated, does your present Gear reduction motors supplier provide you with the tools and assistance that you simply have to rapidly, effortlessly, and reliably do your job? Make certain your supplier can answer these concerns to address the discomfort points that numerous gear motor clients like your self frequently encounter. If they can?ˉt, it might be time for you to appear someplace else.

Because the motor or gearmotor choice procedure starts, the designer should collect the relevant technical and industrial specifications. This initial step is frequently overlooked, however it is really a crucial element within the style procedure. The gathered style inputs info will then be utilized within the choice procedure and can dictate the perfect motor for the application. Failure to collect the correct inputs can lead the designer down an untended path. Because of this, it's useful to make use of the Application Checklist (Table two) when creating the motor specification. These parameters, together with some project particular specifications, will probably be useful when navigating the choice procedure.

Next, the designer should think about what kind of motor technologies very best suits the intended application. Utilizing the style inputs, the Motors Fast Reference Guide (Table three) may be utilized as a choice matrix within the initial step from the choice procedure. This reference guide particulars 4 typical motor kinds and offers common info to think about when choosing every motor. Simply because every application has its personal distinctive traits, it's essential to figure out which from the parameters (e.g. horsepower, efficiency, life, beginning torque or noise ratings) are most significant towards the application below consideration. Throughout the motor choice procedure, by taking a look at the needed speed and torque from the application, it ought to turn out to be evident towards the designer when the motor selected demands a gearbox to meet the essential specifications. If a dc worm gear motor is essential for the application, an additional degree of complexity will probably be added and a number of extra criteria require to become evaluated.

Conceptually, motors and gearboxes can be mixed and matched as needed to best fit the application, but in the end, the complete gearmotor is the driving factor. There are a number of motors and gearbox types that can be combined; for example, the right angle worm, planetary and parallel shaft gearboxes can be combined with permanent magnet DC, AC induction, or brushless DC motors. Though there are a vast number of different motors and gearboxes combinations available, not just any one will work for the application. There will be certain combinations that will be more efficient and cost-effective than others. Knowing the application and having accurate ratings for the motor and gearbox is the foundation for successfully integrating the gearmotor into the system.

Some tips for you:

1. Knowing the Application Requirements

Knowing the specific requirements of your application will help you determine if you need a DC or AC gear motor, and the specific type. Such requirements include:

    Environment: Application and ambient temperature, and ingress protection (IP) rating
    General requirements: Envelope size, side and overhung loads, lubrication type, mounting orientation and mounting type
    Input power source: maximum current (amps), frequency (hertz), voltage and control type
    Gear motor performance: Speed, torque, duty cycle, horsepower and starting and stall torque
    Gear motor specifications: Size, weight, desired noise level, desired maintenance level and life expectancy

2. Choosing the Right Motor

Use the list of application requirements that you gathered and compare them to the specifications of the DC and AC gear motors of interest, such as universal, brushless DC, AC induction and permanent magnet motors. In lieu of a pre-engineered motor, you may find that selecting a gearbox and motor separately may be best for your application.

3. Matching Performance Curves, Pull-Up Torque and Yield Strength to the Gear Motor

The proper torque and speed is important when choosing a gear motor. Use a manufacturer’s or vendor’s overall performance curves concerning torque, speed and efficiency to locate a gear motor that matches your requirements. Following discovering a couple of overall performance curves, yield strengths and pull-up torques that match the application’s requirements, examine the style limitations, like thermal traits, to narrow down the options.

By accounting for all of those elements inside your calculations when selecting a motor and gear ratio, you'll make sure that your robot functions as you intend the very first time about.  The instance issue in the finish of this tutorial will demonstrate how you can undergo the procedure of creating these calculations.

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Servo Motor Control with AdndroiDAQ

Servo motors are common motion control actuators that are used in robotics, radio controlled devices, 3D printers, and other motion drive systems. Using servo motors with AndroiDAQ is easy. This article contains a brief history of the servo motor, some basic operational background for servo motors, and how to connect and use a servo motor with the AndroiDAQ data acquisition and control module.

The steam engine governor is considered to be the first servo mechanism using a powered feedback system. Its first recorded use was in 1868, by JJL Farcot, who described steam engines and hydraulics for use in steering a ship. Servo mechanisms are considered to be closed-loop systems, as the mechanism uses position feedback to control its motion and final position.

Solution

Use PWM to control the width of pulses to a servo motor to change its angle. Although this will work, the PWM generated is not completely stable, so there will be a little bit of jitter with the servo.

You should also power the servo from a separate 5V power supply because peaks in the load current are likely to crash or overload the Raspberry Pi.

To make this recipe, you will need:

    5V servo motor (see “Miscellaneous”)

    Breadboard and jumper wires (see “Prototyping Equipment”)

    1kΩ resistor (see “Resistors and Capacitors”)

    5V 1A power supply or 4.8V battery pack (see “Miscellaneous”)

The breadboard layout for this is shown in Figure 5-1.

The 1kΩ resistor is not essential, but it does protect the GPIO pin from unexpectedly high currents in the control signal, which could occur if a fault developed on the servo.

The leads of the servo may not be the same as the colors indicated in Figure 5-2. It is common for the 5V wire to be red, the ground brown, and the control lead orange.

You can, if you prefer, power the servo from a battery pack rather than a power supply. Using a four-cell AA battery holder with rechargeable batteries will provide around 4.8V and work well with a servo. Using four alkali AA cells to provide 6V will be fine for many servos, but check the datasheet of your servo to make sure it is OK with 6V.

The user interface for setting the angle of the servo is based on the gui_slider.py program intended for controlling the brightness of an LED (“Controlling the Brightness of an LED”). However, you can modify it so that the slider sets the angle, between 0 and 180 degrees (Figure 5-2).

Open an editor (nano or IDLE) and paste in the following code. As with all the program examples in this book, you can also download the program from the Code section of the Raspberry Pi Cookbook website, where it is called servo.py.

Note that this program uses a graphical user interface, so you cannot run it from SSH.

You must run it from the windowing environment on the Pi itself or via remote control using VNC (“Controlling the Pi Remotely with VNC”). You also need to run it as superuser, so run it with the command sudo python servo.py:

from Tkinter import *
import RPi.GPIO as GPIO
import time

GPIO.setmode(GPIO.BCM)
GPIO.setup(18, GPIO.OUT)
pwm = GPIO.PWM(18, 100)
pwm.start(5)

class App:

    def __init__(self, master):
        frame = Frame(master)
        frame.pack()
        scale = Scale(frame, from_=0, to=180,
              orient=HORIZONTAL, command=self.update)
        scale.grid(row=0)


    def update(self, angle):
        duty = float(angle) / 10.0 + 2.5
        pwm.ChangeDutyCycle(duty)

root = Tk()
root.wm_title('Servo Control')
app = App(root)
root.geometry("200x50+0+0")
root.mainloop()

A Servo Motor consists of three major parts: a motor, a controller circuit, and a feedback system, which usually consists of a potentiometer which is connected to the motor’s output shaft. The motor typically drives a set of gears, which turns the output shaft of the motor and the potentiometer simultaneously. The potentiometer’s measured resistance controls the output angle of the motor shaft. This resistance is fed into the servo controller circuit and when the controller circuit detects that the motor position is correct, it stops the servo motor. If the controller circuit detects that the angle is not correct, for whatever the motor it trying to control, it will turn the servo motor the correct direction until the angle is correct. Normally a servo motor is used to control an angular motion of between 0 and 180 degrees. They typically can not turn any further unless they are modified, due to a mechanical stop which is build onto the main output gear or the potentiometer itself. Servo motors are generally used as a high performance alternative to the stepper motor.

Servo motors are controlled by sending to the servo’s control wire a pulse train of variable width, or better, a pulse width modulated signal. This pulse train has to have specific parameters such as a minimum pulse, a maximum pulse, and a repetition rate. This signal is typically derived and sent to the servo control wire by a microcontroller such as the one on AndroiDAQ. The shaft angle of the servo is determined by the duration of the pulse train sent. Given the pulse train’s constraints of having a minimum pulse, a maximum pulse, and a repetition rate, a neutral position is defined. This neutral position is where the servo has exactly the same amount of potential rotation in the clockwise direction as it does in the counterclockwise direction. This neutral position is typically always around 1.5 milliseconds.

Stepper Motor in Cllosed Loop Mode

Due to the limitations of open loop contorl, a closed loop control of stepper motors is used in practice. In a closed loop control, the input controller gets the information about the output through the feedback element. Hence the driver circuit receives the control signal which is based on the feedback information. So switching of the motor takes place by means of train of input pulses, which is generated on the basis of feedback from rotor. Such a switching of the motor is called as closed loop mode of operation of the stepper motor. The block diagram shown in the Fig.A.17 illustrates the closed loop operation of the stepper motor.

Let us consider a closed loop temperature control system. The temperature of the tank is required to be kept constant with the help of controlling the steam flow. There exists a valve whose position is controlled by a stepper motor, to control the steam flow. The actual temperature is sensed by using temperature sensor and feedback is given to the input controller. The input contorller has the reference information corresponding to the desired ideal temperature. It compare the feedback with this reference to generate the appropriate contorl signal. This control signal inturn is given to the driver circuit. The driver circuit control the excitation and logical sequence of the excitation of the phases. This drives the stepper motor and hence valve opening gets controlled appropriately so that steam flow gets controlled. This maintains the temperature of the tank constant. The logical operation of the system is illustrated in the block diagram shown in the Fig. A.18.

In a speed and position control systems, optical encoders coupled to the rotor shaft are used. Simlarly use of microprocessors as an input controller for better accuracy is very commen now a days. The Fig. A.19 shows the use of microprocessor in the closed loop control of the stepper motor.

What are the functionalities of these closed-loop stepper systems?

Closed-loop stepper with step-loss compensation will be the most typical kind of closed-loop stepper manage. The stepper drive operates as a micro-stepping drive and usually receives pulse and path commands to move towards the preferred position. An encoder tracks shaft or load position. If lost actions are detected, a compensation algorithm inserts extra actions to ensure that the motor shaft (or load) arrives in the preferred position. Usually, the stepper-motor drive has settings for two currents: The motor gets operating present when in motion and gets resting present when stopped.

In closed-loop stepper with load-position manage, the stepper drive operates as a typical microstepping drive and usually receives pulse and path commands to move towards the preferred position. The encoder (usually mounted around the load) monitors the load's position. The closed-loop algorithm dynamically tracks the load position and compensates all through the move profile. Usually, the motor gets operating present when in motion and gets resting present when stopped.

Closed-loop stepper servo manage treats the stepper motor like a high-pole-count brushless motor, turning it into a servomotor. A shaft-mounted encoder detects shaft position to figure out the correct present vector. A pulse and path interface might be provided within this kind of drive, however the position controller does not use actions to obtain towards the preferred position. Rather, closed-loop algorithms manage motor torque to servo the shaft into position utilizing a position manage loop (a PID loop for instance). Within this mode, the present setting is dynamic. The stepper drive delivers only the quantity of present required to move the motor shaft and load into position.