Initial Motor Research

From the Paper:

“Our system is synchronized as follows. Since the output frame rate of the PC graphics card is relatively constant and cannot be ?ne tuned on the ?y, we use the PC video output rate as the master signal for system synchronization. The projector’s FPGA also creates signals encoding the current frame rate. These control signals interface directly to an Animatics SM3420D ”Smart Motor” which contains ?rmware and motion control parameters resulting in a stable, velocity-based control loop that ensures the motor velocity stays in sync with the signals from the projector. As the mirror rotates up to 20 times per second, persistence of vision creates the illusion of a ?oating object at the center of the mirror.”

Reference:http://gl.ict.usc.edu/Research/3DDisplay/3DDisplay_USCICT_SIGGRAPH2007.pdf

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Looking into the SM34205D:

http://www.animatics.com/support/104.html

This company has many motors as well as firmware

http://www.animatics.com/download/catalog/Software_Overview_197.pdf

It looks like they have some sort of interface too

http://www.animatics.com/download/catalog/Application_Sizing_Equations_204-205.pdf

I’m not sure but it seems as if their needs to be physical parameters defined for the motor too, like how much torque is needed for the weight of the mirror.

http://www.animatics.com/download/catalog/Class_5_Connectivity_128.pdf

This has to do with connectivity.

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Servomechanism:

A servomechanism, sometimes shortened to servo, is an automatic device that uses error-sensing negative feedback to correct the performance of a mechanism.

The term correctly applies only to systems where the feedback or error-correction signals help control mechanical position, speed or other parameters. For example, an automotive power window control is not a servomechanism, as there is no automatic feedback that controls position---the operator does this by observation. By contrast the car's cruise control uses closed loop feedback, which classifies it as a servomechanism.

Position control

A common type of servo provides position control. Servos are commonly electrical or partially electronic in nature, using an electric motor as the primary means of creating mechanical force. Other types of servos use hydraulics, pneumatics, or magnetic principles. Servos operate on the principle of negative feedback, where the control input is compared to the actual position of the mechanical system as measured by some sort of transducer at the output. Any difference between the actual and wanted values (an "error signal") is amplified (and converted) and used to drive the system in the direction necessary to reduce or eliminate the error. This procedure is one widely used application ofcontrol theory.

Speed control

Speed control via a governor is another type of servomechanism. The steam engine uses mechanical governors; another early application was to govern the speed of water wheels. Prior to World War II the constant speed propeller was developed to control engine speed for maneuvering aircraft. Fuel controls forgas turbine engines employ either hydromechanical or electronic governing.

Rotary or linear

Typical servos give a rotary (angular) output. Linear types are common as well, using a leadscrew or a linear motor to give linear motion.

Servomotor

A servomotor is a motor which forms part of a servomechanism. The servomotor is paired with some type of encoder to provide position/speed feedback. A stepper motor is one type of servomotor. A stepper motor is actually built to move angular positions based upon each possible step around the entire rotation, and may include microsteps with a resolution such as 256 microsteps per step of the stepper motor. A servomechanism may or may not use a servomotor. For example, a household furnace controlled by a thermostat is a servomechanism, because of the feedback and resulting error signal, yet there is no motor being controlled directly by the servomechanism.

RC servos

Small R/C servo mechanism

1. electric motor

2. position feedback potentiometer

3. reduction gear

4. actuator arm

For more details on this topic, see Servo (radio control).
RC servos are hobbyist remote control devices servos typically employed in radio-controlled models, where they are used to provideactuation for various mechanical systems such as the steering of a car, the control surfaces on a plane, or the rudder of a boat.
Due to their affordability, reliability, and simplicity of control by microprocessors, RC servos are often used in small-scale roboticsapplications.
RC servos are composed of an electric motor mechanically linked to a potentiometer. A standard RC receiver sends pulse-width modulation (PWM) signals to the servo. The electronics inside the servo translate the width of the pulse into a position. When the servo is commanded to rotate, the motor is powered until the potentiometer reaches the value corresponding to the commanded position.

Types of performances

Servos can be classified by means of their feedback control systems[3|http://en.wikipedia.org/wiki/Servo_motors#cite_note-3]:

• type 0 servos: under steady-state conditions they produce a constant value of the output with a constant error signal;
• type 1 servos: under steady-state conditions they produce a constant value of the output with null error signal, but a constant rate of change of the reference implies a constant error in tracking the reference;
• type 2 servos: under steady-state conditions they produce a constant value of the output with null error signal. A constant rate of change of the reference implies a null error in tracking the reference. A constant rate of acceleration of the reference implies a constant error in tracking the reference.

The servo bandwidth indicates the capability of the servo to follow rapid changes in the commanded input.

Reference:http://en.wikipedia.org/wiki/Servo_motors

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Stepper Motor:

There are four main types of stepper motors:[1|http://en.wikipedia.org/wiki/Stepper_motor#cite_note-R000534-1]

1. Permanent magnet stepper (can be subdivided into 'tin-can' and 'hybrid', tin-can being a cheaper product, and hybrid with higher quality bearings, smaller step angle, higher power density)
2. Hybrid synchronous stepper
3. Variable reluctance stepper
4. Lavet type stepping motor

Applications

Computer-controlled stepper motors are a type of motion-control positioning system. They are typically digitally controlled as part of an open loop system for use in holding or positioning applications.
In the field of lasers and optics they are frequently used in precision positioning equipment such as linear actuators, linear stages, rotation stages, goniometers, and mirror mounts. Other uses are in packaging machinery, and positioning of valve pilot stages for fluid control systems.

A Stepper Motor System consists of three basic elements, often combined with some type of user interface (Host Computer, PLC or Dumb Terminal):

• Indexers - The Indexer (or Controller) is a microprocessor capable of generating step pulses and direction signals for the driver. In addition, the indexer is typically required to perform many other sophisticated command functions.

• Drivers - The Driver (or Amplifier) converts the indexer command signals into the power necessary to energize the motor windings. There are numerous types of drivers, with different voltage and current ratings and construction technology. Not all drivers are suitable to run all motors, so when designing a Motion Control System the driver selection process is critical.

• Stepper Motors - The stepper motor is an electromagnetic device that converts digital pulses into mechanical shaft rotation. Advantages of step motors are low cost, high reliability, high torque at low speeds and a simple, rugged construction that operates in almost any environment. The main disadvantages in using a stepper motor is the resonance effect often exhibited at low speeds and decreasing torque with increasing speed.[4|http://en.wikipedia.org/wiki/Stepper_motor#cite_note-4]

Theory

A step motor can be viewed as a synchronous AC motor with the number of poles (on both rotor and stator) increased, taking care that they have no common denominator. Additionally, soft magnetic material with many teeth on the rotor and stator cheaply multiplies the number of poles (reluctance motor). Modern steppers are of hybrid design, having both permanent magnets and soft iron cores.
To achieve full rated torque, the coils in a stepper motor must reach their full rated current during each step. Winding inductance and reverse EMF generated by a moving rotor tend to resist changes in drive current, so that as the motor speeds up, less and less time is spent at full current — thus reducing motor torque. As speeds further increase, the current will not reach the rated value, and eventually the motor will cease to produce torque.

Pull-in torque

This is the measure of the torque produced by a stepper motor when it is operated without an acceleration state. At low speeds the stepper motor can synchronize itself with an applied step frequency, and this pull-in torque must overcome friction and inertia. It is important to make sure that the load on the motor is frictional rather than inertial as the friction reduces any unwanted oscillations.

Pull-out torque

The stepper motor pull-out torque is measured by accelerating the motor to the desired speed and then increasing the torque loading until the motor stalls or misses steps. This measurement is taken across a wide range of speeds and the results are used to generate the stepper motor's dynamic performance curve. As noted below this curve is affected by drive voltage, drive current and current switching techniques. A designer may include a safety factor between the rated torque and the estimated full load torque required for the application.

Detent torque

Synchronous electric motors using permanent magnets have a remnant position holding torque (called detent torque or cogging, and sometimes included in the specifications) when not driven electrically. Soft iron reluctance cores do not exhibit this behavior.

Stepper motor ratings and specifications

Stepper motors nameplates typically give only the winding current and occasionally the voltage and winding resistance. The rated voltage will produce the rated winding current at DC: but this is mostly a meaningless rating, as all modern drivers are current limiting and the drive voltages greatly exceed the motor rated voltage.
A stepper's low speed torque will vary directly with current. How quickly the torque falls off at faster speeds depends on the winding inductance and the drive circuitry it is attached to, especially the driving voltage.
Steppers should be sized according to published torque curve, which is specified by the manufacturer at particular drive voltages or using their own drive circuitry.

Reference:http://en.wikipedia.org/wiki/Stepper_motor

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From our Proposal:
“SM34205D Smart Motor - $1200”

Budget Justification:

“Motor - The motor stays in sync with the signals from the projector to rotate the mounted mirror at a constant velocity so the images projected at a certain rate are displayed on the rotating mirror with the right timing. The SM34205D motor was chosen based on its torque, rpm, encoder resolution, and the fact that includes a controller, amplifier, encoder, and communication bus within one self contained package.”

Reference:https://docs.google.com/a/g.rit.edu/document/d/1UmYhzFUGWdrPVFzbwwVY80hfw0eJFAXPOavIVAmpeyc/edit#

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SM34205D:

• NEMA 34 size SmartMotor™
• Integrated motor, controller, amplifier, encoder and communications bus

SmartMotor™ Connector Pinouts| PIN | MAIN POWER | Specifications: | Notes | Diagram |

Torque curves below. How to understand them can partially be seen here:http://www.animatics.com/supports/knowledge-base/smartmotorkb/sizing-the-motor.html?tab=torquecurves

Each set of torque curves depicts limits of both continuous and peak torque for the given SmartMotor™ over their full range speed.

Higher supply voltages will shift the zero torque point of the curves further to the right in the peak torque curve. (operating higher than 70-75 degrees fahrenheit will reach thermal limit faster!

More voltage supply = faster velocity possible for the motor.

Reference:http://www.animatics.com/products/smartmotor/animatics/nema-34-3400-series/sm34205d.html

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Knowledge on Smart Motors:

http://www.animatics.com/support/knowledge-base.html

This site teaches you everything you need to know about smart motors (allegedly).

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SmartMotor 101:

• A smart motor is a control system containing a brushless DC servomotor, motion controller, encoder and amplifier.

Reference:http://www.animatics.com/supports/knowledge-base/smartmotorkb/smartmotor101.html

• Brushless DC servomotor: A servomotor based on the design of a conventional brushless DC motor, with the addition of an amplifier and a feedback device.

Reference:http://www.toolingu.com/definition-460330-42736-brushless-dc-servomotor.html

• Brushless

Main articles: Brushless DC electric motor and Switched reluctance motor

Typical brushless DC motors use a rotating permanent magnet in the rotor, and stationary electrical current/coil magnets on the motor housing for the rotor, but the symmetrical opposite is also possible. A motor controller converts DC to AC. This design is simpler than that of brushed motors because it eliminates the complication of transferring power from outside the motor to the spinning rotor. Advantages of brushless motors include long life span, little or no maintenance, and high efficiency. Disadvantages include high initial cost, and more complicated motor speed controllers. Some such brushless motors are sometimes referred to as "synchronous motors" although they have no external power supply to be synchronized with, as would be the case with normal AC synchronous motors.
Reference:http://en.wikipedia.org/wiki/DC_motor

• Motion Controller:

Motion control is a sub-field of automation, in which the position or velocity of machines are controlled using some type of device such as a hydraulic pump, linear actuator, or electric motor, generally a servo. Motion control is an important part of robotics and CNC machine tools, however it is more complex than in the use of specialized machines, where the kinematics are usually simpler. The latter is often called General Motion Control (GMC). Motion control is widely used in the packaging, printing, textile,semiconductor production, and assembly industries.

Overview

The basic architecture of a motion control system contains:

• A motion controller to generate set points (the desired output or motion profile) and close a position or velocity feedback loop.[1|http://en.wikipedia.org/wiki/Motion_control#cite_note-1]

• A drive or amplifier to transform the control signal from the motion controller into a higher power electrical current or voltage that is presented to the actuator. Newer "intelligent" drives can close the position and velocity loops internally, resulting in much more accurate control.
• An actuator such as a hydraulic pump, air cylinder, linear actuator, or electric motor for output motion.
• One or more feedback sensors such as optical encoders, resolvers or Hall effect devices to return the position or velocity of the actuator to the motion controller in order to close the position or velocity control loops.
• Mechanical components to transform the motion of the actuator into the desired motion, including: gears, shafting, ball screw, belts, linkages, and linear and rotational bearings.

The interface between the motion controller and drives it controls is very critical when coordinated motion is required, as it must provide tight synchronization. Historically the only open interface was an analog signal, until open interfaces were developed that satisfied the requirements of coordinated motion control, the first being SERCOS in 1991 which is now enhanced to SERCOS III. Later interfaces capable of motion control include Ethernet/IP, Profinet IRT, Ethernet Powerlink, and EtherCAT.

Common control functions include:

• Velocity control.
• Position (point-to-point) control: There are several methods for computing a motion trajectory. These are often based on the velocity profiles of a move such as a triangular profile, trapezoidal profile, or an S-curve profile. (Helpful for different angles / slices of the projected image)
• Pressure or Force control.
• Electronic gearing (or cam profiling): The position of a slave axis is mathematically linked to the position of a master axis. A good example of this would be in a system where two rotating drums turn at a given ratio to each other. A more advanced case of electronic gearing is electronic camming. With electronic camming, a slave axis follows a profile that is a function of the master position. This profile need not be salted, but it must be an animated function.

Reference:http://en.wikipedia.org/wiki/Motion_control

• http://lancet.mit.edu/motors/motors3.html

A more physics related background of understanding the torque curve of motors. There is a trade off between torque and speed although speed can be maximized by increasing supply voltage.
? (Torque will decrease and no longer exist with increased speed.  This is the PEAK TORQUE that exists on torque curves.)
In Summary:

Some important things include a:
software interface,
firmware,
the load that the motor can carry ? What it can carry depends on many factors including ones we control like voltage to DC.
its connections.
The torque-speed curves for the motor we picked represents the range of load we can carry within system limitations.
I’m not sure what kind of connection we need to connect motor to projector but it looks like we can just do that through the computer. The motor we chose comes with software that should let us see the speed of the motor and thus attempt to use that information to sync with the projector.