Drive mechanism selection: Difference between revisions

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=Linear motion=
A drive mechanism is the part of a machine that, through power provided by a motor, performs the intended task of a machine. It can for example be a belt moving a box or a ball screw lifting or lowering heavy equipment.
Linear motion is motion in a straight line. It is usually achieved by converting rotational motion to linear motion - such is the case for belt drives, ball screws, etc. but not for linear motors.


To achieve linear motion, consider the following solutions in relation to the factors that are relevant to your application.
Use the table below to identify the type of drive mechanism that is the most suited for your intended application.


{| class="wikitable"
{| class="wikitable" style="text-align:center; vertical-align:middle;"
! Application factors !! Belt drives !! Chain drives !! Rack/Gear and pinion !! Roller Pinon/rack !! Leadscrews !! Ballscrews !! Linear Motors
|- style="font-weight:bold;"
! style="vertical-align:bottom; font-weight:normal; text-align:left;" |
! style="background-color:#D9D9D9;" | Belt drives
! style="background-color:#D9D9D9;" | Chain drives
! style="background-color:#D9D9D9;" | Rack/Gear and   pinion
! style="background-color:#D9D9D9;" | Roller   Pinon/rack
! style="background-color:#D9D9D9;" | Leadscrews
! style="background-color:#D9D9D9;" | Ballscrews
! style="background-color:#D9D9D9;" | Linear Motors
|-
|-
| '''Accuracy''' || Low || Low || Low-High || High || Low || Low-High || High
| style="text-align:right; font-weight:bold; background-color:#D9D9D9;" | Accuracy
| style="background-color:#DA9694;" | Low
| style="background-color:#DA9694;" | Low
| Low-High
| style="background-color:#A8E0B1;" | High
| style="background-color:#DA9694;" | Low
| Low-High
| style="background-color:#A8E0B1;" | High
|- style="background-color:#FEFEA4;"
| style="text-align:right; font-weight:bold; background-color:#D9D9D9;" | Backlash/Vibration
| A  consideration
| A  consideration
| A  consideration
| style="background-color:#A8E0B1;" | Near  Zero
| A  consideration
| A  consideration
| style="background-color:#A8E0B1;" | Near  Zero
|- style="background-color:#A8E0B1;"
| style="text-align:right; font-weight:bold; background-color:#D9D9D9;" | Acceleration
| style="background-color:#FEFEA4;" | Medium
| style="background-color:#DA9694;" | Low
| High
| High
| style="background-color:#DA9694;" | Low
| style="background-color:#FEFEA4;" | Medium
| High
|- style="background-color:#FEFEA4;"
| style="text-align:right; font-weight:bold; background-color:#D9D9D9;" | Speed
| Medium
| style="background-color:#DA9694;" | Low
| Medium
| style="background-color:#A8E0B1;" | High
| style="background-color:#DA9694;" | Low
| Medium
| style="background-color:#A8E0B1;" | High
|- style="background-color:#A8E0B1;"
| style="text-align:right; font-weight:bold; background-color:#D9D9D9;" | Load capacity
| style="background-color:#DA9694;" | Low
| style="background-color:#FEFEA4;" | Medium
| High
| High
| style="background-color:#DA9694;" | Low
| High
| style="background-color:#DA9694;" | Low
|-
|-
| '''Backlash/Vibration''' || A consideration || A consideration || A consideration || Near Zero || A consideration || A consideration || Near Zero
| style="text-align:right; font-weight:bold; background-color:#D9D9D9;" | Length
|-
| Shorter
| '''Acceleration''' || Medium || Low  || High || High || Low  || Medium || High
| Shorter
|-
| Long
| '''Speed''' || Medium || Low  || Medium || High || Low  || Medium || High
| Long
|-
| Shorter
| '''Load capacity''' || Low  || Medium || High || High || Low  || High || Low
| Shorter
|-
| Moderate
| '''Length''' || Shorter || Shorter || Long || Long || Shorter || Shorter || Moderate
|- style="background-color:#FEFEA4;"
|-
| style="text-align:right; font-weight:bold; background-color:#D9D9D9;" | High wear and short life
| '''High wear and short life''' || A consideration || A consideration || A consideration || Long life || A consideration || A consideration || Long life
| A   consideration
|-
| A   consideration
| '''Maintenance''' || A consideration || A consideration || A consideration || Low to none || A consideration || A consideration || Low to none
| A   consideration
|-
| style="background-color:#A8E0B1;" | Long   life
| '''Noise level''' || Medium || High || Medium || Low || High || Medium || Low  
| A   consideration
|-
| A   consideration
| '''Dust and dirt emissions''' || High || High || Moderate || Low to none || Moderate || Moderate || Low to none
| style="background-color:#A8E0B1;" | Long   life
|- style="background-color:#FEFEA4;"
| style="text-align:right; font-weight:bold; background-color:#D9D9D9;" | Maintenance
| A   consideration
| A   consideration
| A   consideration
| style="background-color:#A8E0B1;" | Low   to none
| A   consideration
| A   consideration
| style="background-color:#A8E0B1;" | Low   to none
|- style="background-color:#FEFEA4;"
| style="text-align:right; font-weight:bold; background-color:#D9D9D9;" | Noise level
| Medium
| style="background-color:#DA9694;" | High
| Medium
| style="background-color:#A8E0B1;" | Low
| style="background-color:#DA9694;" | High
| Medium
| style="background-color:#A8E0B1;" | Low
|- style="background-color:#FEFEA4;"
| style="text-align:right; font-weight:bold; background-color:#D9D9D9;" | Dust and dirt emissions
| style="background-color:#DA9694;" | High
| style="background-color:#DA9694;" | High
| Moderate
| style="background-color:#A8E0B1;" | Low   to none
| Moderate
| Moderate
| style="background-color:#A8E0B1;" | Low   to none
|}
|}


=Rotary motion=
=See also=
For applications with heavy loads and slow turning, such as rotation of a crane, slewing bearings are suitable.
[[Guide to machine design]]
 
For applications with several, or several thousand, rotations per minute, rolling bearings are suitable.
 
==Gears==
 
Main article: [[Gear]] for detailed description and gear calculation.
 
Gears, just like spurs and sprockets, are mechanisms used to transfer energy by rotary motion.
 
They can all be used to change the following:
*Speed of rotation
*Direction of rotation
*Amount of torque available to do work
 
==Rolling bearings==
 
Main article: [[Bearing selection]]
 
The table below shows level of suitability of different bearing types for different conditions.
 
[[File:Bearing type selection.png]]
 
This section is based on a table found in SKF handbooks and on the [https://www.engineersedge.com/bearing/bearing_selection.htm Engineers Edge website.]
 
[[File:Bearing types.png|500]]
Image source: https://www.machinedesign.com/learning-resources/whats-the-difference-between/article/21831901/whats-the-difference-between-bearings
 
=Motors=
Main article: [[Motor selection]]
 
A motor converts one form of energy into mechanical energy.
 
==Summary==
Servo motors are suitable for high speed and high acceleration requirements. The trade-off is a higher cost and complexity.
 
Stepper motors are suitable for low speed and low acceleration requirements.
 
DC motors are suitable for continuous rotation at high RPMs and constant torque across the motor’s speed range.
 
{| class="wikitable"
! Attribute !! Stepper motors !! Servo motors !! Brushed DC motors !! Brushless DC motors
|-
| Accuracy || High || High (achieved by adding encoder to the system. ||  None ||  Varies
|-
| Torque at low speeds || High || High ||  - ||  -
|-
| Torque at high speeds || Low (can lose up to 80% torque at high speeds) || High ||  - ||  -
|-
| Cost efficiency || High || Lower (uses rare-earth magnets, may need encoder or gearbox.) || High || Lower
|-
| Lifespan || Long life || Shorter || Shorter ||  -
|-
| Size || Compact || High output power relative to size and weight. || Compact ||  -
|-
| Load capacity || Low (might skip steps at high loads.) || High ||  - ||  -
|-
| Efficiency || Low (constantly draw maximum current independent of load.) || High (80–90% efficiency.) || High ||  -
|-
| Ease of use || • Easily controlled (can be controlled with micro controllers such as the ATmega chips that are readily available on Arduino development boards.) Can stall or lose position without a control loop. || • Higher maintenance if gearbox and encoder is included.
• Limited range of motion; positional rotation servos are limited to 180 degrees of motion.
• Works in AC or DC drive.
|| • Torque to Speed Ratio can be altered (exclusive to brushed motors.)
• High maintenance requirements due to easily worn out as a result of continuous moving contact.
|| • Some brushless motors are difficult to control and require a specialized regulator.
• Low maintenance.
|-
| Applications ||
• floppy disk drives
• flatbed scanners
• computer printers
• plotters
• slot machines
• image scanners
• compact disc drives
• intelligent lighting
• camera lenses
• CNC machines and 3D printers
• Textile machines
• Printing presses
• Medical imaging machinery
• Small robotics
• Welding equipment
||
• Automated manufacturing
• Robotics
• CNC machinery
• Telescopes
• Elevators
• Conveyor Belts
• Camera Auto Focus
• Solar Tracking System
• Metal Cutting & Metal Forming Machines
• Antenna Positioning
• Printing Presses/Printers
• Automatic Door Openers
 
||
• Home appliances
• toys
• electrical propulsion
• cranes
• paper machines
• steel rolling mills
 
||
• Drones
• Electric cars
• Washing machines
• Air Conditioners
• Cordless tools
• Computer
• Fans
• Disk drives
|}
 
==Stepper motors==
A stepper motor enables rotational motion in incremental steps. This makes stepper motors suitable for applications that require precise motion. It also eliminates the need for an encoder (which is used to tell the motors precision.)
 
'''Pros'''
* High accuracy: A stepper motor enables rotational motion in incremental steps. This makes stepper motors suitable for applications that require precise motion. It also eliminates the need for an encoder (which is used to tell the motors precision.)
* High torque at low speeds.
* Relatively inexpensive and widely available.
* Compact.
* Easily controlled (can be controlled with micro controllers such as the ATmega chips that are readily available on Arduino development boards.)
 
'''Cons'''
* Speed limitations; loses most of their torque at high speeds, sometime up to 80%.
* High vibrations levels and proneness to resonance issues.
* Low efficiency; unlike DC motors, stepper motors constantly draw maximum current independent of load.
* Produce high amounts of heat.
* Can stall or lose position without a control loop.
* Load limitations; might skip steps at high loads.
 
'''Suitable applications'''
* floppy disk drives
* flatbed scanners
* computer printers
* plotters
* slot machines
* image scanners
* compact disc drives
* intelligent lighting
* camera lenses
* CNC machines and 3D printers
* Textile machines
* Printing presses
* Medical imaging machinery
* Small robotics
* Welding equipment
 
==Servo motors==
'''Pros'''
* High accuracy; achieved by adding encoder to the system.
* High speed; can maintain high torque at high speed (unlike stepper motors.)
* High efficiency; 80–90% efficiency.
* Does not suffer from vibration or resonance issues.
* Low noise levels at high speeds.
* Servo motors can work in AC or DC drive.
 
'''Cons'''
* May require an encoder and gearbox (which makes the system more expensive).
* Requires more maintenance (if the system includes more parts.)
* Limited range of motion; positional rotation servos are limited to 180 degrees of motion.
 
'''Suitable applications'''
* Automated manufacturing
* Robotics
* CNC machinery
* Telescopes
* Elevators
* Conveyor Belts
* Camera Auto Focus
* Solar Tracking System
* Metal Cutting & Metal Forming Machines
* Antenna Positioning
* Printing Presses/Printers
* Automatic Door Openers
 
 
==Brushed DC Motors==
Even though brushed motors are being replaced by brushless motors in many applications, brushed DC motors are, due to their low cost, used in applications where the host device is likely to fail before the motors, such as home appliances or kids toys. Brushed motors are also used in industrial applications because they can be easily controlled and have their Torque to Speed Ratio altered. This is achieved by changing the operating voltage or the strength of the magnetic field. Depending on the connections of the field to the power supply, the speed and torque characteristics of a brushed motor can be altered to provide steady speed or speed inversely proportional to the mechanical load. Brushed DC motors continue to be used in electrical propulsion, cranes, paper machines and steel rolling mills.
 
'''Pros'''
* Torque to Speed Ratio can be altered (exclusive to brushed motors.)
* Low cost.
* Compact size.
 
'''Cons'''
* High maintenance requirements due to easily worn out as a result of continuous moving contact.
* Speed limitations due to brush heating.
* High maintenance.
* Short life.
 
'''Suitable applications'''
* home appliances
* toys
* electrical propulsion
* cranes
* paper machines
* steel rolling mills
 
==Brushless DC Motors==
'''Pros'''
* Quiet.
* Low maintenance.
* Long life.
 
'''Cons'''
* Expensive.
* Some brushless motors are difficult to control and require a specialized regulator.
 
'''Suitable applications'''
* Drones
* Electric cars
* Washing machines
* Air Conditioners
* Cordless tools
* Computer
* Fans
* Disk drives

Latest revision as of 20:05, 18 February 2023

A drive mechanism is the part of a machine that, through power provided by a motor, performs the intended task of a machine. It can for example be a belt moving a box or a ball screw lifting or lowering heavy equipment.

Use the table below to identify the type of drive mechanism that is the most suited for your intended application.

Belt drives Chain drives Rack/Gear and pinion Roller Pinon/rack Leadscrews Ballscrews Linear Motors
Accuracy Low Low Low-High High Low Low-High High
Backlash/Vibration A consideration A consideration A consideration Near Zero A consideration A consideration Near Zero
Acceleration Medium Low High High Low Medium High
Speed Medium Low Medium High Low Medium High
Load capacity Low Medium High High Low High Low
Length Shorter Shorter Long Long Shorter Shorter Moderate
High wear and short life A consideration A consideration A consideration Long life A consideration A consideration Long life
Maintenance A consideration A consideration A consideration Low to none A consideration A consideration Low to none
Noise level Medium High Medium Low High Medium Low
Dust and dirt emissions High High Moderate Low to none Moderate Moderate Low to none

See also

Guide to machine design

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