CNC Machines, G-Code and Sensors Flashcards
Define “Absolute position”
This is the position of any point on an object relative to the absolute origin
Define “Relative position”
This is the position of any point on an object relative to a temporary origin away from the absolute origin.
What are some examples of CNC machines?
> 2 axis laser cutter
> 5 axis CNC machine
> 3 axis NC milling machine
> Arcade grabbing machine
> Industry 7 DoF Robot
What is G-Code?
This is code that defines where the end effector of the machine moves to and when to turn on and off its end effector
What are the number of poles of a switch?
How many switches are activated by a single mechanism
What are the number of throws of a switch?
The number of possible contacts that the switch can switch to
What is a maintained switch?
The throw position is maintained when switched
What is a momentary switch?
The throw position reverts to a static position when released
What is this switch? [Picture 17]
SPST (Maintained)
What is this switch? [Picture 18]
SPST (Momentary)
What is this switch? [Picture 19]
SPDT (Maintained)
What is this switch? [Picture 20]
SPDT (Momentary)
What is this switch? [Picture 21]
DPST (Maintained)
What is this switch? [Picture 22]
DPDT (Maintained)
What is this switch? [Picture 23]
3P4T
What is a snap action switch?
A moving contact quickly moves from one fixed contact to another fixed contact with minimal relation to the speed at which the switch is operated
What are the properties of a snap action switch?
> Very little force required to activate them
> Repeatable and precise switching action
> Natural hysteresis (movement differential) due to snap action
> Reliable
What sort of switches are used for origin and limit detection?
> SPDT (Momentary)
> 3 Contacts
- Common
- Normally open
- Normally closed
How are magnetic reed switches made?
> They are made using a reed of ferrous metal which is attracted by a magnetic field
> The distance between the reeds is extremely small (μm)
What are the disadvantages of reed switches?
> Reed switch activation is not precisely predictable
> The activation and release is dependent on magnetic field strength
> Limited current capacity
What are the advantages of reed switches?
> Hermetically sealed and therefore can be incorporated into specialist environment
> High speed response time
> No physical contact switch
> They can be made very small
> They have a massive mechanical life
> They are cheap
What is the function of a rotary incremental encoder?
> They inform that a step has taken place
> They inform about the direction of travel
> They inform when you have reached a full rotation
What is the setup of a multiple light source encoder?
> 3 optical transmitters
> 3 optical receivers
> 3 output signals (A,B,Z)
- A and b are shifted by 90° relative to each other.
- Z is used to indicate a full rotation
What is the setup of a single light source encoder?
> 1 Optical transmitter
> 3 optical receivers
> A mask is used to single out each light
What equation is used to calculate the angle between A and B?
SD = (360 / #windows) × (N + 0.25)
How are more finite angle calculated?
This is done by measuring the amount of light that passes through the holes and are detected at A and B
How is the direction determined?
Depending on whether A leads B or B leads A
What is a linear incremental encoder?
> The same as a rotational one but in linear form.
> No disk is used
What is an absolute encoder?
> This is an encoder that works by using gray code to inform the exact position.
> Lots more sensors are required
What is Gray code?
This is a binary sequence where only 1 bit changes at a time
