Lecture 6 Flashcards
What is G code?
Code that is used to control CNC machines
What is absolute positioning?
The co-ordinates of an object is relative to the abosolute origin 0,0
What is relative positioning?
Temporary origins are often used in systems since they allow either the user or the machine to have the freedom to effectively reposition/reset the ‘Origin’ point of an action
What are poles?
How many switches are activated by the same mechanism
What are throws?
How many contacts can the common (COM) pin be switched to
What does a maintained mean in mechanical devices?
Throw position is maintained when switched
What does momentary mean in mechanical devices?
Throw position reverts to a static position when released
What are binary coded switches?
In general, they have one common pin and the other pins are the coded output where the number of pins depends on the number odf bits required to define the position
What switch is regularly used for origin anf limit detection?
The microswitch
What are the different types of microswitches?
Long leaf lever
Roller leaf
Formed leaf lever
Coin door
Micro minature
What is snap action?
A mechanism by which the 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 microswitches?
Very little force is requires to activate them
Repeatable and precise switching action
Natural hysterersis (movement differential) sue to the snap action
Reliable
Over 1,000,000 operation cycles
What is movement differential - MD (differential travel - TD)
The distance or angle of the actuator from the operating position to the releasin position
How can a system origin be found in a motion control system with an origin detection system using a micro-switch?
Increment the motor until OP is reached - The point where the switch is ON
Increment the motor in the opposite direction until the switch reaches in normally open position
Can now determine the switches absolute origin point
What are reed switches?
The reeds are made from ferrous metals such that when a magnetic field is applied, the lines of magnetic fource polarise the reeds and they then attract each other thus making electrical contact. The distance between the reeds is measured in μm
What are the advantages of using reed switches as an absolute origin point?
Hermitically sealed and therefore can be incorporatd into specialist environments
High speed response time
No physical contact to switch
They can be made very small
They have a mechanical lide in excess of 3,000,00 switching cycles
They are cheap
What are the disadvantages of using reed swotched as an absolute origin point?
Reed switch activation is not preciselt predictable
Their activation and release is dependent on the strength of the magnetic filed applied, which could vary over time
Limited current capacity
Where are reed switched used?
Security and safety interlocks
Reed relays
Float switches
Speed detection and positioning in simple anemomenters and wind vanes
What must be considered when choosing an origin detection switch?
Determine required accuracy
Determine actuation method
Determine required travel to operate and reset (MD/DT)
Determine the force required to operated
Determin the contact configuration
What are the envirnomental requirements
Is mechanical life an issue
Is switching frequency an issue
Is actuation speed an issue
