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FINAL DESIGN:

Click here to view the Final Report.

Click here to view the Software.

Click here to download the AutoCad drawings in pdf format.

 

PREVIOUS DESIGN CONCEPTS

Conceptual Design:  Click here to view the Power Point presentation.

Conveyor Starter Panel Design

The electrical design for powering the conveyor is complete.  The overall architecture for the AC portion is shown below.

The system consists primarily of an electrical enclosure with the following four components (1) a fused disconnect, (2) a 24VDC controlled contactor, (3) a commoning bar, (4) and overload relays. 

The fused disconnect provides branch circuit short circuit and overload protection for the motors.  Furthermore, it provides safe power isolation when the power devices and motors need servicing.  The fuses are time delay type to allow for high starting current (locked rotor) transients. 

The contactor is rated the same as the fused disconnect.  It is 24VDC controlled to allow interfacing with emergency stop switches, control switches, and the PLC interlock relay. 

The commoning bar is really just a row of DIN rail mounted terminal blocks with 600VAC capability.  The NEC allows voltage taps off of a branch circuit if the current carrying capacity of the tapped wires are less than 25 ft in length and of 1/3 the current-carrying capacity of the branch circuit.  14 gauge wire will be used throughout the enclosure.

The overload relays are solid state and set to 125% of FLA (full load amps) for each motor.  These devices are required because branch circuit overcurrent devices (ie the time delay fuses) may not "blow" if a motor is overloaded.  The overload relays provide individual protection of the motors; whereas the branch circuit protection only protects the overall circuit against overcurrent. 

Conveyor Electrical Design (DC)

To control the conveyor, a 24VDC circuit is required.  The circuit diagram is shown below.

With the exception of the on/off switch, all components are wired normally closed.  If a wire is broken, the conveyor will not operate.   Conversely, the conveyor will only operate when all components and wiring are physically intact.  This ensures that the conveyor will stop when an e-stop is pressed.

A PLC interlock relay is also inserted in series with the circuit to allow the PLC to stop the conveyor if needed.  The relay was chosen to be wired normally closed to allow the conveyor to run without the PLC operational.  This will allow other experiments to be performed on the conveyor if need be. 

Click here for a report on my design.

Workcell Design

Click here to read about a potential workcell design concept.

The diagram below shows a conceptual layout of the system.

Control Panel

Below is a proposed control panel for the operator interface. 

The “cell selector switch” tells the PLC which workcell will be active.  “1” indicates the standard workcell, and “2” indicates the lean workcell. 

The “mode switch” tells the PLC if the active workcell should be in manual or automatic mode.  In manual mode, the “actuator” and “gate” toggle switches control the workcell; and in automatic mode, the “start”, “stop”, and “home” momentary pushbuttons control the workcell. 

The upper switch near the “ACTUATOR” label controls the large slide (for horizontal control).  If the switch is toggled to the upward position, the large slide will fully retract.  If the switch is toggled to the downward position, the large slide will fully extend.  The lower switch near the “ACTUATOR” label controls the small slide (for vertical control).  If the switch is toggled to the upward position, the small slide will fully retract.  If the switch is toggled to the downward position, the small slide will fully extend.

The toggle switch located next to the “GRIP” labal controls the gripper mounted to the small slide.  If the switch is toggled to the upward position, the grip will fully open.  If the switch is toggled to the downward position, the grip close.

In automatic mode, the START switch is functional.  When pressed, the active workcell will begin its sequence of operations as programmed in the PLC. 

In automatic mode, the STOP switch is functional.  When pressed, the active workcell will stop its sequence of operations at whatever point in the sequence is was at.

In automatic mode, the HOME switch is functional.  When pressed, the active workcell will stop it’s sequence of operations and return to its home position.  Home position is defined as:

  1. The large slide fully retracted,
  2. The small slide fully retracted,
  3. The gripper fully retracted.

The emergency stop switch is always functional.  When pressed, the following will occur:

  1. The conveyor will STOP,
  2. All control valves will be de-energized by the PLC,
  3. All pneumatics will be de-pressurized by the supply valve.

Grippers (4-23-05)

The existing paraellel action Robohand grippers will be used to pick up the 2" wooden block.  No physical modifications will be required to make the grippers adapt to the 2" block.

Two additional angular action grippers will be ordered.  Custom fingers will need to be design and constructed to handle the 2" pvc coupling.  The grippers will also be purchased from Robohand.

 

A custom adapter plate will need to be made for all four grippers to allow them to mount to the actuators. 

Palette Design (4-23-05)

Each palette will be configured as shown in the following diagram.

 

The exisiting pins (non-shaded in the diagram) are existing pins on the palettes that are pressed into the base plate.  They were used to hold a die for a previous product, but now they will serve as the die themselves.  Product A will be a 2x2" wooden block.  Two new pins will be added per palette to help hold the block.  The parallel grippers will be used to move the block.

The four existing pins work fine at holding product B, a 2" pvc coupling.  The angular grippers will be used to move the coupling.

Gantry Design (4-23-05)

Two gantries will hold the standard and lean workcells (actuators + grippers) above the Bosch conveyor.  They will be constructed of aluminum strut extruded tubing made by 80-20 inc.  The strut is of nearly identical construction and style of the Bosch strut for which the conveyor is constructed.  However, the 80-20 strut is far less costly. 

DC Enclosure Design (4-23-05)

A DC enclosure mounts under the conveyor belt drive within vicinity of the AC Enclosure.  It houses the following:

(1) the PLC (programmable logic controller), (2)  pneumatic control valves, (3) a pneumatic supply valve, (4)  an air pressure regulator, (5)  two pneumatic ports for hose connections to the gripper mounted on the standard workcell, (6)  a 120VAC breaker, (7) a 24VDC power supply, (8) a  DC interlock relay, (9)  a terminal strip for electrical connections to the gripper mounted on the standard workcell, (10)  and terminal blocks for wiring connections. 

The following components are mounted to the DC enclosure and accessible outside of the enclosure:

(1) a power switch, (2) and two pneumatic ports (with quick connects) for hose connections to the gripper mounted on the lean workcell. 

If the power switch is turned to ON, the PLC and 24VDC power supply will be energized.  The PLC will then perform per the switch positions on the Control Panel.  (See Control Panel section.)  The 24VDC power supply will energize the inductive proximity switches located on the workcells and conveyor.

The DC interlock relay is controlled by the PLC, and it gives the PLC the capability to shut OFF the conveyor if required.  The relay is wired in series with the two emergency stop switches.

AC Enclosure Design/Operation (4-23-05)

An AC electrical enclosure located underneath the conveyor belt drive contains the main electrical disconnect, branch short-circuit protection, a 24VDC operated motor contactor, individual motor protection relays, and an ON/OFF operation switch. 

            To make the conveyor operational, the following steps must be performed:

  1. Perform a mechanical walkaround to ensure the conveyor is safe for operation,
  2. Ensure that all emergency stop switches are pulled,
  3. On the AC enclosure, switch the disconnect switch to ON ,
  4. On the DC enclosure, turn the power switch to ON.
  5. On the AC enclosure, turn the operation switch to ON.

The PLC does not need to be operational in order for the conveyor to run. 

 

 

© 2005 Sigma Cell - University of Idaho

Last updated 11/27/2005