EGR 450 Manufacturing Controls

Final Project

Vertical Table Height Adjustment Test

Sponsored by
Entela Labs Inc.

August 4, 2000

Ryan Hitchcock
 
 

Project Description:

The intent of this project is to implement the use of a PLC in an application that requires automated control. The application chosen for this project involves a cyclic duration test for commercial tables. This type of test performed by Entela Laboratories is used as a standard method for testing the various vertical height ranges of these tables. The tables are electrically or pneumatically driven and controlled with a handset controller.

Process Description: Vertical Adjustment Test (ANSI/BIFMA X5.5-1998 section 22.2)

22.2.1 Test Setup

1. The unit shall be leveled in the normal operating position and secured to the test platform.
2. Apply a test load of 45kg (100 lb.) through a 305mm (12in.) diameter disk with the center of the disk on a line 305mm (12in.) in from the working edge of the surface or at the midpoint, whichever is nearer the working edge. The side position of the test load is described in Step (a) of the Test Procedure.

22.2.2 Test Procedure

Note: The test device shall apply the forces necessary to achieve the motion required. The latching and/or activating mechanisms may be cycled concurrently or independently for 4,000 cycles.

First Quartile: The unit shall be cycled from the lowest to the 25% position of its total vertical travel. The center of the loading disk shall be positioned 305mm (12in.) in from the left edge of the surface.

Second Quartile: The unit shall be cycled from the 25% to the 50% position of its total vertical travel. The center of the loading disk shall be positioned 305mm (12in.) in from the left edge of the surface.

Third Quartile: The unit shall be cycled from the 50% to the 75% position of its total vertical travel. The center of the loading disk shall be positioned 305mm (12in.) in from the right edge of the surface.

Fourth Quartile: The unit shall be cycled from the 75% to the highest position of its total vertical travel. The center of the loading disk shall be positioned 305mm (12in.) in from the left edge of the surface.

Method of Design:

Given the criteria outlined in the test procedure a state diagram (figure 2.) was used as the design technique to construct the necessary ladder logic. As mentioned earlier, the objective of this program is to accommodate both electric and pneumatic tables. The primary difference between the two types of tables is thedriving mechanisms. The pneumatic table would probably need assistance in the down stroke of the cycle. To offer this assistance a pneumatic cylinder would be used along with the static load. The program was also set up to pause the motion of the table at the end of each stroke this was to ensure that no excessive impact would occur on the driving mechanism of the table. A timer (See photos) was incorporated at the begging of each stroke to monitor the amount of time that it would take to complete the stroke. This was not a requirement for the test method however it could provide useful information for the client. The timer was displayed using the HMI. The timer may also be used as an alarm to indicate that the stroke is taking to long. A counter was also implemented for each quartile of the test to keep track of the number of cycles occurring. Again this was displayed on the HMI for the operator to monitor.

Implementation of Design:

The basic components for this project were compiled and assembled in order to test the basic function of the program. As seen in (figure 3) the first step in this was to wire the start, stop and reset buttons along with the indicator lamp. 125v powered all these components. The optical sensors were mounted to a vertical stand and powered by 24v from the PLC. The solenoids for the pneumatics were also wired to125v.

The handset controller for the table was mounted in a box, which allowed the air-operated plungers to activate the necessary up and down buttons. This would probably need to be updated or modified for each type of table based on the manufactures design changes.

The air actuator and its frame for the pneumatic table setup would need to be fitted to the dimensions of the table. At the time only an electric table was available for testing.
 
 
 

Wiring Diagram
 
 
 
   
 
Upon testing the ladder for the basic functions of the test the next step was to incorporate the HMI. The HMI was primarily used to select the type of table being tested and monitor the states as the test was cycled. The Program for the HMI is of a block formatting were a total of 9 text blocks were created. The process flow for the program is shown below in figure 4. The sequence of text displays for the HMI may be seen in (Photos)

Block Diagram
 
 
 
 

Photos:
 
 
 
 

The HMI showing the time it takes to cycle the table to its upper and lower position.
 
 
 Choosing the negative key will select the pneumatic table. 
 
 

When the table takes to long to reach the end of its stroke a failure state is signaled.
 
 
 
 
 The number of cycles, which have occurred, are displayed during the entire test.
 
 

 
 
  End of Test
 
 
 
 

 Components:

Pneumatic plungers control the handset (enclosed in C-channel).
 

Optical Sensors used for detecting the upper and lower range of the stroke.
 
 
 
 
 
 Front panel and inside of box. The light on the front was used as a visual alarm when a time failure occred.
 
 
 
 Air cylinder (Optional) used only with pneumatic tables to aid in the down stroke of the cycle.
 
 
 
  References:
 
 

Manuals: PLC

Mitsubishi Electric Co.

Mitsubishi Denki Bldg

Mardunouchi Tokyo

Programming Manual Number: JY992D48301

Revision: C

Date: July 1995

HMI

-MELSEC PLC System

MTA-10 Operator Terminal User’s Manual Number: MA-00024

Version: 2.1x

Date: November 1994

MTA-12

Test Standards: Vertical Height Adjustment Test

-BIFMA International

The Business & Institutional Furniture Manufacturer’s Association

4910 60^th St. SE

Grand Rapids, MI 49512

(616) 554-0504

(616) 554-0427 Fax

Desk/Table Products-Tests

Standard

American National Standard for Office Furnishings