A Time Logging Peripheral:
The purpose of this device is to help you improve the efficiency of
your machine, assembly line, or process. TIMELOG measures the time
of one or more events in a machine or process to monitor or troubleshoot
the system. An event is anything that can be converted to an electrical
ON-OFF signal (binary).
Process monitoring --- TIMELOG can be used to measure machine
cycle time, production rate, blocked and starved conditions, and point
to bottleneck areas. Bottleneck may also be referred to as constraint.
Blocked is when a machine is done, but a down
stream interference prevents the done part from being released. Starved
is when a machine is ready to receive a new part, but one is not available. The
slowest stations on your line are the bottlenecks and these should
never be starved or blocked.
Troubleshooting --- TIMELOG allows unattended measurements over
long time periods to trap random intermittent problems in a machine
cycle to help identify the cause. Using RS485 communication the monitoring
computer can be in a protected area at a great distance form the machine
SUMMARY of CHARACTERISTICS:
The maximum number of inputs per TIMELOG module is 16. The maximum
number of TIMELOG modules is about 32, or 512 inputs per serial channel
on the monitoring computer. Of course more than one serial channel
can exist on the computer, and thus more than 512 inputs.
The time resolution is 10 milliseconds (.01 sec.). For most transitions
the short term accuracy is aproximately +/-20 milliseconds. Digital
filtering is used to reduce false transitions. Worst case long term
accuracy is about 4 seconds per day, but all stations can be resynchronized
at any time.
The transition times are stored in an internal buffer of the TIMELOG
module. This allows good timing accuracy determined by the TIMELOG
internal clock. If the internal buffer were not used, then the monitoring
computer would have to scan all of the stations at a high rate in
order achieve 10 millisecond resolution.
The TIMELOG module always operates in a half duplex COMMAND RESPONSE
mode. Communication is via RS232 (single module only and short distance),
RS422 (single module and longer distance), or RS485 (multidrop up
to 32 modules per 2 or 4 wire bus and moderately long distance). Only
one RSxxx mode is selectable for input. But both RS232 and RS4xx
output simultaneously. The RSxxx line drivers are isolated from the
internal circuitry. This minimizes ground loop problems between machines. Maximum
cable length is 18 to 50 ft for RS232, and 1000 ft for RS422 and RS485 at 19.2 kbaud. RS232
and RS485 use a shielded twisted pair. RS422 requires 2 twisted pairs
and shield. Baud rate is 19.2 kilobits per second. Length is dependent
on cable capactance, loading, and baudrate.
The monitoring computer should employ an optically isolated serial
card for RS422 or RS485.
A single bus system with mutiple TIMELOG modules should handle up
to 24 stations with 10 transitions per machine cycle per station with
an average pallet to pallet time of 12 seconds with an
accuracy of approximately +/-20 milliseconds. The 240 transitions per
12 seconds is saturation
for the 19.2 kbaud rate.
Two Typical APPLICATIONs:
Process monitoring --- permanent installation on a machine
or line. In this application more than one TIMELOG module is connected
to a production line. A single TIMELOG module might be connected
to one or two stations. Bottleneck and nearly bottleneck stations need to
be monitored. However, monitoring all stations will provide the greatest
amount of information.
This described application is for a non-synchronous differential
assembly line. However, TIMELOG is applicable to many different lines and
A number of critical stations on the line are connected to the multidrop
bus and to the monitoring computer. This system can be used for blocked
and starved detection and thus determinition of one or more bottlenecks. Especially
useful on nonsynchronous lines.
Typical signals for each station are ---
(1) On-deck pallet present and in position to be released to the station. The
pallet sensor should only indicate presence when this pallet is essentially
against the on-deck pallet stop. If this signal is NOT present at
the time the in-station operation is done, than a starved condition
(2) Pallet clamped.
(3) Good part present in-station.
(4) Part reject in this station.
(5) Down-stream is clear. There is enough space down stream for the
in-station pallet to be released and not block the complete entry
of the on-deck pallet into the station. This is usually a photocell
beam diagonally across the line and intercepted by the pallet base. If
down-stream is NOT clear, then the station is blocked. Even if no part is on the
pallet we need to know if the pallet blocks the station.
At the on-deck pallet position of each station a photocell or prox
switch sensor is used to detect the presence of the on-deck pallet. This
is one input to the TIMELOG module.
If the pallet clamp function operates as soon as the pallet is in
place in station and releases as soon as the station function is done,
independent of blockage, then station cycle time can be determined
from this single input. The minimum pallet-to-pallet time can be
calculated by adding pallet transfer time to the station cycle time. From
this the instantaneous throughput, and various averages of this station
can be calculated. However, averages are better determined from a time
span and the number of parts with that time.
A good part present signal is another input, as well as reject from
this station. Last if the pallet position following this station
has a pallet present detector, then blockage of this station can be detected.
For a well designed station these signals will inherently be available.
This is 5 inputs and 10 transitions per machine cycle.
Three other useful signals from the machine are AUTO, BYPASS, and
over-cycle time limit.
For any line the maximum throughput is achieved when the slow stations
are never blocked, and never starved. A TIMELOG monitoring system
can help achieve this goal.
Software for the monitoring computer for this application is custom
and special order.
Troubleshooting --- semi-permanent or temporary installation
on a machine.
Monitor several functions on a single station for time study, troubleshooting
intermittent problems, machine or part program development, or studying process timing variance. The monitoring
computer can be remotely located and thus unobtrusive.
This involves connecting interface modules 24 v and/or 120 v to the
selected machine points. The input interface modules are connected
to the TIMELOG module which in turn is connected to a computer. In
this application the input modules could be permanently or semipermanently
connected to the machine, and the TIMELOG module moved from machine
A software package TIMCOL16 is run on the PC under PC or MS DOS to
One time we solved a
problem in about two days that the electricans had been working on for over a
month. This was not a reflection on their capability, but rather
a problem that was very hard to see and might occur once every few hours. It
was an intermittent PLC I/O module in a very complex machine cycle.
If you are looking for intermittent problems, then both the TIMELOG
module and the PC should be connected to an uninterruptable power
Initial optimization of a machine is a useful function of TIMELOG.