Mitsubishi
Electric FA IndustrialProductsCorporation
MITSUBISHI ELECTRIC
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Proposal for Replacement of Electric Hoists

To:“From Hoists with Creep Speed Inverter Hoists”
3. Maintenance

1. Introduction
Electric hoists are used for transportation in factories and warehouses as well as precision works suchas assembly of industrial machinery. High performance is required for electric hoists, such as stopping
at a fixed position and starting and stopping without shock. Increasing demand for easy operation isexpected due to the reduction of skilled labor for crane operation.
Hoists with creep speed are useful and have been widely used for precision works. Here, we would liketo propose our inverter hoist which is applied to new uses and in new areas and enjoying popularity. In
the following sections, differences between a hoist with creep speed and an inverter hoist, amaintenance comparison, and features of the inverter hoist are presented for your consideration.

2. Differences between hoist with creep speed and inverter hoist
Figure 1: Comparison between hoist with creep speed and inverter hoist
Models: 2.8ton capacity, monorail type, creep speed hoisting/lowering or inverter hoisting/lowering
Model
Inverter hoist
Hoist with creep speed
ItemMitsubishi
function
S-2.8-LMVT3
U-2.8-LMH3
code

Compared to hoists with creep speed (driven by contactors), inverter hoists can significantly reducerunning costs (maintenance expenses). Major reasons are: Soft starting and soft stopping of inverter hoists reduce shock and lessen the load on structuralmembers.
• Especially on wire ropes and hoisting deceleration gears
 Inverter hoists basically decelerate to stop by braking control of about 6 Hz.
• This considerably improves the durability of brake disks. Note: No load high-speed function may
cause brake disks wear due to shock, etc.
 Non-contact design of inverter hoists doesn't impose a strain on controllers.
E.g. 3-year use with replacement of brake discs, electromagnetic contactors and wire ropes
at annual inspection (once a year):<Hoist with creep speed><Inverter hoist>
Replacement ofPart expense
5,200 yen (main)
5,200 yenbrake disc+ 3,900 yen (creep control )Note: OnlyClutch brake disc

Replacement ofelectromagneticcontactor
External
dimensions

Hoistingspeed(60 Hz)
WeightNumber ofparts(excl. bolts,etc.)

Replacement ofwire rope

0.0167 - 0.167 m/s (0.25 m/s)
1 - 10 m/min (No load high-speed function:15 m/min)
390 kgHoist motor: 38 parts
Controller
CPU board, Power board, Drive board:
1 part eachElectro-magnetic switch: 1 for brake

0.0167/0.167 m/s
1/10 m/min
520 kgHoist motor: 94 parts
Controller
Electro-magnetic switch:4 for hoisting+2 relay for changing speed2 for brake

Sway amplitude of lifting load(500 kg load)

Shock ofstarting andstopping

Swayamplitude(mm)Note: 1ton rated-loadhoists were used
for this test.

Standard type hoist

Sway amplitude of all models
reached a maximum when
stopped.
The maximum sway of thecreep speed hoist and standard
S-type hoist were about 9 times
and 14 times larger thaninverter hoist respectively.

Hoist with creep speed

Operation
StoppedHigh-speed
hoisting

StoppedHigh-speed
hoisting

Stopped― yen

condensers
have a finite life,and need to be
replaced about
every 10 years.

Part expense

5,200 yen

Working expense

3 hr × 5,000 yen

1 hr × 5,000 yen

Part expense

51,200 yen/6 parts

3,400 yen/1 part

Working expense

2 hr × 5,000 yen

0.2 hr × 5,000 yen

Part expense

20,000 yen

20,000 yen (per 1.5 years
due to longer durability)

Working expense

1.5 hr × 5,000 yen

1.5 hr × 5,000 yen

Three years

354,000 yen

98,800 yen

There is a huge gap—approximately 260,000 yen in maintenance expenses in three years (per unit).

4. Features of inverter hoist
The inverter is specifically designed for hoists to improve environmental resistance andmaintainability.
Setting can be changed to suit your operation and improve ease of use.
(1) Adjustable speed setting (1/10 speed to standard speed)(2) No load high-speed function (1.5x faster with 7.5ton orless, 2.0x faster with 10ton or more)(3) The upper and lower limit levels of stop positions are adjustable
via electronic limit switches.
(4) Failure history Display, the number of starts, and operating hours are included as standardfeatures.
Advanced technologies make it possible to respond to various situations depending on the use:
(1) Speed coordination function – Prevents load tilt and ensures safety when hoisting one load with
two hoists(2) Light-load high-speed function – When the load is automatically detected to be 25% of the rated
load or less, the speed is changed to 1.5x to 2x faster than the standard speed.
(3) Multiple speed function – Useful in automatic operations using a sequencer(4) Position detection 7-point output – Provides operation information via relay output