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This story covers only lifting columns and solutions used in regular high adjustable desks. In general it fits to other microprocessor controlled adjustable systems with electric motors as linear actuators and high load columns.

Technical examples are from Linak Deskline range as most advanced system.

The purpose of this document is height adjustable desk troubleshooting and cover system sold by us:

All models bought from us directly or indirectly ( around 80% of all desk frames sold was sold to furniture manufacturers ) are very strong and durable, they work for more than 10 years without any defects and maintenance. Therefore it is always little surprise when desk doesn’t follow command from handcontrol.

Linak has good troubleshooting guide https://ipaper.ipapercms.dk/Linak/FINNISH/BROCHURE/deskline-troubleshooting-guide-eng/?page=6

which covers ONLY original Linak systems.

I’ll add some more moments on this and some technical details, also procedures for other systems. However, all systems works very much the same manner.

Feel free to jump over next sections to maintenance, diagnostic and troubleshoot article.

For those readers who want to dive into technical details are next chapters. It would be useful for furniture designers as well.

It is not AI created document, use keywords from here to get another ( and sometimes better ) explanation.

Synchronized Height Adjustability BASICS.

Linak Deskline system supports 1 up to16 lifting column synchronized movement with heigh accuracy ( Linak Deskline technical documentation doesn’t have information on tolerances ). However, this is less than 1mm relative height difference between columns and depends on column technical design. And it doesn’t matter on load on each column in system, movement is perfectly synchronized.

How does it works?

Inside each column is electrical motor with attached pulse counter microprocessor. Pulse counter supplies control box with information about turns made by motor and direction. Control box drives electrical motor in relation with information from pulse counters from all columns in system.

If system has only one column in system, it works in the same manner, except synchronization.

One column is CONTROL columns, others follows this column position.

As standard MIN height is from where system starts counting. During use control box counts back and force pulses from CONTROL column, synchronizing other columns with CONTROL column position.

Sounds simple. In reality this is very complicated process and related with many technical difficulties. Let’s skip those and focus on practical side.

CONNECTING CABLES control box - column

Linak Deskline use MOLEX 6 pin female connectors on booth motor cable ends and female / male connectors for extension cable. In cable are:

Cable length is critical and max recommended length is 3m = 2m extension cable +1m motor cable.

The first limitation is signal from pulse counter: too long cable can cause signal distortions.

The second limitation is power line length: too long cable to fully loaded column can cause overload error in CBD6 because of voltage drop in DC lines ( low voltage running columns at first line ).

In situation when 3m cable length is not enough, add one more CBD6 closer to column and use multiparalel connection with other CBD6 ( more below).

Problems caused by wrong cable length are very rare, however, good to know.

COLUMN HEIGHTS and SYNCHRONIZATION precision.

Everything starts from Built in Dimension ( named used also as column min height, fully retracted column, column initialization height ). If we go to Linak Deskline data sheet ( lets use my favorite DL21 https://cdn.linak.com/-/media/files/data-sheet-source/en/lifting-column-dl21-data-sheet-eng.pdf ), we can find significant tolerances ± 5mm for BID.

Next step is STROKE ( or adjustment range ), for DL21 it is ± 3mm.

These numbers are little confusing in relation with statement “high accuracy”. Let’s look on meanings

STROKE. Mechanical stroke VS stroke set by system control box.

BID.

These notes are good to know for system design and understanding terms and meaning.

After initialization columns in the system works perfectly synchronized, where relative difference between columns are from:

These are very small numbers, haven’t managed to measure in real life.

What’s inside THE COLUMN?

Nothing special:

  1. Electric motor with pulse counter microprocessor.
  2. Lead Screw connected to columns metal casing.
  3. Sliding bushings between metal components in telescopic joint.

Again, sounds simple. But is not at all.

All elements are very well balanced, all items has high mechanical precision. Column assembling is state of art process.

System INITIALIZATION.

Is most important procedure for any synchronized height adjustable system.

When first connected control box doesn’t know at what position columns is system are ( also if there is only 1 column ). Process named INITIALIZATION ( sometimes RESET also SYSTEM SET, do not use those ) is necessary for system to place all columns in system in the same ( and known for control box ) position.

In modern synchronized systems initialization process is based on power overload method: when column is at lowest position and cant mask any further movement, control box increase power on column till it reaches certain level. All force created by electric motor is applied to LEAD SCREW ONLY, not to column components, only lead screw.

If columns are NOT in lowest position, control box drives all columns down in SLOW SPEED. In case columns were not in the same position, system waits till all columns reaches lowest position.

During initialization process ALL safety system are DEACTIVATED. In case the column movement down is blocked, column mechanism can break or system can identify wrong height for this column.

When Linak control box finds all columns and accept their min position, system moves all columns back up for some distance. ( 1-2mm ) This is system min height and pulse counter for CONTROL column is ready to start counting back and force.

This process is technical the same for practically all columns on market, the differences are at operational side: how to start it, how it ends.

Because of wide column range Liank CBD6 control box also makes max height initialization, expect some column types, if there is default stroke setting into control box ( no set stroke value in control box):

This is very useful function when columns with different stroke are used in one synchronized system: system automatically sets system stroke = shorter stroke from column into system.

Height control in height adjustable desk system.

Only after system initialization, controllable and synchronized movement up & down is possible.

As mentioned above, one columns is CONTROL column, pressing button up or down ( or controlling over Bluetooth, which actually is just another cover for hand control ) control box activates movement and counts pulses from motors microprocessor, controlling height position and movement direction.

Control box drives other columns connected to the same position as CONTROL column has. This process is controlled by very advanced algorithm to make it smooth and inviable for user.

System stops movement and enters into error mode as soon CONTROL columns movement is not as it should be according to control algorithm, or CONTROLLED columns doesn’t follow CONTROL column position.

All this doesn’t matter on load distribution between columns, it works perfectly synchronized or stops because of column overload.

Lifting capacity, power, speed, load bearing.

These terms are widely misused. And used mostly without any understanding on real meaning behind them.

Lets look on this from lifting column position.

Usually focus is on LIFTING UP.

From technical point of view LOAD BEARING is more complicated system state: when desks stands still, there is no electrical power applied to motor. Why then column doesn’t slide down under load? Because of:

NOTE. Linak has friction brake inside starboard columns ( 38mm/sec unloaded speed ) or electrically controlled stop system inside moder high speed columns.

System control box monitors motor position, microcontroller inside column never sleeps, as long as it connected to grid. Even when it is in deep sleep mode ( Zero power consumption mode ). For certain period of time also when it disconnected from grid.

If control box senses even minor movement / column height change, it enters into INITIALIZATION mode signaling about lost position.

Linak Deskline columns has special parameter SELF LOCKING telling how big load can be placed un column to keep it at position, without external power.

Therefore, if column has 80kg self locking, then 2 column desk can keep in position desk with total weight 160kg.

Simple calculation. Just one question: how we calculate LOAD ON COLUMN. Standard approach is evenly distributed weight on centered weight. However, when speaking about load ON COLUMN we must take in consideration also frame & table top, which makes sometimes 50kg & more.

Lifting capacity, power and lifting speed is closely related parameters.

Linak Deskline column data sheets has information about relation between load on columns & lifting speed. The name for this relation is POWER curve. However, this is measurement made in IDEAL CONDITIONS. Columns are not mounted under table top, connected with frame beams as it is in real life conditions.

In real life columns are not parallel to each other, there are other bending moments as result more friction in column. Also load distribution cant be perfect. And uneven leveling caused more load on one column, if there are more than 3 columns in system.

Without diving very deep into technical details:

Practical advice on safe side: max lifting = 70% of max load bearing for evenly distributed load.

Simple calculation shows that about 70% from electrical power applied to system is used to overcome loses in columns: friction in column, power loses in motor. In simple words: Linak CBD6 control box delivers 200W to system. 70% transforms into heat. 200W control box actually is 140W heater, if system runs at full load. This not exact number, just indication for further conversation.