The Linear Chain saves wire harnesses from dying

For decades, wiring harnesses for cars have been damaged by cold temperatures and had to be scrapped. The Linear Chain is now putting an end to this

Philipp Schmalzhaf - Sales Manager - GROB Antriebstechnik GmbH

by Philipp Schmalzhaf, Sales Manager

Wiring harnesses and the linear chain - GROB Drive Technology GmbH

What the Linear Chain has sparked worldwide

The capabilities of the Linear Chain from GROB have assisted Wokingham based Maypole Engineering in the design and manufacture of a turnkey conveyor and oven system for the main BMW Mini wiring loom. Its compact design and ability to operate without pneumatics helped ensure the success of the project. In fact, the system could become a BMW standard – Maypole reports it now has enquiries for further systems from South Africa, China and the Netherlands.

Why do wiring harnesses "die"?

Wiring looms manufactured in Europe for the BMW Mini production lines at Cowley in Oxfordshire arrive in blue harness bags. However, a problem was identified with the looms arriving in winter. Due to the cold weather, some components; due to the loom temperature within the bag, became damaged during assembly. As each wiring harness is for a specific car, damaged components mean scrap looms.

“We were approached by BMW to tender for a system that would gently heat the looms to make certain parts more pliable and fit for assembly,” explains the company’s Managing Director, Stuart MacSwan. “Our successful proposal was based on a 9 yards oven system with a powered, Linear Chain driven conveyor that would allow BMW to heat 20 bags simultaneously in a 20 minute timeframe – thus delivering a one minute production cycle time.”

BMW application with a Linear Chain - GROB Drive Technology GmbH

How was this problem specifically addressed?

Maypole devised an automatic chain loop system within the oven to meet the criteria. The loading end is a manual feed system that allows the pallets to be returned to the load area after the harness heating bag has been delivered to the vehicle. The basis of the transportation system relies on a Linear Chain from GROB.

“We’ve used this product from GROB before and they work well,” says Mr. MacSwan. “For this application our casing is mounted vertically and therefore the product is a compact solution. The product allowed extended linear motion for very small space requirement. Furthermore, being electrically driven it eliminated the need for pneumatics, which is a huge advantage in a system like this.”

In its magazine, the chain is stored spirally within a narrow chamber making the Linear Chain ideal for applications demanding long strokes where space is at a premium. The device provides high positioning accuracy, constant stroke speed and shock-free motion with no elastic hysteresis under load. It's been designed for a long operational life and minimal maintenance.

The pushing application on the oven system at BMW Mini requires a 1 yard transfer, which is completed in four seconds. Each bag with wiring harness weighs around 25kg (55lbs). The oven system heats the bags at a temperature of 60°C (140°F), allowing the nominal core temperature within the bag to rise by 11°C (52°F).

The project was carried out by our partner R.A. Rodriguez in the UK.

Linear Chain BMW application - GROB Drive Technology GmbH

"BMW Mini UK is delighted with the results of the heating system, as the wiring harness can now be much more easily installed in the vehicle," says Mr. MacSwan. "Not only that. Fixing grommets that were previously very difficult to fit now snap in very easily."

An exceptional case becomes the standard

The system was installed at Cowley in the summer of 2013 and it's been working without issues for three shifts a day ever since. As a result of the success, other BMW plants have since made enquiries that could see the system become standard at this automotive giant. According to Mr. MacSwan as many as four or five further systems could be commissioned in the next year or so. The system adheres to all safe working standards and can be applied to any size of harness heating bag.

Linear Chain SK - GROB Drive Technology GmbH

Fact Sheet

The Linear Chain is available in three installation sizes, allowing stroke lengths of up to 5 meters and a maximum thrust force of up to 35,000N.

FAQs about Linear Chains

A Linear Chain is a type of chain that can be both pulled and pushed. When the chain links are pushed together, they stay stable and rigid, allowing you to move things forward. It’s often used in machines to lift or push objects.

What a Linear Chain is and where it is used - GROB GmbH chevron_right

Depending on the size, the driving speed is usually below 50rpm.

Yes, lifting systems with multiple chains connected together are common.

The chain of the Linear Chain consists of links that rest on the shoulders and pins of the succeeding link. The chain of the Tower Chain is constructed with U-shaped chain links, providing greater stability and enabling unguided strokes of over 4m.

In standard applications, Linear Chains can be operated with a speed of 250mm/s. Special applications have already been implemented with speeds exceeding 800mm/s.

Yes, the use of stainless steel materials is a common practice for environments with aggressive media.

Yes, depending on the proximity to the product, the chain can also be completely made of stainless steel.

  1. When under pressure load: depending on the control, 100% repeatability can be achieved.
  2. Under changing loads: the control system must consider the backlash at the sprocket and manufacturing tolerances in the chain links.
  1. The load must always be guided
  2. Acceleration should be controlled via a ramp
  3. The chain cannot perform a swiveling movement
  4. The permissible buckling length must not be exceeded

No, within the buckling range, Linear Chains can also be used without guidance.

  1. Electronic bridge: If each lifting element of the system is driven by a motor, electronic synchronization can be achieved through encoders.
  2. Mechanical linkage: More cost-effective and fail-safe are cardan shafts and bevel gearboxes, which can connect all lifting elements of a system together.

The polygon effect occurs when a chain is positively driven by a sprocket. In this case, the chain cannot run perfectly circularly on and off the sprocket, causing deviations in the path of the traction medium. The speed of the chain then fluctuates periodically around a mean speed, which can manifest as vibrations in the chain.

Since the chain undergoes radial movement due to the polygon effect, the guide plates are extended, and minimal play is allowed. This helps mitigate this effect.

No, swiveling movements are not possible with the Linear Chain.

65% with chain magazine, 80% with free chain.

No, the load must always be guided.

There is no calculation basis for this. The buckling length has been determined through tests. You can find a corresponding diagram for horizontal applications here: General Catalog 2023 (grob-antriebstechnik.de). For vertical applications, please contact us.

No, a Linear Chain can never take over the guiding itself. The load must be guided.

  1. Lubrication system: attached lubrication brushes extend the lifespan.
  2. Chain magazine: the chain can be rolled up behind the housing.
  3. Reduction gear: especially useful in lifting systems to reduce torque through gears.
  4. Force sensor: for measuring axial load and protection against overload.

We always recommend using our standard link to connect your load. Utilize all the holes to ensure proper loading of the chain. Dimensions for the front link can be found here: General Catalog

As standard, GROB chains are galvanized. For environments with aggressive media, stainless steel chains can be used.

  1. Standard: 180°C (356°F)
  2. High-temperature continuous: 550°C (1022°F)
  3. High-temperature short-term (under 2 minutes): 1050°C (1922°F)
  1. The load must be guided
  2. The Linear Chain size must be chosen correctly
  3. It should be driven over a ramp

Yes, hardened chain links achieve a lifespan four times longer.

  1. A chain magazine winds the chain in multiple circular paths. Advantage: greater space saving.
  2. A chain cover protects the chain attached to the housing. Due to the attachment, the chain aligns itself and thus halves the stroke length. Advantage: more cost-effective.

Yes, the chain can be stored perpendicular to the lifting movement, such as 90°, or even 180° (parallel) to the lifting movement, as in the case of tool tables. The lift then operates on the table, while the storage runs parallel underneath it.

The T-guide was developed when space for the standard rail above the sliding surface was lacking. In one application example, the customer needed to maneuver with a forklift. The T-guide rail was then embedded in the floor, allowing the vehicles to continue maneuvering undisturbed.

No, you should provide a brake on the motor.

Check for dirt or worn-out parts. Thorough cleaning and, if necessary, replacement of damaged components may solve the problem. If the Linear Chain is noisy after acquisition, system tensions could be responsible.

The different installation positions do not affect the usability of Linear Chains (e.g., through oil sight glasses or similar). By simply changing the mounting side of the mounting brackets, the mounting sides can be adjusted as needed.

There's no calculation basis for this. Tests have shown that for standard chains, 250,000 cycles, and for hardened chains, 1,000,000 cycles represent realistic values.

Question not included?

You can find more application examples and drive solutions here

Linear Chain - GROB Antriebstechnik GmbH

What is a Linear Chain?

Discover the basics of Linear Chains and the impressive technology behind them in our beginner article. We explain how Linear Chains work and the important role they play in various applications. Dive in and learn why Linear Chains are a key component for precise linear movements.

Learn more

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Thomas Moeschle

Thomas Möschle, Key Account Manager