Control Arm

Clansman Dynamics has developed and patented a Control Arm and force feed back system which solves well known problems that have existed with competitors’ machines since they were first developed 25 years ago. The system uses the standard Master Arm / Slave Arm principle but with a completely different, and now well proven, arrangement.

Tired arms arise for 2 reasons:

  • With competitors’ manipulators the operator grips the control handle and has no support for his own lower arm. The Clansman arrangement provides 100% support to the operator’s arm regardless of the position of the Master Arm and does not tire the operator’s arm.
  • With competitors’ manipulators the operator always has to overcome a load caused by seal friction and the force of the force feed back system itself. With the new Clansman arrangement the operator only has to work against the tiny friction force from low friction bearings while he keeps the Master Arm synchronised with the Slave Arm. The Clansman system of force feed back does not tire the operator.

Key Design Features

The Clansman solution provides a very precise, comfortable,

robust and easy to maintain Master Arm.

  •      Variable, dual motor,  electric force feedback system.
  •      Precise, reliable and robust design.
  •      Ergonomic, injection moulded control handle with aluminium switch plate.
  •      High-quality microswitch selection, 10,000,000 cycle lifespan.
  •      Use of well-proven commercial parts.
controlHandle3

Why roller bearings?

Clansman Dynamics uses large spherical roller bearings and taper roller bearings throughout the range of machines.

One competitor uses PTFE spherical bushes. Another competitor uses a mixture of needle roller bearings, roller bearings and steel spherical bushes.

It is worth noting that one large Italian foundry which has destroyed a machine from one competitor and which has 4 limping machines from another has made a campaign change to replace spherical steel bushes not with PTFE spherical bushes which would have been a straight swap but has machined new parts with larger bores for roller bearings.

 

There is no denying that manipulators present a severe test of any bearing because of shock loadings, dirty environment and the fact there is not much more than a 90 degree movement on any joint.

However some facts are known:

  • We know that steel sphericals last about 9 – 18 months.
  • We know that needle roller bearings lose rollers, are less good for shocks than large rollers and store less grease between the rollers.
  • We know from information supplied by the bearing manufacturers, that even the theoretical life for PTFE spherical is very unsatisfactory.
  • We know that properly selected spherical roller bearings give a better result even than plain roller bearings because they self align.
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Manipulator Fatigue

Manipulators on a tough duty in a forge or foundry may be doing a cycle every 6 seconds and for 24 hours per day – that is more than 7 times the number of cycles that might be performed by a standard hydraulic manipulator. The result is an unacceptable number of failures in competitors’ manipulator structures after quite short operational periods.

Clansman Dynamics has recognised the problem and produced a design which allows for a cycle every 6 seconds and a 10 year life.

Clansman Dynamics Solution

The first step was to develop a computer programme which would calculate stresses for all positions of the manipulator with no assumptions.

Nobody should trust such a computer programme without verifying with a scale model and then strain gauging of the prototype machine. These were the second and third steps taken by Clansman Dynamics engineers after the machine had been designed to the correct standards.

One competitor uses PTFE spherical bushes. Another competitor uses a mixture of needle roller bearings, roller bearings and steel spherical bushes.

It is worth noting that one large Italian foundry which has destroyed a machine from one competitor and which has 4 limping machines from another has made a campaign change to replace spherical steel bushes not with PTFE spherical bushes which would have been a straight swap but has machined new parts with larger bores for roller bearings.

There is no denying that manipulators present a severe test of any bearing because of shock loadings, dirty environment and the fact there is not much more than a 90 degree movement on any joint.

Precise knowledge of stress levels is critical!

International standards are available for the design of structures which will not fail. These standards describe the types of loading, materials, permitted stress levels for a certain life, etc.

One line of permitted stress levels taken from a typical table shows the nature of the problem:

Number of Cycles (millions) 0.125 5 10 20 40
Years in Operation 0.03 1.25 2.5 5 10
Permissible fatigue stress N/mm2 221 156 143 131 120
Permissible fatigue stress Tons/in2 15 10.6 9.7 8.9 8.16

In simple terms this example shows that if the complex stress calculations are wrong by 10% then the life of the structure may be reduced from 40 million cycles to 20 million cycles or worse.

It is useless to achieve the correct stress criteria by simply adding weight. Instead it is necessary to use steel sections with a larger modulus, steel castings where weld fatigue problems are especially difficult, weld and profile details which avoid stress concentrations, bearings which are correctly sized and whose life calculations have been checked by a leading bearing manufacturer such as SKF or FAG.

Above all, knowledge is required. Check this out with our competitors. Fatigue avoidance is vital but only a start: shock and stall loads must also be taken into account and their effects engineered out.

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Roll Axis - Accessible Seals

Clansman Advantages:

  • Clansman Dynamics offer 360 degree rotation as standard (competitors can provide this too).
  • 360 degrees rotation means a hydraulic rotary joint to get oil down to the grippers.
  • And there is far less danger of dirt ingress.
  • There is no gearbox. This avoids backlash and wobble.
  • The motor is the same direct drive motor as on Axes 1 and 4 so there is no wobble.
  • Only one spare motor seal set or motor need be carried as a spare and 3 axes are covered.
  • Clansman Dynamics puts the seals for this joint in a simple seal housing at the top of axis 6.
  • Competitors put the seals for this joint down in between the 2 taper roller bearings.

Clansman seal replacement steps:

  • Remove seal housing.
  • Change seals.
  • Replace housing.

How The Competitor Replaces a Seal:

  • Remove hoses
  • Remove hydraulic motor.
  • Remove adapter plate.
  • Remove high ratio gearbox.
  • Remove adapter plate.
  • Remove large hex nut and tab washer.
  • Jack out roll shaft from taper roller bearings.
  • Reach into housing to change seals.
  • Check grease seal is not damaged, if yes jack off taper roller rings and replace bearings.
  • Replace shaft.
  • Torque up large hex nut.
  • Refit plate.
  • Replace adapter plate.
  • Refit motor.
  • Refit hoses.

A 500 kg capacity manipulator may need a force in the horizontal cylinder of around 17 tonnes to push the arms out from minimum radius. Larger machines will need larger forces, so a cylinder is supplied to push with this force. However once the load has reached top dead centre it needs no force for the other half of the horizontal stroke because gravity can do the work.

This means that if the operator stalls the machine against the floor or a conveyor the cylinder force of around 17 tonnes plus the self weight of the manipulator, act together to cause very large stall loads on the machine. This leads to breakages because in certain positions of the machine, the bending moments which these forces cause, are large.

In the diagram it can be seen that all the force from the cylinder is available for doing damage.

But the force still exists because the cylinder knows only to push with a force of 17 tonnes.

So Clansman Dynamics cuts that force to a negligible figure once the manipulator is beyond a certain point in the envelope. The operator is completely unaware of the change of mode. There is no loss in performance.

But Selective Force Limitation gives a 40% reduction in the forces that act to destroy the manipulator (and conveyors, monorails, etc.).