Acta  Montanistica  Slovaca     Ročník 11 (2006), mimoriadne číslo 1, 1-9 

 
the pumps [9]. This mode makes it possible to store the energy independent of operation. The oil stored       
in the accumulator can be boosted into the circuit when an extra speed is desired. 

Heave Compensation. Three different types of compensation are possible with the RamRig

©

: the active 

compensation, the passive compensation and the semi active compensation. 

Active Heave Compensation. The  active  compensation  is  done  by  means  of  letting  a  heave  sensor               

to control the pumps. The vessel heave velocity and the vessel position are used as inputs to the pump 
setpoint. The actual position and velocity are measured and used as corrective  values,  determining                      
the setpoint of the pump and consequently the cylinder position in a closed loop regulator. Hoisting and 
lowering is possible by operating the control stick and moving the position setpoint for the cylinders. 

Passive Heave Compensation. The passive compensation  is done by means of the same accumulator 

used for the storing of energy. The gas pressure in the piston accumulator and the pressure vessels connected 
to the accumulator is variable. Prior to a passive compensation operation, the piston in the  accumulator                  
is centered and the gas pressure is set equal to the load pressure measured  in  the  cylinder.  When                         
the equilibrium is reached, a hydraulic connection by means of cartridge valves is opened and the cylinder 
piston rests upon a gas spring. The cylinder and the accumulator piston will now act the in inverse phase, i.e. 
when the cylinder is moving downward the accumulator piston is moving upwards and vice versa.                     
The apparent Weight on Bit variations are due to various losses within the hydraulic circuit. Typical losses 
are mechanical in addition to losses connected to the fluid flow and pressure variations in the pressure vessels 
due to the compression when the accumulator piston is moving. The maximum heave compensation depends 
on whether the rig is operating in the regenerative mode or not. The typical values of maximum heave are            
7.6 and 15.2 m in the normal and the regenerative mode, respectively. Hoisting and lowering can be done                    
by adding or removing the fluid from the circuit. Due to the pressure balance, the level will stabilise and 
prevent the accumulator piston from reaching the end stroke before the ram cylinders start to move.  

Semi Active Heave Compensation.  Temi  semi  active  compensation  is  done  by  over-pressurizing                

the pressure vessels creating a positive force on the piston side of the cylinders and operating the pumps               
on the rod side. The pump output is controlled by a heave sensor as in the active compensation. Hoisting              
and lowering is performed as in the passive compensation. 

 

Safety 

 

Braking. The braking of the load is done by means of an increase of the pressure on the piston side.   

The force equals the product of the pressure and the area of the  surface  on  which  the  pressure  acts.             
The acceleration is simply the force divided by the mass. The mass is constant, so an increase in the pressure 
at  the  piston  side  will  result  in  an  immediate  acceleration  against  the  velocity  direction.  Even                             
at the maximum load, there is still 35 Bar available for the braking purposes, which can instantaneously stop 
any load. The instantaneous stop of the load must be avoided due to the high stresses applied to the structure. 
This is done by using a filter at the operator stick to slow a sudden operator input.  

Floor Saver. Compared  to  a  winch-like  drawwork,  the  position  monitoring  of  the  cylinder  is  easy               

and reliable. There is an incremental pulse counter integrated in the cylinder assembly, with  an  accuracy                
of 1/10 mm. A continuous monitoring of the load velocity, weight, and the position allows for an effective 
monitoring of the kinetic energy of the load. The control system calculates the necessary braking distance 
based on the above mentioned parameters. If the operator moves the load beyond the point where braking 
should start, the control system will interfere and brake the load at the calculated distance. The compensation 
is  

± 0.06 [m] while the rig amplitude is ± 3.5 m. Hence, the RamRig

©

 compensation capacity in this mode               

is well within the design criteria for permissible position variations. 

 

The rack and pinion rigs 

 

History of Rack and Pinion Rigs, [25]. The rack and pinion technology has been with us in various 

applications for decades. The method is well known for a long durability and a high efficiency. The 
experience on the using rack and pinion technology in the drilling industry dates back to the mid 80’s, when 
it was used mainly for the pipe handling equipment and other relatively slow moving machines. With the 
forming of Engineering and Drilling Machinery (EDM) in 1997, significant advances and refinements of the 
technology contributed to several patent applications which later have been granted internationally. During 
the late 90’s, EDM was engaged in several projects involving the equipment for workover and snubbing 
operations in the North Sea area. At that time, such operations were dangerous to people and surroundings, 
often consisting of a suitable or not suitable equipment stacked on the top of each other without a consistent 
design and consideration to the HSE and the optimal functionality. To improve the situation, EDM designed 
a workover machine utilizing the rack and pinion technology allowing a faster and simpler rig up and rig 
down, a lower weight and a higher safety level. The main value, however, was that the rig could easily shift 

   3