The invention relates to a method and arrangement in the condition monitoring of gaps and leaks in the operating devices of a point-controlled set of booms in a work machine, in which the set of booms comprises, as consecutive parts

• a ring frame to be attached rigidly to the work machine,

• a base part of a hoist mounted rotatably in bearings on the ring frame,

• a first boom pivoted to the base part,

• a second boom pivoted to the first boom,

• a possible third boom as a telescopic structure.

The set of booms includes operating devices for operating each part with the aid of a control system and the control system includes sensors measuring the relative posi tion of each part relative to the previous one, starting from the base part, thus provid ing position data. A control command given by the operator as to the direction and speed of motion of the end of the set of booms is implemented using the speeds of motion measured by the sensors of the various booms of the set of booms. An im portant sub-area in the condition monitoring of a set of booms is the condition moni toring of its operating devices, because the main deviations arise in the operating de vices due to leaks in the operating devices' hydraulic components. The set of booms' operating devices creep with age in any case.

In a rotation device, the movement of the piston or rotation motor only creates move ment once the operating device has moved by the amount of backlash. In a set of booms, leaks in a hydraulic cylinder create continuous creep relative to time.

The term base part generally refers to the first part of the boom supported on a ring bearing, so that it also applies to a pillar-shaped base part.

The ring frame may be on a tiltable base. Here a rigid attachment refers to the ring frame not being able to rotate in the work machine. The above factors can also be measured in as such known ways using various inertia measurement units (IMU) and devices, such as various MEMS sensors, in which an inclinometer and/or gyroscope can advantageously be included. In an inertia meas urement unit, an inclinometer detects acceleration forces, including the Earth's gravi ty, relative to at least one and preferably three axes at right-angles to each other.

Such an inclinometer arrangement determines its momentary position very precisely relative to the Earth's gravity, i.e. the gravity vector. In addition, the inertia measure ment unit's gyroscope means determine the movement's/rotation's angle velocity and angular acceleration data. Such a gyroscope arrangement permits the piece's state of motion to be determined and these data can be utilized in determining the attitude and state of motion of individual booms of the set of booms and thus also in the con trol of the set of booms and the point of the set of booms. Definition of the angle atti tude of the rotation device can also be included in the control of the set of booms and the point of the set of booms.

Such position calculation and control of the boom point is described, for example, in the following literature references:

• Bjorn Lofgren: Kinematic Control of Redundant Knuckle Booms, Licentiate the sis, Department of Machine Design, Royal Institute of Technology, Stockholm, 2004

• Bjorn Lofgren: Kinematic Control of Redundant Knuckle Booms with Automatic Path-Following Functions, Doctoral thesis, Department of Machine Design, Royal Institute of Technology, Stockholm, 2009

• Mikkel M. Pedersen, Michael R. Hansen, Morten Ballebye: Developing a Tool Point Control Scheme for a Hydraulic Crane Using Interactive Real-time Dy namic Simulation; Modelling, Identification and Control, Vol. 31 , No. 4, 2010, pp. 133-143, ISSN 1890-1328

• https://wiki.metropolia.fi/displav/sensor/Acceleration+senso rs;

Sakari Lukkarinen 19.5.2015

A point-controlled set of booms is never entirely stable, but even in new hydraulic cyl inders minor leaks and backlash must be accepted as tolerance. This means that af ter some time the boom's point is not in the position calculated by software. The con dition of the set of booms is monitored and at regular intervals the set of booms' co- ordinates are synchronized, so that during operation the position error of the set of booms' point is less than 20 cm in various co-ordinates. As the machine ages, or even earlier if some part malfunctions, the creep of the set of booms per unit of time increases. Because the machine operators' subjective estimates of the amount of creep per unit of time vary greatly, it is difficult to decide what the correct action would be in maintenance operations. Though regular compensation of backlash / creep is known, its link to condition monitoring has been limited.

The invention is intended to create an improvement in the said maintenance problem and to permit the objective monitoring of leaks and gaps. The invention's characteris tic features are stated in the accompanying Claims. A service centre, which may be very far from the machine's site of operation, can now receive accurate data on the magnitude of creep. In the service centre, there is preferably a server apparatus for recording and processing the measurement values needed in long-term monitoring. Here the term service centre refers to an entity physically separate from the work ma chine, for example a service managing equipment, which monitors the service re quirements or condition of the machine. In addition, the creep can be advantageously divided into sub-factors, so that a possibly faulty part can be defined beforehand. The relative increase in creep per unit of time is a sign of a more serious fault and this can now be easily detected using the method according to the invention. The same basic method can be used to monitor backlash in gears, when the moment of time t2 is de tected from the set of booms' start in the direction of rotation.

In forest machines, both the rotation device and the hoisting boom itself are subject to great stress. In the set of booms of a conventional forest machine, there are at most two folding booms and a possible multi-part telescopic boom (forwarder). The rotation device's mechanism and pinion racks and gearwheels wear, creating a clearly detect able gap. In cylinder operating devices, their spillover increases as a result of wear.

In a forwarder the set of booms' net moment, i.e. the value depicting its load capacity, is 100 - 200 kNm. In harvesters the net moment is 150 - 300 kNm. If the rotation de vice's great loading is also taken into account, in forest machines condition monitoring is very useful, as backlash in gears can increase very rapidly. In the invention, the work machine's point-controlled boom positioning system can be utilized to a considerable extent. In addition, the control system is equipped with means for detecting when the machine is not moving, which detection can trigger a measurement period. At its simplest, two consecutive position detections between a selected period of time are compared to each other. The difference is compared to a preset criterion, giving as a result the state of the work machine. This either meets the criterion, or in a worse case the creep has really increased over the permitted limit.

Gap/creep values are preferably collected in a memory, so that each creep value can be compared to previous measurements and a possible deviating change detected.

As such, other types of sensor too can be used. For example, angle-sensors could be used in each pivot.

What is important however, is that momentary position data can be calculated for the boom's point or some other reference point, using the sensor and structure data.

The control device continuously calculates the booms' positions. By utilizing a so- called Jacobian matrix, the desired movement of the boom point is divided into parts for the various booms. The operator's control command to move the boom's point is implemented by dividing the control command into individual boom's movements to move the boom point according to the control command, using the booms' attitudes and states of movement as measured by the sensors. One technique is disclosed in application FI20135085, in which the direction and speed of movement of the set of booms are implemented using the speeds of movements of the various booms of the set of booms.

The machines' operating devices are hydraulically operated, particularly all the oper ating devices (cylinders) of the set of booms. Electrification is, however, progressing and in the future the sets of booms will at least partly operated by electricity, i.e. elec trical operating devices will then be in use.

If it is wished to check for creep in a set of booms, the consecutive position data of the end point and possible other reference points are saved in the memory. A select- ed number of co-ordinates in a stable state saved at temporally regular intervals are them saved in the memory. Saving starts from the beginning, when movement of the set of booms is detected, when the previous reference point loses its significance. When measuring the gap in gearings, the time difference has, as such, no signifi cance, because the absolute circumferential shift of the point of the boom tells the moment in time when the gap has ended. The gap in the toothing is obtained from the operating device's sensor as the distance travelled by a tooth, until the first tooth reaches the power-transmitting tooth. By using nearly the same monitoring operation, the hydraulic cylinders' leaks and gaps in the rotation device are obtained for the con dition monitoring.

In one embodiment a trend value is calculated from the gap/creep values, and an alarm is given if the trend value rises over a set limit. Here trend means a temporal derivative. An increase in the trend's angular coefficient thus causes an alarm.

Figure 1 shows a set of point-controlled booms (forwarder)

Figure 2 shows another set of point-controlled booms (harvester)

Figure 3 shows the hydraulic and electrical control relating to the point-control of Fig ure 1

Figure 4 shows a flow diagram of the implementation of the condition monitoring Figure 5 shows the point control’s creep trend value in long-term monitoring.

According to Figure 1 , attached to the work machine is a base 10, in which is a rota tion ring 12, in which there is, in turn, a lower 121 and upper 122 ring mounted in bearings relative to each other. The upper ring 122 is rotated by a rack mechanism 101 operated by hydraulic cylinders, in which there is a magnetostrictive linear sensor S1 .

The hoist's pillar 14 is attached to the rotation ring's 12 upper part 122. A hoisting boom 16 is in turn pivoted to it, and then in turn a folding boom 18, in which is a tele scopic extension 19. It has an operating device 192 schematically marked in the fig ure. A grab or harvester is attached to the pivot's 20 pin 201 . In the base 10 is an acceleration sensor SO. This is not entirely essential. Monitoring can take place in a set of co-ordinates according to the pillar 14. In the pillar 14 is a sensor S2, in the hoisting boom 16 a sensor S3, and in the folding boom a sensor S4, which are all also acceleration sensors. In the telescopic extension 182 is a magneto strictive linear sensor S5. The control of the set of booms is monitored simultaneous ly. The set of booms' controlled immobility is then detected. When the set of booms moves due to a control signal, recording of the co-ordinates is started from the begin ning. When controlled immobility is detected, two recorded co-ordinate values are compared temporally to each other. If the difference (D) is greater than a selected cri terion, a creep alarm is made, which can mean, for example, an increase in the gap between the gearwheel and the pinion rack, or a leak in a hydraulic cylinder or other hydraulic-system component.

According to one embodiment, the measurement period is started manually. This is a clear operating instruction. The work machine's control may issue a reminder of this maintenance measure. This has the advantage of a very clear result, as the operator concentrates on the measurement, generally a few minutes being enough.

Alternatively, the measurement period is started automatically when the said stable state is detected. Because work is not interrupted, the measurement period starts again and again, until the work machine has been stationary for long enough.

The creep values are preferably saved in the memory for long-term monitoring. For example, in weekly monitoring a deviating speed of change may be seen well before hand, indicating a serious fault.

The set of booms of Figure 2 differs in its base from the structure in Figure 1 . The up per part 122 of the rotation ring 12 is equipped with internal toothing and is rotated by a motor 101 ', which rotates a gearwheel against the internal toothing. Connected to the motor 10T is a rotation-angle sensor S1 , which functionally corresponds to Figure 1 's magnetostrictive sensor, i.e. it provides data on the rotation angle. As such the sensor SO is not essential. Comparison can be made either in pairs or relative to the pillar 14 (Figure 1 ) or the functionally corresponding lug 14’.

According to Figure 3, the cylinders 101 , 142, 162, and 192 are operated by propor tional valves 1012, 1422, 1622, and 1822. Electrical control takes place through ancil lary control elements C1 , C2, C3, and C4 from the control system C. This is actually part of the work machine's control system, but for clarity it is shown here as a sepa rate part. The control system receives data from both the sensors SO ... S5 and a keyboard 34 (or a graphical interface's cursor). The results are shown on the system's display 32. The data are preferably sent to the service centre's 35 server 36, which calculates the trend value from consecutive creep values and similarly from the gaps.

More specifically, operation takes place as follows.

• the position of the boom's point is saved

• the control system saves in its memory means the consecutive position co

ordinates of each sensor

o P1_t1 , P1_t2, P1_t3... P1_tn

o P2_t1 , P2_t2, P2_t3... P2_tn

o P3_t1 , P3_t2, P3_t3... P3_tn

o .. ..

o Pn_t1 , Pn_t2, Pn_t3... Pn_tn

• the control system monitors the gaps in such a way that

- the measurement period starts with a stability condition, in which the control command is not performed and the measurement period is interrupted, if a control command appears,

- when the control command is not performed and the measurement period is interrupted, if a control command appears,

- the control system calculates the relative position At1 = At1 (P1_t1 ; P2_t1 ;

P3_t1 ....Pn_t1 ) of one or more sensors relative to the first or any of the previous sensors at the moment in time ti using the measured sensor data, - the control system calculates the relative position At2= At2 (P1_t2; P2_t2; P3_t2;Pn_t2) of the corresponding sensors relative to each other at the moment in time t2 using the measured sensor data,

- the system calculates the difference in the relative positions of one or more sensors at selected consecutive moments in time, when the stability condi tion has been met, D = At2[]— At1 [], and

- the calculated D-value is shown to the operator.

When monitoring of the gaps of the rotation device's toothings, the moment in time t2 is determined from the start of movement of the part to be rotated, when the meas ured difference is recorded as an absolute value.

The operations described above are implemented with the aid of software belonging to the control system.

The system can include a functionality, by which the set of booms is rotated manually from one extreme position to the other. The area of free movement depicts the size of the gaps. By saving these values and comparing them to previous values the en largement of a gap can be detected.

The same inventive idea also contains a variation, in which the position sensors are used to detect a situation, in which a control command is given for rotation and it can be seen from the sensor's value that the cylinder or motor moves. Then follow the response from the hoisting boom or pillar's sensor to see when the set of booms be gins to move. Thus a gap is detected by running a control command. The stability condition is then slightly different compared to the previous one, in which monitoring always starts only if a control command does not come.

In Figure 4, monitoring starts when the work machine starts and then it is always on. Here, the period starts by registering the point's position (50). The operation can in clude a condition, according to which the point must be in a specific area farther away, i.e. the set of booms folded out, when creep will be detected more easily. The detected attitude values measured (51 ) from the sensors are saved in the memory register. From these, the position data (52) are calculated using the boom's geometry data, for example the position of the point at the moment to. The same is repeated at regular intervals, so that at the moment ti (5 s— 30 min from the previous one) new attitude values (53) are obtained and new position data (54). During service breaks etc., longer monitoring periods can be used and more precise information obtained. It will then be easier to decide the leak's location. During the machine's operation, criti- cal changes can be detected over even short (5 - 30 s) periods.

The difference in the consecutive position data divided by the time interval is the creep value A _t ^ , which is saved in the memory (60).

The creep value A _t ^ is compared to a first limit value D ₀ k (62), by which an alarm (65) is given if necessary. If consecutive creep values D _1h are saved in the memory, a trend (63) depicting the speed of change in creep can be calculated from them.

Condition monitoring of the gap in the rotation device's toothing takes place in other wise the same way, except that instead of a moment in time ti the start of movement of the rotation is monitored. Sensor S2 detects, for example the start of movement and sensor S1 the gap (difference at moments ti and to).

According to Figure 5, the trend value gives considerable added value in the long term monitoring of the work machine. The trend, i.e. a measured derivative of the measured creep values, reveals to service operations a developing faultiness much earlier, possibly even before the local alarm limit is exceeded. The same trend phenomenon as above, i.e. an accelerated increase indicating an approaching component failure, can be seen in the condition monitoring of the tooth ing.