Patent Description:
A typical harvester for logging has a hydraulically powered chain saw for cutting trees. Different trees may have different densities, and the settings for one tree may not be optimal for another type of tree or the same type of tree at a different weather. For example, trees may be more difficult to saw during winter, when the wood is dry and hard, and easier to saw during spring when it is warmer and the trees have more sap.

The harvesters may need to be configured for each type of tree, with respect to a number of parameters to optimize the efficiency. Such parameters may, for example, be saw chain speed, the type of wood, season, weather, chain quality, etc. However, most commonly, the harvesters are configured once, and then used with the same parameters even if the environment changes. That is, most harvesters are used with a less than optimal configuration as the configuration may not be updated as often as needed.

It should be noted that industry safety standards are provided for harvesters. For example, there is a standard for maximum chain speed, ISO <NUM>, limiting the maximum chain speed to <NUM>/s. This limitation may decrease the efficiency of the harvester to less than maximum.

Hence, there is a need for an improved harvester with better efficiency, which may utilize a maximum chain speed.

<CIT> relates to a chain saw, wherein the chain of the saw blade is driven by a motor. The chain saw is driven as a function of the maximum allowed performance of the drive motor of the chain saw.

<CIT> relates to a sawing machine comprising a saw chain and a hydraulic system including a sensor for measuring the hydraulic pressure.

<CIT> relates to a felling saw recovery control, wherein the associated motor should be operated at a target speed.

However, the prior art documents referred to are not able to provide the above-mentioned desired performance of a harvester.

An object of the present disclosure is therefore to mitigate at least some of the drawbacks described above. To achieve this, a control unit for controlling a saw in a harvester according to claim <NUM> and a method for controlling a saw in a harvester according to claim <NUM> are provided.

Hence, according to a first aspect of the present invention, a control unit for controlling a saw in a harvester is provided. The saw is driven by a first hydraulic system and the saw is adapted to apply a saw pressure on a sawing area during sawing. The control unit comprises a sensor for measuring a pump pressure of the first hydraulic system. The control unit is configured to, in response to the pump pressure being above a first predetermined value, decrease the saw pressure applied by the saw during sawing, or, in response to the pump pressure being below a second predetermined value, increase the saw pressure applied by the saw during sawing, wherein the saw is operated by an actuator. The control unit is further adapted to control a pressure in a second hydraulic system driving the actuator. The control unit is configured to monitor a first pump pressure in the first hydraulic system during a sawing cycle and to control the actuator during a subsequent sawing cycle based on the first pump pressure.

According to a second aspect of the present invention, there is provided a method for controlling a saw in a harvester. The saw is driven by a first hydraulic system and the saw is adapted to apply a saw pressure on a sawing area during sawing. The method comprises the step of obtaining a pump pressure from a pump of the first hydraulic system. The method further comprises to, in response to the pump pressure being above a first predetermined value, decrease the saw pressure applied by the saw during sawing, or, in response to the pump pressure being below a second predetermined value, increase the saw pressure applied by the saw during sawing. The method further comprises the steps of operating the saw by an actuator, and controlling a pressure in a second hydraulic system driving the actuator, monitoring a first pump pressure in the first hydraulic system during a sawing cycle, and controlling the actuator during a subsequent sawing cycle based on the first pump pressure.

In this way, the control unit may control a pressure applied by the saw during its operation. During an operation of the saw, the load applied on the saw by the material may depend on one or more sawing conditions. For example, the orientation of the saw during operation, the properties of the material to be sawed, the speed of the saw through the material to be sawed, etc., may influence the saw. It will be appreciated that an overload of the saw by applying too much pressure against the sawing area during operation may be avoided by the present invention, as the control unit may estimate the load applied on for the saw and decrease the pressure on the sawing area.

This may be beneficial, for example, if the tree is more difficult to saw through than the saw is configured for.

For example, the control unit may control the operation of the saw in case the material (e.g. wood) is easier or harder to saw through than what the saw is configured for. The control unit may sense a pressure of the system that is lower (or higher) than a first (or second) predetermined value, and then increase (or decrease) the saw pressure of the saw on the sawing area. The present invention is highly beneficial in that the control unit may adapt the operation of the saw such that the sawing may be performed at an efficiency, or at least close to a maximum efficiency, without overloading the hydraulic system powering the saw.

Sawing systems according to the prior art may try to keep the saw at a maximum speed for the saw. However, an operation of this kind may lead to power loss or malfunctions in the system, e.g. due to an overload of the hydraulics of the system. The purpose of the sawing systems of the prior art is to avoid that the motor is overloaded, being a completely different concept than that of the subject-matter of the present application of performing the control based on the pump pressure of the pump for not overloading the pump and/or keeping a maximum power of the pump during the operation of the saw. Notably, for many systems according to the prior art, it is assumed that the energy source can deliver more power than the motor can handle. In contrast, the purpose of the subject-matter of the present application is that the control unit controls the pump, and the motor (only) performs the work which the pump can deliver. More specifically, the prior art does not teach, nor suggest, any sensor for measuring a pump pressure of the first hydraulic system and a control unit which is configured to, in response to the pump pressure being above a first predetermined value, decrease the saw pressure applied by the saw during sawing or in response to the pump pressure being below a second predetermined value, increase the saw pressure applied by the saw during sawing. Instead, it should be noted that the kind of arrangements found in the prior art merely try to keep the saw at a maximum speed.

It has been realized that the saw may be operated even in a case of a relatively high load applied on the saw, if the pressure applied by the saw on the sawing area is adapted to accordingly, so that overloading the saw may be avoided. It should be noted that the effect of a driving hydraulic system is limited, and that the work applied by the saw affects the driving hydraulic system. By the control unit and method of the present disclosure, a maximum sawing effect may be obtained while at the same time utilizing the hydraulic system at a maximum (or close to maximum) effect. This may be achieved by adapting the sawing pressure based on the pump pressure of the hydraulic system, i.e. adapting the sawing operation based on the load the pump is subjected to. The control unit may decrease or increase the pressure applied by the saw during sawing in accordance with the measured pump pressure. The decrease or increase of the pressure applied by the saw during sawing via the control unit may be implemented by monitoring a pump pressure of a pump driving a hydraulic system for powering the saw. In this way the load on the saw may be estimated and monitored. An increase in the pump pressure of the hydraulic system may indicate that the saw cannot be operated to a maximum extent and that the saw may be overloaded, or may be close to be overloaded. Similarly, a decrease in the pump pressure may indicate that the saw may use more power without being overloaded. In this way, the sawing may be controlled to be operated at a maximum sawing speed or pressure, or at least close to a maximum sawing speed or pressure, without overloading the saw, and thereby the hydraulic system.

As the saw is driven by the hydraulic system, the pressure may increase when the pressure applied by the saw is increased. When the pressure in the system exceeds, or is close to exceed, the maximum pressure of the system, the pump in the hydraulic system may be overloaded and may stop providing a flow in the hydraulic system. That is, when the saw is overloaded, the system driving the saw may also be overloaded. The control unit may control the pressure applied by the saw during sawing to stay close to a maximum sawing pressure and speed, without overloading the saw. In this way, the risk of the system being overloaded may be decreased, while utilizing the maximum effect of the hydraulic system.

To reach the maximum effect or performance of the sawing system, the pressure in the hydraulic system may be kept close to a pressure maximum. This provides a flow close to a maximum flow of the system that may be used during sawing to control the sawing speed of the saw. Having a close to maximum pressure and a close to maximum flow in the hydraulic system provides for utilizing the saw at a close to maximum performance, for example, by decreasing the sawing time. Utilizing the saw at a close to maximum performance may also decrease the risk of problems related to a slower operation of the saw, such as a risk for end splits, lowered performance (i.e. cut time), higher risk for operators of the saw, etc..

In previous sawing systems for harvesters, the sawing needed to be programmed and controlled based on a specific set of parameters, such as the type of tree intended for sawing or the saw itself. In contrast, with this control unit, the optimal performance of the saw may be determined during sawing by monitoring the pump pressure. That is, the sawing may be adaptive to the current environment, and does not have to be based on a previously set configuration.

In this way, the pressure applied by the saw may be adapted to the capacity of the hydraulic system, not just the saw, as the pressure applied by the saw is based on the pump pressure.

It will be appreciated that the term "saw" may refer to any type of saw configured to be driven by a hydraulic system. For example, but not limited to, the saw may be a chain saw driven by a flow of the hydraulic system, or a circular saw or a band saw.

The saw may have a sawing member, i.e. a member or portion moving to saw through, for example, a tree. The saw may also have a sawing direction, i.e. a direction through, for example, the tree or item the saw is to saw through. The term "sawing area" is therefore to be interpreted as the area on which the saw saws with the sawing or rotating member through the item. Further, the term "sawing speed" or "movement speed" of the saw is to be interpreted as the speed of the saw in the sawing direction, i.e. in a direction through the tree or log. A "saw pressure applied by the saw during sawing" is to be interpreted as related to the speed of the saw in the sawing direction, thereby applying a force or a pressure on the sawing area. Accordingly, it should be noted that by the expression "the saw being adapted to apply a saw pressure on a sawing area during sawing", the saw is applied to a sawing area (e.g. of the wood) during sawing, the saw is accordingly and consequently adapted/configured to apply a saw pressure on this sawing area.

The term "hydraulic system" may be interpreted as any hydraulic system suitable for driving or powering a saw. It may be a load-sensing hydraulic system. Typically, hydraulic systems comprise a pump and a hydraulic valve for determining or altering the current flow or pressure in the system.

By "pump pressure" it is meant the pressure created by the pump, i.e. the pressure downstream from the pump and upstream from the saw.

The sensor may be any device or sensor capable of measuring or determine a pressure in the hydraulic system.

By "predetermined value", it is here meant a desired value and/or reference value.

It will be appreciated that the "first predetermined value" and the "second predetermined value" may be related. For example, the second predetermined value may be within an interval from the first predetermined value. Alternatively, they may be equal. It will also be appreciated that the control unit may determine that a measured value is higher or lower than the first predetermined value or the second predetermined values based on it being within an interval from the values.

It will be appreciated that by the wording that the control unit is configured to decrease or increase the pressure applied by the saw during sawing, it is understood that substantially any unit(s), element(s), system(s) or the like, e.g. comprising one or more actuator(s) and/or hydraulic systems, may be connected or coupled between the control unit and the saw.

According to an embodiment, the control unit may be configured to monitor the pump pressure in the first hydraulic system periodically or continuously. The monitoring may be performed by periodical measurements by the sensor at any suitable time interval. For continuous monitoring the time periods may be relatively small.

In this way, the control unit may relatively quickly adapt the pressure according to the monitored pump pressure. This may lead to a more efficient system as the pressure applied by the saw during sawing may be quickly adapted to changes in the environment that makes it easier or more difficult to saw. This further allows for improving the efficiency of the sawing while decreasing the risk for overloading the saw.

According to an embodiment, the control unit may be configured to output a control signal for controlling the saw pressure applied by the saw during sawing. For example, the control unit may be configured to output a control signal on a CAN-bus.

The embodiment is advantageous in that the control unit may control a pressure applied by the saw during sawing based on the control signal.

According to an embodiment, the saw is inclinably arranged in the system, and the increase or decrease of the pressure applied by the saw during sawing is further based on an inclination of the saw.

This allows for adapting the pressure applied on the saw based on the type of sawing performed, i.e. the inclination of the saw. Typically, the saw may be inclined downwards during cutting of a tree trunk, and inclined upwards during felling of a tree. These types of harvesting may require different pressures applied by the saw on the sawing area.

According to an embodiment, the system is intended for sawing of wood, and the increase or decrease of the pressure applied by the saw during sawing is further based on at least one property of the wood. For example, the control unit may be configured to cut a specific type of wood or tree and adapt the pressure applied by the saw accordingly.

The saw is operated by an actuator. The actuator is hydraulically driven and the control unit is adapted to control the actuator. The control unit may be further adapted to control a pressure in a second hydraulic system driving the actuator.

By controlling the actuator operating the saw, the saw may continue to operate the sawing at maximum speed, and the pressure applied by the saw on a sawing area may be controlled by the actuator.

According to the invention, the control unit is configured to monitor a first pump pressure in the first hydraulic system during a sawing cycle and to control the actuator during a subsequent sawing cycle based on the first pump pressure.

In this way, the controlling of a subsequent sawing cycle may be influenced by data from a previous sawing cycle. This may be beneficial as the sawing characteristics between sawing cycles may be similar. For example, a subsequent sawing cycle may be performed for the same or a similar type of wood at the same or a similar temperature as the previous sawing cycle.

In an example, but not limited to, the starting pressure applied by the saw on the sawing area for a subsequent sawing cycle may be determined based on the monitored sawing cycle. In this way, the sawing cycle may start at a pressure which is based on a previous sawing cycle, and thereby reduce the risk of any misconfiguration in the beginning of the sawing cycle. This may lead to a more efficient sawing cycle.

According to an embodiment, the control unit is comprised in a sawing system. The sawing system further comprises a saw, a first hydraulic system for driving the saw, an actuator for operating the saw, and a control unit according to any embodiment for controlling the actuator. The system may, for example, be configured to be arranged on a harvester or on another vehicle or machine where a sawing system is needed.

According to an embodiment, the saw is a chain saw. The chain saw may comprise a saw sword and a rotating member comprising the chain, wherein the rotating member rotates around the saw sword. The rotating member may be driven by the hydraulic system. The pressure in the hydraulic system may increase when a pressure applied on the rotating member is increased, since the chain may move more slowly through the material that is being cut. Correspondingly, the pressure in the hydraulic system may decrease when the pressure applied on the rotating member is decreased, as the chain may move faster through the material that is sawed.

According to an embodiment, the system further comprises a second hydraulic system, wherein the actuator is driven by the second hydraulic system. The hydraulic system may cause movements of the actuator depending on a pressure from the hydraulic system to the actuator.

The actuator may alternatively be driven by an electrical system or another type of system suitable for driving the actuator.

According to an embodiment, the second hydraulic system is the same as the first hydraulic system.

In this way, only one hydraulic system is needed for the operation of the saw, including the sawing member. Further, as many already existing systems have one hydraulic system, the control unit may be relatively easily installed in an existing system.

According to an embodiment, the second hydraulic system comprises a valve for controlling a pressure in the second hydraulic system. In this way, the pressure applied by the saw during sawing, as controlled by the actuator, may be controlled by the control unit via the valve.

Further objectives of, features of, and advantages with the present inventive concept will become apparent when studying the following detailed disclosure, the drawings and the appended claims. Those skilled in the art will realize that different features of the present inventive concept can be combined to create embodiments other than those described in the following.

The above, as well as additional objects, features and advantages of the present inventive concept, will be better understood through the following illustrative and non-limiting detailed description of preferred embodiments of the present inventive concept, with reference to the appended drawings. In the drawings like reference numeral will be used of like elements unless stated otherwise.

All the figures are schematic, not necessarily to scale, and generally only show parts which are necessary in order to elucidate the embodiments, wherein other parts may be omitted.

Detailed embodiments of the present inventive concept will now be described with reference to the drawings. The present inventive concept may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided by way of example so that this disclosure will convey the scope of the inventive concept to those skilled in the art.

Embodiments of the present inventive concept generally relate to a control unit <NUM> for controlling a saw <NUM> in a sawing system as shown in <FIG>. The saw <NUM> is driven by a hydraulic system <NUM>. Such hydraulic systems <NUM> generally comprise a pump <NUM>, a tank <NUM> and a motor for driving the pump <NUM>. The pump <NUM> may be a fixed displacement pump or a pump with a variable displacement. The motor may be any type of motor suitable for driving a pump, for example a combustion engine such as a diesel motor or an electrical motor.

The saw <NUM> is in this example a chain saw. The saw <NUM> comprises a saw sword <NUM> and a rotating member <NUM>. The rotating member <NUM> may be a saw chain. The rotating member <NUM> may be driven by the hydraulic system <NUM>. The rotating member <NUM> has a rotational direction <NUM>. The sawing system further comprises an actuator <NUM>, a cylinder <NUM> and a second hydraulic system <NUM> for operating the saw <NUM>. The second hydraulic system <NUM> may drive the cylinder <NUM> which acts on the actuator <NUM>. The second hydraulic system <NUM>, the cylinder <NUM> and the actuator <NUM> may be comprised in an actuator unit for operating the saw <NUM>. The saw sword <NUM> has a sawing direction <NUM>.

Alternatively, the saw <NUM> may be a band saw, a circular saw or another type of saw suitable for cutting wood <NUM> and configured to be driven by a hydraulic system.

The sawing system further comprises a control unit <NUM>. The control unit <NUM> has a sensor <NUM> for measuring a pump pressure of the pump <NUM>. The control unit <NUM> may also comprise a processing unit <NUM> to which the measured pump pressure may be communicated. The processing unit <NUM> may perform any calculations in the control unit <NUM>.

The control unit <NUM> may detect that the saw <NUM> or saw system <NUM> is working at a workload of the saw <NUM> which is close to, or even above, a maximum workload, based on the measured pump pressure being above a first predetermined level. The first predetermined level may, for example, be related to the maximum pump pressure for the pump <NUM>. Alternatively, the first predetermined level may be related to other components in the sawing system or driven by the hydraulic system <NUM>. In response to the measured pump pressure being above the first predetermined level, the control unit <NUM> may output a control signal for decreasing the pressure applied by the saw <NUM> on the sawing area. The control unit <NUM> may alternatively determine that the saw <NUM> or the sawing system <NUM> is not working at a workload close to or above the first predetermined level based on the measured pump pressure being below a second predetermined level. In response to the measured pump pressure being below the second predetermined level, the processing unit <NUM> may output a control signal for increasing the pressure applied by the saw <NUM> on the sawing area.

The control unit <NUM> may output the control signal indicating a pressure to be applied by the saw on a sawing area, or a change in the pressure to be applied, via a CAN-bus <NUM>. It should be noted that any type of communication means may be used instead of the CAN-bus <NUM>.

The control unit <NUM> may periodically or continuously monitor the pump pressure. For example, the sensor may measure the pressure every <NUM> seconds, <NUM> seconds, <NUM> second or at any other suitable time interval. For continuous monitoring, the time period may be relatively small.

The harvesting system <NUM> may further comprise a second hydraulic system <NUM> for operating the saw <NUM>. The second hydraulic system <NUM> may comprise a control unit <NUM> and a hydraulic actuator <NUM> for operating the actuator <NUM>.

The actuator unit may receive the control signal sent from the control unit <NUM> via the CAN-bus <NUM>. The actuator unit may control the movements of the saw <NUM> in the sawing direction <NUM> according to the control signal sent from the control unit. For example, the actuator unit may move the saw <NUM> faster in the sawing direction <NUM> to increase the pressure or move the saw <NUM> at slower in the sawing direction <NUM> to decrease the pressure.

An example for the control process for the control unit <NUM> is now described with reference to <FIG> shows two graphs, wherein Pa indicates a measured pump pressure over time and Pc indicates a value of the control signal sent by the control unit. More specifically, Pc indicates a pressure applied by the saw on a sawing area during sawing in response to the measured pressure Pa.

As the pump starts in the example illustrated in <FIG>, both of Pa and Pc start at low values. The pump pressure is thereafter brought to its maximum working level, wherein Pa = Pa-max. The control unit may, in response to the pump pressure reaching maximum working level, set Pc at its preferred level, Pc Set. At point B the measured pump pressure increases, which may be due to the start of sawing or another external event. In response to an increase in the pump pressure, the control unit may determine a steering signal Pc indicating a decrease in the pressure applied by the saw. At point C the control unit may determine another, lower steering signal Pc since the increase in pump pressure has not yet declined. At point D in time, the pump pressure starts to decline, and the control unit determines a steering signal Pc indicating an increase in the pressure applied by the saw during sawing. At point E the control unit may determine to keep the steering signal Pc at the same level as before, as the measured pressure Pa has not recently changed. At point F in time, the measured pump pressure Pa is declining, which may be due to a change of the characteristics of the wood (tree/log) or another external event. The control unit may, in response to the measure pump pressure Pa declining, determine a steering signal Pc that indicates an increase in the pressure applied by the saw during sawing.

There may be different types of sawing performed by the sawing system <NUM>, for example felling and cutting. In those different types of sawing, the inclination of the saw <NUM> may be different. The control unit <NUM> may determine the control signal based on the inclination of the saw <NUM>. The inclination may be controlled by an operator operating the sawing system, or it may be pre-programmed based on a current sawing cycle. For example, the control unit <NUM> may determine a control signal indicating a decrease in the pressure applied by the saw on the sawing are based on a downward inclination, which would commonly be used during cutting. The control unit <NUM> may determine a control signal indicating an increase in the pressure applied by the saw during sawing based in an upward tilt, which would commonly be used during felling.

A vehicle which comprises a control unit and a hydraulic system as described above will now be described with reference to <FIG> shows a schematic view of a sawing system <NUM> and a control unit <NUM> comprised in a vehicle <NUM>. The vehicle <NUM> may be a harvester for logging, but also other applications for the sawing system <NUM> and the control unit <NUM> are envisaged. The vehicle <NUM> comprises a hydraulically driven sawing arm <NUM>, a vehicle body <NUM> and a cab <NUM> at the vehicle body <NUM>. An operator may drive the vehicle <NUM> and operate the arm <NUM> from within the cab <NUM>.

The vehicle <NUM> further comprises a sawing head <NUM> arranged at an end of the crane <NUM>. The sawing head <NUM> comprises two holding portions <NUM>, <NUM> and a saw <NUM>. The saw <NUM>, in this example, comprises a saw sword <NUM> and a rotating member <NUM>. However, other types of saws may be used. The saw <NUM> is able to move between a folded state, wherein the saw <NUM> is arranged in the sawing head <NUM>, and between an extended state, wherein a portion of the saw <NUM> has passed the holding portion <NUM> in the sawing direction. The holding portions <NUM>, <NUM> may be arranged around a tree or log <NUM> to hold the tree <NUM> or log in place during sawing by the saw <NUM>.

The sawing system further comprises a pump <NUM> and an engine <NUM> for driving the pump <NUM>, both arranged at the body <NUM> of the vehicle <NUM>. The sawing system <NUM> further comprises an actuator <NUM> arranged at the sawing head <NUM> for operating the saw <NUM>. The actuator <NUM> may be comprised in an actuator unit (not shown in <FIG>).

During a sawing cycle, the crane <NUM> may be operated by an operator such that the two holding portions <NUM>, <NUM> are arranged around a tree <NUM>. At the start of a sawing cycle the saw may be arranged in the sawing head <NUM>. The rotating member may rotate around the saw sword by means of the hydraulic system. To start the sawing, the <NUM> saw may be operated by the actuator to apply a pressure against a sawing area on the tree <NUM>. During sawing the control unit may monitor the pump pressure of the pump <NUM> and adjust the pressure applied on the sawing area of the tree as described above with reference to <FIG> and <FIG>.

The person skilled in the art realizes that the present invention by no means is limited to the embodiments described above.

Claim 1:
A control unit (<NUM>) for controlling a saw (<NUM>) in a harvester, the saw being driven by a first hydraulic system (<NUM>) and the saw being adapted to apply a saw pressure on a sawing area during sawing, wherein the control unit comprises:
a sensor (<NUM>) for measuring a pump pressure of the first hydraulic system;
and wherein the control unit is configured to:
in response to the pump pressure being above a first predetermined value, decrease the saw pressure applied by the saw during sawing or
in response to the pump pressure being below a second predetermined value, increase the saw pressure applied by the saw during sawing,
wherein the saw is operated by an actuator (<NUM>), and the control unit is further adapted to control a pressure in a second hydraulic system (<NUM>) driving the actuator,
characterised in that
the control unit is configured to monitor a first pump pressure in the first hydraulic system during a sawing cycle and to control the actuator during a subsequent sawing cycle based on the first pump pressure.