Effectiveness and Injury Risk during Timber Forwarding with a Quad Bike in Early Thinning

Within the majority of forest areas where timber is harvested for industrial and energy purposes, working technologies using highly efficient multi-operational machinery and equipment are employed. The situation is different in fragmented, privately owned forests. In such forests, timber harvesting is mainly based on motor-manual technologies with a high proportion of manual labor, both at the stage of felling and timber processing and at the stage of its transport. The study aimed to characterize the work time structure of the ATV unit driver and his helper, to determine the productivity of this team, and to estimate the risk of injury during manual loading and unloading. Based on the data collected during the field research, the theoretical work time structure, work productivity and costs, and injury risk were estimated as a result of using a professional small trailer equipped with a hydraulic crane for timber forwarding, designed for aggregation with the ATV. The average, calculated productivity of timber forwarding (over an average distance of about 500 m) with manual loading and unloading was almost twice as low as the estimated average productivity of forwarding with mechanical loading and unloading using a hydraulic crane. The total unit costs (including labor costs) of forwarding with manual loading and unloading were almost threefold higher than those of forwarding using a trailer with a hydraulic crane. The use of small forest trailers equipped with a hydraulic crane not only ensures higher productivity and cost effectiveness but also allows reducing (even by several percent) the inconvenience of manual timber handling and the risk of strain of the musculoskeletal system.

Novel Concept for Electro-Hydrostatic Actuators for Motion Control of Hydraulic Manipulators

Self-contained hydraulic cylinders have gained popularity in the recent years but have not been implemented for high power articulated hydraulic manipulators. This paper presents a novel concept for an electro-hydrostatic actuator applicable to large hydraulic manipulators. The actuator is designed and analyzed to comply with requirements such as load holding, overload handling, and differential flow compensation. The system is analyzed during four quadrant operation to investigate energy efficiency and regenerative capabilities. Numerical simulation is carried out using path control and 2DOF anti-swing of a hydraulic crane as a load case to illustrate a real world scenario. A comparison with traditional valve-controlled actuators is conducted, showing significantly improved efficiency and with similar dynamic response, as well as the possibility for regenerating energy.

An Energy Efficient Method for Controlling Hydraulic Actuators Using Counterbalance Valves with Adjustable Pilot

Counterbalance valves (CBVs) are widely used in hydraulic machines handling gravitational loads. They are usually adopted in hydraulic circuits that set the flow to the actuator with either metering control strategies or primary control strategies. In these circuits, the CBV does not determine the actuator velocity, but it establishes a proper counterpressure that balances the actuator during overrunning loads. A well-known problem of CBVs is the excessive power consumption introduced into the circuit, which is due to an excessive pressurization of the flow supply. This paper presents a solution for using CBVs to control the actuator velocity while also reducing energy consumption. The method consists in controlling the pilot port of the CBV through an external pressure source (adjustable pilot). The solution is first studied analytically, considering all the possible loading conditions at the actuator. Two different control strategies are presented: the "Smart CBV", where the CBV does not control the actuator velocity but it minimizes the system pressure; and the "Smart System" that uses the CBV to efficiently control the actuator velocity during overrunning load conditions. An experimental validation of the proposed solutions is also provided, taking as reference a truck-mounted hydraulic crane. The results of the proposed solutions are compared to those achieved by the traditional circuit of the reference hydraulic crane which uses standard CBVs. For both cases of "Smart CBV" and "Smart System", a remarkable power saving respectively up to 75% and up to 90% is observed.

Estimation of Productivity and Costs of Using a Track Mini-Harvester with a Stroke Head for the First Commercial Thinning of a Scots Pine Stand

The aim of the present work was to estimate the productivity and costs of timber harvesting and forwarding during the first commercial thinning of a Scots pine stand. Three harvesting models were introduced and compared: narrow trail, wide access trail, and schematic extraction. The analyzed harvesting equipment consisted of a track mini-excavator (34 kW) with a stroke harvester head (gripping range 4–30 cm), and a farm tractor coupled to a logging trailer with a hydraulic crane. Merchantable timber (roundwood with a minimum diameter of 5 cm inside bark) was harvested from a 25-year-old planted Scots pine stand growing on a grid of 1.4 m × 1.8 m. The study showed the productivity of the mini-harvester ranged from 3.09 to 3.47 m3/PMH15 (productive machine hours plus 15 min), and that of the forwarding equipment to be 4.07 m3/PMH15. The analyzed model of productivity as a function of tree volume and thinning intensity was statistically significant, but the intensity parameter was significant only on plots located along wide access trails (3.7 m) and insignificant on plots located along narrow access trails (2.5 m). The distance between trees was not found to be significant. The calculated net machine costs for the forwarding equipment and track mini-harvester were EUR 36.12 and 52.47 per PMH, respectively. An increase in the usage rate of the harvesting equipment to 80% would reduce the harvesting and forwarding costs to EUR 22.07/m3.