Harvester shakes up pistachio orchards

Erick Nielsen Enterprises, Inc. (ENE) is a family owned and operated agribusiness located in Northern California. ENE specializes in custom orchard services, including mechanical pruning of many orchard types, and prune and pistachio harvesting equipment.

Gavin Nielsen, design engineer at ENE, explained, “We design and manufacture high-end orchard equipment to operate in our own custom harvesting fleet, allowing us to provide our customers maximum productivity and efficiency when it matters most — during the hectic harvest season. We offer both bulk and bin style harvesting equipment to suit customer needs. Our bulk harvesting system features one of the largest, yet most compact bankouts (transfer equipment) and bulk trailers in the industry. Double belts in our bulk trailers allow us to convey a clean, undamaged product.”

Pistachios are harvested by shaking a tree, collecting everything that falls from it, and conveying the material to a station that separates the crop from debris. A challenge to this type of harvesting is to shake the tree hard enough and fast enough for maximum yield, yet avoid damaging the tree by shaking it too hard or too fast. Also, older trees usually require a different shaking pattern than young trees do. If the same shaking signature were used for all trees, either excessive crop would remain on the tree, or the tree could be damaged. Nielsen continued, “We utilize computer-generated shaker patterns to effectively shake crop from tender, young trees as well as large, old trees without causing damage.”

Shakin’ all over

Nielsen said that pistachio (and prune) harvesting involves two machines, a shaker and a receiver. Each machine requires an operator to drive and steer the vehicle and control the harvesting operations. The receiver and shaker are self-propelled vehicles with an moveable deck that each operator positions under a tree. The decks are angled downward toward the base of the tree, so anything shaken loose from the tree falls down the decks to a conveyor at the bottom of the receiver. The conveyor is driven by a hydraulic motor, and the crop is subsequently separated from debris via an integral blower (also driven by hydraulic motor)and ultimately conveyed to bins or a trailer.

But the real action is at the shaker, which grips the trunk (typically 8 to 18 in. diameter) of a tree and shakes it. Nielsen explained, “The operator extends an arm with a shaker head attached to it. The shaker head has a hydraulic clamping system to firmly grip the tree’s trunk. Once this occurs, a pair of hydraulic motors — each with a displacement of 40 cc/rev —spins two eccentric weights (each with a range of 20 lbm to 100 lbm) at speeds to 1100 rpm, which produce vibration that is transferred up into the trunk, branches, etc. This vibration causes the crop to fall from the tree.

“The design of the shaking head holds two advantages over alternative equipment. First, an operator can change the shaking frequency simply by turning a dial from within the cab. This allows tuning the output to a particular tree or orchard. Second, the geometric placement of the shaking system allows us to efficiently transmit more shaking energy to the trunk of the tree.”

A time to reap

Nielsen continued, “The operator establishes the shaking process by setting an electronic timer for duration of shake and setting shaking frequency dials to the desired value. The timer setting depends on parameters such as structure of the tree, maturity of the crop, how plentiful the crop is, etc. Typically speaking, though, most shake periods last only 1 to 4 sec.

“Once the operator has lined up the shaker head with the tree, he or she extends the head to position it on the trunk. After the head has been centered, the operator activates clamping cylinders, which grip the trunk of the tree with a force based on a preset clamping pressure. Reaching the preset pressure (1100 psi, in this case) shifts sequencing valves which, automatically initiate the shake pattern. The shaking period terminates when the timer runs out.

“The operator then unclamps the head from the tree and retracts the head back toward the machine chassis. This process is repeated at each tree, typically moving at speeds of four to seven trees per minute.

“A major benefit of our design is the extremely quick, in-field tuning capability. An ideal orchard would be completely uniform. In reality, though, every tree is different within an orchard — and especially orchard to orchard — depending on soil type, irrigation, sunlight penetration, pruning practices, and other factors. As the tree topology changes, the effectiveness of a given shaking input changes. This machine gives us the ability to re-optimize our input to the tree to accomplish the highest crop removal while preventing damage to the tree. It is also extremely helpful to minimize the necessary shake time if desired. In a recent trial we were able to set our shake duration to less than 50% of the baseline.

Hydraulics makes the shakes

The shaking system uses two 75-cc/rev hydraulic pumps, which have electronic displacement control (EDC) that is regulated by electronic amplifiers set by dials in the cab. We use low power potentiometers to communicate EDC pump position to the amplifiers. The amplifiers are voltage-controlled current drivers, so they can provide a constant current as specified by a constant voltage from the potentiometers. Because the EDC pumps use a constant current as a setpoint in their internal closed-loop displacement control system, this helps us stay load and temperature independent.