by

Victor Duraj, John A Miles, Jim M Meyers;

Development Engineer, Bio & Ag Engineering Dept. (UCDavis); Professor, Bio & Ag Engineering Dept. (UCD); Specialist, School of Public Health (UCBerkeley); University of California, Davis, CA, USA

Written for Presentation at the

1999 ASAE/CSAE-SCGR Annual International Meeting

Sheraton Centre Hotel

Toronto, Ontario Canada

July 18-21, 1999

The California winegrape industry, accounting for over 90% of the nation’s winegrape production, employs over 31,000 workers many of whom perform labor intensive tasks. In northern California’s Napa and Sonoma Counties, which together account for nearly half of all winegrape acreage in the state, much of the harvest is still performed by hand for reasons related to terrain and to winemaker preferences. This kind of work is generally thought to be very physically demanding and potentially injurious.

A current University of California study to assess the efficacy of engineering interventions for significantly reducing targeted ergonomic risk factors and resulting work-related musculoskeletal diseases (MSDs) is being conducted in the vineyards of Napa and Sonoma counties. A review of the health records for MSDs for a thirty month period among 194 workers of three cooperating vineyard companies showed that back injuries predominate and that lifting during harvest and tractor/equipment predominate reported causes (Meyers et al., 1998). One of the high risk tasks identified in this work was elevating the winegrape harvesting tub – sometimes weighing up to eighty pounds when full – and dumping it into trailer bulk bins. Another high risk task identified by Meyers was removing leaves that entered the bin by way of the harvesting tubs. These harvest-related tasks are further negatively characterized by worker consensus perception of difficulty and by high ergonomics risk factor evaluations.

Though the University of California study has generally looked to rather simple engineering interventions to address selected elements of the overall harvest job, there appeared to be a cooperator-supported opportunity to pilot test interventions of a more complex nature. Subsequently, one of the pilot interventions was identified as a trailing conveyor system that could reduce ergonomics risk factors and could improve product quality. The existing risk factors include elevating the harvesting tubs overhead to empty them into field transport bins and poor posture associated with removing errant leaves from the bin. The quality improvement opportunity is associated with the removal of leaves from the grapes in the bin. The design would therefore consider a waist level hopper for dumping full tubs of grapes and a sorting conveyor for inspecting and removing poor-quality grape clusters.

Manual harvest techniques are typically focused around tractor-towed bulk bin-trailer units (Figures1 and 2). Two systems are common: one utilizes multiple 4-foot by 3-1/2-foot by 29-inch tall plastic pallet-style containers on a roller-based trailer, and the other utilizes a 4-foot by 8-foot by 39-inch tall steel bin on a designed-to-fit trailer. Both of these systems operate on the principle of filling the bins in the vine row, delivering the full bin to a staging area, exchanging bins, and returning immediately to the harvesting crew with an empty bin. The off-loaded full bins are transported to the winery on a flatbed truck or trailer. Both systems involve work actions that clearly draw attention to ergonomics issues. However, the steel bin system was selected for intervention because of multiple cooperators’ express interest and current focus on the steel bin system. Additionally, the particularly interested cooperator could provide a variety of field sizes and trellis types all in close proximity to a central shop facility capable of providing any necessary mechanical support.

Vineyard layouts and harvest operations have evolved to where little extra clearance remains between the equipment and the vines. Vine rows are spaced on centers that range from 9-1/2 to 12 feet, and new vineyards can be found to have 8-foot spacing. When foliage and trellis systems are taken into account, the non-obstructed width of the 9-1/2-foot row can be less than seven feet. Wider vine rows often include double-trellis systems with a fairly narrow clear passage as well. These dimensions make it difficult if not impossible for a worker to comfortably pass between a bin trailer and a vine.

Whether utilizing the steel or the plastic bin systems, the harvesting crew spreads out across at least three rows and works to fill the bulk bin traveling in the middle row. This means a worker must somehow transport his/her tub of grapes into the middle row in order to dump the tub into the bin. Depending on trellis system, pruning style, and irrigation system, a worker may have to duck under a vine, step over an irrigation line but under the vine, or simply walk through some foliage in order to reach the middle row. Frequently the workers in the adjacent row dump their full tub by literally throwing themselves against the vine (supported by trellis wire) with their full tub above their head throwing the grapes over vines, which are 6 to 7 feet high, into the bin. This allows a rather quick alternative to an awkward posture required for ducking through the trellis system. Another alternative employed by various crews is sliding full tubs under the vine in exchange for another crew member’s partial or empty tub. This means some workers have to lift a higher number of tubs than other workers.

Although both the plastic and steel style systems pose similar ergonomics problems, the following information focuses on the steel bin system. The steel bin is four feet wide, eight feet long, and when on the trailer the top edge is located approximately fifty inches above ground. This height requires a worker to lift the full harvesting tub over his/her head in order to empty the tub into the bin. Because a full tub weighs an average 58 pounds, the dumping action requires strength and coordination. It involves using a thigh to help accelerate the tub upward, inverting the hand position for proper grip, and then combining arms, shoulders, back, and legs in a coordinated thrust, propelling the grapes into the bin.

In order to keep the number of leaves in the trailer bins to a minimum, one crew member (or sometimes two) works at the bin to remove many of the errant leaves (Figures 3 and 4). The worker stands on narrow extensions attached to the sides of the trailer near the bottom of the bin, bends over and into the bin, and reaches as far as possible to grab and remove the leaves. However, until the bin is one-third full, the worker may actually be inside the bin and standing in the grapes. Entry and exit involve ergonomically undesirable actions related to posture, hand grip, stability, and footing. Additionally, while inside of the bin, the worker remains in an extremely stooped posture for long periods of time. Also, from a product quality standpoint, there are sanitation and crushed-grape issues.

The leaves find their way into the bin primarily because they are collected in the tubs. Leaves remain attached to the grape clusters when the grapes are cut from the vines. Other leaves simply fall from the vine into the tub as the worker’s cutting actions cause the vine to shake. Because workers are paid on a group production incentive basis, they focus foremost on tonnage, move as fast as possible, and pay little attention to leaves.

To cut grape clusters from the vine, a worker stands facing the vine, reaches in with the non-dominant hand, grasps a grape cluster, and cuts it free with a curved knife held in the dominant hand (Figure 5). As each cluster is cut, it is dropped towards a plastic tub lying on the ground at the worker’s feet. The worker must frequently alter his/her body position to see, reach, cut, and dispose of the grape clusters.

After harvesting the immediate area of his/her current location, the worker moves along the vine to reach new clusters. When moving, the worker must either stoop to lift and place the tub or push it with a foot to slide it along with a sideways leg movement. Prior to moving the tub, the worker stoops to gather up clusters that missed the tub and to remove visible leaves that fell into the tub (Figure 6).

When the tub is full (between 50 and 60 but sometimes over 70 pounds) the worker stoops to lift it and carries it to the bulk bin and dumps the grapes in over a 50-inch high container lip. Workers often carry tubs in overhead or shoulder height positions to dump them in the trailer. Alternatively, workers may lift the tubs to the trailer from knuckle height.

The trailer conveyor system consists of a feed hopper, an elevating conveyor, a sorting conveyor, two workstations, and an onboard power supply all attached to a square tube frame mounted on a single axle (Figure 7). Workers empty their harvesting tubs into the hopper at the rear. The winegrapes are metered via 3-inch cleats on the 18-inch wide speed-variable elevating conveyor to the sorting conveyor. A worker(s) stands on the workstation platform(s) adjacent to the sorting conveyor to remove loose leaves, leaves attached to grape clusters, debris, and unacceptably poor grape clusters or portions thereof. The winegrapes proceed along the slightly inclined conveyor and are deposited into the center of the bulk bin on the bin trailer in front. The sorting conveyor, as well as the elevator, can be started and stopped from either workstation. The gasoline engine of the power unit can be shutdown via either of the two emergency stop buttons; one is located at the conveyor start/stop pushbutton station and the other is located over the hopper at the rear. The gasoline engine-powered electric generator is rope-started from ground level, but it can be fitted with a remote start switch and battery system.

The conveyor system is pulled by an existing combination of tractor and bulk bin trailer. The connection is by a simple pin. While the bulk bin trailer is being filled, the trailer conveyor is towed into, within, and out of vine rows by the leading tractor and bulk bin trailer. When the bulk bin has been filled, the trailer conveyor is disconnected, and the tractor pulls only the bulk bin trailer to the field staging area where full bins are exchanged for empty ones. The returning tractor with trailer then backs in to the vine row and is manually reconnected to the trailer conveyor system.

The extreme postures and ranges of motion required in both the harvesting and the leaf-removal tasks drew attention to the idea of an elevating conveyor with a sorting station. The design was tailored to a typical vineyard of one of the project’s cooperating vineyard companies for reasons of express interest, of vineyard size, of a range of vine row widths, and of proximity to a central shop facility capable of independent support. The following items were identified as design issues for any prototype design and are elaborated upon following the list:

• Existing tractor-trailer unit serves as tow vehicle.
• Proper vehicle tracking and maneuverability into, within, and out of vine rows.
• Appropriate tongue weight for towing stability and manual handling.
• An onboard power source.
• Waist-high hopper at bottom of elevator.
• Little or no back-up of workers at hopper to empty tubs.
• Speed control capability for the elevator.
• Dual workstations for workers sorting leaves and poor clusters.
• Readily accessible start/stop/e-stop belt controls.
• Appropriate belt speed for sorting conveyor.
• Semi-automatic distribution of grapes into bulk bin.
• Capability for nighttime operation.
• Disregard of adjacent-row harvesting.

The typical tractor used at the particular vineyard is a 44 pto-hp, four-wheel drive tractor. Operational constraints of this project included a provision to be able to switch back to the existing harvest method with little or no impact on the harvest production. This constraint – along with others described later - suggested the use of an independent conveyor trailer as opposed to a single integrated conveyor-and-bin trailer. The existing bin trailers (as pictured earlier) include a rear hitching point used for transporting multiple empty trailers with bins behind a single tractor. Though these hitches are not robust enough for pulling full bins, the hitches were deemed adequate to support the tongue weight of and to be able to exert pulling forces associated with the conveyor trailer. A fully loaded bin-and-trailer weighs approximately 4500 pounds. A fully loaded conveyor system weighs approximately 2000 pounds, comprised of the hardware’s weight of 1400 pounds and estimated weights of two workers combined and resident grapes of 325 and 275 pounds, respectively.

In selecting the existing tractor-and-trailer unit as a tow vehicle for the conveyor trailer, the resultant double-trailer system introduced potential tracking and maneuverability issues. The most important one was the system’s ability to enter and exit every third vine row provided with headlands no wider than about sixteen feet. (As mentioned earlier, workers spread across three vine rows with the bin traveling down the middle one.) Because these maneuvers involve small clearances and skilled tractor operation, the additional difficulty associated with a second trailer would have to be minimized by designing proper tracking for the second trailer. For this proper tracking to occur, the axle of the conveyor trailer would need to be approximately 4 feet behind the hitch point, or in other words it would have to be as far back from the hitch as the bin trailer’s axle is forward of the hitch.

The overall trailer length, 11 feet and 3 inches, also was also limited by tracking considerations. While a vine row exit maneuver was being performed, the end of the trailer, which is the hopper, would move rather quickly to the opposite side and could strike that vine’s end-post if the hopper were to be located too far back. Because the hopper would not be as wide as the widest part of the system, the distance from the trailer conveyor axle to the back of the hopper could be significantly greater than the distance from the axle to the hitch.

The width of the trailer conveyor was another important dimension for successful tracking; the width would have to be a little less than the width of the bulk bin trailer. Observations of a tractor and bulk bin in operation indicated that the wheel fenders – the trailer’s outermost protrusions – would pass the trellis end-post with very little clearance.

A slightly positive trailer tongue weight was a significant design constraint for two reasons. First, during hitching activities, a worker would be required to manually balance the system while the tractor/bin trailer unit backed-up to it. Second, while the system was being moved slowly in the vine row, sorting workers would be standing on the workstation and could be further jostled about if the tongue were to begin oscillating up and down at the hitch point. By optimizing the location of the axle, the angles of the elevating and sorting conveyors, and the location of the generator, a desirable tongue weight would be achieved with the addition of only a minor amount of ballast placed near the front of the tongue. Because the workstations were located almost directly above the axle, the addition of workers would not upset the weight balance.

A gasoline-engine powered generator was specified to provide onboard power for the electric motor belt drives and the overhead fluorescent light. The onboard-power feature was included in the initial design criteria to help isolate the system from the towing unit. This was an important consideration for minimizing potential interference with the fast-paced harvest and for maximizing opportunity for a variety of trials in different locations with different vineyards.

Electricity was chosen over hydraulic power for several reasons. First, available electrically-powered elevator and a conveyor equipment would require only modest physical modifications for incorporation into the design. Additionally, the electric elevator drive already included a speed-control device. Second, a generator was readily available. Third, field and maintenance crews at the primary research site were already accustomed to similar generators used in light booms for nighttime harvest operations.

The full-load current draw of the elevator motor, the sorting conveyor motor, and the overhead fluorescent was calculated to be within the capabilities of the 3500 Watt generator available to the project. No additional fuel storage was included as refueling was not an issue to the cooperating vineyard company.

The exhaust was routed forward of the sorting stations with an elevated discharge. The exhaust piping was shielded to protect the workers.

The hopper height of approximately 30 inches was determined by modeling the desired dumping motions of a worker of 5’8" in height, the average for the project’s predominantly Hispanic worker population. To allow for potential variation in hitch positions on existing bin trailers and for probable empirical adjustments in the field, the trailer conveyor hitch was made to be adjustable. The adjustment range provides a hopper height range of 6 inches.

The use of a sorting conveyor requires a measured feed system, in this case provided by a hopper and elevator. The hopper design capacity was limited to about 150 pounds, or about three tubs, of grapes due to anticipated vine row clearances during turns. To achieve desirable ergonomics associated with the trailer conveyor system, workers would be expected to empty their tubs one worker at a time. The designed time for elevating the equivalent of one full tub of grapes from the hopper was about 4 seconds, depending on the speed setting of the elevator.

The selected elevator was fitted an adjustable speed control. The specified motor RPM, speed control range, gear box, and final sprocket ratio was designed to provide an elevator belt speed range of 32 to 50 feet per minute. Speed adjustments are made while the elevator is running.

Sorting stations were placed on either side of the conveyor. When production or quality requirements necessitate additional staffing, two workers can be accommodated. Perforated sheetmetal grating provided foot traction and vibration-dampening flexing. The top of the grating was set at 20 inches above ground, providing for a minimum amount of clearance between the station and the wheels underneath. The station was 38 inches long, determined by the distance from behind the wheel to a point forward that would remain clear of the bulk bin during a tight turn. The conveyor was mounted at an angle of 10-1/2 degrees to provide clearance between the conveyor and the bulk bin in front. The inclined conveyor resulted in a guardrail height that sloped from 34-1/2 inches to 38-1/2 inches over a distance of 22 inches. The width of the station, as measured from the outside personnel guardrail to the sorting conveyor was 24 inches. The sorting station mountings included slotted joints to allow an unused station to be relocated 3 inches closer to the conveyor when vine row clearances are extremely tight.

A sorting belt speed of 34 feet per minute was obtained through the use of a gear head motor and chain-and-sprocket speed reduction. The conveyor did not have any speed control, but its drive system design included room for sprocket changes.

The start/stop and primary e-stop controls for the elevator and sorting belts were centrally located for easy access from either workstation. A secondary e-stop control was located above the hopper for easy access from behind the trailer. The start/stop controls served to switch power to the two motor drives, and the e-stop control served to ground the ignition system of the gasoline engine of the onboard generator unit. To restart the generator, a worker would have to reset the tripped e-stop and then manually restart the generator with its pull cord. (The electric start option was not included in this prototype design.)

The sorting conveyor discharge point was located nearly in the center of the bulk bin. Continual discharge of the fruit was expected to result in a mound that naturally spread about the bulk bin. Though consideration was given to including a forward/rear divert chute to be operated from the workstation, the final design did not include such a device.

Because this vineyard did occasionally perform nighttime harvest operations, for which it used multiple row-wide light booms mounted on dedicated tractors, the trailer conveyor system included a fluorescent light fixture above the sorting conveyor.

As mentioned earlier, some workers empty their tubs from the adjacent row. This was not an element of the harvest job that was addressed by the trailing conveyor designed and built for this pilot test. Future designs could include row transfer methods such as conveyors, chutes, or tub exchange systems.

After an initial orientation and training session with the cooperating vineyard company’s selected harvest crew and maintenance personnel, the trailer conveyor was put into use in harvest activities. The trailer conveyor tracked directly behind the bulk bin trailer and none of its front- or rear-most points interfered with the trellis posts located at the ends of the vine rows.

The hopper height allowed for relative easy emptying of the tubs. The lip of the tub was rested on the edge of the hopper, and then the tub was inverted and emptied. The hopper served to effectively support about half of the tub’s weight during the emptying motion. The hitch had to be adjusted to accommodate different bulk bin trailer hitch heights resulting from structural trailer differences.

The hopper was able to accommodate most workers in their desire to quickly empty their tub without having to wait for the worker in front of them. However, some workers had to wait several seconds while another worker was emptying a tub or while the height of winegrapes in the hopper dropped.

The elevating conveyor was able to completely empty the hopper of grape clusters, leaving only a few individual grapes and some juice in the removable bottom pulley pan. During high loading of the system some grape clusters did fall over the side of the elevator and onto the ground. The sides were extended and issue was resolved.

The initial sorting conveyor speed was slightly too high to handle the fluctuating throughput rates. A modest sprocket change was made to reduce the speed from 34 feet per minute to 26 feet per minute, to the satisfaction of the sorting workers. The side rails were extended by 2 inches to accommodate the higher loading per unit length of the belt and to provide the workers with greater confidence when searching for, handling, and inspecting problematic grape clusters. The sorter(s) appeared to be much more effective in removing most leaves than they are in the conventional system.

The distribution of grapes in the bulk bin from the centrally located discharge of the sorting conveyor required no attention until the bin was about two-thirds full; at this point the peak of the mounded grapes was backed up to the sorting conveyor discharge point. Subsequently, a garden rake – used in the existing harvest system – was used by the tractor driver/supervisor to distribute the grapes to the bin’s four corners and front and back regions. Future work on this system could include an improved distribution system.

The onboard gasoline engine-powered generator was able to provide adequate power for the two motors and overhead lighting. There were complaints regarding the noise of the generator; workers are accustomed to hearing only the tractor engine and only for the relatively short periods when the bulk bin is moved within or in or out of the row. Future work should include considerations of a generator relocated to the front of a dedicated tractor. Future work could also include noise abatement and the consideration of hydraulic or battery power.

Although there were occasional generator reliability problems, the trailer conveyor system was received well by the workers and by management. After initial independent use by the selected crew, other crews also used the system.

A conveyor-based winegrape loading system was designed for reducing ergonomic hazards associated with manual harvest of winegrapes in northern California’s Napa and Sonoma Counties, where manual methods predominate and the acreage represents nearly half of the state’s total. Previously identified high risk jobs include elevating 58 pound average harvesting tubs over a 4 foot high bulk-bin lip and removing leaves from these bulk bins by bending into or standing inside the bulk bins. With a focus on these two jobs, the resulting design included a waist level hopper, a variable speed cleat-style elevator, and a sorting conveyor with an elevated workstation on each side. These items, plus a 3500-Watt electric generator, were mounted on a custom-built trailer. The weight of the system, without two sorting-station workers and resident grapes, was 1400 pounds. The maximum width was 70 inches, and the overall length was 14 feet 3 inches. A telescoping hitch was set three feet behind the front-most point of the assembly. The system was designed to hitch and adjust to the existing tractor and bulk-bin trailer units.

Field observations of the system in use indicated that workers emptied their harvesting tubs very nearly as productively as they did by lifting the tub over the high container lip, but they could do this with better posture and less physical effort. Field observation also indicated that the workstations provided effective opportunity for sorting out leaves and poor grapes while eliminating the ergonomic risks associated with the previous method. Qualitative inspections indicated a higher product quality when the conveyor system was in use. The cooperators’ field workers and management expressed interest in continued trial use and development of the system.

These preliminary results on the conveyor-based system encourage further work on remaining issues such noise abatement, fruit distribution within the bulk bin, hopper size, and the larger issue of adjacent-row harvesting.

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