Grass trimmer
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Revision as of 16:02, 2 February 2014
![Figure 1: Electric Grass Shears Dissected and Analyzed [homelite.com]](/ddl/index.php/Image:Homelite_grass_shears.jpg)
Contents |
Executive Summary
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Electric grass shears are a small, hand-held device which trim grass using oscillating blades. They are commonly used to trim the edge of a lawn, along a garden, or other places that a mower cannot reach. Electric grass shears offer an alternative to both string trimmers (aka weed whackers or weed eaters) and hand shears – all for cutting edges of lawns so they look nice and well-kept.
This report contains a detailed analysis of the use and design of Homelite electric grass shears, purchased for $30 from Home Depot. From our own use of the product, comments from existing users, and online reviews we found that from a user’s perspective the electric grass shears are overall very effective in trimming grass but have limited battery life (which also degrades over time), require the user to pull the trigger constantly during use as a safety feature (which can be half an hour or more), blades jam in thick grass, and blades dull over time.
findings from dfma, dfe, fmea
After analyzing how the product is used and problems with the current design, we have the following recommendations for improvement:
- Use a removable battery so that the user can switch to another fully charged battery if other is completely discharged
Major Stakeholders
Manufacturers
- Low cost materials, parts, and manufacturing equipment
- Minimal assembly labor
- Reliable supply chain
Distributors
- Compact packaging to reduce shipping costs
- Lightweight to reduce shipping and material handling costs
- Durable to prevent damage during product shipping
Retailers
- Compact packaging to reduce shelf-space costs
- Aesthetically pleasing packaging and product to draw customer interest
- Good quality and performance to prevent returns and improve customer loyalty
End Users
- Function as expected – trim grass effectively and efficiently
- Reliable and long product life-time
- Safety features to prevent harm to user during use (very important since sharp, oscillating blades are on product)
- Easy to use
- Battery life to last user’s duration of grass trimming
- Ergonomic to prevent harm and injury to user’s hand
- Lightweight to prevent excessive strain on user’s muscles
- Compact for portability and small storage space
- Reasonable recharge time
- Easy to maintain
- Aesthetically pleasing
Use Study
Steps for Use
Initial Assembly
1. Connect charger to grass trimmer and let charge for 10 hours
2. Open the black bottom cover
3. Insert blades into latch
4. Close by sliding in black bottom cover
5. Slide the locking switch
Grass Trimming
1. Hold down the lock down button
2. Press the switch trigger
3. Bending down and holding the trimmer parallel to the ground, slide the trimmer over the grass
4. Let go of both the trigger and the lock down button to power off
Our Experience Using Product
The grass shears came in a rectangular, cardboard box. The box was plain and contained no padding. Included in the box were:
- Main shears assembly
- Attachable cutting blades
- User manual
- Charging unit.
Removing contents from the packaging was simple. The parts were all in working order; there was no visible damage.
The battery came in a very low (nearly uncharged) state. The instruction manual advised charging overnight, or at least 10 hours. The instruction manual also stated that the charger should be removed when the shears are fully charged. Unfortunately, the shears have no battery charge indicator. This is a fairly simple indicator, which is included on many consumer items. The lack of an indicator on this product is unfortunate. We charged the shears and began assembly. The only assembly required was the insertion of the cutting blades into the main assembly. We then began product testing.
The product is operated using a two-button mechanism- meaning, two buttons must be depressed, simultaneously, in order to actuate the cutting blades. The buttons are located at the top and bottom of the shear handle. This is a safety feature, used to avoid accidental operation of the cutting mechanism.
The product was used to cut moderately high grass, bushes and thin branches. The product cut through all three media, with ease. The largest branch tested was about 1/4” in diameter. Cutting of thicker branches may be feasible, but it not tested in this study. When cutting taller grass, it was harder to see the work that the shears were doing, because the cut grass fell on top of the shears and impeded view.
The battery life was tested by running continuously (not cutting any grass) and was found to be 25 minutes. The manufacturers claimed that the device would last for 1 to 2 hours which may be correct depending on how often the device is switched on an off.
Overall, the product accomplishes the job for which it was built- cutting grass and light brush, with precision. The price ($30) seems reasonable for the level of performance provided.
Other Customers' Experience Using Product
After discussing the product with customers who have used the product and reading online reviews, we have found that customers are generally satisfied with the performance of electric grass shears (in general, not restricted to the specific product analyzed in this report). They thought it functioned well and found it easy to use. However, were dissatisfied with its battery life, having to pull the trigger constantly during use, occasional jamming, blade dulling, and limited ability to cut thick and wet grass. Users consistently compared the product to its alternatives because the product is not a must-have - it is a nice-to-have. Compared to string trimmers, electric grass shears are more precise, less expensive, quieter, more compact, lighter, easier to use, and do not throw grass into gardens, but cannot cut as thick grass. Compared to hand shears, they are less strenuous for the user's hands and easier to use, but more expensive and require more storage space.
Electric grass shears also come in two other variants: Some are sold with long poles so that the user can stand while using the device (user gets less precision but is more comfortable). Others are sold with an additional attachment to replace the grass blades with hedge blades for trimming hedges and bushes.
Mechanical Function
The device uses a rechargeable battery to provide power to a motor. Recharging the device is accomplished by plugging the device into a wall outlet via a power adapter. When the user deactivates the safety and pulls the trigger, a switch supplies power to the motor. The motor in turn rotates a gear set. The gear shaft connects to a link mechanism that rotates one of the blades back and forth relative to the other (using a rotating cam in a slot).
Design for the Environment
When designing for the environment, the main focus is to design a product that is environmentally friendly. The environmentally friendliness of a product is measured by the amount of greenhouse gases emitted during production and during the use of the product.
