Handloom Dobby Weaving | Handloom Dobby meaning and its description| Types of Handloom Dobby |
Introduction
A "Dobby" is a shedding device attached to a loom for produceing of variety of small motifs (design or patterns). The capacity of Dobby system is not more than a 64 Nos of shafts or stick. It is extra warp attachment design produce. It is a design tool. It is mounted on top of the loom. It is commonly used when the number of healds increases we can use the dobby to make the design.
Dobby is a mechanism attached to a loom for weaving a small geometrical pattern. Dobby carries the limitation of the design harness.
Types of Dobby-
1. Single Lift
2. Double Lift
And also varieties of Dobby found in different region of the country-
a. Country dobby:
It is made of wood and consisted of some levers actuated by Tappets fixed on a barrel. As the tappet is fixed, only one kind of design with slight variation is possible for each Dobby.
Example:- Groove dobby (Found in Odisha), Peg Dobby (Found in West Bengal), Lattice Dobby (Found in Andra Pradesh)
b. Englisb dobby:
It is made up of iron, which is strong enough to actuate smoothly any reasonable numbers of healds.
Example:- Varanasi Dobby (Found in Uttar Pradesh).
Dobby in Handloom Weaving: Definition, Types, Parts, Working Principle and Uses
Introduction
Dobby is an important shedding mechanism used in handlooms and power looms to produce small, repeated, and geometric woven designs. It provides controlled lifting and lowering of selected heald shafts according to a predetermined pattern.
Compared with a simple treadle-operated shaft loom, a dobby mechanism makes it possible to produce more complex designs without requiring a separate treadle for every possible shedding combination.
Dobby is widely used for producing patterned fabrics such as stripes, checks, small geometric motifs, textured structures, honeycomb effects, and other figured designs.
For textile and handloom students, understanding the dobby mechanism is important because it connects design planning, shedding, shaft selection, and fabric construction.
What is Dobby?
A dobby is a mechanical or electronic shedding device used to control the movement of multiple heald shafts in a loom according to a predetermined design or lifting plan.
The word "dobby" is commonly associated with a shaft-control mechanism. Instead of manually operating individual shafts through numerous treadles, the dobby selects the required shafts automatically according to the design.
Simple Definition
Dobby is a shedding mechanism that controls selected heald shafts according to a predetermined pattern to produce figured designs in woven fabric.
Why is Dobby Used in Weaving?
In a basic shaft loom, the weaver may operate shafts using treadles. This arrangement is suitable for relatively simple structures.
When the design requires many different shaft combinations, manual treadle operation becomes complicated.
A dobby helps by:
Selecting the required shafts
Repeating the lifting plan accurately
Increasing the number of possible shaft combinations
Reducing manual effort
Producing regular and precise designs
Making repeated figured patterns easier to weave
Principle of Dobby
The basic principle of a dobby is controlled shedding.
During weaving, selected heald shafts are raised while the remaining shafts stay down or move according to the required shedding plan. This creates an opening called the shed, through which the weft is inserted.
The sequence of shaft movements follows the design plan.
Basic sequence
Design → Lifting Plan → Shaft Selection → Shedding → Weft Insertion → Beat-up → Repeat
The dobby mechanism therefore acts as the link between the designing system and the shedding mechanism of the loom.
Main Parts of a Dobby Mechanism
The exact construction varies according to the type and manufacturer of the dobby, but a conventional mechanical dobby may include the following components.
1. Dobby Head
The dobby head is the main mechanism responsible for controlling the shaft selection and lifting sequence.
It receives the design information and operates the shaft-control mechanism accordingly.
2. Pattern Chain
In a conventional mechanical dobby, a pattern chain carries the information required to operate the design.
The chain is made from a series of connected units or lags. The arrangement of pegs or selecting elements determines which shafts are operated for each pick.
3. Lags
Lags are the individual sections or bars used in a mechanical pattern chain.
The arrangement of selecting pegs on the lags represents the required lifting plan.
4. Pegs or Selecting Elements
Pegs are positioned according to the design requirement.
Depending on the dobby construction, the presence or absence of a peg causes the corresponding mechanism to select or not select a particular shaft.
5. Hooks and Knives
Mechanical dobbies commonly use hooks, knives, or related lifting components to transmit the selection from the pattern mechanism to the shaft-control system.
Their exact arrangement depends on the type of dobby.
6. Shaft Selection Mechanism
The shaft selection mechanism determines which heald shafts must move for each pick.
This is one of the most important functions of the dobby.
7. Harness or Shaft Connection
The selected movement is transmitted to the heald shafts through suitable connections.
The shafts then move upward or downward to form the required shed.
8. Heald Shafts
Heald shafts carry the healds through which the warp ends pass.
The shafts are raised or lowered according to the lifting plan.
9. Drive Mechanism
The drive mechanism synchronizes the dobby operation with the loom cycle.
In a handloom, the mechanism may be connected to the loom's operating system. In power looms, the dobby is synchronized with the machine drive.
Types of Dobby
Dobbies can be classified in different ways depending on their operating principle and method of pattern selection.
1. Mechanical Dobby
A mechanical dobby uses mechanical components to read and execute the lifting plan.
Pattern information may be stored using a pattern chain, lags, pegs, or similar mechanical selection arrangements.
Advantages
Simple operating principle
Durable construction
Suitable for repeated designs
Does not require electronic control
Limitations
Design changes can require physical modification
Mechanical components require adjustment and maintenance
Pattern preparation can be time-consuming
2. Electronic Dobby
An electronic dobby uses electronic control to select the required shafts.
The design information can be entered or transferred electronically, depending on the machine and control system.
Advantages
Faster design changes
Accurate pattern control
Easier storage of multiple designs
Greater flexibility
Reduced mechanical pattern preparation
Electronic dobbies are particularly useful where frequent design changes and higher production flexibility are required.
3. Positive and Negative Dobby Systems
Dobby mechanisms may also be described according to how the shafts are controlled.
Positive Dobby
A positive system provides controlled movement of the shafts in both directions according to the mechanism's design.
Negative Dobby
In a negative system, the mechanism generally provides the lifting action while the return movement is achieved through another force or arrangement, such as springs, weights, or other loom mechanisms.
The exact arrangement depends on the particular dobby design.
Working Principle of a Mechanical Dobby
The working of a mechanical dobby can be understood in the following steps.
Step 1: Design Preparation
The required fabric design is first converted into a lifting plan.
The lifting plan indicates which shafts must be raised for each pick.
Step 2: Pattern Preparation
The lifting plan is transferred to the pattern chain or corresponding mechanical programming system.
Step 3: Pattern Selection
As the loom operates, the pattern mechanism presents the programmed selection to the dobby.
Step 4: Shaft Selection
The dobby mechanism selects the required shafts according to the programmed design.
Step 5: Shaft Movement
The selected shafts are lifted or controlled to produce the required shed.
Step 6: Weft Insertion
The shuttle or other weft insertion device passes through the shed.
Step 7: Beat-up
The reed beats the newly inserted weft into position.
Step 8: Next Pick
The dobby advances to the next design instruction and selects the next shaft combination.
This process continues repeatedly to produce the complete fabric design.
Dobby Design Preparation
Correct design preparation is essential for successful dobby weaving.
The general process is:
Fabric Design → Design Graph → Lifting Plan → Shaft Plan → Dobby Programming → Weaving
1. Fabric Design
The desired pattern is first prepared according to the intended fabric structure and appearance.
2. Design Graph
The design may be represented on graph paper or in textile-design software.
Each square or group of squares represents a specific warp-weft interlacement or lifting requirement.
3. Lifting Plan
The design is converted into a lifting plan.
The lifting plan determines which shafts should be raised for each pick.
4. Shaft Assignment
The warp ends are distributed among the required heald shafts according to the draft.
5. Dobby Programming
The lifting information is transferred to the mechanical or electronic dobby.
6. Trial Weaving
A sample is woven and checked for:
Pattern accuracy
Float length
Selvedge condition
Fabric structure
Warp tension
Weft insertion
Repetition of the design
Role of Drafting in Dobby Weaving
Drafting determines the order in which warp ends are distributed through the heald shafts.
For example, a simple draft may be:
1 – 2 – 3 – 4
or
1 – 2 – 3 – 4 – 3 – 2
The selection of draft depends on the required fabric structure and design.
The draft and lifting plan must work together correctly. An incorrect draft can produce an incorrect or distorted pattern even when the lifting plan itself is correct.
Dobby and Shedding
Shedding is the process of separating the warp threads to create a passage for the weft.
There are generally three basic shed conditions:
Open shed
Closed shed
Semi-open shed
The dobby controls the shafts so that the appropriate shed is produced for each pick.
What Designs Can Be Produced by Dobby?
Dobby is particularly suitable for small and repeated designs.
Common examples include:
Stripes
Checks
Small geometric motifs
Honeycomb structures
Bird's-eye effects
Herringbone effects
Small figured patterns
Texture effects
Rib structures
Decorative borders
Repeated motifs
Small dobby figures
The exact design capability depends on the number of shafts, dobby capacity, draft, lifting plan, and fabric construction.
Dobby vs Ordinary Shaft Loom
| Feature | Ordinary Shaft Loom | Dobby Loom |
|---|---|---|
| Shaft control | Mainly treadle/manual | Dobby mechanism |
| Design capacity | Relatively limited | Higher |
| Repeated figured designs | Limited | Easier |
| Shaft selection | Manual | Mecha |
Comments
Post a Comment