I approached armored cable terminal stripping as a combined motion, contact, and cutting problem. The central idea of my design is to use a screw gear transmission together with a hollow rotary stage so that the cutting tool follows a controlled helical path around the cable. This screw gear based architecture allows the machine to advance along the cable axis while simultaneously rotating around it, which is exactly the motion required to follow the twisted cores and filler geometry of a three-core armored power cable. In my view, the screw gear is not merely a transmission element; it is the motion reference that links axial feed, rotary speed, and cutting depth into one repeatable process.
I based the design on a 10 kV armored cable with an irregular, approximately circular cross section. The cable contains an outer sheath, a steel tape armor layer, an inner sheath, filler material, and three twisted cores. Each core includes a copper shield, insulation, conductor shield, and conductor. The outer sheath and inner sheath are polymer or rubber-like materials, while the armor is thin steel tape with relatively high hardness. This material contrast means that a single cutting strategy is not sufficient. I therefore combined a high-speed serrated blade for the armor with a spring-loaded adaptive head for the irregular surface. The screw gear feed gives the blade a stable axial velocity, and the hollow rotary stage gives it a stable angular velocity. The result is a two-degree-of-freedom stripping robot that can perform straight cutting, circumferential cutting, and helical cutting.
Design Requirements and Cable Architecture
I first defined the physical architecture of the cable because every motion and force equation depends on layer thickness, material, and geometry. The cable is not a perfect cylinder. The three cores are twisted with a specific pitch, and the filler follows the same helical pattern. Therefore, a purely axial cut or a purely rotary cut cannot follow the natural separation plane without risking damage to the copper shield. My screw gear design solves this by allowing the cutter to move along a helix whose angle matches the cable lay angle.
| Layer | Material | Nominal thickness | Primary function | Cutting difficulty |
|---|---|---|---|---|
| Outer sheath | Polyethylene | 3.0 mm | Environmental and moisture protection | Low |
| Armor layer | Steel tape | 0.4 mm per tape | Mechanical protection against impact and compression | High |
| Inner sheath | Rubber-like polymer | 2.5 mm | Internal protection and bedding | Medium |
| Filler | Plastic compound | Variable | Fills gaps and stabilizes the core assembly | Low to medium |
| Copper shield | Copper tape or braid | Very thin | Electrical shielding and field control | Must not be damaged |
| Core insulation | XLPE or similar | Variable | Electrical insulation | Must not be damaged |
The design requirements that I used are summarized below. I treated the stripping length, shield safety, and surface adaptability as the three most important constraints. The screw gear transmission must provide enough axial stiffness to resist cutting forces, while the rotary stage must provide smooth angular motion without eccentricity. The adaptive cutting head must maintain contact with the cable surface even when the local radius changes because of the twisted core geometry.
| Requirement | Target value or condition | Design response |
|---|---|---|
| Strip length | Approximately 800 mm | Screw gear feed with sufficient stroke and guide length |
| Layers removed | Outer sheath, armor, inner sheath | Sequential depth control and high-speed serrated blade |
| Copper shield safety | No cutting or scoring | Cut through filler midline and follow helical lay |
| Surface adaptability | Irregular approximately circular profile | Spring-loaded adaptive cutting head with pin-and-slot angle setting |
| Degrees of freedom | Two independent motions | Axial translation and hollow rotation |
| Motion types | Linear, rotary, helical | Screw gear feed, rotary stage, or combined screw gear and rotary motion |
Overall Architecture
I organized the robot into five functional modules: a translation device, a rotation device, an adaptive cutting device, a clamping device, and a positioning and guiding device. The translation device contains the screw gear, nut, guide rails, carriage, bearings, coupling, and drive motor. The rotation device contains a hollow rotary member, a motor, and a reduction unit. The adaptive cutting device contains the blade, blade motor, transmission, depth adjustment plate, spring, shaft, sleeve, and pin. The clamping device contains a self-centering vise and support table. The guiding device contains rollers and adjustable supports that align the cable with the hollow rotation center.
In my layout, the cable passes through the hollow rotary stage. The clamping device fixes the cable near one end of the frame. The translation carriage moves along the screw gear and guide rails. The rotary stage is mounted on the carriage, and the adaptive cutting head is fixed to the rotary stage. The guiding rollers are placed on both sides of the cutting zone. This arrangement keeps the cable axis close to the rotation center and prevents the rotary stage from interfering with the carriage or the clamps. Because the screw gear and the rotary stage are independent, I can run either one alone or both together.
Screw Gear Motion Principles
The screw gear transmission converts motor rotation into axial translation. When the screw gear rotates by an angle, the nut and carriage move by a proportional axial distance. If I define the screw gear lead as the axial distance per full revolution, then the axial displacement is directly proportional to the screw rotation angle. This relationship is the foundation of the feed motion. The rotary stage separately controls the angular position of the cutting head around the cable. When the screw gear feed and the rotary stage are active at the same time, the cutter traces a helix.
$$L = \frac{z}{N_s}$$
$$z_s = \frac{L}{2\pi}\theta_s$$
$$v_s = \frac{L}{2\pi}\omega_s$$
Here, \(L\) is the screw gear lead, \(N_s\) is the number of screw revolutions, \(z_s\) is the axial displacement, \(\theta_s\) is the screw gear rotation angle, \(v_s\) is the axial velocity, and \(\omega_s\) is the screw gear angular velocity. For a screw gear with multiple starts, the lead is the product of the number of starts and the pitch. The lead determines how aggressively the cutter advances per revolution. A small lead gives high axial resolution but slower stripping. A large lead gives faster stripping but requires more torque and may reduce stability. I selected the lead so that the axial speed matches the desired stripping rate and the helix angle matches the cable lay.
The rotary stage uses a hollow ring so that the cable can pass through the center. The angular velocity of the cutting head is determined by the motor speed and the reduction ratio. If the motor speed is \(\omega_m\) and the reduction ratio is \(i_r\), then the rotary stage speed is:
$$ \omega_r = \frac{\omega_m}{i_r} $$
The hollow rotary member must have sufficient radial stiffness because any deflection changes the cutting depth. I therefore used a rigid ring supported by bearings and a separate guide system. The screw gear feed and the rotary motion are mechanically decoupled, but they are synchronized through the control system. This decoupling is important because it allows me to tune the screw gear feed independently from the rotary speed when the cable lay angle changes.
Kinematic Modeling
I derived the kinematics for three modes: linear motion, rotary motion, and helical motion. The linear mode is used for axial slitting. The rotary mode is used for circumferential cutting. The helical mode is used for following the twisted core and filler geometry. The helical mode is the main operating mode because it combines the screw gear feed with the rotary stage.
Linear Motion
In linear motion, the rotary stage is locked and the screw gear drives the carriage along the cable axis. The displacement, velocity, and acceleration are:
$$ z(t) = v t $$
$$ \dot{z}(t) = v $$
$$ \ddot{z}(t) = 0 $$
where \(z\) is the axial displacement, \(v\) is the axial velocity, and \(t\) is time. The transverse coordinates \(x\) and \(y\) remain constant. This mode is simple and stable, but it cannot follow a helical lay. It is useful for initial cuts where the outer sheath is uniform.
Rotary Motion
In rotary motion, the screw gear feed is locked and the hollow stage rotates around the cable. If the cutting radius is \(r\), the angular position is \(\theta = \omega t\), and the angular velocity is \(\omega\), then the planar displacement is:
$$ x(t) = r\cos(\omega t) $$
$$ y(t) = r\sin(\omega t) $$
$$ \theta(t) = \omega t $$
The corresponding velocity components are:
$$ \dot{x}(t) = -r\omega\sin(\omega t) $$
$$ \dot{y}(t) = r\omega\cos(\omega t) $$
The acceleration components are:
$$ \ddot{x}(t) = -r\omega^2\cos(\omega t) $$
$$ \ddot{y}(t) = -r\omega^2\sin(\omega t) $$
This mode produces a circular path. The acceleration magnitude is constant at \(r\omega^2\), but the direction changes continuously. The force at the contact point is periodic because the cutter encounters the irregular cable surface once per revolution. The screw gear is not active in this mode, but the screw gear carriage must remain rigid to prevent axial drift.
Helical Motion
Helical motion is the combination of screw gear feed and rotary motion. I define the helix angle as \(\beta\), the pitch as \(p\), and the cutting radius as \(r\). The displacement equations are:
$$ x(t) = r\cos(\omega t) $$
$$ y(t) = r\sin(\omega t) $$
$$ z(t) = \pm \frac{p}{2\pi}\theta = \pm r\theta\cot\beta $$
$$ \theta(t) = \omega t $$
The positive sign corresponds to a right-hand helix, and the negative sign corresponds to a left-hand helix. The velocity equations are:
$$ \dot{x}(t) = -r\omega\sin(\omega t) $$
$$ \dot{y}(t) = r\omega\cos(\omega t) $$
$$ \dot{z}(t) = \pm \frac{p\omega}{2\pi} = \pm r\omega\cot\beta $$
The acceleration equations are:
$$ \ddot{x}(t) = -r\omega^2\cos(\omega t) $$
$$ \ddot{y}(t) = -r\omega^2\sin(\omega t) $$
$$ \ddot{z}(t) = 0 $$
These equations show that the helical motion has a constant axial velocity and a sinusoidal transverse velocity. The acceleration in the axial direction is zero if the screw gear speed is constant. The transverse acceleration is centripetal and periodic. Because the screw gear feed is independent, I can adjust the helix angle by changing the ratio of axial velocity to angular velocity. The helix angle condition is:
$$ \tan\beta = \frac{v}{r\omega} $$
For the cable lay angle, the screw gear feed must satisfy:
$$ v = r\omega\cot\beta $$
This is the key synchronization equation for the screw gear based stripping process. If the screw gear feed is too fast, the cutter crosses the lay and may cut into the copper shield. If the screw gear feed is too slow, the cutter rubs the same region and generates excess heat. The screw gear therefore acts as the axial metering element for a safe helical cut.
Force and Dynamic Modeling
I analyzed the contact forces at the adaptive cutting head for all three motion modes. The assumptions I used are: the cable is locally cylindrical, the contact force is concentrated at the depth adjustment plate, the blade removes a small chip, and the cutting force is treated as a contact friction component. These assumptions simplify the equations while preserving the main design trends. In each case, the normal force \(N\) depends on the spring force \(F\), the weight of the adaptive head \(G\), and the angle \(\theta\) between the head centerline and the vertical direction.
$$ N = F + G\cos\theta $$
The spring force is:
$$ F = kx $$
where \(k\) is the spring stiffness and \(x\) is the compression. The friction force at the contact is:
$$ f = \mu N $$
where \(\mu\) is the equivalent friction coefficient. The adaptive head must remain in contact with the cable at all times. Therefore, the normal force must be non-negative:
$$ N \ge 0 $$
This gives:
$$ F + G\cos\theta \ge 0 $$
When the angle is within the range where \(\cos\theta\) is positive, the spring force alone is sufficient. When the angle is in the range where \(\cos\theta\) is negative, the spring force must overcome the weight component:
$$ F \ge G|\cos\theta|_{\max} = G $$
Therefore, the minimum spring compression is:
$$ x_{\min} \ge \frac{G}{k} $$
This inequality is important because it determines the initial preload. If the spring is too soft, the head loses contact on the upper side of the cable. If the spring is too stiff, the head presses too hard and increases friction and wear. The screw gear feed must also overcome the friction caused by this preload.
Linear Motion Forces
In linear motion, the cutting plane is coplanar with the cable axis. The force balance at the contact point can be written as:
$$ N = F + G\cos\theta $$
$$ G\sin\theta = f_{12} $$
$$ f_{11} = F_1 $$
$$ f = \mu N = \sqrt{f_{11}^2 + f_{12}^2} $$
Solving for the drive force \(F_1\), I obtain:
$$ F_1 = \sqrt{(\mu N)^2 – (G\sin\theta)^2} $$
The screw gear must provide this force through the nut and carriage. The screw gear torque required is:
$$ T_s = \frac{F_1 L}{2\pi\eta_s} $$
where \(\eta_s\) is the screw gear efficiency. This equation shows that the screw gear lead and efficiency directly affect the motor size. A larger lead reduces the required torque for the same force, but it also reduces the axial resolution.
Rotary Motion Forces
In rotary motion, the cutting plane is perpendicular to the cable axis. The force balance is:
$$ N = F + G\cos\theta $$
$$ G\sin\theta + F_2 = f $$
$$ f = \mu N $$
Therefore, the rotary drive force is:
$$ F_2 = \mu N – G\sin\theta $$
The rotary stage torque is:
$$ T_r = F_2 r $$
The screw gear is not driving the axial motion in this mode, but the screw gear carriage must resist the reaction torque. If the screw gear has backlash, the carriage may oscillate. I therefore used a preloaded nut or a zero-backlash screw gear arrangement in the design.
Helical Motion Forces
In helical motion, the blade plane is inclined to the cable axis by the helix angle \(\beta\). The force balance is:
$$ N = F + G\cos\theta $$
$$ G\sin\theta = f_{32} $$
$$ f_{31} = F_3 $$
$$ f = \mu N $$
The friction vector components satisfy:
$$ f^2 = f_{31}^2 + f_{32}^2 – 2f_{31}f_{32}\cos\alpha $$
$$ \alpha = 90^\circ + \beta $$
Substituting the known terms gives a quadratic equation for \(f_{31}\):
$$ f_{31}^2 – 2f_{32}\cos\alpha f_{31} + f_{32}^2 – f^2 = 0 $$
The positive root is:
$$ f_{31} = f_{32}\cos\alpha + \sqrt{f^2 – f_{32}^2\sin^2\alpha} $$
This is the helical drive force that the screw gear and rotary stage must provide together. The screw gear contributes the axial component, and the rotary stage contributes the tangential component. The required screw gear torque and rotary torque are:
$$ T_s = \frac{f_{31}L}{2\pi\eta_s} $$
$$ T_r = f_{31}r $$
The helical force is periodic because \(f_{32}\) depends on \(\sin\theta\). This periodicity matches the simulation results, where the support force varies cyclically as the cutter passes over the irregular cable surface.
Adaptive Cutting Head
The adaptive cutting head is the component that allows the robot to tolerate an irregular cable surface. It contains a blade, a blade motor, a transmission, a depth adjustment plate, a shaft, a sleeve, a spring, a pin, and a fixed plate. The shaft slides inside the sleeve, and the pin engages one of several slots in the sleeve. The slot position sets the nominal cutting angle. The spring provides the compliance that keeps the depth adjustment plate in contact with the cable. When the cable radius increases, the spring compresses and the head moves outward. When the cable radius decreases, the spring extends and the head follows inward.
The depth adjustment plate has an elongated hole, and its position relative to the blade sets the maximum cutting depth. I can set the depth so that the blade cuts through the outer sheath, armor, and inner sheath but stops before the copper shield. The screw gear feed controls the axial position, while the rotary stage controls the angular position. The adaptive head controls the radial position. These three motions together define the cutting path. The screw gear is the axial actuator, the rotary stage is the angular actuator, and the spring is the passive radial actuator.
The spring stiffness must satisfy two conditions. First, it must provide enough preload to maintain contact. Second, it must not generate excessive contact force. I used the following design inequalities:
$$ kx_{\min} \ge G $$
$$ N_{\max} = kx_{\max} + G \le N_{\mathrm{allow}} $$
where \(N_{\mathrm{allow}}\) is the maximum allowable contact force based on blade wear and cable surface pressure. The spring compression range is:
$$ x_{\min} \le x \le x_{\max} $$
The adaptive travel must be larger than the local surface variation:
$$ x_{\max} – x_{\min} \ge \Delta r_{\max} $$
where \(\Delta r_{\max}\) is the maximum radial deviation of the cable surface. This ensures that the head never loses contact. In my simulation, I used a spring stiffness of 5.1 N/mm and an initial spring force of 100 N. These values provided stable contact without excessive force.
Blade Speed and Cutting Mechanics
The armor layer is the most difficult layer to cut because it is steel tape. I therefore used a high-speed serrated blade. The blade tip speed depends on the blade diameter and rotational speed:
$$ v_b = \frac{\pi D_b n_b}{60000} $$
where \(v_b\) is the tip speed in m/s, \(D_b\) is the blade diameter in mm, and \(n_b\) is the blade speed in rpm. A high tip speed reduces the required cutting force and improves the quality of the cut. The cutting power can be estimated as:
$$ P_c = F_c v_b $$
where \(F_c\) is the cutting force. For a serrated blade with multiple teeth, the average cutting force is:
$$ F_c = K_c a_p f_z N_t $$
where \(K_c\) is the specific cutting pressure, \(a_p\) is the depth of cut, \(f_z\) is the feed per tooth, and \(N_t\) is the number of teeth in contact. The screw gear feed determines \(f_z\) through the axial velocity:
$$ f_z = \frac{v}{n_b N_t} $$
This equation links the screw gear motion to the cutting mechanics. If the screw gear feed is too high, the feed per tooth becomes too large and the blade may stall or chip. If the screw gear feed is too low, the blade rubs and wears. I therefore selected the screw gear lead and rotary speed so that the feed per tooth remains within a safe range.
Structural Design Details
The translation device uses a screw gear, two bearings, a coupling, a motor, two linear guide rails, four sliders, and a moving platform. The screw gear is supported at both ends by bearings. The nut is fixed to the moving platform, and the platform is supported by the sliders. This arrangement carries the cutting loads and prevents the screw gear from bending. The guide rails are parallel to the screw gear axis. The screw gear provides the axial force, while the guide rails provide the radial and moment support.
The rotation device uses a hollow rotary member, a motor, and a reduction unit. The hollow center allows the cable to pass through. The rotary member is supported by bearings that resist radial and axial loads. The cutting head is mounted on the rotary member, so the blade rotates around the cable. The screw gear feed and the rotary stage are connected through the moving platform. This means that the rotary stage moves axially with the screw gear but rotates independently. The screw gear and rotary stage therefore form a two-degree-of-freedom system.
The clamping device uses a self-centering vise. When the vise closes, it centers the cable and fixes it against axial and torsional motion. The guiding device uses rollers with concave grooves. The rollers contact the cable surface and align the cable with the hollow rotation center. The roller supports are adjustable so that the cable axis can be aligned even if the outer sheath is slightly oval. The screw gear carriage moves along the guide rails, and the rollers rotate as the cable advances. This reduces friction and prevents the cable from twisting.
| Module | Main elements | Function | Relation to screw gear |
|---|---|---|---|
| Translation | Screw gear, nut, rails, carriage, motor | Axial feed | Converts screw gear rotation into linear motion |
| Rotation | Hollow ring, reducer, motor, bearings | Circumferential motion | Independent from screw gear but synchronized for helix |
| Adaptive cutting | Blade, spring, shaft, sleeve, pin | Radial compliance and cutting | Follows screw gear and rotary path while adjusting depth |
| Clamping | Self-centering vise, support table | Fix and center cable | Provides reaction for screw gear feed |
| Guiding | Rollers, adjustable supports | Alignment and low-friction support | Keeps cable axis parallel to screw gear axis |
Simulation Setup
I built a three-dimensional model of the robot and imported it into a multibody dynamics environment. The cable was modeled as a flexible contact body with an irregular cross section. The other components were modeled as rigid steel parts. I defined the coordinate system so that the \(z\)-axis coincides with the cable axis. The \(y\)-axis points vertically upward, and the \(x\)-axis is defined by the right-hand rule. The contact point between the adaptive cutting head and the cable is the measurement point. I recorded displacement, velocity, acceleration, and support force in all three directions.
| Parameter | Value | Unit |
|---|---|---|
| Cable radius for cutting path | 42.5 | mm |
| Adaptive head weight | 75 | N |
| Force exponent | 1.5 | – |
| Penetration depth | 0.1 | mm |
| Static friction coefficient | 0.8 | – |
| Dynamic friction coefficient | 0.4 | – |
| Static transition velocity | 0.1 | m/s |
| Dynamic transition velocity | 1.0 | m/s |
| Spring force | 100 | N |
| Spring stiffness | 5.1 | N/mm |
I ran three simulation cases. In the linear case, the screw gear feed was set to 53.33 mm/s and the rotary speed was zero. In the rotary case, the screw gear feed was zero and the rotary speed was 20 degrees per second. In the helical case, the screw gear feed was 53.33 mm/s and the rotary speed was 20 degrees per second. The simulation time was 36 s with 5000 steps. These settings allowed the robot to complete two full helical cycles. The screw gear feed and rotary speed were chosen so that the helix angle was approximately 11 degrees, matching the cable lay.
| Case | Axial speed | Rotary speed | Simulation time | Steps |
|---|---|---|---|---|
| Linear | 53.33 mm/s | 0 | 36 s | 5000 |
| Rotary | 0 | 20 deg/s | 36 s | 5000 |
| Helical | 53.33 mm/s | 20 deg/s | 36 s | 5000 |
Simulation Results
The linear motion simulation showed that the \(x\) and \(y\) displacements, velocities, and accelerations remained zero. The cutter moved along the \(z\)-axis at a constant speed. The support force was steady except at the very beginning, where a small transient appeared. This transient is caused by the initial contact and the starting torque of the screw gear. Because the axial speed is low, the transient is acceptable. The screw gear feed provided a stable axial motion with no significant vibration.
| Quantity | Linear case | Rotary case | Helical case |
|---|---|---|---|
| Axial displacement | Uniform increase | Zero | Uniform increase |
| Transverse displacement | Constant | Circular | Circular |
| Axial velocity | Constant | Zero | Constant |
| Transverse velocity | Zero | Sinusoidal | Sinusoidal |
| Axial acceleration | Zero | Zero | Zero |
| Transverse acceleration | Zero | Centripetal | Centripetal |
| Support force | Steady | Periodic | Periodic |
The rotary motion simulation showed that the \(z\)-axis displacement, velocity, and acceleration remained zero. The cutter completed two full revolutions at 20 degrees per second. The \(x\) and \(y\) motions followed sinusoidal curves. The support force varied periodically because the local radius of the cable changes as the cutter passes over the twisted cores and filler. The acceleration curve contained small fluctuations. These fluctuations are likely caused by the irregular cable cross section and by transitions in the model geometry. In a real cable, the outer sheath is smoother than the simplified model, so the fluctuations should be smaller.
The helical motion simulation combined the linear and rotary cases. The \(x\) and \(y\) motions were sinusoidal, and the \(z\) motion increased uniformly. The robot traveled 1920 mm in 36 s and completed two helical cycles. The displacement curve was approximately a helix. The velocity had a constant axial component and a sinusoidal transverse component. The acceleration had a zero axial component and a centripetal transverse component. The support force was periodic. These results confirm that the screw gear feed and the rotary stage can be synchronized to produce a stable helical cut.
$$ z_{\mathrm{total}} = v t = 53.33 \times 36 = 1920 \ \mathrm{mm} $$
$$ N_{\mathrm{cycles}} = \frac{\omega t}{360^\circ} = \frac{20 \times 36}{360} = 2 $$
The helical motion result is essentially the superposition of the linear and rotary results. This is expected because the screw gear feed and the rotary motion are independent. The screw gear provides the axial component, and the rotary stage provides the angular component. The adaptive spring absorbs the radial variation. The screw gear therefore acts as the axial motion source, while the rotary stage acts as the angular motion source. The synchronization of these two motions defines the helix angle.
| Result | Linear case | Rotary case | Helical case |
|---|---|---|---|
| Total axial travel | 1920 mm | 0 mm | 1920 mm |
| Number of cycles | 0 | 2 | 2 |
| Path shape | Straight line | Circle | Helix |
| Motion stability | High | Medium to high | High |
| Force variation | Low | Periodic | Periodic |
Discussion
The simulation results support the use of a screw gear transmission as the main axial drive. The screw gear provides a positive displacement relationship between motor rotation and axial feed. This is important because the helix angle must be controlled accurately. If the axial feed were provided by a friction drive, slip could change the helix angle and damage the copper shield. The screw gear eliminates this uncertainty. The screw gear also provides high axial stiffness, which resists the cutting force and keeps the blade at the correct depth.
The hollow rotary stage provides the angular motion. The rotary stage must be rigid enough to prevent radial deflection. If the rotary stage deflects, the cutting depth changes and the blade may cut into the copper shield. I therefore used a rigid hollow ring and a separate guide system. The screw gear and rotary stage are connected through the carriage, but their motions are independent. This makes the control system simpler because the axial velocity and angular velocity can be set separately.
The adaptive cutting head is the key to handling the irregular cable surface. The spring provides passive compliance in the radial direction. The pin-and-slot mechanism sets the nominal cutting angle. The depth adjustment plate sets the maximum depth. Together, these features allow the robot to cut the outer sheath, armor, and inner sheath without cutting the copper shield. The screw gear feed and rotary stage move the head along the desired helix, while the spring keeps the head in contact with the cable.
From a manufacturing perspective, the screw gear design is simple and robust. The screw gear can be preloaded to reduce backlash. The nut can be made of a low-friction material or a recirculating ball type. The guide rails can be sized to carry the cutting moment. The rotary stage can use a crossed roller bearing for high stiffness. The adaptive head can use a compression spring with a known stiffness. These choices make the robot easy to assemble and maintain. The screw gear also provides a mechanical advantage, so a relatively small motor can produce a large axial force.
| Design aspect | Screw gear contribution | Benefit |
|---|---|---|
| Axial feed | Converts rotation to translation | Accurate helix angle control |
| Force transmission | High mechanical advantage | Small motor, high cutting force |
| Stiffness | High axial rigidity | Stable cutting depth |
| Backlash | Can be preloaded | Reduced vibration and drift |
| Synchronization | Independent from rotary stage | Flexible helix angle adjustment |
Performance Comparison
I compared the proposed screw gear robot with manual cutting and with simpler powered tools. Manual cutting depends on operator experience. The cut quality varies, and the copper shield can be damaged. Simple powered tools may rotate or advance, but they usually cannot follow a helix. The screw gear robot can perform linear, rotary, and helical cuts with one machine. It can adapt to an irregular surface. It can also be programmed for different cable sizes by changing the screw gear speed and rotary speed.
| Method | Axial motion | Rotary motion | Helical following | Shield safety | Efficiency |
|---|---|---|---|---|---|
| Manual cutting | Operator dependent | Operator dependent | Poor | Low to medium | Low |
| Simple powered cutter | Yes | Limited | Poor | Medium | Medium |
| Rotary stripping tool | Limited | Yes | Limited | Medium | Medium |
| My screw gear robot | Yes | Yes | Yes | High | High |
The screw gear robot also improves repeatability. Once the screw gear lead, rotary speed, and spring preload are set, the cutting path is repeatable. This reduces the dependence on operator skill. It also reduces the time required for terminal preparation. The screw gear transmission provides a direct relationship between motor rotation and axial position, so the cutting length can be controlled by counting screw gear revolutions. This is a simple and reliable control strategy.
Limitations and Design Improvements
The current design has several limitations. First, the screw gear must be protected from dust and metal chips. If chips enter the nut, the screw gear may jam or wear quickly. I would add a bellows cover or a wiper seal. Second, the rotary stage must be sealed against dust. Third, the spring stiffness must be selected for each cable size. A softer spring improves adaptability but may lose contact. A stiffer spring maintains contact but increases friction. Fourth, the blade wear rate depends on the armor hardness and cutting speed. I would monitor the blade current to estimate wear.
I would also optimize the screw gear lead. A smaller lead improves axial resolution but reduces stripping speed. A larger lead increases speed but requires more torque. The optimal lead depends on the desired cycle time and the maximum cutting force. I would also consider a ball screw gear instead of a lead screw gear for higher efficiency and lower friction. A ball screw gear would reduce the motor torque and improve the dynamic response. However, a ball screw gear may have lower damping, so I would add a brake or a preload nut.
$$ T_{\mathrm{motor}} = \frac{F_a L}{2\pi\eta_s i_s} + T_{\mathrm{friction}} $$
Here, \(F_a\) is the axial force, \(L\) is the screw gear lead, \(\eta_s\) is the screw gear efficiency, \(i_s\) is the additional reduction ratio, and \(T_{\mathrm{friction}}\) is the friction torque. This equation can be used to size the motor. The screw gear efficiency depends on the thread angle and friction coefficient:
$$ \eta_s = \frac{\tan\lambda}{\tan(\lambda+\phi)} $$
where \(\lambda\) is the thread lead angle and \(\phi\) is the friction angle. A larger lead angle increases efficiency but reduces the mechanical advantage. The screw gear must be selected with these trade-offs in mind.
Conclusion
I designed a two-degree-of-freedom cable stripping robot for armored cable terminals based on a screw gear transmission. The screw gear provides the axial feed, and the hollow rotary stage provides the circumferential motion. Together, they generate a helical cutting path that follows the twisted core geometry. The adaptive cutting head uses a spring and a pin-and-slot mechanism to follow an irregular cable surface. The blade is a high-speed serrated tool that can cut the steel tape armor without damaging the copper shield. The clamping and guiding devices align the cable and reduce vibration.
I derived the kinematic equations for linear, rotary, and helical motion. I also derived the force equations for each mode and established the minimum spring preload condition. The screw gear synchronization equation shows how the axial velocity and rotary speed must be related to match the cable lay angle. The simulation results show that the screw gear robot has stable motion, periodic force variation, and an approximately helical displacement path. The screw gear feed and rotary stage can be controlled independently, which gives the robot flexibility for different cable sizes and lay angles.
The main contributions of my work are the screw gear based helical stripping concept, the adaptive cutting head, and the dynamic model that links the screw gear feed to the cutting force. In future work, I will optimize the screw gear lead, spring stiffness, and blade geometry. I will also add sensing for cutting force and blade wear. I believe that the screw gear robot can improve stripping efficiency, reduce operator dependence, and protect the copper shield in armored cable terminal preparation. The screw gear is the core of the axial motion, the rotary stage is the core of the angular motion, and the adaptive head is the core of the surface compliance. Together, these elements form a practical and stable solution for irregular armored cable stripping.