Joint not found while trying controlling robotiq_2finger_gripper

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Hello,

I am new to ROS and trying to control the robotiq_2finger_gripper which I have attached to a very simple robot arm I made. The robot consists of 2 spherical and one revolute joint with the gripper at the very end. To attach the gripper, I just added the URDF lines of the gripper to the end of my URDF file and attached the last link to the gripper_base_joint. This is my URDF file

<robot <a="" href="http://xmlns:xacro="http://www.ros.org/wiki/xacro%22" name="pend_bot">xmlns:xacro="http://www.ros.org/wiki/...></robot>

<!-- <xacro:include filename="$(find robot)/urdf/my_robot.gazebo" /> -->

<!-- <xacro:include filename="$(find robot)/urdf/materials.xacro" /> -->
<!-- <robot name="pendulum_robot"> -->
<link name="world">
</link>

<joint name="base_joint" type="fixed">
    <parent link="world"/>
    <child link="body_link"/>
    <axis xyz="0.0 0.0 0.0"/>
    <origin xyz="0.0 0.0 0.0" rpy="0.0 0.0 0.0"/>
</joint>

<!-- First Link -->
<link name="body_link">
    <visual>
        <origin xyz="0 0 0.5" rpy="0 0 0"/>
        <geometry>
            <box size="0.1 0.1 1.0"/>
        </geometry>
    </visual>

    <collision>
        <origin xyz="0 0 0.5" rpy="0 0 0"/>
        <geometry>
            <box size="0.1 0.1 1.0"/>
        </geometry>
    </collision>

    <inertial>
        <origin xyz="0 0 0.5" rpy="0 0 0"/>
        <mass value="1"/>
        <inertia ixx="0.08417" ixy="0.0" ixz="0.0" iyy="0.08417" iyz="0.0" izz="0.001666667"/>
    </inertial>
</link>


<!-- Shoulder Joint -->
<joint name="shoulder_y" type="revolute">
    <parent link="body_link"/>
    <child link="dummy_link_1"/>
    <axis xyz="0 1 0" />
    <origin xyz="0.0 0 1.05" rpy="0 0 0"/>
    <limit effort="500" velocity="2.0" lower="-3.14" upper="3.14"/>
    <!-- <dynamics damping="0.2"/> -->
</joint>

<link name="dummy_link_1">
    <inertial>
        <mass value="0.025" />
        <inertia ixx="5.8083e-4" ixy="0" ixz="0" iyy="3.0833e-5" iyz="0" izz="5.9083e-4" />
    </inertial>
</link>

<joint name="shoulder_z" type="revolute">
    <parent link="dummy_link_1"/>
    <child link="dummy_link_2"/>
    <axis xyz="0 0 1" />
    <!-- <dynamics damping="0.2"/> -->
    <limit effort="500" velocity="2.0" lower="-3.14" upper="3.14"/>
</joint>

<link name="dummy_link_2">
    <inertial>
        <mass value="0.025" />
        <inertia ixx="5.8083e-4" ixy="0" ixz="0" iyy="3.0833e-5" iyz="0" izz="5.9083e-4" />
    </inertial>
</link>

<joint name="shoulder_x" type="revolute">
    <parent link="dummy_link_2"/>
    <child link="bicep_link"/>
    <axis xyz="1 0 0" />
    <!-- <dynamics damping="0.2"/> -->
    <limit effort="500" velocity="2.0" lower="-3.14" upper="3.14"/>
</joint>


<!-- Bicep Link-->
<link name="bicep_link">
    <!-- <pose>0 0 0 0 0 0</pose> -->

    <visual>
        <origin xyz="0 0 0.275 ...